Surface adsorption sites, conformation, density

As the adsorption site density (Fig. 12) or total free energy of adsorption increases, one moves from the realm of reversibility to that of irreversibility. As proteins can undergo conformational and orientational changes on a surface, they can optimize their interfacial interactions so as to provide the maximum free energy of adsorption. Such conformational alterations are relatively slow and hence very time-dependent. 

The protein s intrinsic properties (size, molecular weight, 3-D structure, surface site density, conformational stability) are all very important and must be fully characterized and understood in order to interpret adsorption data. 

As has been depicted in Fig. 1, various conformations are possible for adsorbed polymers, depending on polymer-polymer, polymer-solvent, and polymer-interface interactions and the flexibility of polymers. To determine experimentally the conformation of adsorbed polymers only adsorption isotherm data are insufficient. The average thickness of the adsorbed polymer layer, the segment density distribution in this layer, the fraction of adsorbed segments, and the fraction of surface sites occupied by adsorbed segments must be measured. Recently, several unique techniques have become available to measure these quantities. 

I nations 82 and 83 distinguish between inner-sphere and outer-sphere complexes of a surface bound Pb(II). Actual bond lengths, conformations, and site energies for coordination complexes on a real surface may vary from one site to n not her. The postulated reactions do, however, provide a means of estimating how adsorption density responds in a semiquantitative way to changing medium conditions. See, for example, Schindler and Stumm (1987) for a comprehensive discussion of acid-base and complexation equilibria at oxide-water interfaces. 

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