Adsorption and reduction of glutathione disulfide on α-Al2O3 nanoparticles: experiments and modeling

Glutathione disulfide (GSSG; γ-GluCysGly disulfide) was used as a physiologically relevant model molecule to investigate the fundamental adsorption mechanisms of polypeptides onto α-alumina nanoparticles. Its adsorption/desorption behavior was studied by enzymatic quantification of the bound GSSG combined with zeta potential measurements of the particles. The adsorption of GSSG to alumina nanoparticles was rapid, was prevented by alkaline pH, was reversed by increasing ionic strength, and followed a nearly ideal Langmuir isotherm with a standard Gibbs adsorption energy of -34.7 kJ/mol. Molecular dynamics simulations suggest that only one of the two glutathionyl moieties contained in GSSG binds stably to the nanoparticle surface. This was confirmed experimentally by the release of GSH from the bound GSSG upon reducing its disulfide bond with dithiothreitol. Our data indicate that electrostatic interactions via the carboxylate groups of one of the two glutathionyl moieties of GSSG are predominantly responsible for the binding of GSSG to the alumina surface. The results and conclusions presented here can provide a base for further experimental and modeling studies on the interactions of biomolecules with ceramic materials.