Catanionic surfactant vesicles as a platform for probing protein-carbohydrate multivalent interactions

Abstract

This thesis describes the work on understanding the phase behavior of mixed surfactant systems and on the surface-functionalization and modification of catanionic vesicles with an aim toward probing protein-carbohydrate multivalent interactions. To understand the phase behavior of aqueous mixture of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS) solutions at micromolar surfactant concentrations, calculations were performed in conjunction with fluorescence correlation spectroscopy (FCS) studies to probe the composition and size of aggregates formed at low concentration. Toward this end, the critical micelle concentration (cmc) of CTAT was measured to be 0.12-0.35 mM and cmc of SDBS to be 2.2-2.8 mM, both values agree with literature values. The critical aggregation concentration (cac) for the mixtures of CTAT and SDBS having a 1.8-fold molar excess of CTAT was measured to be 2.6 μM. Using these measured values, for CTAT-rich mixtures, the mole fraction of CTA+ in the vesicle bilayer is calculated to be 0.56 at the cac. The interaction parameter is calculated to be -24. These calculations in this thesis suggest that the surface charge at low surfactant concentration near the cac. This theoretical prediction was supported by FCS studies of DNA and CTAT-rich vesicles binding near the cac. Next the catanionic vesicle outer membrane was functionalized by hydrophobic insertion of hydrocarbon chain of the glycoconjugate n-dodecyl-β-D-glucopyranoside (C12-Glu). Kinetics of multivalent interactions between the lectin concanavalin A and C12-Glu was studied by cryo-TEM and stopped-flow turbidometry. Inhibition multivalent binding studies were conducted and a potential new tool has been developed in evaluating multivalent inhibition.