Adhesion Phenomena at the Interface between Biomolecules and Silica

Circular dichroism (CD) spectroscopy is one of the few experimental techniques sensitive to the structural changes that peptides undergo when they adsorb on inorganic material surfaces. Although the theoretical calculation of the CD spectrum of a molecule in a given conformation can be routinely performed, the inverse problem of extracting atomistic structural details from a measured spectrum is not uniquely determined. Complicated is the case of oligopeptides, whose folding/unfolding energy landscapes are often very broad and shallow. A modeling method is presented, which allows to predict the helicity loss of a peptide upon interaction with silica colloids in water, in quantitative agreement with experimental measurements. CD ellipticity for a given wavelength is calculated as an external collective variable by means of reweighting the biased trajectory obtained using the peptide-SiO2 surface distance and the structural helicity as two independent, internal collective variables.