MAGNETIC-RESONANCE STUDIES OF POLYPEPTIDES ADSORBED ON SILICA AND HYDROXYAPATITE SURFACES

Solid-state C-13 and H-2 nuclear magnetic resonance were used to reveal differences in conformation and local mobility between polypeptides in the bulk-solid and surface-adsorbed states. Carbon-13 chemical shifts show that the alpha-helical structures of longer chain solid poly-L-lysine and poly-L-glutamic acid are largely replaced by a more extended conformation upon adsorption. These shifts also identify specific side-chain functional group interactions with surface sites. Restriction of side-chain amino group rotation, revealed in H-2 NMR experiments, demonstrates the strength of these adsorbate-surface interactions. Measurements of C-13 rotating-frame spin-lock relaxation and cross-polarization dynamics indicate that, in general, both side-chain and backbone motions of adsorbed poly-L-lysine and poly-L-glutamic acid are diminished relative to the bulk-solid state. Taken together, these results suggest that the polypeptides adsorb in a flat, relatively extended conformation through strong electrostatic interactions of side-chain functional groups with the surface. This work demonstrates the effective use of conventional solid-state NMR analysis for studying conformational and motional behaviors of surface-adsorbed polymers.