Water vicinal

If a surface precipitate of metal hydroxy-polymer has formed on an adsorbent, the -pH relationship for the coated adsorbent should resemble closely that observed for particles consisting purely of the hydroxy-polymer or the hydrous oxide of the metal (15). This kind of evidence for Co(ll), La(lII), and Th(lV) precipitation on silica colloids was cited by James and Healy (15). It should be noted, however, that the increase in C toward a maximum value often occurs at pH values well below that required thermodynamically to induce bulk-solution homogeneous precipitation of a metal hydrous oxide (15, 16). If surface precipitation is in the incipient stage under these conditions, it must be a nucleation phenomenon. James and Healy (15) argue that the microscopic electric field at the surface of a charged adsorbent is sufficiently strong to lower the vicinal water activity and induce precipitation at pH values below that required for bulk-solution precipitation of a metal hydrous oxide. 

Figure 11.1. Schematic views of various ways in which an organic chemical, i, may sorb to natural inorganic solids (a) adsorption from air to surfaces with limited water presence, (b) partitioning from aqueous solutions to the layer of vicinal water adjacent to surfaces that serves as an absorbent liquid, (c) adsorption from aqueous solution to specific surface sites due to electron donor-acceptor interactions, (d) adsorption of charged molecules from aqueous solution to complementarily charged surfaces due to electrostatic attractions, and (e) chemisorption due to surface bonding or inner sphere complex formation.

Figure 11.16 Relationship between sorbed and dissolved amphi-phile concentrations (upper isotherm plot). These different parts of the isotherm reflect changes in the solid surface as sorption proceeds, possibly explainable by the following in portion (I) with low dissolved concentrations, sorption occurs via ion exchange and related mechanisms. At some point, sufficient near-surface concentration enhancement occurs that micelles form there (Ha) and rapid coagulation between oppositely charged micelles and the surface follows (lib). When the surface becomes fLilly coated with such micelles, additional sorption is stopped (III). In portion III, the solid surface charge is converted from one sign to the other, implying sorbates must become physically associated with the particle surface, as opposed to simply being present in the diffuse double layer or the vicinal water layer.

Fig. 2 A, B. Three layers model of water at the interface with mineral according to Dorst-Hansen164) O = clathrate-like ordering ] = water-dipole. A Vicinal water near non-polar surface. Extensive clathrate-like ordering near interface but minimal disordered region. B Vicinal water near polar surface, disordered region...

The above account has provided sufficient background for analysis of the properties of aqueous solutions. The analysis has been restricted to bulk water the properties of water near interfaces, including biological surfaces, is very interesting but outside the scope of this review. It should be noted, however, that the properties of vicinal water differ from those of bulk water, these differences being important in biological systems (Drost-Hansen, 1972 1973). Thermal anomalies in the properties of water also seem explicable in terms of interfacial phenomena (Drost-Hansen, 1968). 

Ideally, models of vicinal water should eventually "explain all established experimental facts. There is a long way to go However, some general observations have been made. One is that, against a variety of hydrophobic phases (silver iodide, mercury, air) water molecules appear to be oriented with the negative ends of the molecules pointing outward (sec. 3.9). In other words, the polarization of water adjacent to silver iodide and mercury is similar to the spontaneous polarization of water surfaces. The implication is that near such surfaces water-water interactions play at least an important role as water-surface interactions. Another observation, relevant for the interpretation of electroklnetic phenomena, is that tangentially immobile surface layers do occur near both hydrophilic and hydrophobic surfaces. 

Before applying such models to vicinal water, they should be checked to account for the properties of bulk water (molar Internal energy, pressure, specific heat, singularity at 4°C, etc.), which is sometimes done l, and for the surface tension as a function of temperature, which is a more critical test but rarely done. ... 

The characteristics of water near a solid are significantly different from those in the bulk phase of water. This water is recognized as vicinal water in biological science. The vicinal water is the surface state of water in contact with a solid surface. The vicinal water has several transition temperatures that influence the properties of the vicinal water, among which the major transition temperature is 15°C. 

The method suggested in the present paper provides the correlation volume. The thickness of the layer of water thus calculated, which is affected by a solute molecule, indicates how deeply a single solute molecule has perturbed the structure of the vicinal water molecules. 

The diffusion coefficient for water in the cytoplasm of various cells has been determined with a satisfactory precision. It has been found that the movement of water molecules inside living cells is not much different and is reduced by a factor of between 2 and 6, compared with the self-diffusion coefficient for pure water. According to Mild and Lpvtrup (1985), the most likely explanation of the observed values is that part of the cytoplasmic water, the vicinal water close to the various surface structures in the cytoplasm, is structurally changed to the extent that its rate of motion is significantly reduced, compared with the bulk phase. 

Many mathematical descriptors for sorption isotherms have been proposed. One of the more famous is that of Brunauer et al. (1938), the B.E.T. isotherm, which is based on the concept of a measurable amount of monomolecular layer (vicinal) water for a particular food. Wolf et al. (1985) compiled 2201 references on sorption isotherm data for foods. An example of the type, detail, and accuracy of sorption isotherm data available in the literature is presented in Table 3.2. 

The above picture of water/oxide interface does not obviously show the simultaneous, primary and secondary adsorption on non-dissociated water molecules. In their review, Etzler and Drost-Hausen wrote [89] Furthermore, as mentioned elsewhere in this paper (and other papers by the present author and associates), it is obvious that vicinal water is essentially unaffected by electrical double layers . Several properties of the vicinal water appear to be similar for various solid surfaces characterized by various point of zero charge (PZC) values (the paradoxical effect ). It is therefore to be expected that the contribution to the changes of the heat of immersion with changing pH, produced by the secondarily adsorbed vicinal water, is negligible. 

Evidence for Vicinal Water in Cells Nature of Bulk and Cell-Associated Water... 

The purpose of this chapter and the next is two-fold first, to gather and review some of the evidence for structural changes in water and aqueous solutions adjacent to an interface, and secondly, to illustrate how these structural effects are manifested in the functioning of cells. What is addressed is not only the structure of bulk water but also the unique aspects of water in cells or near any surfaces. We refer to water near interfaces as vicinal water after the Latin word for neighbor. It is the vicinal water that suggests itself as the most likely site for most of the intermediary metabolism in living cells. 

Some most impressive computer simulations have been made in efforts to model the structure of liquid water. Yet, because these calculations usually are based on pair additivity of the potentials for the H-bonded water molecules, the possibility exists that subtle effects may escape the theoretician, as no means are provided to incorporate the possibility of extensive cooperativity—an aspect that Henry Frank (1972) has so eloquently stressed. Very likely, this is the crux of the problem of interfacially modified water if nothing else, the thermal anomalies (discussed below) in the properties of vicinal water strongly implicate cooperativity on a large scale—a collective behavior of water molecules that no existing potential function is able to reproduce. The cooperativity reflects nonpair additivity, and it does not seem plausible that effective potential energy functions can be devised that will remedy the specific lack of a detailed understanding of many-body interactions in water. Attempts to allow for cooperativity have been made by Finney, Barnes, and co-workers, notably Quinn and Nicholas (see Barnes et al., 1979). 

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