research on water molecules

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Rethinking H2O: Water Molecule Discovery Contradicts Textbook Models

By University of Cambridge January 15, 2024

Researchers have overturned traditional models of how water molecules behave at the surface of saltwater, revealing new insights into ion distribution and orientation. This breakthrough, achieved through advanced techniques, has significant implications for climate science and technology. Credit: SciTechDaily.com

Groundbreaking research shows that water molecules at the saltwater surface behave differently than previously thought, offering new perspectives for environmental science and technology.

Textbook models will need to be re-drawn after a team of researchers found that water molecules at the surface of salt water are organized differently than previously thought.

Many important reactions related to climate and environmental processes take place where water molecules interface with air. For example, the evaporation of ocean water plays an important role in atmospheric chemistry and climate science. Understanding these reactions is crucial to efforts to mitigate the human effect on our planet.

The distribution of ions at the interface of air and water can affect atmospheric processes. However, a precise understanding of the microscopic reactions at these important interfaces has so far been intensely debated.

Graphic representation of the liquid/air interface in a sodium chloride solution. Credit: Yair Litman

Innovative Research Techniques

In a paper published today (January 15) in the journal Nature Chemistry , researchers from the University of Cambridge and the Max Planck Institute for Polymer Research in Germany show that ions and water molecules at the surface of most salt-water solutions, known as electrolyte solutions, are organized in a completely different way than traditionally understood. This could lead to better atmospheric chemistry models and other applications.

The researchers set out to study how water molecules are affected by the distribution of ions at the exact point where air and water meet. Traditionally, this has been done with a technique called vibrational sum-frequency generation (VSFG). With this laser radiation technique, it is possible to measure molecular vibrations directly at these key interfaces. However, although the strength of the signals can be measured, the technique does not measure whether the signals are positive or negative, which has made it difficult to interpret findings in the past. Additionally, using experimental data alone can give ambiguous results.

The team overcame these challenges by utilizing a more sophisticated form of VSFG, called heterodyne-detected (HD)-VSFG, to study different electrolyte solutions. They then developed advanced computer models to simulate the interfaces in different scenarios.

Revolutionizing Traditional Models

The combined results showed that both positively charged ions, called cations, and negatively charged ions, called anions, are depleted from the water/air interface. The cations and anions of simple electrolytes orient water molecules in both up- and down-orientation. This is a reversal of textbook models, which teach that ions form an electrical double layer and orient water molecules in only one direction.

Co-first author Dr Yair Litman, from the Yusuf Hamied Department of Chemistry, said: “Our work demonstrates that the surface of simple electrolyte solutions has a different ion distribution than previously thought and that the ion-enriched subsurface determines how the interface is organized: at the very top there are a few layers of pure water, then an ion-rich layer, then finally the bulk salt solution.”

Co-first author Dr Kuo-Yang Chiang of the Max Planck Institute said: “This paper shows that combining high-level HD-VSFG with simulations is an invaluable tool that will contribute to the molecular-level understanding of liquid interfaces.”

Professor Mischa Bonn, who heads the Molecular Spectroscopy department of the Max Planck Institute, added: “These types of interfaces occur everywhere on the planet, so studying them not only helps our fundamental understanding but can also lead to better devices and technologies. We are applying these same methods to study solid/liquid interfaces, which could have potential applications in batteries and energy storage.”

Reference: “Surface stratification determines the interfacial water structure of simple electrolyte solutions” by Yair Litman, Kuo-Yang Chiang, Takakazu Seki, Yuki Nagata and Mischa Bonn, 15 January 2024, Nature Chemistry . DOI: 10.1038/s41557-023-01416-6

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Water pp 21–40 Cite as

Understanding the Structure and Function of Water at the Molecular Scale

• Sheng Meng 3 &
• Enge Wang 4  
• First Online: 20 June 2023

298 Accesses

If you had to choose “what is the most important substance in nature”, I’m afraid most people’s answer would be: water! This is probably one of the beliefs that have remained constant throughout the history of mankind. We have to ask: What is it about water and why is it so magical?

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Meng, S., Wang, E. (2023). Understanding the Structure and Function of Water at the Molecular Scale. In: Water. Springer, Singapore. https://doi.org/10.1007/978-981-99-1541-5_2

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A Novel Tool for Visualization of Water Molecular Structure and Its Changes, Expressed on the Scale of Temperature Influence

Zoltan kovacs.

1 Department of Physics and Control, Faculty of Food Science, Szent István University, H-1118 Budapest, Hungary

Bernhard Pollner

2 Department for Hygiene and Medical Microbiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria; [email protected]

George Bazar

3 Department of Nutritional Science and Production Technology, Faculty of Agricultural and Environmental Sciences, Kaposvar University, H-7400 Kaposvar, Hungary; uh.balirga@razab

Jelena Muncan

4 Biomeasurement Technology Laboratory, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan; pj.ca.u-ebok.elpoep@nacnumj

Roumiana Tsenkova

Aquaphotomics utilizes water-light interaction for in-depth exploration of water, its structure and role in aqueous and biologic systems. The aquagram, a major analytical tool of aquaphotomics, allows comparison of water molecular structures of different samples by comparing their respective absorbance spectral patterns. Temperature is the strongest perturbation of water changing almost all water species. To better interpret and understand spectral patterns, the objective of this work was to develop a novel, temperature-scaled aquagram that provides standardized information about changes in water molecular structure caused by solutes, with its effects translated to those which would have been caused by respective temperature changes. NIR spectra of Milli-Q water in the temperature range of 20–70 °C and aqueous solutions of potassium chloride in concentration range of 1 to 1000 mM were recorded to demonstrate the applicability of the proposed novel tool. The obtained results presented the influence of salt on the water molecular structure expressed as the equivalent effect of temperature in degrees of Celsius. The temperature-based aquagrams showed the well-known structure breaking and structure making effects of salts on water spectral pattern, for the first time presented in the terms of temperature influence on pure water. This new method enables comparison of spectral patterns providing a universal tool for evaluation of various bio-aqueous systems which can provide better insight into the system’s functionality.

1. Introduction

Recently, water has become more and more important subject of studies, as evidenced by the increasing number of water-related publications in various fields of science [ 1 , 2 , 3 , 4 ]. Water is fundamental to life—it is one of the essential and widely distributed components of biologic systems, which can be considered as a biomolecule in its own right [ 5 , 6 ]. Different scientific fields have been studying water from different aspects, trying to reach better understanding of its properties, structure and functions, yet still, our picture of water as a substance is rather incomplete. Spectroscopy methods, which are based on interaction of light and matter, have contributed a lot to our understanding of water. Recently, established, scientific discipline of aquaphotomics aims to integrate the knowledge these methods acquired about water based on its interaction with light, into one “omics” discipline which relates the structure of water with its functionality, and whose ultimate objective is better understanding of water as a matrix of aqueous and biologic systems [ 7 ]. In this regard, aquaphotomics have made significant novel discoveries, and utilized the properties of water in various application fields ranging from water and food quality monitoring, microbiology, to biomeasurements, biodiagnostics and biomonitoring [ 8 , 9 , 10 ]. Owing to the wide range of aqueous systems and biologic systems aquaphotomics studied, some novel, surprising insights have been discovered, which place focus on importance of water structure, hydrogen bonding and temperature.

The effect of temperature has always been one of the most studied phenomena in spectroscopy with respect to its influence on water structure. The very terms “structure-makers” and “structure-breakers” are coined to describe substances which induce changes in the water structure and consequently its spectrum, comparable to decrease in temperature and increase of temperature, respectively. Effects of salts or sugars are commonly described using those terms [ 11 , 12 , 13 ]. The known influence of temperature on hydrogen bonding in water is something that can be used as an etalon for better understanding of how substances affect the structure of water in various solutions. Among many others, principal component analysis and two-dimensional correlation spectroscopy [ 14 ] or multivariate curve resolution-alternating least squares technique [ 15 ] were used to describe the effects of temperature perturbations on the NIR spectra of water in terms of hydrogen bonding either alone or in comparison to salt perturbation.

Aquaphotomics studies made some further steps uncovering that various phenomena, related to biomolecules or functionality of living organisms and aqueous systems can be described as related to specific water molecular structure and presented using spectral pattern.

For example, in one work, concerned with the detection of UV-induced damage on DNA structure, it was found that the aqueous solutions of UVC-damaged DNA caused increase in hydrogen bonded water—i.e., that damaged DNA was a structure-making element causing changes of water similar to low temperature [ 16 ]. In another study, which explored cold tolerance ability of different soybean cultivars, it was found that the water structure in the leaves of those cultivars with higher cold tolerance ability even at low temperatures preserved the water in less-hydrogen bonded state compared to those cultivars who are more susceptible, as if the environmental temperature would have been in fact higher [ 17 ]. What these novel insights into the water structure and analogy with temperature influence provided is a novel knowledge and better understanding of the water functionality at different levels of organization of biologic systems.

One of the main visualization and analytical tools of aquaphotomics, is the so-called aquagram [ 8 , 18 ] which provides a comprehensible demonstration of the ratios of different water species present in a sample. Aquagrams have been found very useful in many applications, such as diagnosis of estrus in giant pandas [ 19 ], orangutans [ 20 ] and cows [ 21 ] and showing the different water spectral patterns of probiotic and non-probiotic bacteria strains [ 22 ], or for example, revealing different types of water in the soft contact lenses, in a completely nondestructive manner [ 23 , 24 , 25 ]. The cited references demonstrated the usefulness of the presentation of the water spectral patterns in aquagrams.

In order to unify the relation between water species depicted by aquagrams and related water functionalities we propose to use temperature as a common denominator to express changes of light absorbance at each of the water vibrational frequencies as changes caused by the most influential perturbation for water—temperature. Considering the advantages of better understanding of the functionality of water structure if the analogy is made with the influence of temperature, the objective of this work was to develop a novel method and a visualization tool, so called temperature-based aquagram which translates the effects of any type of perturbation of water structure in aqueous or biologic systems to the equivalent effects that would have been caused by the temperature changes and expressed in temperature units. The need to introduce the temperature-based aquagrams arose from the experiments on more complex systems, such as previously described, where it was observed that certain phenomena, (caused by solutes for example) have effects on the water molecular structure of the system and contribute to its functionality in the way analog to the changes in temperature.

In a study concerned with classification of bacteria based on the probiotic strength it was found that the strong probiotic bacteria, compared to the moderately strong strains or non-probiotic strains, create less hydrogen-bonded water species ( Figure 1 ) [ 22 ]. On the other hand, the spectra of pure water at different temperatures show shift of the main band towards the shorter wavelengths with increasing temperature [ 14 ], i.e., showing that increase in temperature results in breaking of the hydrogen bonds. If the two cases are compared, it can be seen that probiotic bacteria affect surrounding water similarly to the influence of temperature increase, as if they are a structure-breaking element [ 22 ]. This conclusion supports the novel insight into molecular mechanisms of how probiotics work–they increase solubility of substances in water [ 26 ], just like the increase in temperature of the water would contribute to better solubilization.

Water spectral pattern presented on aquagrams shows different water structure in different bacteria strains (Reprinted with permission from Slavchev, A., Kovacs, Z., Koshiba, H., Nagai, A., Bázár, G., Krastanov, A., Kubota, Y. and Tsenkova, R. 2015. [ 22 ]).

From this example, it can be seen that comparisons with effect of temperature can be useful and contribute to better intuitive understanding of the functionality of the studied system. Recalling the soybean cultivars example, the role of many substances that plants accumulate in response to cold stress, becomes more obvious—their function is to provide a certain water molecular structure in the leaves as if the temperature of the environment is different [ 17 , 27 ].

