Doctor of Philosophy (PhD)
The synthesis and sequential surface characterization of silica-polypeptide composite particles is described. Nearly monodisperse colloidal silica cores were obtained by the alkaline hydrolysis of tetraethyl orthosilicate (TEOS). The hydrodynamic radius can be easily controlled in the range of ƒî 20-140 nm by the water/TEOS ratio in the starting reaction mixture. The surface of the synthesized silica cores was further passivated/functionalized (P/F) by a mixture of (3-aminopropyl) trimethoxysilane (APS) and methyl-trimethoxysilane (MTMS). The amino groups were quantified using UV-Vis spectrometry after reaction with ninhydrin. The use of zeta potential measurements of the P/F silica particles at low pH is presented as a potential alternative for the quantification of surface amino groups. The amino groups on the P/F silica cores were used as initiators for the polymerization of N-carboxyanhydrides (NCAs) yielding silica-polypeptide composite particles. The polypeptide content of silica-PBLG (silica-poly(ƒ×-benzyl-L-glutamate)) was controlled when the synthesis was performed by sequential addition of N-carboxyanhydride (monomer). The polypeptide shell in a ¡§wet¡¨ state was visualized by using positive staining with osmium tetroxide (OsO4) vapors when the particles were dispersed in pyridine. The stained composite particles were observed using transmission electron microscopy (TEM). They appear as spheres with a light corona around them. The use of an internal negative control that can be easily observed in the same field presents a compelling argument for the hypothesis that the observed corona is the polypeptide shell. The benzyl groups of PBLG on silica-PBLG composite particles were removed by reaction with hydrogen bromide yielding silica-PLGA (poly(L-glutamic acid)) particles. The hydrodynamic radii and zeta potential were studied as function of pH. The silica-PLGA composite particles appear extended and negatively charged at high pH and compact and neutral at low pH. This can be attributed to the changes on the PLGA shell. Silica-PCBL (poly(carbobenzyloxy-L-lysine)) composite particles were synthesized by the reaction of P/F silica cores with the respective NCA. The PCBL shell apparently undergoes a temperature-induced conformation transition as suggested by nuclear magnetic resonance and dynamic light scattering measurements.
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Soto-Cantu, Erick Isael, "Synthesis and Surface Characterization of Silica-Polypeptide Composite Particles" (2008). LSU Doctoral Dissertations. 214.
Paul S. Russo