Doctor of Philosophy (PhD)
The investigation of polypeptide composite particles, PCPs, is described. The production of mesoporous and polycolloid architectures is also addressed. PCPs were prepared by both growing form and grafting to method. They consist of a core made of silica, silica-coated magnetite or silica-coated cobalt. Some of the particles were covalently labeled with fluorescein isothiocyanate. Several polypeptides were chosen for attachment on the core: poly(γ-stearyl-L-glutamate), PSLG, poly(Nε-carbobenzyloxy-L-lysine), PCBL and poly(o-benzyl-L-tyrosine), PBTY. Attachment of a well-characterized alkyne-end terminated PSLG and PCBL to an azide- functionalized particle yielded PCPs with a desired sparse coverage. A blend of techniques such as FTIR, XPS, TEM, HTEM, XRD, GPC, MALDI-TOF, DLS, and SQUID was used to confirm their production and to investigate their properties. The near superparamagnetic PCBL-CPs showed thinning behavior when subjected to stress. PSLG-CPs dispersed in different surfactant aqueous solutions and also enabled the immobilization by adsorption of a lipase from Candida rugosa. Dispersed in a liquid crystal PSLG matrix they rendered interesting morphologies. Mesoporous silica structures, some called geodesics, were obtained by prolonged storage in a slightly basic solution of ammonium hydroxide. Treatment with 3mM NaOH of fluorescent silica and PCPS yielded interesting mesoporous structures. Silica fluorescent particles were easily up-taken in the living cells of the Arabidopsis thaliana leaf. A concentrated NaOH solution (~10%) was used to cleave the polypeptide shell and measure the molecular weight. The helix conformation of the shell and the molecular weight, were confirmed by GPC assays. PCBL-CPs underwent to an inverse helix-to-coil transition in m-cresol as a function of temperature. The transition was followed by DLS, DSC, NMR T1 and SAXS. The results obtained with the blend of these techniques suggested a complicated landscape for the transition. The conformational change is not a pure coil-to-helix transition, rather transient states were identified. Polycolloid architectures were obtained by using enzymatic (Horseradish peroxidase) and photolytic catalysis (PICUP-Photo-induced Cross-linking of Unmodified Proteins). Comparison between the two approaches emphasized the facile preparation of the polycolloid structures by PICUP. The technique was suitable for preparation of different architectures obtained by patterning the reaction vessels. PICUP also enabled the formation of permanent magnetic PCP chains.
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Rosu, Cornelia, "Silica Polypeptide-Based Colloids: Physical Properties and Novel Materials" (2013). LSU Doctoral Dissertations. 339.