As a rule protein binding to surfaces occurs on a two-dimensional lattice of binding sites (for review see [1] ). Present evidence strongly indicates that the fundamental postulates of Langmuir [2] for monolayer adsorption are invalid in such systems. Typically the consequences of lattice binding are multivalence, negative cooperativity (Freundlich-type isotherms) and adsorption-desorption hysteresis [1,3]). We have detected protein adsorption hysteresis on surfaces of agarose, quartz glass, PDLLA and titanium with or without covalent surface modifications e.g. with alkyl silanes or biotin. As proteins phosphorylase b (mr = 196 kDa), fibrinogen (mr = 340 kDa), bone morphogenetic protein 2 BMP-2 (mr = 26 kDa) and avidin (65 kDa) were studied (see also [4]). Characteristic for protein adsorption hysteresis are long-lived metastable states attributed to local energy minima, which can be evaluated for apparent thermodynamic state functions of the thermodynamically irreversible process. The hysteresis cycle itself generates entropy (DiS) from which the DiG associated with the conformational change of the protein on the surface can be calculated [3]. As will be shown the binding constants (KA) for the desorption branch of proteins lie in the range of 109-1013 M-1 and the apparent molar Gibbs free energies of the irreversible process (DiG) in the range of  -9 to -40 kJ Mol-1.          [1]    Hlady, V., Buijs, J., & Jennissen, H.P. (1999) Methods for Studying Protein Adsorption. Methods Enzymol., 309,  402-429.         [2]    Langmuir, I. (1940) Monolayers on solids. J Chem Soc London, 1940,  511-543.         [3]    Jennissen, H.P. (1985) Protein Adsorption Hysteresis. In 'Surface and Interfacial Aspects of Biomedical Polymers' Vol.2, Protein Adsorption., (Andrade,J.D., ed),  pp. 295-320. Plenum Press, New York.         [4]    Dohle, D.-S., Pasa, S.D., & Jennissen, H.P. (2010) Fibrinogen adsorption hysteresis on ultra-hydrophilic titanium surfaces. Biomaterialien, 11 (S1),  25.

Protein adsorption on surfaces is a thermodynamically irreversible process

243rd National Meeting (2012)

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