The concept of the novel visualization tool—a temperature-based aquagram—was developed similarly to the one Bernal and Fowler introduced long ago—the so called “structural temperature” concept [ 28 ]. The “structural temperature” is the respective temperature at which pure water would have effectively the same molecular structure as the water of the aqueous system under study. At the time of introduction, no adequate method that could describe that structure was found; there were propositions that it can be estimated based on the measurements of viscosity, Raman spectra or X-ray diffraction. In addition, the intended purpose was mainly concerned with the applications in analysis of electrolyte solutions, and since the concept did not offer the possibility to separate effects of the individual ions, the entire idea was more or less abandoned [ 29 ]. However, the structural temperature concept fits well into the framework of aquaphotomics, which places the water spectral pattern and the respective water functionality of the system in the central place. In contrast to “reductionistic omics methods” which are focused on isolating the biomolecules and separation of elements of the system, the aquaphotomics views each aqueous or biologic system as a whole, where all the components of the system exert their influence on the water matrix, whose structure is directly related to the function of the system [ 9 , 10 ]. Just like the temperature is the macroscopic, measurable characteristic, arising from the molecular structure of the system, so is the light absorbance at each water specific vibrational frequency, and one can benefit from expressing one in the terms of another.

The purpose of this study is to introduce a novel visualization tool, which expresses the effects of any type of perturbation of water molecular structure in aqueous or biologic systems to the equivalent effects that would have been caused by the temperature and expressed in temperature units. To illustrate this, we have chosen a simple salt solution and a concentration as a major perturbation. Salt is chosen as it is not near infrared active substance, hence the changes in absorbance of the solutions are only due to the changes in water molecular structure [ 15 , 30 ]. Following the steps provided in the study, one can easily replicate the experiment, develop the temperature-based aquagrams and use it further for specific purposes. While in this study, the analysis and the results are presented for only 1st overtone of water region, the same methodology is applicable for any region of the water absorbance spectra. This new method provides numerical results on a clearly defined scale with confidence intervals. It enables the comparison of results across time and different experiments and provides information about the statistical significance of the found differences.

2. Results and Discussion

The spectral data in the wavelength interval of 1300 to 1600 nm for the two experiments were separately subjected to principal component analysis (PCA). The PCA score plots demonstrated the multidimensional patterns of the spectral data. Specifically, the highest variations displayed in the first principal components (PC1) were related to temperature and concentration of potassium chloride, representing 99.3% and 99.1% of the spectral variation in case of the temperature and the potassium chloride experiments, respectively. The PCA results did not show outliers either in the temperature or the potassium chloride datasets. The raw and 2nd derivative spectra of the two experiments were analyzed separately to discover the wavelengths exhibiting the largest changes caused by the temperature and salt perturbations.

2.1. Results of Temperature Experiment

The raw and 2nd derivative absorbance (logT −1 ) spectra in the spectral range of 1300 to 1600 nm of Milli-Q water in the temperature range of 20 to 70 °C are shown in Figure 2 . The main feature of the NIR spectrum of water is a broad peak around 1450 nm, comprised of several overlapping bands, described mainly as the 1st overtone of the OH stretching vibration [ 31 ]. This observation is confirmed by the second derivative spectra which indicated very intense bands at 1412 and 1462 nm. These bands are well known as bands associated with free water molecules [ 32 , 33 , 34 ] and strongly hydrogen-bonded water [ 14 , 35 ], respectively.

Raw and 2nd derivative (calculated with Savitzky–Golay filter using 2nd order polynomial and 21 points) absorbance (logT −1 ) spectra in the spectral range of 1300–1600 nm (OH first overtone) of Milli-Q water in the temperature range of 20–70 °C ( n = 78).

From a spectroscopic point of view, an increase in temperature has been interpreted as a decrease of number of hydrogen bonds [ 14 , 34 ], while others explain it via weakening of hydrogen bonds [ 36 ]. There is agreement, regardless of one’s preferred theory, that the change of temperature causes alteration in hydrogen-bonding configurations of water as described in more details previously [ 37 ].

Figure 2 shows a “blue shift”, i.e., movement of the main band towards the shorter wavelengths with increasing temperature and an isosbestic (temperature invariant) point. These phenomena are well studied in scientific literature [ 14 , 34 , 38 ]. Evidence clearly suggest that less hydrogen-bonded water is predominant at higher temperature, while spectra acquired at low temperature are represented mostly in the more hydrogen-bonded area where water molecules form species with one (S1), two (S2), three (S3) and four (S4) hydrogen bonds [ 39 ].

Despite the competing theories about the water structure, aquaphotomics identifies water-specific absorbance bands with higher variations caused by respective perturbation for the system of interest and uses them to depict the unique spectral pattern as an integrated marker of the system–perturbation interaction. The presentation of the 12 specific water coordinates [ 7 ] of the spectra of Milli-Q water acquired in the temperature range of 20 to 70 °C together with the 95% confidence intervals is given in Figure 3 a,b, calculated with the temperature-based aquagram calculation method. In the case of working with more complex system, it would be advisable to follow the protocol of aquaphotomics analysis which can provide more thorough examination of activated water absorbance bands and not necessarily limit the presentation to only the 12 coordinates as is chosen here. The aquagram provides an easy-to-comprehend presentation of the phenomena described above, i.e., the change of the strongly and weakly hydrogen-bonded patterns, based on Figure 2 . The movement of the higher absorbance towards shorter wavelengths with increasing temperature is convincing. The scales of the aquagrams ( Figure 3 a,b) express the effect of perturbation occurring at the 12 coordinates (i.e., in the defined wavelength ranges) in degrees Celsius equivalent. Therefore, in this specific example the radial values show the temperatures corresponding to the signal acquisitions (20 to 70 °C). The plotted dashed and dotted lines represent the upper and lower confidence levels of the aquagram values, respectively, for each single analyzed temperature step. There was no overlapping of the confidence intervals (95%) of the Milli-Q samples measured at different temperature observed, meaning that 2 °C temperature changes caused statistically significant effects on the individual coordinates (i.e., in the defined wavelength ranges). The stability of the temperature-based aquagram calculation is presented in Figure 3 b, by depicting only three selected temperature levels (20, 30 and 40 °C). Though the spectral dataset used to calculate the temperature-based aquagram of Figure 3 b is only a subset of the dataset used to calculate Figure 3 a, the shape and the range are the same in both cases. This type of stability was not possible with the “classic” aquagram ( Figure 3 c,d). These examples present the applicability and the additional benefits of the newly developed temperature-based aquagram for the evaluation and presentation of the water species in the 12 coordinates (representing defined wavelength ranges) through the evaluation of a well-known perturbation, i.e., the effect of temperature on the water spectral changes.

Aquagrams of Milli-Q water in the temperature range of 20–70 °C, ( a , b ) with 95% confidence intervals calculated with temperature-based aquagram calculation method, ( c , d ) calculated with the classic calculation method, ( a , c ) all the 26 temperature steps ( n = 78) and ( b , d ) on three selected temperature steps ( n = 9) to show the stability of the methods (UCL—upper confidence level, LCL—lower confidence level).

2.2. Results of Potassium Chloride Experiment

The raw and 2nd derivative absorbance (logT −1 ) spectra of the aqueous solutions of 0.001 to 1 M potassium chloride salt in the 1300–1600 nm wavelength range (OH first overtone) are presented in Figure 4 . The main component of the aqueous solution, other than water, is KCl, which has no absorption in the NIR region; thus, it is not surprising that the spectra show a broad peak around 1450 nm. The second derivative spectra also provide similar patterns to those of the Milli-Q water acquired at different temperature, indicating bands at 1412 and 1462 nm. The trend of the shift in the peak position was similar to that observed in the temperature-perturbed pure water (i.e., the peak moves towards lower wavelengths as temperature is increased), but the actual peak locations were different from those for the pure water. The effect of low concentrations of salts diluted in water has been illustrated by the changes in the OH bonding of water molecular systems in many experiments [ 15 , 40 , 41 , 42 ]. As salts do not absorb NIR light, accurate measurement of even low concentration of salts, published in the above-mentioned papers, means salts change the surrounding water molecular structure according to the number of the solvent molecules in the solution which still can restructure the water molecular system.

Raw and 2nd derivative (calculated with Savitzky–Golay filter using 2nd order polynomial and 21 points) absorbance (logT −1 ) spectra in the range of 1300–1600 nm (OH first overtone) of 0.001–1 M KCl solutions ( n = 180).

This phenomena is not new; Bernal and Fowler [ 28 ] showed that the addition of electrolytes changes the spectrum of water in the infrared overtone region. Lin and Brown [ 43 ] also analyzed the effects of different salts on water spectra, and the authors were able to build accurate regression models using the spectral range of 1490 to 1610 nm for salt content prediction.

The spectra shown in Figure 4 imply that the increasing concentration of KCl causes “blue shift”, i.e., a shift towards the spectral range referring to the band of less hydrogen-bonded water molecules. Our findings, hence show a good agreement with the results of previous research [ 15 , 40 , 41 , 42 ].

A more detailed evaluation of the proposed 12 specific water coordinates [ 7 ] of the spectra of the aqueous solutions of potassium chloride compared to the spectra of water is provided in Figure 5 . The plots show the aquagrams of the single concentration levels together with the respective 95% confidence intervals calculated with the “classic” method ( Figure 5 a) and the new temperature-based aquagram calculation method ( Figure 5 b). The relative position of the patterns of the single concentration levels shows some similarity for the two methods. Furthermore, in both methods, spectral patterns of the highest concentration range (100–1000 mM) show the highest difference from the spectra of the lower ranges and Milli-Q samples (the latter one in black). This pattern explains the same phenomena which were found based on the raw spectra, i.e., a higher concentration of salt create water with less hydrogen bonds and decreases the number of water species to more hydrogen bonds. For the higher concentration ranges the aquagrams of the individual concentrations do not overlap, i.e., addition of 0.01 or 0.1 M KCl caused statistically significant change at the individual coordinates.

Aquagrams with 95% confidence intervals of Milli-Q water ( n = 150) and 0.001–1 M KCl solutions ( n = 180) calculated with the classic ( a ) or the temperature based aquagram ( b ) calculation methods on the individual concentrations (UCL—upper confidence level, LCL—lower confidence level).

However, the results also show an increasing tendency of the C7 coordinate (1432–1444 nm) with increasing concentration of KCl, which can be assigned to water molecules with one hydrogen bond (S1), meaning that increase in concentration of salt leads to increase in the number of these molecules [ 39 ].

The dominantly higher effect of the higher concentrations on the spectral pattern hides the pattern of the lower concentrations; therefore, the calculation of the aquagrams were performed using the spectral data set for the two lowest concentration ranges only ( Figure 6 ). The phenomena of the higher concentrations on the water spectral pattern, namely the higher concentration being more dominantly a structure breaker, can be observed in case of the concentration of samples at the concentration range of 10 to 100 mM. It is interesting to note the similarities to the pattern of the aquagrams calculated on all the three ranges ( Figure 5 b).

Aquagrams with 95% confidence intervals of Milli-Q water ( n = 150) and 0.001–0.1 M KCl solutions ( n = 120) calculated with the temperature based aquagram calculation method on the individual concentrations (UCL—upper confidence level, LCL—lower confidence level).

