The structure of water
Introduction
Water is an essential component in physical, chemical and biological processes. Water is so familiar to us; we use water for drinking, cooking, bathing, farming and cleaning. Yet we marvel at its many unusual and fascinating properties [1]. Water has a simple molecular formula H2O, but unusual chemical and physical properties. However, compared to compounds with similar atomic organisation and molecular size water has unexpected properties. For example, simple molecules, H2S, NH3, HF, all exist in gaseous form while H2O exists as liquid at room temperature having a substantially higher boiling point, melting point, heat of evaporation, and surface tension. Up to now, a total of 72 abnormal physiochemical behaviours have been associated with water [2].
Water's unexpected and surprising behaviours are well documented in the literature. Various studies have identified phenomena which have evidence that are sometimes backed up by rigorous proofs and other times requiring proofs. For example, Pollack [3] found that water molecules to behave differently in the presence of charged surfaces. The water molecules become structured in arrays or strata when they interact with charged surfaces such as those presented by proteins. They are ordered like crystals such as ice and exclude particles and solutes as they form. The space formed during this process is called an exclusion zone (EZ) [4]. EZs are characterised by the exclusion of microsphere suspensions, colloids, dyes and some solutes from boundary layers 100–300 μm in thickness. Das [4] has established the EZ phenomenon based on the separation of charge between the (negatively charged) interfacial EZ water and the bulk (proton-enriched) water zone beyond the EZ (termed as PEZ). Das [4] hypothesizes that based on charge separation, there is a significant electrostatic force to exist between the EZ and PEZ. In another study [5], the sharp increase of EZ size associated with micromolar anesthetic concentrations found to follow a similar pattern to induction of general anesthesia, from the excitation stage (Stage II) to the depression and overdose stages of surgical anesthesia (Stages III and IV). The results were consistent with the hypothesis that anesthetics may act on water, a fundamental organizational component common to all cells. Further, it has also been found that even the positive air ions can compromise interfacial water negativity which may explain the known negative impact of positive ions on health [6].
The emergence of bound water was analysed by Del Giudice et al. [7] and Del Giudice and Preparat [8]. They introduced a concept called “Coherence Domain” (CD) which is a region spanned by the fluctuation of electromagnetic field (emf) whose size is just the wave length of the fluctuation. While CDs are spherical in bulk water, along a protein chain, water molecules are compelled to align their electric dipoles to the chain. Thus, the CD takes the shape of a tube with a thickness of a water molecule and a length of emf wavelength (which can be in the region of 0.063–1.26 mm) [7]. Therefore, the protein is dressed by a monolayer of water which in turn allows up to 10 monolayers of water to formed coaxially. Decrease in effective dipole density of the dressed protein as well as the in the dielectric constant of bound water limit the number of water monolayers. Thus, an emf excitation on the protein surface will travel only in the direction parallel to the backbone of the protein. The tubular protein-bound water system formed will be of 1 mm segments connected by “gap-junctions” filling with noncoherent water where electrolyte and other solutes are dissolved and approached the protein backbone.
Because of the abnormal physiochemical behaviours, a small group of scientists believe that water exist as water clusters instead of a single molecule in nature [[9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]]. A water cluster is an aggregation of many water molecules, denoted as (H2O)n; it could also be termed as water aggregates. Research on water clusters deals with their shape, size and stability in their gas, (H2O)n, gas, liquid, (H2O)n, liquid and solid forms, (H2O)n, solid. So far most of the studies are on small water clusters with water molecules, ranging from 2 or 3 up to just under a thousand [37,38]. Various instruments are employed to study water clusters [[39], [40], [41], [42], [43], [44], [45], [46], [47]]. There are around 50 water models proposed [48]. The shape of a water cluster with 6 water molecules could be prism, cage, book or ring [49].
From 2013 a group of researchers have shown images of large water clusters, which have diameters from several to more than a hundred micrometres [50,51]. Because of the large sizes of water clusters, scientists can observe the shape of water clusters with the naked eye. In the study of Shu et al. [50], sodium chloride solutions of different concentration were made in order to prove the existence of salt particles in both dilute and concentrate solutions. The solutions were taken from a sample bottle with a pipette and put on a glass slide under a microscope. Both water clusters (then referred to as ‘watery balls’) and salt particles were observed. It was questioned whether the images were caused by impurities. To eliminate/reduce the adverse effect of impurities, sodium chloride solutions were filtered, then a drop of solution was taken for observation. Surprisingly, the watery balls were still in the solution and could be sampled from a sample bottle and put under a microscope. The watery balls were found to be very stable when pipetted and it was reasoned that the watery balls were water clusters. That was the first time an image of a water cluster has been reported. The watery balls are spherical. It was proposed that we generally could not see water clusters in bulk but we could see them if a salt particle entered a water cluster causing changes in its reflective properties. In 2015 the group showed that water clusters in bulk have different sizes and size distribution [51].
In this paper the following is reported: The dynamics of water clusters during salt dissolution; dissolution of calcium carbonate in water; the difference and similarity in images of water clusters and air bubbles; force balance inside a water cluster; images of water clusters both in bulk and at a molecular level.
Section snippets
Materials and methods
Milli Q Water, salts, both sodium chloride and calcium carbonate, were used in the study. Milli Q Water is ultrapure water having a resistance of 18.2 MΩ at 25 °C. Both salts are analytical grade. Sodium chloride has a purity of 99.50% whilst calcium carbonate has a purity of 99%.
Two kinds of microscopes were used for the study of water clusters and their dynamics. The microscope used for observing salt particles inside a water cluster was an inverted IX83 Olympus wide-field microscope with
Results and discussion
Dynamics of water clusters during salt dissolution. Water clusters are the main components of a water solution and present everywhere in bulk. We cannot generally see water clusters in bulk. Once a salt particle/salt aggregate enters them the reflective properties change and the water clusters become visible. Fig. 1 show salt particles inside water clusters. There are faint white specs in the black outer layer that represent salt particles. Arrows are used to indicate the approximate positions
Conclusion
In this paper, we have shown the structure of water and reported the images and the dynamics of water clusters during salt dissolution. From the images of water clusters taken by a microscope we could see that there are two phases in a water cluster. We proposed that the outer layer of a water cluster is liquid while the inner layer is gas. The gas phase in the inner layer as well as the large sizes of water clusters might be the main reasons for the abnormal behaviours of water clusters. We
CRediT authorship contribution statement
Li Shu: Conceptualization, Methodology, Validation, Investigation, Resources, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition. Leonardo Jegatheesan: Writing - review & editing. Veeriah Jegatheesan: Resources, Writing - review & editing, Visualization, Funding acquisition. Chun Qing Li: Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
Authors thank Desmond Lau, Helen Forrester and Jeffrey Crosbie of ARC Centre for Nanoscale Biophotonics (CNBP), RMIT University, Australia for their assistance and support in accessing and operating the inverted IX83 Olympus wide-field microscope. Sincere thanks to Philip Francis and Edwin Mayes at RMIT Microscopy and Microanalysis Facility for their help.
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