Intrinsic barrier electrostatic effects

Electrostatic effects may significantly affect intrinsic barriers or intrinsic rate constants, especially when there is a positive charge directly adjacent to the carbon that gets deprotonated, as exemplified by Equation (16). Keeffe and Kresge92 have shown that a large body of data on the... 

CH=NH,118 CH=S,118 CH=OH,120 and N02H.117 The most comprehensive study which also incorporates results form earlier work is that by Bernasconi and Wenzel118 the present discussion is largely based on this paper and on references 113, 117, and 120. A major conclusion is that even though the intrinsic barriers of these gas phase reactions depend on the same factors as solution phase proton transfers such as resonance, polar, and polarizability effects, the relative importance of these factors is quite different in the gas phase, and electrostatic effects involving the proton-in-flight constitute an important additional factor. 

A quantitative understanding of how enzymes catalyze rapid proton abstraction from weakly acidic carbon acids is necessarily achieved by dissecting the effect of active site structure on the values of AG°, the thermodynamic barrier, and AG int, the intrinsic kinetic barrier for formation of the enolate anion intermediate. The structural strategies by which AG° for formation of the enolate anion is reduced sufficiently such that these can be kinetically competent are now understood. In divalent metal ion-independent reactions, e.g., TIM, KSI, and ECH, the intermediate is stabilized by enhanced hydrogen bonding interactions with weakly acidic hydrogen bond donors in divalent metal-dependent reactions, e.g., MR and enolase, the intermediate is stabilized primarily by enhanced electrostatic interactions with... 

Biological membranes arc composed of lipids and proteins, the lipids building up the bimolecular leaflet, which is the major permeability barrier, and the proteins providing the essential biological functions, The proteins can be either intrinsic proteins embedded in the lipid biiayers and having accessible polar surfaces on both sides of the bilayer, or they are mainly bound to the bilayer surface by electrostatic interactions. When proteins are incorporated into lipid bilayers or bound to the surface of the lamellae, the lipid packing in the gel phase is perturbed and the transition profiles obtained by DSC are changed in a characteristic way. Numerous studies of lipid-protein interactions have been performed in the past and the effects on the DSC transition curves have been modeled [99-104]. 

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