The aquagrams of the higher concentrations (10–100 mM) show consistency with the previous findings regarding the structure-breaking characteristic as displayed in Figure 6 . More specifically, the higher concentration samples present higher absorbance values in the range between 1342 and 1374 nm, i.e., C01-C03 that refer to the 1st overtone of free OH stretch (OH–(H 2 O) n , n = 1…4) [ 44 , 45 ] and 1440 and 1452 nm, i.e., C07-C08 that are known as the bands of water hydration [ 35 ] and water molecule connected to another water molecule (S 1 ) [ 14 , 46 ] and the symmetric and asymmetric stretching of first overtone of water [ 35 , 46 , 47 ]. However, in the range between 1476 and 1512 nm, i.e., C10-C12, the higher concentration samples show lower values and these wavelengths are usually assigned to strongly hydrogen bonded water [ 14 , 35 ] and aqueous protons ([H + •(H 2 O) 6 ]–H 2 O in H 5 O 2 + symmetric stretch) [ 48 ]. These findings also mean decreasing concentration of salt causes a shift towards longer wavelengths, i.e., the range referring to the band of more hydrogen bonded water molecules.

Using the additional benefit of the temperature-based aquagram calculation method, further results can be achieved from Figure 6 . The addition of, for instance, 0.1 M potassium chloride to Milli-Q water results in water structural changes equivalent to changes caused by temperature of about 0.65, 0.6, 0.3, 0.1, 0.2 0.6, 1.8, 1.2, 0.2, −0.1, −0.3 and −0.6 °C at C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11 and C12 coordinates, respectively. Furthermore, having calculated the confidence intervals, the statistical significance of the differences is also available. For example, calculations showed that addition of 0.02 M KCl to Milli-Q caused change equivalent to the change due to 0.33 and 0.23 °C temperature increase at coordinates C07 and C08 when compared to pure Milli-Q, which was found significant ( p = 0.05), too.

The aquagrams of the lowest concentration range (1–10 mM) calculated with the temperature-based aquagram method is shown in Figure 7 to further evaluate the findings of the effects of decreasing concentrations of salt. The results suggest that we can observe concentration levels of 5 to 10 mM that cause a shift towards longer wavelengths, i.e., the range referring to the band of more hydrogen-bonded water molecules compared to the spectrum of Milli-Q water. These findings imply that salts can also have structure-breaker and structure-maker effects on water structure similar to the behavior of sugars [ 13 ]. However, the aquagrams of the even lower concentrations (1 to 5 mM) also show alteration with nearly the same deviation, but towards shorter wavelengths. This may suggest that changing between structure-breaker and structure-maker properties of salt exist at such a low concentration, but the discernment of these minor changes would require very accurate measurements.

Aquagrams with 95% confidence intervals of Milli-Q water ( n = 150) and 0.001–0.01 M KCl solutions ( n = 60) calculated with the temperature based aquagram calculation method on the individual concentrations (UCL—upper confidence level, LCL—lower confidence level).

3. Materials and Methods

3.1. samples.

Two experiments with different sources of perturbations were conducted to demonstrate the procedure of temperature-based aquagram development and show the advantages in comparison to the representation of spectral data using classic aquagrams. In both experiments, pure Milli-Q water was used as a sample (Milli-Q purification system (Millipore, Molsheim, France, resistance = 18 MΩ) and in the first experiment perturbation of the sample was caused by changes in temperature, while in the second one, by changes in the concentration of salt.

3.2. The Temperature Experiment

The effect of temperature perturbation on water near-infrared spectra has been well-studied and is thoroughly described in the literature [ 14 , 34 , 49 ]. Therefore, the experiment was performed on Milli-Q water in the temperature range of 20 to 70 °C to acquire spectra which could be used for the evaluation of the aquagram methods. The Milli-Q water was produced by a Milli-Q purification system (Millipore, Molsheim, France, resistance = 18 MΩ). The spectral acquisition was performed at 2 °C increments, resulting in 26 temperature steps in the range of 20 to 70 °C.

3.3. The Potassium Chloride Experiment

The addition of salt to water at different concentrations is also an often evaluated perturbation [ 42 , 50 ]. Therefore, an experiment was performed with different concentrations of aqueous solutions of potassium chloride. Potassium chloride (KCl, M = 74.56 g mol −1 , purity min. 99.0% mass/mass) was purchased from Wako Pure Chemical Industries, Ltd. (Kobe, Japan). Aqueous solutions were prepared in different concentrations of KCl, in the range of 1 to 1000 mM. Three concentration ranges were prepared: Range A, from 100 to 1000 mM concentration, in steps of 100 mM; Range B from 10 to 100 mM, in steps of 10 mM and finally, Range C, in 1 to 10 mM in 1 mM concentration steps. Each dilution was prepared by serial dilution from the stock samples with the highest concentration in a given range (A, B or C) and prepared in two replicates, resulting in two independently prepared sets of samples. Stock solutions were prepared and further serially diluted with added Milli-Q water step-by-step to reach the appropriate concentrations—a solution created in each step was further diluted to prepare the next lower concentration.

3.4. NIR Spectral Acquisition

A FOSS-XDS spectrometer (FOSS NIRSystems, Inc., Hoganas, Sweden) equipped with a Rapid Liquid Analyzer module including a temperature-controlled 1 mm pathlength cuvette holder was used to measure transmittance spectra (logT −1 ) of the Milli-Q samples for the temperature experiment and of the aqueous solutions for the KCl experiment. Spectral acquisition was performed by saving three consecutive spectra in the range of 400–2500 nm at 0.5 nm spectral steps. Each saved spectrum was the average of 32 successive scans.

A thermal bath with continuous water circulation was attached to the Rapid Liquid Analyzer module to ensure the required temperature of the sample during scanning in the range of 20 to 70 °C at 2 °C increments.

The same apparatus was used to provide a constant temperature of 28 °C where each aqueous solution of potassium chloride was incubated for 90 s to equilibrate to the required temperature before scanning. Milli-Q water samples were measured as every fifth sample during the KCl experiment to provide environmental controls.

The total number of spectra for the temperature experiment was 78 (26 temperature steps × 3 consecutive scans) and for the KCl experiment was 330 (30 concentrations × 2 repeats × 3 consecutive scans + 150 Milli-Q control scans) ( Appendix A Dataset).

The FOSS-XDS instrument was operated using VISION 3.5 software (FOSS NIRSystems, Inc., Hoganas, Sweden). In both experiments, reference spectra were recorded before every sample.

3.5. Statistical Data Analysis

Only the wavelength interval of 1300 to 1600 nm, corresponding to the first overtone of the O–H stretching band [ 51 ] was used for the evaluations. For the purpose of explaining methodology of how to develop temperature-based aquagrams, in this study, the focus is placed on this particular part of the water absorbance spectra, because it is best understood so far in the terms of the water molecular species whose absorbance bands are well-resolved and their assignments known [ 7 ]. In the first overtone of water as a result of systematization of experimental work done on many different systems, not only different aqueous solutions, but also a great variety of biologic systems under different perturbations 12 water absorbance bands termed WAMACs (Water Matrix Coordinates)–each range from 6 to 12 nm width, were discovered [ 7 ]. The great body of evidences in scientific literature provided the meaning to these ranges—i.e., it was possible to connect each of these 12 coordinates to specific water molecular species. In aquaphotomics studies the 12 WAMACs are called, coordinates because they represent windows in the spectra through which water structure of the system under study can be observed. In this study, the 12 WAMACs will be used to develop aquagrams, but it should be noted that the methodology explained is applicable for any region of the water absorbance spectra; it is not necessarily limited to the coordinates chosen here. Here, we chose for the reason of simplicity and because they are well-understood to use only those. However, depending on the system under study and the range of the spectra used, the reader is advised to follow the aquaphotomics protocol of analysis for extraction of the “activated water absorbance bands–WAMACs [ 8 ] and then follow the further instructions to develop temperature-based aquagrams as described below.

Before the development of aquagrams, exploratory analysis was performed. First, Principal component analysis (PCA) [ 52 ] was used to describe multidimensional patterns in the spectral data and to discover outliers. The raw and 2nd derivative spectra were plotted to visualize the spectral changes induced by temperature perturbation and by the perturbation of salt concentration on the spectra of Milli-Q water and aqueous solutions of potassium chloride, respectively. The 2nd derivative spectra were calculated using a Savitzky–Golay filter [ 53 ] using the 2nd order polynomial and 21 points.

3.5.1. Calculation Protocol of “Classic” Aquagram

The absorbance values at specific water matrix coordinates (WAMACs) [ 7 ] define the water spectral pattern (WASP), which is different for different perturbations. The WASP can be visualized by a chart called the aquagram [ 18 , 19 ]. This representation of the WAMACs was first introduced by Tsenkova [ 18 ]. This aquagram (from now on called the “classic” aquagram) displays the multiplicative-scatter-corrected (MSC) (or standard-normal-variate (SNV)) transformed, normalized and averaged absorbance values of different samples or sample groups at 12 specific characteristic wavelengths. As, mentioned, these specific wavelengths were experimentally discovered as absorbance bands of specific water molecular species in previous studies and are later confirmed by overtone calculations of already reported water absorbance bands in the infrared range [ 7 ]. The aforementioned water absorbance bands cover various form of water molecular species and are thus useful to depict characteristic spectral patterns in the first overtone region of water. This calculation can be summarized by Equation (1).

where, A λ ′ —value on aquagram for a given wavelength; A λ —absorbance after MSC applied on 1st overtone region of OH (i.e., 1300–1600 nm); μ λ —mean of all spectra for the examined group at a given wavelength (after MSC applied); σ λ —SD of all spectra for the examined group at a given wavelength (after MSC applied); λ —12 wavelengths (1342, 1364, 1374, 1384, 1412, 1426, 1440, 1452, 1462, 1476, 1488, 1512 nm) [ 7 ].

The classic aquagram shows the relative fingerprint, i.e., the WASPs, in the context of all spectra in the examined group [ 18 , 19 , 21 , 54 ].

Recently, this aquagram calculation method was extended by adding the possibility to observe the statistical significance of the differences presented on the aquagrams. Therefore, besides the average spectra of the individual groups used to plot the aquagrams, the respective confidence intervals are also calculated using the so-called Bootstrap method [ 55 ]. This improvement makes it possible to plot the aquagrams together with their upper and lower 95% confidence interval limits.

3.5.2. Calculation Protocol for Newly Developed (Temperature-Based) Aquagram

The newly developed temperature-based aquagram calculation algorithm presents the respective water matrix coordinates in units equivalent to change in temperature and includes the respective confidence intervals. Therefore, it gives rise to the possibility to compare the WAMACs across time and also across different experiments and it provides information about the statistical significance of the differences.

The new calculation method is based on the comparison of the areas (under the ranges of the above-mentioned 12 specific water coordinates [ 7 ]) of the respective test sample spectra and the spectra of Milli-Q water. This method aims to express the spectral pattern changes in units equivalent to the change of temperature that would cause the observed change. The calculation of this aquagram concept (from now called the temperature-based aquagram) can be summarized in the following steps. Note that the calculation steps are explained for one coordinate (C01 representing spectral range between 1336 and 1348 nm, as an example) out of the 12 coordinates (C01-C12, i.e., defined wavelength ranges) to give an easily understandable description, but the same steps have to be repeated for each of the 12 coordinates. The main calculation steps are summarized in a chart to provide an overview of the developed method ( Appendix B Figure A1 ).

The dataset of the experiment of interest is defined as the experimental dataset.

