The Structure and Dynamics of Poly(l-lysine) in Templated Silica Nanocomposites

Abstract

Biologically templated nanoparticles are of interest for a variety of biological applications and for controlling the porosity and other properties in nanocomposites. Solid-state NMR has been used to characterize polypeptide/silica composites templated from the poly(L-lysine) solutions in the α-helix, β-sheet, and random coil conformations. The results show that the poly(L-lysine) retains its solution conformation in the nanocomposites when templating from the α-helix or /3-sheet conformation, but the random coil conformation is partially converted to the α-helical form during nanocomposite formation. The dynamics of poly(L-lysine) are restricted by incorporation into the composite compared to bulk poly(L-lysine) at the equivalent relative humidity. Bulk and film poly(L-lysine) samples undergo transitions from the random coil to the /?-sheet to the α-helix conformation with increasing relative humidity, but these transitions are suppressed in the silica composite. { 1 H- 31 P} NMR studies show that inorganic phosphate is incorporated into the random coil-templated composite and that part of the phosphate is closely associated with the poly(L-lysine). The implications for biomimetic nanocomposites formation are considered.