Thermodynamic investigation of effect of salt concentrations on denatured α-Amylase adsorbed onto a moderately hydrophobic surface

The displacement adsorption enthalpies (Delta H) of denatured alpha-Amylase (by 1.8 mol L-1 GuHCl) adsorbed onto a moderately hydrophobic surface (PEG-600, the end-group of polyethylene glycol) from solutions (x mol L-1 (NH4)(2)SO4, 0.05 mol L-1 KH2PO4, pH 7.0) at 298 K are determined by microcalorimeter. Further, entropies (Delta S), Gibbs free energies (Delta G) and the fractions of Delta H, Delta S, and Delta G for net adsorption of protein and net desorption of water are calculated in combination with adsorption isotherms of alpha-Amylase based on the stoichiometric displacement theory for adsorption (SDT-A) and its thermodynamics. It is found that the displacement adsorptions of denatured alpha-Amylase onto PEG-600 surface are exothermic and enthalpy driven processes, and the processes of protein adsorption are accompanied with the hydration by which hydrogen bond form between the adsorbed protein molecules favor formation of beta-sheet and beta-turn structures. The Fourier transformation infrared spectroscopy (FTIR) analysis shows that the contents of ordered secondary structures of adsorbed alpha-Amylase increase with surface coverages and salt concentrations increment.