The average spectra of the groups of interest (in this case, salt concentration levels) are calculated in the experimental dataset together with their respective confidence intervals using the Bootstrap method [ 55 ], yielding as many single, unique spectra as there are groups are in the experimental dataset (plus their upper and lower 95% confidence interval limits).

Scheme of the calculation for Area under the curve (AUC) aquagram method. Spectrum of pure water with highlighted subranges of the 12 specific water matrix coordinates (WAMACs).

• Step 4. The ratio of the area under the curve for each single coordinate is calculated with respect to the full area under the curve for the first overtone OH region (i.e., the area of C01 is divided by the full area under the spectrum in the range of 1300 to 1600 nm). This is done for every single average spectrum, in the reference dataset and the experimental dataset (together with the respective confidence interval limits for the experimental dataset). This calculation step provides normalized values and avoids possible differences due to scattering and/or pathlength effects.
• Step 5. Based on the reference dataset, a continuous array of values for the relative area of C01 (as calculated in Step 1) is calculated for a continuous temperature range from 20 to 70 °C using local polynomial regression. This is an essential step in order to accommodate the data from an experiment performed at specific temperature—see Step 6.
• Step 6. The basic principle of the temperature-based aquagram method is to compare the effect of the perturbation used on the system under study which resulted in a certain water spectral pattern to the effect the temperature changes would induce in pure water. Thus, any perturbation can be expressed as an equivalent temperature effect on a Milli-Q water sample. It is necessary to perform a “local calibration” with the reference dataset around the temperature of the experimental dataset. Therefore, in this step, the temperature calibration range is defined. This range is used to express the effect of perturbation in degrees Celsius equivalent. For this, a symmetrical scale is defined from the reference dataset (calculated at Step 5) using two degrees, plus and minus around the temperature of the experiment (hence, a span of 4 °C). For example, if the experiment was performed at 25.0 °C, then the calibration range of 23.0 to 27.0 °C would be used.
• Step 7. The temperature calibration equation, the relationship between the change of the temperature and change of the area of C01 at the temperature of the experiment, is determined based on the calculation performed in Step 5 on the reference dataset. (It is known how the area of C01 changes as a function of temperature described by a linear function). Therefore, it is easy to compare the changes for areas for C01 for the experimental dataset (calculated at Step 3) to the changes of the area of C01 caused by temperature, i.e., to express the changes in C01 in units of temperature (degrees Celsius) equivalent.
• Step 8. The calculated temperature (degrees Celsius) equivalent value for every group of the experimental dataset is finally visualized together with the respective 95% confidence intervals in a radar chart, where the units of the axes are in degrees Celsius.
• Step 9. The calculation and visualization of the results were performed using the R programing language [ 56 , 57 ].

4. Conclusions

Recently, aquaphotomics has been introduced to focus on water as a key component for providing information about the function of the entire system. Non-destructive NIR spectroscopy and aquaphotomics have been applied to explain new phenomena in the field of life sciences. In contrast to reductionistic methods in which biomolecules and other elements are analyzed separately from the system, aquaphotomics studies the aqueous systems through its water matrix.

In the present study, a newly developed temperature-based aquagram calculation method is presented as an additional tool to express the changes of water molecular structure in aqueous systems which are caused by perturbations different from temperature. Although the need to introduce temperature-based aquagrams originated from experiments on complex systems, the successful application of the new aquagram calculation method was demonstrated through the evaluation of the results of well-known phenomena. The results of temperature and salt perturbations on Milli-Q water are demonstrated in the present study.

The effect of temperature on the spectral pattern of Milli-Q water acquired in the temperature range of 20 to 70 °C is presented with the temperature-based aquagram calculation method. The method provides the presentation of the phenomena demonstrating blue shift in the first OH overtone range with increasing temperature. Furthermore, the scale of the aquagram expressed the effect of perturbation in degrees Celsius equivalent.

Aqueous solutions of potassium chloride were chosen for the experiment as KCl has no absorption in the NIR region. Thus, its effect on water spectral patterns can be clearly evaluated and presented as caused by temperature changes at respective wavelengths. Furthermore, it demonstrates that the method is invariably applicable for evaluation the effects of all types of solutes. The new temperature-based aquagram calculation method provided further information about the magnitude of the change. In other words, the results were displayed on a degree-Celsius scale that showed how much a given sample would have needed to have been warmed up or cooled down in each of the single coordinates (C01 to C12) to achieve the same results as the actual measurement, while all measurements were performed at precisely the same temperature.

Adding 0.1-M potassium chloride to Milli-Q water resulted in structural changes equivalent to an approximately 0.6 °C temperature increase in the less hydrogen-bonded, and 0.3 °C temperature decrease in the more hydrogen-bonded areas of the OH first overtone spectral region.

The examples presented here confirm the applicability and the additional benefits of the temperature-based aquagram calculation method. They provide a demonstration of the ratio of the different water species existing in different aqueous and biologic systems. Additionally, this new type of aquagram calculation displayed the spectral patterns in a meaningful scale and stable pattern independent of any modification of the evaluated dataset, which gives rise to the opportunity to compare results not only within a single chart, but also across time and different experiments.

This newly developed tool is especially suitable for visualizing water structure evolution and phase transitions, for example, in the food preservation industry, pharmaceutical development, material science and related applications.

The presented new chemometric tool, developed in R-Project, is freely accessible as an R-package from GitHub repository [ 58 ] and can be used in various fields of NIR spectroscopy and water research.

Acknowledgments

Authors are grateful to Professor David Funk for his help to revise the manuscript from language editing and from scientific point of view.

Dataset. Raw spectral data used for the calculations presented in this study. Both data of temperature experiment and potassium chloride experiment is included in this dataset where the column experiment describes which spectra belong to which experiment.

Workflow of the calculation protocol of temperature-based aquagram.

Author Contributions

All authors contributed to this research. The design of the experiments was performed by Z.K., B.P. and R.T., Z.K. and B.P. did the recording and the processing of the NIRS data, as well as the result of the evaluation and implementing the concept in R-project. The manuscript was written by Z.K., B.P., G.B. and J.M., R.T. assisted in writing the study and revised it. Z.K., R.T., G.B. and J.M. contributed to designing the research and revise the manuscript. The work presented in the study was conceived within research projects led by R.T. and Z.K. All authors have read and agreed to the published version of the manuscript.

Authors acknowledge the financial support of the ÚNKP-19–4 New National Excellence Program of the Ministry for Innovation and Technology (Z.K.), János Bolyai Research Scholarship of the Hungarian Academy of Sciences (Z.K.) and by the European Union and co-financed by the European Social Fund through project No. EFOP-3.6.3-VEKOP-16–2017–00005. JM gratefully acknowledges the financial support provided by Japanese Society for Promotion of Science ( {"type":"entrez-protein","attrs":{"text":"P17406","term_id":"114259","term_text":"P17406"}} P17406 ).

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability: Samples of the compounds KCl are available from the authors.

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2 (page 14) p. 14 The water molecule and its interactions

• Published: August 2015
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‘The water molecule and its interactions’ discusses the structural and electrical properties of the water molecule. A water molecule is made up of two hydrogen atoms connected by covalent bonds to one oxygen atom. Water molecules interact with each other through a type of interaction called hydrogen bonding. A tetrahedral arrangement of four water molecules around a central one is the key to understanding water. It helps to explain the structure of water in its various states, its properties, and how it interacts with other kinds of molecules, allowing exploration of the properties and behaviour of the wide range of chemical, physical, and biological systems in which water is involved.

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 1.

• Hydrogen bonding in water

Hydrogen bonds in water

• Capillary action and why we see a meniscus
• Surface tension
• Cohesion and adhesion of water
• Water as a solvent
• Specific heat, heat of vaporization, and density of water
• Importance of water for life
• Lesson summary: Water and life
• Structure of water and hydrogen bonding

Introduction to the properties of water

• Solvent properties of water : Learn how and why water dissolves many polar and charged molecules.
• Cohesion and adhesion of water : Water can stick to itself (cohesion) and other molecules (adhesion).
• Specific heat, heat of vaporization, and density of water : Water has a high heat capacity and heat of vaporization, and ice—solid water—is less dense than liquid water.

Polarity of water molecules

Hydrogen bonding of water molecules, attribution:, works cited.

• "Bacterial cell structure." Wikipedia. June 24, 2015. Accessed July 5, 2015. https://en.wikipedia.org/?title=Bacterial_cell_structure .
• "Properties of water." Wikipedia. May 27, 2016. Accessed May 28, 2016. https://en.wikipedia.org/wiki/Properties_of_water .
• Reece, J. B., L. A. Urry, M. L. Cain, S. A. Wasserman, P. V. Minorsky, and R. B. Jackson. "Polar covalent bonds in water molecules result in hydrogen bonding." In Campbell Biology , 45. 10th ed. San Francisco, CA: Pearson, 2011.

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13.5: The Structure and Properties of Water

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• Page ID 41392

With 70% of our earth being ocean water and 65% of our bodies being water, it is hard to not be aware of how important it is in our lives. There are 3 different forms of water, or H 2 O: solid (ice), liquid (water), and gas (steam). Because water seems so ubiquitous, many people are unaware of the unusual and unique properties of water, including:

Boiling Point and Freezing Point

Surface tension, heat of vaporization, and vapor pressure.

• Viscosity and Cohesion
• Solid State
• Liquid State

If you look at the periodic table and locate tellurium (atomic number: 52), you find that the boiling points of hydrides decrease as molecule size decreases. So the hydride for tellurium: H 2 Te (hydrogen telluride) has a boiling point of -4°C . Moving up, the next hydride would be H 2 Se (hydrogen selenide) with a boiling point of -42°C . One more up and you find that H 2 S (hydrogen sulfide) has a boiling point at -62°C . The next hydride would be H 2 O (WATER!) . And we all know that the boiling point of water is 100°C . So despite its small molecular weight, water has an incredibly big boiling point. This is because water requires more energy to break its hydrogen bonds before it can then begin to boil. The same concept is applied to freezing point as well, as seen in the table below. The boiling and freezing points of water enable the molecules to be very slow to boil or freeze, this is important to the ecosystems living in water. If water was very easy to freeze or boil, drastic changes in the environment and so in oceans or lakes would cause all the organisms living in water to die. This is also why sweat is able to cool our bodies.

Besides mercury, water has the highest surface tension for all liquids. Water's high surface tension is due to the hydrogen bonding in water molecules. Water also has an exceptionally high heat of vaporization . Vaporization occurs when a liquid changes to a gas, which makes it an endothermic reaction. Water's heat of vaporization is 41 kJ/mol. Vapor pressure is inversely related to intermolecular forces, so those with stronger intermolecular forces have a lower vapor pressure. Water has very strong intermolecular forces, hence the low vapor pressure, but it's even lower compared to larger molecules with low vapor pressures.

• Viscosity is the property of fluid having high resistance to flow. We normally think of liquids like honey or motor oil being viscous, but when compared to other substances with like structures, water is viscous. Liquids with stronger intermolecular interactions are usually more viscous than liquids with weak intermolecular interactions.
• Cohesion is intermolecular forces between like molecules; this is why water molecules are able to hold themselves together in a drop. Water molecules are very cohesive because of the molecule's polarity. This is why you can fill a glass of water just barely above the rim without it spilling.

