Conformational processes hydration effects

Many liquid detergent products contain components that serve as product viscosity modifiers, added to achieve the desired consistency of the commercial product. Cellulosic polymers, for instance, are an excellent example of such an additive and various polysaccharides are capable of gelation under specific thermal conditions. In such cases, heat transfer during manufacture may be required to complete hydration and effect the necessary conformational change in the select polymer system [85], in the appropriate aqueous environment. Products requiring controlled heat transfer processes may include various dental creams, shampoos, built liquid detergents, and hard surface cleaners. 

The trans bicyclic orthoester must exist in the conformation 95 and the primary stereoelectronic effects permit the ejection of the methoxy group Ohly, yielding the bicyclic lactonium ion which after hydration (-97) and cleavage will give the hydroxy-lactone % only. The process 97 - 90 cannot occur with stereoelectronic control its energy barrier must therefore be higher than in other cases. Kaloustian and Khouri (61) have shown that the reaction of sodium methoxide with the bicyclic salt % gave the trans orthoester specifically. 

Another aspect of these problems is the effect of ions existing in the electrolytic solutions that constitute the fluid component of the cytoplasm. These ions can affect the conformation, interactions and biochemical functions of molecules in the cell. The Hofmeister series, which was first noted in 1888 [95], is invoked in this more modem context. It ranks the relative influence of ions on the physical behaviour of a wide variety of aqueous processes ranging from colloidal assembly to protein folding. The influence of an ion on the properties of macromolecules was initially thought to arise, at least in part, from its capacity of modifying bulk water stmcture. However, recent time-resolved and thermodynamic studies of water molecules in salt solutions show that bulk water structure is not central to the Hofmeister effect. Models are now being developed that take into account direct interactions between ion and macromolecule, and the interactions with water molecules that are operative in the first hydration shell of the macromolecule. 

Effect of hydration on the properties of biosystems was extensively studied both experimentally and by computer simulations. We have already considered how biological activity and conformational dynamics of hydrated biomolecules (Section 6) as well as conductivity of biosystems (Section 7.1) develop upon hydration. Now we analyze some other physical properties of hydrated biosystems (first, their dynamical properties) in relation to the percolation transition of water. Typical biomolecular surface is characterized by heterogeneity (presence of strongly hydrophilic and strongly hydrophobic groups), roughness, and finite size (closed surface of a single biomolecule). These features determine several steps in the process of hydration of biomolecules. 

In dilute aqueous solutions, biomolecules are completely covered by water molecules. The structure of water near a boundary essentially differs from the structure of bulk water (see Sections 2 and 5). Specific water structure is seen in one or two water layers near hydrophilic surfaces, whereas the rest of liquid water is bulk-like. This is also the case for the surfaces of biomolecules, which allow consideration of hydration water as a separate subsystem. Conformational transitions and aggregation of biomolecules occur in dilute solution due to variations of temperature and/or pressure and due to additions of some cosolvents. It is natural to expect that these biologically important processes are related to the changes in the state of hydration water shell. First, we consider the effect of heating on the state of hydration water shell and on the properties of biomolecules. Then, we discuss the dynamic transition of biomolecules and pressure-induced denaturation in relation with the liquid-liquid transitions of hydration water. 

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