Structure and formation of self-assembled monolayers of helical poly (γ-benzyl L-glutamate) by surface plasmon resonance and infrared spectroscopy

The self-assembly of a rigid, rod-like, alpha-helical polypeptide was investigated on gold substrates. A disulfide labeled poly(gamma-benzyl-L-glutamate) (PBLG) was prepared by a novel synthetic route wherein the polymerization of the N-carboxyanhydride was initiated with an amine terminated disulfide. Two different SSPBLG materials with molecular weight of I I and 28 kDa were prepared and characterized using dielectric spectroscopy. The kinetics of self-assembly of the two polypeptides was studied using surface plasmon resonance (SPR) and the organization of the self-assembled monolayers (SAMs) was characterized by polarization-modulation infrared absorption spectroscopy (PM-IRRAS). SPR revealed that self-assembly of the high molecular weight polypeptides on gold substrates proceeds rapidly on a time-scale of minutes and is comparable to the time of assembly of simple n-alkanethiols. The increase in length of the polypeptide led to an increase in the dipole moment from 156 to 363 D. The enhanced electrostatic interactions in the SAMs were manifested as an increase in the average tilt of the helix axis from the normal to the surface and monolayers with smaller thickness. (C) 2002 Elsevier Science B.V. All rights reserved.