Solid State (Ice)

All substances, including water, become less dense when they are heated and more dense when they are cooled. So if water is cooled, it becomes more dense and forms ice. Water is one of the few substances whose solid state can float on its liquid state! Why? Water continues to become more dense until it reaches 4°C. After it reaches 4°C, it becomes LESS dense. When freezing, molecules within water begin to move around more slowly, making it easier for them to form hydrogen bonds and eventually arrange themselves into an open crystalline, hexagonal structure. Because of this open structure as the water molecules are being held further apart, the volume of water increases about 9%. So molecules are more tightly packed in water's liquid state than its solid state. This is why a can of soda can explode in the freezer.

Liquid State (Liquid Water)

It is very rare to find a compound that lacks carbon to be a liquid at standard temperatures and pressures. So it is unusual for water to be a liquid at room temperature! Water is liquid at room temperature so it's able to move around quicker than it is as solid, enabling the molecules to form fewer hydrogen bonds resulting in the molecules being packed more closely together. Each water molecule links to four others creating a tetrahedral arrangement, however they are able to move freely and slide past each other, while ice forms a solid, larger hexagonal structure.

Gas State (Steam)

As water boils, its hydrogen bonds are broken. Steam particles move very far apart and fast, so barely any hydrogen bonds have the time to form. So, less and less hydrogen bonds are present as the particles reach the critical point above steam. The lack of hydrogen bonds explains why steam causes much worse burns that water. Steam contains all the energy used to break the hydrogen bonds in water, so when steam hits your face you first absorb the energy the steam has taken up from breaking the hydrogen bonds it its liquid state. Then, in an exothermic reaction, steam is converted into liquid water and heat is released. This heat adds to the heat of boiling water as the steam condenses on your skin.

Water as the "Universal Solvent"

Because of water's polarity, it is able to dissolve or dissociate many particles. Oxygen has a slightly negative charge, while the two hydrogens have a slightly positive charge. The slightly negative particles of a compound will be attracted to water's hydrogen atoms, while the slightly positive particles will be attracted to water's oxygen molecule; this causes the compound to dissociate. Besides the explanations above, we can look to some attributes of a water molecule to provide some more reasons of water's uniqueness:

• Forgetting fluorine, oxygen is the most electronegative non-noble gas element, so while forming a bond, the electrons are pulled towards the oxygen atom rather than the hydrogen. This creates 2 polar bonds, which make the water molecule more polar than the bonds in the other hydrides in the group.
• A 104.5° bond angle creates a very strong dipole.
• Water has hydrogen bonding which probably is a vital aspect in waters strong intermolecular interaction

Why is this important for the real world?

The properties of water make it suitable for organisms to survive in during differing weather conditions. Ice freezes as it expands, which explains why ice is able to float on liquid water. During the winter when lakes begin to freeze, the surface of the water freezes and then moves down toward deeper water; this explains why people can ice skate on or fall through a frozen lake. If ice was not able to float, the lake would freeze from the bottom up killing all ecosystems living in the lake. However ice floats, so the fish are able to survive under the surface of the ice during the winter. The surface of ice above a lake also shields lakes from the cold temperature outside and insulates the water beneath it, allowing the lake under the frozen ice to stay liquid and maintain a temperature adequate for the ecosystems living in the lake to survive.

• Cracolice, Mark S. and Edward Peters I. Basics of Introductory Chemistry . Thompson, Brooks/Cole Publishing Company. 2006
• Petrucci, et al. General Chemistry: Principles & Modern Applications: AIE (Hardcover). Upper Saddle River: Pearson/Prentice Hall, 2007.

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• Corinne Yee (UCD), Desiree Rozzi (UCD)

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Who was dr. masaru emoto.

Dr. Masaru Emoto, the Japanese scientist who revolutionized the idea that our thoughts and intentions impact the physical realm, is one of the most important water researchers the world has known. For over 20 years until he passed away in 2014, he studied the scientific evidence of how the molecular structure in water transforms when it is exposed to human words, thoughts, sounds and intentions.

The extraordinary life work of Dr. Emoto is documented in the New York Times Bestseller, The Hidden Messages in Water . In his book, Dr. Emoto demonstrates how water exposed to loving, benevolent, and compassionate human intention results in aesthetically pleasing physical molecular formations in the water while water exposed to fearful and discordant human intentions results in disconnected, disfigured, and “unpleasant” physical molecular formations. He did this through Magnetic Resonance Analysis technology and high-speed photographs.

See the following water crystal photographs from Dr. Emoto’s work. Each water crystal you see was exposed to the word it has written next to it prior to being photographed:

His research also showed us how polluted and toxic water, when exposed to to prayer and intention can be altered and restored to beautifully formed geometric crystals found in clean, healthy water. The following photos are images of photographs of the the water in the Fujiwara Dam before and after the Reverend Kato Hoki, chief priest of Jyuhouin Temple, offered an hour long prayer over it.

How Music Affects Water?

Dr. Emoto also studied how sound affects water. The Emoto music studies demonstrate how certain types of sound, like classical music, generate beautiful crystalline patterns, while heavy metal music, generate ugly and distorted crystalline formations. In the images below you see the crystalline formation resulting from water being exposed to Mozart’s Symphony No. 40 and then in contrast what the water crystal image looks like after listening to heavy metal music.

Dr. Masaru Emoto put Water as a Living Consciousness on the map for the scientific world. He showed us how water is an energy capable of more than we ever imagined. The power human thoughts, sounds and intentions has to strengthen and disempower is one of the greatest discoveries of our time.

His work has us question, if water is affected by the words, intentions, and energies, what about human beings, who are made of mostly water? If we transform the water and thoughts we are made of, what else is possible?

There are legions of scientists who have built upon the breakthroughs of Dr. Emoto and are offering practical technologies for everyday life. One such example who we find particularly inspiring is the Austrian Engineer Bernard Ratheiser. Since 1994, he has developed devices that restructure water molecules and assist water in being its highest vibration as living energy.

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Water crystals and structured water.

With vortexing and sacred geometry along with nature’s energies through precious stones, Bernhard Ratheiser has created a way for water to be revitalized when it passes through one of his water structuring devices. Every measurement in his beautiful devices is designed to evoke the energy of the cosmos and realign water with the energy of creation.  

When water passes through his UMH Devices, everything life supporting in the water is enhanced, energy increases, memory is erased, and toxins are energetically neutralized. The following are actual photos of water that passed through the UMH device using the Emoto Protocol and demonstrates how inherent spring water quality is restored. You can see how the water crystal photos before and after passing through the UMH Master whole house device result in a significant improvement in crystalline structure.

Another of our collections, VitaJuwel, asked the Hadolife Laboratories in Austria, which was co-founded by Dr. Masaru Emoto and his oldest student to take microscopic photos of water before and after it had been treated with VitaJuwel.   You can see the stunning result below that’s an example of the crystalline structure you’ll be drinking in the water you can charge in the  VitaJuwel Wellness bottl e found at The Wellness Enterprise.

We live in exciting times when new technologies like water structuring devices are making it easy for us to access water’s highest vibration. Our understanding of the natural world is moving to new levels as technology embraces the truth of structured water science with sacred geometry, vortexing, and gemstones.

Dr. Zach Bush: Water and Memory

Thanks to how Dr. Masaru Emoto’s work opened the door to understanding water and memory, many doctors, scientists and researchers have made exciting new discoveries.  One of those doctors is triple board certified M.D,  Zach Bush.   In the following video, Zach Bush shares that there is no part of the human brain that holds long term memory, but there is, however, evidence that memory is held elsewhere. Watch the video below to hear what he has to say about where and how and how memory is held in the human body.

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The shape of water: What water molecules look like on the surface of materials

Scientist combine data analysis techniques with molecular dynamics simulations to understand the structure of water on material surfaces.

Tokyo University of Science

image: Combination of data analysis techniques with molecular dynamics simulations can help us understand the structure of water on material surfaces. view more 

Credit: Tokyo University of Science

Understanding the various molecular interactions and structures that arise among surface water molecules would enable scientists and engineers to develop all sorts of novel hydrophobic/hydrophilic materials or improve existing ones. For example, the friction caused by water on ships could be reduced through materials engineering, leading to higher efficiency. Other applications include, but are not limited to, medical implants and anti-icing surfaces for airplanes. However, the phenomena that occur in surface water are so complicated that Tokyo University of Science, Japan, has established a dedicated research center, called "Water Frontier Science and Technology," where various research groups tackle this problem from different angles (theoretical analysis, experimental studies, material development, and so on). Prof Takahiro Yamamoto leads a group of scientists at this center, and they try to solve this mystery through simulations of the microscopic structures, properties, and functions of water on the surface of materials.

For this study in particular, which was published in the Japanese Journal of Applied Physics , the researchers from Tokyo University of Science, in collaboration with researchers from the Science Solutions Division, Mizuho Information & Research Institute, Inc., focused on the interactions between water molecules and graphene, a charge-neutral carbon-based material that can be made atomically flat. "Surface water on carbon nanomaterials such as graphene has attracted much attention because the properties of these materials make them ideal for studying the microscopic structure of surface water," explains Prof Yamamoto. It had been already pointed out in previous studies that water molecules on graphene tend to form stable polygonal (2D) shapes in both surface water and "free" water (water molecules away from the surface of the material). Moreover, it had been noted that the probability of finding these structures was drastically different in surface water than in free water. However, the differences between surface and free water have to be established, and the transition between the two is difficult to analyze using conventional simulation methods.

Considering this situation, the research team decided to combine a method taken from data science, called persistent homology (PH), with simulations of molecular dynamics. PH allows for the characterization of data structures, including those contained in images/graphics, but it can also be used in materials science to find stable 3D structures between molecules. "Our study represents the first time PH was used for a structural analysis of water molecules," remarks Prof Yamamoto. With this strategy, the researchers were able to obtain a better idea of what happens to surface water molecules as more layers of water are added on top.

When a single layer of water molecules is laid on top of graphene, the water molecules align so that their hydrogen atoms form stable polygonal structures with different numbers of sides through hydrogen bonds. This "fixes" the orientation and relative position of these first-layer water molecules, which are now forming shapes parallel to the graphene layer. If a second layer of water molecules is added, the molecules from the first and second layers form 3D structures called tetrahedrons, which resemble a pyramid but with a triangular base. Curiously, these tetrahedrons are mostly pointing downwards (towards the graphene layer), because this orientation is "energetically favorable." In other words, the order from the first layer translates to the second one to form these 3D structures with a consistent orientation. However, as a third and more layers are added, the tetrahedrons that form don't necessarily point downwards and instead appear to be free to point in any direction, swayed by the surrounding forces. "These results confirm that the crossover between surface and free water occurs within only three layers of water," explains Prof Yamamoto.

The researchers have provided a video of one of their simulations where these 2D and 3D structures are highlighted, allowing one to understand the full picture. "Our study is a good example of the application of modern data analysis techniques to gain new and important insights," adds Prof Yamamoto. What's more, these predictions should not be hard to measure experimentally on graphene through atomic-force microscopy techniques, which would, without a doubt, confirm the existence of these structures and further validate the combination of techniques used. Prof Yamamoto concludes: "Although graphene is a rather simple surface and we could expect more complicated water structures on other types of materials, our study provides a starting point for discussions of more realistic surface effects, and we expect it will lead to the control of surface properties."

Website: https://www.tus.ac.jp/en/mediarelations/

Takahiro Yamamoto has been with the Tokyo University of Science since 2003, when he joined as a research associate in the Department of Physics. Since then, he progressively climbed until obtaining the title of Professor at the Departments of Liberal arts (Physics) and Electrical Engineering. He now manages his own lab group, who focus on using quantum theoretical simulations to understand the physical properties of materials. In addition, he works at the Water Frontier Science and Technology Research Center, where he is the leader of a research group that aims to understand the properties of surface water through theoretical studies and simulations.

