Organophilic colloidal particles with a synthetic polypeptide coating

Composite colloidal particles with a silica core and a synthetic, homopolypeptide shell have been produced by initiation of benzyl-L-glutamate N-carboxyanhydride monomer from primary amine functionalized silica particles. The resulting poly(gamma-benzyl-alpha,L-glutamate)-coated spheres were characterized by electron microscopy, dynamic light scattering, infrared spectroscopy, and thermogravimetry. The poly peptide shell accounts for about 20% of the total mass of the particles, which are reasonably uniform in size. Infrared spectra show an alpha-helical secondary structure, but other conformations are not excluded. A geometrical analysis is applied to calculate the maximum number of amino groups that might realistically participate in initiation. The actual shell thickness is smaller than expected on the basis of these geometrical considerations, which reflects undesired termination steps or the conversion of some monomer to unattached polymer by trace initiator impurities.