Hydrophilic Silica-Polypeptide Composite Particles

Composite, pH-responsive particles have been synthesized by covalently attaching a simple polypeptide to a silica core. The synthesis begins with the production of organophilic poly(benzylglutamate)-coated silica particles.\footnote{Fong,B.; Russo, P.S. Organophilic Colloidal Particles with a Synthetic Polypeptide Coating. \textit{Langmuir} \textbf{1999}, $15$, 4421-4426.} The particles are rendered hydrophilic by cleaving the benzyl side group by treatment with hydrogen bromide in benzene. The resulting poly(glutamic acid)-coated silica spheres exhibit a change in hydrodynamic radius in response to pH stimulus. The size transition is due to a change in the polypeptide conformation, as deduced from circular dichroism measurements.