This work was supported in part by Grants-in-Aid for Exploratory Research (Nos. 17H02756 and 16H02079) from the Japan Society for the Promotion of Science (JSPS). This work was also supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) under the Program for the Strategic Research Foundation at Private Universities, 2015-2019.

Japanese Journal of Applied Physics

10.7567/1347-4065/ab6564

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

The Role of Water Network Chemistry in Proteins: A Structural Bioinformatics Perspective in Drug Discovery and Development

Affiliation.

• 1 Department of Pharmacoinformatics, National Institute of Pharmaceutical Education and Research, Niper Sas Nagar, India.
• PMID: 35894474
• DOI: 10.2174/1568026622666220726114407

Background: Although water is regarded as a simple molecule, its ability to create hydrogen bonds makes it a highly complex molecule that is crucial to molecular biology. Water molecules are extremely small and are made up of two different types of atoms, each of which plays a particular role in biological processes. Despite substantial research, understanding the hydration chemistry of protein-ligand complexes remains difficult. Researchers are working on harnessing water molecules to solve unsolved challenges due to the development of computer technologies.

Objectives: The goal of this review is to highlight the relevance of water molecules in protein environments, as well as to demonstrate how the lack of well-resolved crystal structures of proteins functions as a bottleneck in developing molecules that target critical therapeutic targets. In addition, the purpose of this article is to provide a common platform for researchers to consider numerous aspects connected to water molecules.

Conclusion: Considering structure-based drug design, this review will make readers aware of the different aspects related to water molecules. It will provide an amalgamation of information related to the protein environment, linking the thermodynamic fingerprints of water with key therapeutic targets. It also demonstrates that a large number of computational tools are available to study the water network chemistry with the surrounding protein environment. It also emphasizes the need for computational methods in addressing gaps left by a poorly resolved crystallized protein structure.

Keywords: Bioinformatics; Directionality; Drug discovery; Molecular Dynamics; Thermodynamics; Water network; water map.

Copyright© Bentham Science Publishers; For any queries, please email at [email protected].

Publication types

• Computational Biology*
• Drug Discovery
• Proteins / chemistry
• Water* / chemistry

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Novel hydrogel removes microplastics from water

by Shreya Gangwal, Indian Institute of Science

Microplastics pose a great threat to human health. These tiny plastic debris can enter our bodies through the water we drink and increase the risk of illnesses. They are also an environmental hazard; found even in remote areas like polar ice caps and deep ocean trenches, they endanger aquatic and terrestrial lifeforms.

To combat this emerging pollutant, researchers at the Indian Institute of Science (IISc) have designed a sustainable hydrogel to remove microplastics from water. The material has a unique intertwined polymer network that can bind the contaminants and degrade them using UV light irradiation. The research is published in the journal Nanoscale .

Scientists have previously tried using filtering membranes to remove microplastics. However, the membranes can become clogged with these tiny particles, rendering them unsustainable. Instead, the IISc team led by Suryasarathi Bose, Professor at the Department of Materials Engineering, decided to turn to 3D hydrogels.

The novel hydrogel developed by the team consists of three different polymer layers—chitosan, polyvinyl alcohol and polyaniline—intertwined together, making an Interpenetrating Polymer Network (IPN) architecture. The team infused this matrix with nanoclusters of a material called copper substitute polyoxometalate (Cu-POM).

These nanoclusters are catalysts that can use UV light to degrade the microplastics. The combination of the polymers and nanoclusters resulted in a strong hydrogel with the ability to adsorb and degrade large amounts of microplastics.

Most microplastics are a product of the incomplete breakdown of household plastics and fibers. To mimic this in the lab, the team crushed food container lids and other daily-use plastic products to create two of the most common microplastics existing in nature: polyvinyl chloride and polypropylene.

"Along with treatment or removal of microplastics, another major problem is detection. Because these are very small particles , you cannot see them with the naked eye," explains Soumi Dutta, first author of the study and SERB National Post-doctoral fellow at the Department of Materials Engineering.

To solve this problem, the researchers added a fluorescent dye to the microplastics to track how much was being adsorbed and degraded by the hydrogel under different conditions. "We checked the removal of microplastics at different pH levels of water, different temperatures, and different concentrations of microplastics," explains Dutta.

The hydrogel was found to be highly efficient—it could remove about 95% and 93% of the two different types of microplastics in water at near-neutral pH (∼6.5). The team also carried out several experiments to test how durable and strong the material was. They found that the combination of the three polymers made it stable under various temperatures.

"We wanted to make a material that is more sustainable and can be used repetitively," explains Bose. The hydrogel could last for up to five cycles of microplastic removal without significant loss of efficacy. What's more, Bose points out, is that once it has outlived its use, the hydrogel can be repurposed into carbon nanomaterials that can remove heavy metals like hexavalent chromium from polluted water.

Moving forward, the researchers plan to work with collaborators to develop a device that can be deployed on a large scale to help clean up microplastics from various water sources.

Journal information: Nanoscale

Provided by Indian Institute of Science

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EDITORIAL article

This article is part of the research topic.

Dynamics at Surfaces: Understanding Energy Dissipation and Physicochemical Processes at the Atomic and Molecular Level

Editorial for Dynamics at Surfaces: Understanding Energy Dissipation and Physicochemical Processes at the Atomic and Molecular Level. Provisionally Accepted

• 1 Graz University of Technology, Austria
• 2 Swansea University, United Kingdom
• 3 Technical University of Munich, Germany
• 4 University of Surrey, United Kingdom

The final, formatted version of the article will be published soon.

The study by A. Sabik et al. investigates the surface dynamical motion of cobalt phthalocyanine molecules on silver using helium spin-echo (HeSE) spectroscopy, revealing that the activation energy for lateral diffusion decreases with temperature, leading to a transition from single jumps to predominantly long jumps at higher temperatures. It highlights the importance of considering a wide temperature range to capture the complete dynamics of molecular motion on surfaces. Using the same method, S. Kyrkjebø et al. illustrate a stark contrast in water mobility across graphenecovered and bare Ir(111) surfaces. On graphene-covered Ir(111), water molecules exhibit significantly hindered diffusion, attributed to the trapping at specific sites within the surface's corrugated structure. Their findings not only advance our understanding of water-surface interactions but also implicate potential impacts on the development of anti-icing and anti-corrosion materials. Via atom-surface scattering, P. Maier et. al. study the surface properties of 1T-TaS2 and TlBiTe2, contrasting electron-phonon coupling between these materials, and potential implications for phase transitions driven by phonons. The study of thermal expansion and interaction potentials offers valuable Figure 1. Energy dissipation processes are ubiquitous on surfaces and interfaces, from molecular motion to the formation of thin-films, determining adsorption, desorption and dissociation processes of molecules as well as the energetics upon molecular scattering from surfaces.insights into the complex behaviour of these compounds, contributing to a broader knowledge of charge-density wave systems and topological insulators. The scattering of keV protons through graphene is studied by J. Bühler et al. who challenge prior assumptions of the process. By incorporating the lattice thermal motion in simulations, they uncover that previously observed phenomena, such as the outer rainbow scattering, are artefacts of statistical averaging. At the same time, they illustrate new avenues for detailed studies of proton-graphene interactions and the orientations of graphene membranes. A. C. Dorst et al. study the recombinative desorption of O atoms from Ag(111) by combining ion imaging techniques with temperature-programmed desorption. The hyperthermal velocity distribution of the resulting O2 is consistent with activated recombinative desorption but lower than state-of-the-art calculations currently predict. These results, therefore, provide a valuable benchmark for refining theoretical models of metal oxidation processes. The influence of vibrational excitation on the sublimation of CO2 is investigated by C. Jansen et.al, where they use a laser to excite the antisymmetric stretch vibration (ν3) of the CO2 impinging on the CO2 ice. They report that exciting ν3 has a negligible effect on either the sticking of CO2 to the ice, or the resulting structure of the CO2 ice despite the additional vibrational energy being greater than the CO2 desorption energy. P. Floß et al. studied the surface-induced vibrational energy redistribution of methane scattering from Ni(111) and Au(111). Quantum state and angle-resolved measurements reveal a stark contrast in the vibrational energy conversion from ν3 to ν1 modes of methane, underlining the catalytic superiority of Ni( 111) over the more inert Au(111). It thus shows a direct correlation between surface-induced vibrational energy redistribution efficiency and catalytic activity. A. Tetenoire et al. elucidated the complex interplay between electrons and phonons in driving the photoinduced desorption and oxidation of CO on ruthenium surfaces. They demonstrate that phononic excitations play a pivotal role in CO desorption, while both electronic and phononic excitations significantly contribute to CO oxidation. Their research opens new avenues for optimising photochemical reactions on metal surfaces. Neubi F. Xavier Jr and co-workers investigate graphene nanoribbons (GNRs) as potential catalysts for catalytic methane decomposition using density functional theory. They find that armchair edges offer lower energy barriers for hydrogen desorption, compared to zizag edges on GNRs, indicating a better regeneration potential. Highlighting GNRs as comparable to metallic catalysts for methane decomposition, their research may pave the way for sustainable hydrogen production and emphasises the significance of nanomaterials in catalytic processes for green technology. The study by M. K. Prabhu and I. M. N. Groot demonstrates direct synthesis of metallic 1T Co-promoted MoS2 without intercalating agents via growth in a highly reducing environment. High-pressure in-situ reactor scanning tunnelling microscopy measurements, reveal the transformation from a disordered CoMoSx phase at low temperatures to crystalline 1T slabs at around 600 K. It highlights the importance of reducing conditions in materials growth thus avoiding the need of additional chemicals. In their mini review, H. Ueta et al. summarise recent studies on ortho-para conversion of hydrogen in molecular chemisorption and isolated matrix systems. These have found that nuclear-spin conversion can occur on a timescale of seconds, even for non-magnetic surfaces, and that the surface can provide a pathway for dissipating the accompanying change in rotational energy.The collection of 11 articles within this research topic, though only a fraction of the extensive work in the field, highlights that understanding energy dissipation and transfer at interfaces is an extremely active area of research being studied with state-of-the-art methods both experimentally and theoretically. The importance of understanding these surface dynamical processes at the molecular level, focusing on phenomena such as photoinduced reactions, vibrational energy redistribution, and molecular diffusion on surfaces cannot be overstated. Advancements in both experimental setups and theoretical models have opened up new avenues. For example, experiments include the dynamics of larger and more complex molecules and studies of more complex surfaces compared to flat metal substrates, including two-dimensional materials and heterostructures. Similarly, enhanced computing power and the utilisation of computational clusters have enabled more sophisticated ab initio calculations, incorporating phenomena like non-adiabatic effects and quantum friction (Alducin et al., 2017;Chadwick and Beck, 2017;Yu et al., 2023). Furthermore, the integration of machine learning approaches promises to refine theoretical analysis further (Jiang et al., 2016;Kapil et al., 2022). Thus, the studies do not only shed light on the underlying atomic-level interactions but also pave the way for optimising materials for specific technological applications, from optoelectronics to hydrogen production.However, challenges remain, e.g. in extending ab initio methods to larger systems and longer timescales and in conducting experiments under conditions that more closely mimic "real-life" parameters in catalysis to name a few (Yang and Wodtke, 2016). Moreover, while theory does well in studying specific nanosystems, there is still a need for experimental development to measure dynamical processes at tailored nanostructures or in confinement (Sacchi and Tamtögl, 2023;Yu et al., 2023). By overcoming these challenges and unravelling the mechanisms governing energy dissipation at interfaces, our community can unlock a new era of material fabrication and device control. For example, imagine designing catalysts with unparalleled efficiency, tailoring self-assembly processes for nanomaterial fabrication, or even manipulating environmental interactions on a molecular level. Future research will thus be pivotal for advancing various applications, including catalysis, energy production, and materials science by providing insights into the interaction mechanisms between molecules and surfaces, the influence of surface properties on these interactions, and the development of novel materials with enhanced functionalities.

