Solid-state NMR structural studies of peptides immobilized on gold nanoparticles

In this paper we describe solid-state NMR experiments that provide information on the structures of surface-immobilized peptides. The peptides are covalently bound to alkanethiolates that are self-assembled as monolayers on colloidal gold nanoparticles. The secondary structure of the immobilized peptides was characterized by quantifying the Ramachandran angles Φ and ψ. These angles were determined in turn from distances between backbone carbonyl 13 C spins, measured with the double-quantum filtered dipolar recoupling with a windowless sequence experiment, and by determination of the mutual orientation of chemical shift anisotropy tensors of 13 C carbonyl spins on adjacent peptide planes, obtained from the double-quantum cross-polarization magic-angle spinning spectrum. It was found that peptides composed of periodic sequences of leucines and lysines were bound along the length of the peptide sequence and displayed a tight α-helical secondary structure on the gold nanoparticles. These results are compared to similar studies of peptides immobilized on hydrophobic surfaces.