Colloidal Crystals of Silica−Homopolypeptide Composite Particles

Abstract

Colloidal particles of uniform size can crystallize in suspension. The large lattice spacing of these crystals leads to diffraction of visible light. Such systems have been considered as optical filters, intensity limiters, photonic bandgapmaterials, andsensors.1-6 Crystallizable colloidal particles are also useful model systems for studying orderdisorder transitions and crystal growth rate.7-9 The most popular formulations are polymer latex or silica. A few years ago, this laboratory described core-shell colloids in which a silica core was coated with poly(γ-benzyl-Lglutamate), PBLG, a helical, rodlike homopolypeptide.10 Compared to previous polypeptide-coated particles,11,12 excellent, latex-like particle uniformity was achieved. The shells of those particles were largely in the R-helical conformation. The following factors motivate continued interest in silica core/homopolypeptide shell composite particles: the helix-coil transition may lead to a responsive, configurable surface; polypeptides display a very rich chemistry; tethering polypeptides to a rigid core may alter their tendency to form cholesteric liquid crystals; colloids with a chiral surface may be useful for some separations. In this short contribution, we describe silica colloidal particles coated with a different homopolypeptide, poly( -carbobenzyloxy-L-lysine) or PCBL. The resultant coreshell particles display crystalline order not yet observed in the PBLG-coated spheres.