The Influence of Hydrophobic Interactions

If upon electron transfer one of the products becomes significantly more hydro-phobic (or, vice versa, hydrophilic) than in the initial state, this product may leave the water // membrane interface and immerse itself in the depth of the membrane (or, vice versa, desorb into the aqueous phase). It has been demonstrated that such spatial separation of the products may lead to a significant inhibition of their recombination [158-160]. 

The 1-2 order of magnitude decrease of the rate constant for the recombination of PET products, in comparison with the homogeneous solution, was also observed by Matsuo and co-workers [167, 168]. In their studies one of these products was hydrophilic and thus located in the aqueous phase, while the other was hydrophobic and thus immersed in the membrane. Such a decrease of the rate is, apparently, a common feature of the reactions providing electron transfer across the membrane // water interface between the reagents with substantially different hydro-phobidty. 

---

Immobilization of the enzymes to solid surface induces structural changes, which may affect the entire molecule. The study of conformational behavior of enzymes on solid surface is necessary for better imdeislanding of the immobilization mechanism. However, the immobilization of enzymes on alginate beads is generally rapid, and depends on hydrophobic and electrostatic interactions as well as on external conditions such as pH, temperature, ionic strength and nature of buffer [11,12], Enzymes denatirration may occttr tmder the influence of hydrophobic interactions, physicochemical properties of the alginate beads or due to the intrinsic properties of the enzyme. 

The Influence of Hydrophobic Interactions on Conformational States of Synthetic Polyelectrolytes... 

As mentioned earlier, proteins are subject to cold denaturation because they exhibit maximal stability at temperatures greater than 0°C. The basis of this effect is the reduction in the stabilizing influence of hydrophobic interactions as temperature is reduced. Recall that the burial of hydrophobic side-chains in the folded protein is favored by entropy considerations (AS is positive), but that the enthalpy change associated with these burials is unfavorable (AH, too, is positive). Thus, as temperature decreases, there is less energy available to remove water from around hydrophobic groups in contact with the solvent. Furthermore, as temperature is reduced, the term [— TAS] takes on a smaller absolute value. For these reasons, the contribution of the hydrophobic effect to the net free energy of stabilization of a protein is reduced at low temperatures, and cold-induced unfolding of proteins (cold denaturation) may occur. 

The nature of hydrophobic interactions and their effects on the structure and properties of water have been extensively studied, particularly for small molecules (i 3). In contrast, the introduction of hydrophobic associations into synthetic water-soluble polymers to control solution rheology has received rather limited and recent study (4-7). To better understand the relationships between polymer structure and solution properties, we have synthesized and characterized a series of copolymers of acrylamide and N-substituted alkylacrylamides and terpolymers containing anionically charged carboxyl groups. Solution properties of these systems have been obtained in both the dilute and semidilute concentration regime, to probe the influence of intra- and intermolecular interactions. In addition, the influence of the shear field and solvent quality on the associations was studied. 

Influence of Hydrophobic Interactions of Non-Polar Groups of Macromolecules in Water on the IMM of the Polymer... 

Simplistically stated, the hydrophobic effect may be defined as the tendency of water to reject any contact with substances of a nonpolar or hydrocarbon nature. The existence of this effect was first recognized in the study of the extremely low solubility of hydrocarbons in water. The principles involved were later successfully applied to the elucidation of the native conformation of protein molecules by Kauz-mann The application of these ideas to the study of membrane structures has been advanced by Singer. Recently, Tanford published an entire book on the hydrophobic effect, including the influence of this interaction on the formation of micelles, lipid bilayers, membranes and other ordered structures. Aside from Singer s and Tanford s" statements on the decisive role of the hydrophobic effect on lyotropics, the lyotropic liquid-crystal literature seems peculiarly unaware of this phenomenon. Winsor s extensive review with its systematic analysis (R-theory) of the many lyotropic phases does not take the hydrophobic effect into account. More recent reviews of lyotropic liquid crystals do not mention the phenomenon. We hope that the present discussion will help to advance the realization of the importance of the hydrophobic effect to lyotropics. The material of the following sections is taken chiefly from Ref. [3] with some assistance from Refs. [2] and [4]. 

---