Superparamagnetic Core-shell Silica- Polypeptide Composite Particles

Core-shell composite particles have been prepared, each consisting of a silica-coated cobalt center to which a homopolypeptide shell, either poly ($\varepsilon $-carbobenzyloxy-L-lysine) or poly ($\gamma $-benzyl-L-glutamate), is attached covalently. Core particles were decorated with a mixture of amino groups and passivating groups through silylation reactions. The amino groups initiated the polymerization, with attachment, of $N$-carboxyanhydride monomers, resulting in a homopolypeptide shell. Characterization by dynamic light scattering confirmed the helix-coil transition of the particles through repeated heating and cooling cycles in an organic solvent. The living nature of the polypeptide shell has also been confirmed. The particles have a size and uniformity that leads to formation of colloidal crystals. Magnetometer measurements suggest the particles are superparamagnetic.