Studies on the conformational change of adsorbed BSA onto a moderately hydrophobic surface at different denaturant concentrations and surface coverages

This paper is aimed at investigating the conformational change of denatured bovine serum albumin (BSA) in combination with thermodynamic functions and their fractions, adsorption isotherms, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). Microcalorimetric measurements of displacement adsorption enthalpies DeltaH of denatured BSA (by guanidine hydrochloride (GuHCl)) adsorbed onto a moderately hydrophobic surface (PEG-600) from solutions were carried out. The contents of secondary structure elements of BSA in solutions and in the adsorbed state were determined by FTIR and the thermal stability of adsorbed BSA was measured by DSC. The adsorption thermodynamic functions DeltaH, DeltaS, DeltaG, and their fractions were calculated based on the thermodynamics of the stoichiometric displacement theory for adsorption (SDT-A) and adsorption isotherms. The results showed that the surface can provide energy to denatured BSA and make it gain a more ordered conformation with GuHCl concentration increment. At a given GuHCl concentration, although the ordered secondary structure of adsorbed BSA molecules decreased, their tertiary structure may be more perfect with surface coverage increment. The thermodynamic analysis of four subprocesses associated with adsorption also confirmed the increment of conformational gain.