Binding of water

Binding of Water in Cavities Inside Protein Molecules... 

Hydration consists of the binding of water dipoles to ions or ionic groups, to dipoles, or polar groups. Hydration takes place in solid substances as well as in solution. 

Other supportive evidence for a specific water-solid interaction is available from thermal studies showing the amount of nonfreezable water [57-59], nuclear magnetic resonance [29,60-66], and diffusion studies [67,68]. The evidence is less clear, however, concerning whether there is distinct binding of water to... 

Association constant (M-1) for the binding of water by crown ethers to form a 1 1 complex. Estimated accuracy 10% c Molar ratio solubilized water/crown ether... 

Hydration The binding of water molecules by adsorpUon onto sohd surfaces or through electrostaUc... 

It should also be borne in mind that cation-radicals are strong Lewis acids and can act as acceptors of the nucleophile electron pair to form a coordinative bond. Such a process was well documented (Gould et al. 2003, references therein). The Lewis-type binding of water by the aminosilane cation-radical appeared to be crucial for fragmentation with the formation of an a-amino carborad-ical. The latter plays an important role in the efficiency of photographic systems. Scheme 5.18 illustrates this coordinative-promoted fragmentation of the cation-radical. 

So far the discussion of the goethite/hematite equilibrium refers to aqueous systems in which the water activitY (i. e. relative humidity), anp, is unity. In many cases, however, the water activity may be <1. This applies to soils and sediments where can be lowered by the binding of water in pores. When considering the dehy-droxylation reaction. 

The cycle ends with the binding of water to the regenerated Ti02 surface. 

Emulsions have been introduced in MIP synthesis by Japanese researchers in the early nineties. The aim was to create materials suitable for the recognition and binding of water-soluble substrates, most notably metal ions. Fatty acids, sometimes additionally functionalised with polymerisable groups, were employed both as surfactants and as functional monomers for ion binding. With the aid of these molecules, oil-in-water (O/W) emulsions of crosslinking and nonfunctional... 

The mucins of the eyelid margin trap particulate matter, which on squeezing of the lids move the material onto the base of the eyelashes. Eyelid closure results in compression of the film, temporarily increasing the thickness of the tear film mucins in the tears must support changes in dimensions and anchor the hydrated film to the surface. The elasticity of the mucins, provided by uncoiling regions in the structure coupled with the binding of water, maintains the hydration of the cornea. 

We interpret this observation as implying that, for these condensates, the effect upon mechanical stability is determined primarily by the binding of water to the ethylene oxide units which are anchored to the rubber-water interface by the fatty-alcohol moiety of the condensate. In the case of condensates for which the overall mole ratio of ethylene oxide to fatty alcohol exceeds ca. 30, the effect upon mechanical stability is much greater than would be expected on the basis of the total amount of ethylene oxide which has been added to the latex, as evidenced by the... 

The subtle differences between sugar molecules which cause such dramatic effects (Le. Dulcitol verses sorbitol) are possibly caused by adverse interactions either with water or the amino acids of the protein. It is possible that under certain conditions the position of hydroxyl groups causes strong binding of water and leads to confirma-tional distortion of the protein rather than stabilization. Monsan and Combes (13) have suggested that this is due to excessive binding to the stabilizer thus disrupting the protein surface/water interactions. As yet we have no evidence to further elucidate this theory. 

At the same time, a conclusive and sufficiently reliable answer is frequently required. We may be interested in, for example, the question of the possibility of dissociative adsorption, or the problem of the existence of some chemisorption structures as in the discussion (see below) on the coordinative binding of water molecules by silicon atoms, etc. Ab initio calculations are required in these cases. They are needed as well to check some principal conclusions based on semiempirical schemes. Also, they are useful in providing the basis for proper choice and improving the parametrization of semiempirical methods. Therefore the nonempirical approach is finding ever-increasing application to the surface problems. 

Binding of water molecules to side-chains follows an even broader distribution because many side-chains are flexible and mobile and the waters are poorly ordered. Many water molecules are located outside the inner , better-defined hydration sphere. The O -Ow distance distribution of water molecules around the carboxylate groups of Asp, Glu, and of C-termini is fairly clear, 2.5 to 3.1 A with mean value near 2.77 A, whereas Ser, Thr, iyr, Asn, Gin display wider distributions with a mean value at 2.80 A [596] for more details, see Part IV, Chap. 23. 

Although FI and aw may be the same throughout some system, both Fly and t in Equation 2.11 may vary. For example, water activity in the bulk of the solution may be predominantly lowered by solutes, whereas at or near the surface of colloids the main factor decreasing ciw from 1 could be the interfacial attraction and binding of water. As already indicated, such interfacial interactions reduce the activity coefficient of water, yw. 

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