Keywords: Surface chemistry, Catalysis, Ab initio (calculations), Energy Transfer, Scattering spectroscopy, Nanotechnology / nanomaterials, Thin film growth and stability, surface diffusion

Received: 03 Apr 2024; Accepted: 10 Apr 2024.

Copyright: © 2024 Tamtögl, Chadwick, Lechner and Sacchi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mx. Anton Tamtögl, Graz University of Technology, Graz, Austria

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• Published: 03 February 2017

Ultrahigh-resolution imaging of water networks by atomic force microscopy

• Akitoshi Shiotari 1 &
• Yoshiaki Sugimoto 1  

Nature Communications volume  8 , Article number:  14313 ( 2017 ) Cite this article

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• Atomic force microscopy
• Supramolecular chemistry

Local defects in water layers growing on metal surfaces have a key influence on the wetting process at the surfaces; however, such minor structures are undetectable by macroscopic methods. Here, we demonstrate ultrahigh-resolution imaging of single water layers on a copper(110) surface by using non-contact atomic force microscopy (AFM) with molecular functionalized tips at 4.8 K. AFM with a probe tip terminated by carbon monoxide predominantly images oxygen atoms, whereas the contribution of hydrogen atoms is modest. Oxygen skeletons in the AFM images reveal that the water networks containing local defects and edges are composed of pentagonal and hexagonal rings. The results reinforce the applicability of AFM to characterize atomic structures of weakly bonded molecular assemblies.

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Introduction

Mechanisms of ice growth on metal surfaces are determined by the adsorption structure of the first water layer. Water in the first layer on the surfaces creates various hydrogen (H)-bonding networks, including one-, two- and three-dimensional (1D, 2D and 3D) structures, where the ice rules 1 are frequently broken. The water networks on well-ordered metal surfaces generally form periodic phases, which readily turn into other phases depending on the surface structures, temperature and coverage. Moreover, heterogeneous catalysis of metals facilitates dissociative reactions of water to yield hydroxyl (OH) groups, which further complicates the structures of the H 2 O–OH mixed layers. The configurations of the first water layers have been investigated with spectroscopic methods, such as vibrational spectroscopy, photoelectron spectroscopy and thermal desorption spectroscopy 2 , 3 , 4 . Although these methods are well-established and easily analysable, they average out wide-range information on the surface. Therefore, local structures (vacancies, impurities, dissociative products and layer edges), which may have different configurations and properties from the intact water networks, are generally undetectable or buried in the main peaks in the spatially averaged spectra. However, such local defects in water layers on metals play an important role in the catalysis and wettability; on copper (Cu) surfaces, for example, OH groups initiate a low-temperature water-gas shift reaction 5 , and behave as anchors for adsorbing onto the substrate 6 and as bonding sites for the second water layer 7 .

Scanning tunnelling microscopy (STM) is known to be a useful tool for investigating local structures in water networks at the single-molecule level. Since various H-bonding networks on metal surfaces have already been observed directly and characterized, STM brings innovative information to the experimental methodology of water–solid interfaces 3 , 4 , 8 , 9 , 10 , 11 , 12 . Hitherto STM was employed to trace thermal diffusion of individual water molecules 13 , induce dissociation of water 14 , 15 , 16 , fabricate H-bonding complexes 16 , 17 , 18 and control H-atom dynamics 16 , 17 , 18 , 19 , 20 , 21 on surfaces. In particular, recent STM studies visualized the intramolecular structures of water monomers and small clusters on an ultrathin NaCl film 18 and controlled the direction of H-bonds in the cluster 20 . On the other hand, it remains difficult to identify the atomic configurations of self-assembled water networks on metal surfaces by topographic STM images alone, and thus STM-based information is best supported with vibrational spectroscopy and/or theoretical calculations 7 , 22 , 23 . This is mainly because STM images reflect both electronic states near the Fermi level and geometries of the adsorbates.

As well as STM, non-contact atomic force microscopy (AFM) is a powerful option for visualization and analysis of surface structures 24 . Non-contact AFM has a remarkable range of applications, including atomic-resolution imaging of insulators 24 and chemical identification of individual atoms 25 ; however, water-layer studies using non-contact AFM have been notably scarce 26 . For aromatic molecules on surfaces, on the other hand, Gross et al . 27 have proposed that the spatial resolution of AFM can be significantly enhanced by using probe tips functionalized by molecules such as carbon monoxide (CO). Carbon skeletons in the molecules can then be visualized 27 owing to the sensitive detection of the repulsive forces between atoms in the adsorbate and the sharpened tip apex 28 . H bonds between organic molecules are also potentially visualized 29 , even though the results of these imagings remain controversial 28 , 30 . This imaging technique has already been applied to various organic molecules 31 , 32 and non-carbon materials such as iron clusters 33 and metal chalcogenide thin films 34 , 35 . In contrast to the rigid and stable materials, water molecules in the first layers would form various adsorption geometries differing from the monomeric configurations, owing to H bonds 16 , 18 , 22 , 36 . Therefore, it was unobvious whether AFM can/cannot non-destructively visualize atomic structures of the weakly bonded molecular assemblies.

Here, we aim to visualize water networks on a metal surface with non-contact AFM at much higher spatial resolution than in existing STM images. We focus on water adsorbed onto a Cu(110) surface, on which many different kinds of H-bonding networks can be formed 7 , 16 , 19 , 22 , 23 , 37 , 38 , 39 , 40 , 41 .We demonstrate the application of AFM with a functionalized probe tip to the visualization of water networks, including their defects, edges and domain boundaries.

Visualization of 1D water chains on Cu(110)

( a ) Schematic of STM/AFM measurement for pentagonal water chains on Cu(110) with a CO-terminal tip. Red, black, white and brown spheres show O, C, H and Cu atoms, respectively. ( b ) Side-view schematic of the water chain 22 . Red (yellow) spheres represent O atoms of horizontal (vertical) H 2 O. ( c ) STM image of the water chains on Cu(110) with a CO-terminal tip (sample bias V =30 mV, tunnelling current I =20 pA). The zigzag chains have terminals (red ellipses). ( d , e ) STM ( V =30 mV, I =20 pA) and AFM ( V =0 mV, oscillation amplitude A =2 Å) images, respectively, of a water chain including a kink and a terminal. An atomic structure of the chain is superposed in d . Note that the other possible structure is shown in Supplementary Fig. 5 . The tip height in e was set over the bare surface under the same conditions as in d . ( f ) Δ f map of the pentagonal chain at a tip height Δ z =−2 Å ( A =1 Å). ( g ) Δ f ( Δz ) curves recorded over the markers in f . ( h ) Force map of the chain at Δ z =−1.95 Å after subtraction of the force for the bare surface F Cu . ( i ) Force curves over the makers in f after subtraction of F Cu (Δ z ). Scale bars, 50 Å ( c ); 10 Å ( d , e ); 3 Å ( f , h ).

Figure 1c shows typical STM image of the water chains on Cu(110) at 4.8 K. By using a probe tip functionalized by a CO molecule 27 , 42 ( Fig. 1a ), the zigzag shape of the STM image is emphasized ( Supplementary Fig. 1 and Supplementary Note 1 ); however, the pentagonal bonding structure is still hardly discriminated. The zigzag chains have ‘terminals’ where the chain elongation along the [001] direction is ended (the red ellipses in Fig. 1c ), and ‘defects’ where the zigzag manner is locally broken. Some of the defects correspond to ‘kinks’ deflecting the 1D chains ( Fig. 1d ). An AFM image of the water chain with the CO-terminal tip ( Fig. 1e ) clearly reflects the atomic position of O atoms, in contrast with an STM image of the same area ( Fig. 1d ). For AFM, the frequency shift (Δ f ) was measured in constant-height mode 27 . An intact chain is observed as fused pentagonal rings in complete agreement with the model proposed previously ( Fig. 1a,b ). To identify the source of the observed structure, a 3D force map 43 was recorded over the pentagonal chain ( Fig. 1f–i ; see also Supplementary Fig. 2 and Supplementary Note 2 ). The imaging mechanism is consistent with that for organic molecules; the Pauli repulsion between the atoms on the surface and CO at the tip apex leads to high Δ f contrasts 27 . The zero-force distance for vertical H 2 O (the yellow curve in Fig. 1i ) is displaced by 0.34 Å towards the vacuum relative to that for horizontal H 2 O (red), because the O atom of vertical H 2 O is 0.39 Å more protruded than that of horizontal H 2 O (ref. 22 ), as shown in Fig. 1b . As a result of this displacement, vertical H 2 O is the most repulsive to the tip at a tip height Δ z of about −2 Å ( Fig. 1h,i ) and the Δ f intensity of vertical H 2 O at the tip height (the yellow curve in Fig. 1g ) is higher than that of horizontal H 2 O (red). On the other hand, the centre of a pentagon where no molecules exist (the black dot in Fig. 1f ) is still attractive at Δ z ≈−2 Å (the black curve in Fig. 1i ) due to attractive interactions of the surrounding molecules such as van der Waals forces.

Characterization of local defects in 1D water chains

The high-resolution AFM images enable each local defect in the 1D water chains to be characterized. Three kinds of terminals are mainly observed: a pentagonal ring (type i; Fig. 2a–c ), a pentagonal ring with an additional vertical H 2 O (type ii; Fig. 2d–f ) and two fused pentagonal rings (type iii; Fig. 2g–i ). The STM image of type i ( Fig. 2a ) is very similar to that of type ii ( Fig. 2d ), but the corresponding AFM images clarify the structural difference ( Fig. 2b,e ). We also find a small cluster imaged as tetraphyllous-shaped protrusions with STM ( Fig. 2j ). The corresponding AFM image ( Fig. 2k ) indicates that the cluster is composed of a hexagonal ring surrounded by four pentagonal rings, suggesting that it consists of 16 H 2 O molecules ( Fig. 2l ). Because the cluster is predominantly observed at relatively low coverages at 78 K ( Supplementary Fig. 6 ), this is a stable structure at the initial stage. This cluster has a similar structure to the terminal of type iii; at the terminal, the 1D chain is elongated from one of the four fused pentagonal rings, whereas the nearest neighbouring pentagonal ring is broken ( Fig. 2i ). This suggests that the ‘tetraphyllous cluster’ probably corresponds to a core for growing the 1D chain to yield a type-iii terminal. We also observed several kinds of defects and kinks, which are composed of fused pentagonal (and hexagonal) rings ( Supplementary Fig. 7 ). Note that OH groups are probably included in some of the fused hexagonal defects ( Supplementary Fig. 8 and Supplementary Note 5 ).

STM (top) and AFM (middle) images of terminals for the pentagonal water chains. An atomic structure of each terminal is superposed on the Laplacian-filtered AFM image (bottom). ( a – c ) Pentagonal terminal. ( d – f ) Pentagonal terminal with an additional vertical H 2 O. ( g – i ) Fused hexagonal and pentagonal terminal. ( j – l ) ‘Tetraphyllous cluster’ consisting of four pentagons. The images in a , b are magnified and 180°-rotated versions of those in Fig. 1d,e , respectively. The images in d , g were obtained at V =30 mV and I =20 pA, the image in j at V =50 mV and I =20 pA, the images in e , h at V =0 mV, A =2 Å, and Δ z =0 Å, and the image in k at V =0 mV, A =1 Å, and Δ z =0 Å. The tip height Δ z in e , h , k was set over the bare surface under the same conditions as in d , g , j , respectively. Scale bar, 5 Å.

