Influence of macroscopic and microscopic interactions on kinetic rate constants.: III.: Determination of von Smoluchowski's f-factor for HSA adsorption onto various metal oxide microparticles, using the extended DLVO approach

The adsorption of human serum albumin (HSA) onto hydrophobic talc and various types of hydrophilic silica has been studied. The kinetic adsorption constants for each case were determined experimentally, using time-resolved fluorescent spectroscopy. Von-Smoluchowski's f-factor, a measure of the dominance of the macroscopic protein repulsion by the solid surface, was determined for each protein-surface system. The free energies of both macroscopic (repulsive) and microscopic (attractive) interactions between HSA and solid substrata were calculated via extended DLVO (XDLVO) analysis. The combination of such kinetic and thermodynamic data can lead to the estimation of a number of other parameters which are characteristic for each system and contain significant information, such as the mean microscopic and macroscopic-scale interaction energies between protein and solid substratum and the ratio of unfavorable to favorable protein orientations during adsorption, as well as the average net total ratio of repulsion over attraction. The latter was found to be inversely proportional to the amount of HSA adsorbed onto the various mineral particles, after 1 h exposure. Furthermore, detailed examination of all kinetic adsorption parameters leads to the conclusion that the equilibrium affinity constant, extrapolated to zero time (K-aff(t-->0)) is the parameter which rather accurately defines the specific interactions for a given protein-solid substratum system. However the most precise characterization of a given protein-substratum system is defined by both the specific (microscopic) adsorption (k(a)(mic)) and the specific (microscopic) desorption (k(d)(mic)) rate constants, which are obtained after elimination of the influence of the aspecific (macroscopic) factors which strongly influence the overall rate constants (k(a) and k(d)). (C) 2001 Elsevier Science B.V. All rights reserved.