Synthesis and Characterization of Superparamagnetic Silica--Homopolypeptide Composite Particles

Hierarchical construction and characterization of core-shell composite particles of interest are presented. The research described shows interest in new types of polymers that provide chirality and responsiveness which have been ignored for so long. The general synthetic design described in this document can be readily used as a model for other systems. Core-shell composite systems of interest consist of silica or silica-coated cobalt cores grafted with a homopolypeptide shell, mostly poly(epsilon-carbobenzyloxy-L-lysine) or poly(gamma-benzyl-L-glutamate). Core particles were decorated with amino groups through a silylation reaction. The amino groups initiated the polymerization (with attachment) of N-carboxyanhydride (NCA) monomers, resulting in a homopolypeptide shell. Homopolypeptide-grafted particles were considered as hierarchical systems due to the two levels of responsiveness. The first level of responsiveness is due to the superparamagnetic nature of the core and the second level of responsiveness is through the thermally responsive polypeptide shell. Both levels of response were confirmed with several characterization methods. Characterization by electron microscopy and dynamic light scattering (DLS) confirmed the uniformity of the particles. Magnetic properties of the silica-coated cobalt core and polypeptide-grafted particles were investigated with a superconducting quantum interference device (SQUID). DLS and digital polarimeter demonstrated helix-coil transitions of the particles through continuous heating and cooling cycles in m-creso