Determination of apparent thermodynamic parameters for adsorption of a midchain peptidyl residue onto a glass surface

Abstract

Protein adsorption onto the surface of an implanted material is widely recognized as an important factor controlling the biological response. Although numerous studies have been conducted to investigate protein adsorption behavior, very little is actually understood regarding the specific molecular events involved in protein-surface adsorption processes. As a basic science approach to investigate protein-surface interactions, an experimental method is developed and applied to determine apparent thermodynamic parameters for the adsorption of a single midchain peptidyl residue onto a glass surface. This article presents the results of adsorption studies for four molecular weight ranges of poly-L-lysine onto glass microspheres in physiologic saline at four temperatures. Isotherm data plots are constructed and the apparent changes in enthalpy (DeltaH degrees ), entropy (DeltaS degrees ), and Gibbs' free energy (DeltaG degrees ) are calculated assuming a Langmuir-like model for adsorption. Estimates of apparent DeltaH degrees, DeltaS degrees, and DeltaG degrees for the adsorption of a single midchain lysine residue are determined from the initial slopes of the plots of the apparent thermodynamic parameters versus the degree of polymerization of the adsorbed poly-L-lysine. It is proposed that the generation of such molecular-level adsorption data is a necessary step toward the goal of understanding, predicting, and controlling protein-surface interactions.

A Simple Way of Calculating the Change in the Gibbs' Free Energy of Ion Adsorption Reactions

“…The results obtained by from their studies of the interaction of proteins in aqueous suspensions with fumed silica indicated that the change in the Gibbs' free energy on protein adsorption depended on the pH, concentration, types of proteins and their preparation techniques. From investigations of protein-surface interactions, Latour et al (2000) developed an experimental method for determining the thermodynamic parameters for the adsorption of a single mid-chain peptidyl residue onto a glass surface.…”

“…Because there are difficulties in undertaking direct measurements of the real change in the Gibbs' free energy for an adsorption reaction, the standard Gibbs' free energy change, ∆G 0 , has often been used by many authors (Naiya et al 2008;Nabi et al 1999;Singh 2000;Sazonova et al 2001;Dursun 2006) for predicting the nature of the reaction as well as for calculating two other closely related thermodynamic parameters, viz. the standard enthalpy change, ∆H 0 , and the standard entropy change, ∆S 0 (Mustafa et al 2002;Rauf and Tahir 2000;Latour et al 2000;Tahir and Rauf 2003;Singh and Nayak 2004). To calculate ∆G 0 for an adsorption reaction, it is necessary to employ an important parameter -the equilibrium coefficient for the reaction -and, thus, the calculation of ∆G 0 is highly dependent on adsorption model analyses (Mirji 2006;Nabi et al 1999;Sahu et al 2000;Tahir and Rauf 2003).…”