Peptides that have a-helical structures in solution have been adsorbed to anionic and cationic colloidal silica substrates in aqueous solution, and the orientation and conformation of the adsorbed peptides have been studied by H-1 NMR and circular dichroism. The peptides, which are composed of aspartate, alanine, and arginine segments, adsorb to charged colloidal silica such that the complementary-charged amino acid side chains are adjacent to the substrate surface. The intramolecular interactions that stabilize the a-helical structure are perturbed by the intermolecular interactions established upon adsorption, and the peptides undergo a conformational change upon adsorption to the substrate surface. Partial helicity loss propagates from one or both of the peptide termini, although the adsorbed molecules retain some a-helical structure.