High-resolution imaging of a water-hydroxyl network on Cu(110)

Even if H atoms are almost invisible, the distance between O atoms correlates highly with the strength of H bonds and can be sensitively detected by AFM with CO-terminal tips. To demonstrate that, we observed a H 2 O–OH mixed network on Cu(110), which was formed by partial dissociation of water after the sample was annealed at 160 K. At the temperature, OH groups are yielded by water dissociation and coexists with remaining H 2 O molecules 37 . The islands appear as ‘crooked bands’ elongated along the [001] direction ( Fig. 3a ; see also Supplementary Fig. 9 and Supplementary Note 6 ), which are quite similar to the appearance of H 2 O/O/Cu(110) at 155 K (ref. 41 ). However, the atomic structure of the bands was not resolved by STM (ref. 41 ). On the other hand, a CO-terminal tip enables the STM image to show a honeycomb structure ( Fig. 3a ). In the AFM image at the same region, each O atom is resolved ( Fig. 3b ). This island is composed only of hexagonal rings, whereas we also find several pentagonal rings remaining at the edges of another island ( Supplementary Fig. 9 ). Remarkably, the hexagonal rings (especially inside the island) in Fig. 3b seem to be asymmetric. The superposed lines in Fig. 3c show the apparent O–O bonds in the oxygen skeleton of the island. In the image, three O–O bonds (dotted lines; with the lengths of ∼ 4 Å) are much longer than the other bonds (solid lines; 2–3 Å). The inhomogeneous O–O distances originate from the mixture of intact H 2 O molecules and dissociative OH groups.

( a ) STM image of H 2 O/Cu(110) after annealing at 160 K ( V =50 mV, I =20 pA). The image was obtained at 4.8 K with a CO-terminal tip. ( b ) AFM image of the island in a ( V =0 mV, A =1 Å, Δ z =−1 Å). The tip height Δ z was set over the bare surface under the same conditions as a . ( c ) AFM image magnified at the upper part of b . The solid (dotted) lines represent the apparent O–O bonds with lengths of less (more) than 3.1 Å. ( d ) Schematic structure of the p (2 × 6) H 2 O–OH network on the surface 7 . ( e ) Proposed inside structure of the island superposed on the Laplacian-filtered image in c . Note that other possible structures are shown in Supplementary Fig. 5 . Scale bar, 5 Å.

We ascribe this structure to the p (2 × 6) network with a component ratio of 2 H 2 O:1 OH (refs 7 , 45 ; see Fig. 3d ). In the network, two OH groups face each other without H-bonds, namely, Bjerrum defects 7 . These defects have no H bond between the OH groups, whereas OH behaves as a good acceptor to provide strong H bonds with the two adjacent H 2 O molecules (blue lines in Fig. 3d ). Therefore, the hexagonal ring shows a long O–O side between the OH groups (at a distance of 3.2 Å), two short sides between H 2 O and OH (2.5 Å) and four middle-level sides between H 2 O molecules (2.7–2.8 Å). We assign the long O–O bonds (the dotted lines in Fig. 3c ) to Bjerrum defects. The direction of the long O–O bonds is partially oriented, corresponding to a domain boundary. We tentatively proposed the inside structure of the island including the boundary as shown in Fig. 3e . This assignment indicates that the apparent O–O bond length between the OH groups is 4.0±0.2 Å, that between H 2 O and OH is 2.5±0.3 Å and that between H 2 O molecules is 2.8±0.2 Å ( Supplementary Fig. 10 and Supplementary Note 6 ). Although the apparent bond lengths in AFM images with CO-terminal tips become exaggerated 46 , the bond distances are in good agreement with those in the theoretical model ( Fig. 3d ). According to the model, O atoms of both H 2 O and OH locate at an almost identical height along the surface normal 45 , which is also in good agreement with the similar appearance of the hexagonal vertices in the AFM image. The experimental image is comparable to our simulated AFM images based on the model in Fig. 3d , rather than those for the ‘H-down’ model consisting of H 2 O without OH (ref. 45 ; see Supplementary Fig. 11 and Supplementary Note 7 ).

In addition, this island has two discriminating protrusions (the red arrows in Fig. 3a ) probably corresponding to H 2 O in the second layer 7 . The structure proposed in Fig. 3e suggests that the second-layer molecules are located at the bridge site between OH and horizontal H 2 O. Because Bjerrum defects become an H-bonding acceptor for the second layer 7 , the admolecules are probably H-bonded to the lower OH group and oriented to the adjacent H 2 O.

Capture of an H-bonging recombination

Finally, we demonstrate a capture of an H-bonding rearrangement. Unlike covalently bonded organic molecules, H-bonding networks can be rearranged readily. High-resolution imaging of such ‘flexible’ structures allows us to trace the recombination of the bonding structure. The Cu(110) surface on which pentagonal 1D chains have been formed ( Fig. 1c ) was further exposed to H 2 O gas in a small amount at 6 K. The low-temperature dosing allows H 2 O molecules to adsorb onto the surface as isolated monomers which are observed as round protrusions 16 , 19 (the solid red arrows in Fig. 4a ). On the other hand, several molecules are attached to the 1D chains, which are imaged like knobs of the zigzag chain with STM (the dotted orange arrows). The AFM image in Fig. 4b shows that the additional H 2 O molecules are located at the vertices of the pentagonal rings, indicating that they are H-bonded to vertical H 2 O. During successive scanning, the additional H 2 O moved to the next vertical H 2 O ( Fig. 4c ). We note that the AFM images in Fig. 4b,c have scratching noises over the chains because another H 2 O molecule was attached to the tip apex together with CO and/or another H 2 O molecule (probably bonded onto horizontal H 2 O) diffused rapidly along the pentagonal chain. An interaction with the tip was probably responsible for the hopping motion of the attached molecules. As schematically shown in Fig. 4d , H 2 O monomers attached to vertical H 2 O are expected to be a horizontal configuration located on the trough between the Cu rows, which is different from the bonding site of isolated monomers (the atop site) 16 . Applying voltage pulses rarely induced the bonding of isolated monomers to the chains ( Supplementary Fig. 12 and Supplementary Note 8 ), which is compatible with the different configurations. This result implies that vertical H 2 O in the pentagonal chains acts as an ‘active site’ to trap a free H 2 O molecule. Above 150 K, the pentagonal unit with an additional H 2 O molecule may turn into a hexagonal ring ( Fig. 3 ) via partial dissociation to yield OH groups.

( a ) STM image of pentagonal H 2 O chains along with additional H 2 O monomers on Cu(110) with a CO-terminal tip ( V =50 mV, I =20 pA). The solid red (dotted orange) arrows show H 2 O monomers detached from (attached to) the chains. ( b , c ) AFM images of two H 2 O monomers attached to the chain ( V =0 mV, A =1 Å, Δ z =−0.5 Å). The images in b , c were obtained successively with a duration of 17 min per image. The tip height Δ z was set over the bare surface under the same conditions as in a . ( d ) Top-view (top) and side-view (bottom) schematic illustrations of a proposed atomic structure of a pentagonal chain with additional H 2 O monomers. Orange spheres represent O atoms of the attached H 2 O. Scale bars, 50 Å ( a ); 5 Å ( b , c ).

In summary, we observe H-bonding water networks and their defects with a combination of STM and non-contact AFM. In the first layer on Cu(110), water networks are constructed by pentagonal and hexagonal H-bonding units. In the water networks, the atomic structures of local defects, which are still rendered unspecifically with STM, can be well-characterized with AFM. We also demonstrate that rearrangements of readily convertible bonds, such as H-bonds, can be traced by high-resolution AFM imaging in real time. These results reinforce that the application of AFM with molecular functionalized tips to water networks constitutes a second breakthrough—after the application of STM—in the science of water–solid interfaces.

Experimental setup

The STM/AFM experiments were carried out in an ultrahigh-vacuum chamber (Omicron low-temperature STM/AFM system) at 4.8 K. A tuning fork with an etched tungsten tip was used as a force sensor 47 (resonance frequency f 0 =20.1 kHz, spring constant k 0 ≈1.8 × 10 3  N m −1 , quality factor Q ≈3 × 10 4 ). STM images were measured in constant-current mode. AFM measurements were operated in frequency-modulation mode with an oscillation amplitude A =1–2 Å. The frequency shift (Δ f ) was measured in constant-height mode at the sample bias V =0 mV.

Single-crystalline Cu(110) was cleaned by repeated cycles of Ar + sputtering and annealing to ∼ 600 °C. The probe tip was sometimes poked slightly into the clean surface so that its apex was coated with Cu atoms. Distilled water was purified by freeze-and-pump cycles. The clean surface was sequentially exposed to H 2 O gas at 78 K and CO gas at 8 K via a tube doser positioned a few centimetres away from the sample surface. To achieve high-resolution images, a CO molecule coadsorbed onto the surface was picked up to attach to the tip apex 27 , 42 .

3D force mapping

We obtained 1024 Δ f (Δ z ) curves for a pentagonal water chain on Cu(110) with a CO-terminal tip (32 point × 32 point; Fig. 1f ), as described in ref. 48 . Before the measurement of each curve, the tip was set over the yellow marker in Fig. 1f , and atom tracking was conducted with the tunnelling-current feedback loop closed (set point of V =50 mV and I =20 pA) in order to compensate for the thermal drift 49 . The origin of Δ z is defined by the tip height set at the tracking point. The positive (negative) value of Δ z means the tip height is further from (closer to) the sample than the set-point height. The force curve F (Δ z ) at each measurement point was calculated from the Δ f (Δ z ) curve by using the Sader formula 50 . The force curves are displayed after subtraction of the force curves obtained over the bare Cu surface F Cu (Δ z ) in order to clarify the short-range force distribution ( Fig. 1h ). The force maps are also displayed after subtraction of the force value for the bare surface at the same Δ z ( Fig. 1i and Supplementary Fig. 2 ).

Data availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

Additional information

How to cite this article: Shiotari, A. & Sugimoto, Y. Ultrahigh-resolution imaging of water networks by atomic force microscopy. Nat. Commun. 8, 14313 doi: 10.1038/ncomms14313 (2017).

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Acknowledgements

We thank H. Okuyama for valuable discussions. This work was supported by JSPS KAKENHI Grant Numbers JP15H06127, JP15H03566, JP16K13680, JP16H00933 and JP16H00959. A.S. acknowledges the support of the Kurita Water and Environment Foundation. Y.S. acknowledges the support of the Iketani Science and Technology Foundation, the Noguchi Institute, the Japan Association for Chemical Innovation and the Murata Science Foundation.

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Akitoshi Shiotari & Yoshiaki Sugimoto

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Both authors designed and planned the experiments, and discussed the results. A.S. performed the experiments and wrote the manuscript.

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Shiotari, A., Sugimoto, Y. Ultrahigh-resolution imaging of water networks by atomic force microscopy. Nat Commun 8 , 14313 (2017). https://doi.org/10.1038/ncomms14313

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Received : 17 November 2016

Accepted : 13 December 2016

Published : 03 February 2017

DOI : https://doi.org/10.1038/ncomms14313

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