New applications for surfactant based colloidal systems: an experimental and computational approach

Abstract

Surfactants such as cetyltrimethylammonium (CTA+) and cetylpyridinium (CP+) have diverse applications in various biological and industrial processes. In this dissertation, these surfactants with bromide counterions have been used to produce bromine in situ by the oxidation of the bromide anions using benzoyl peroxide (BPO) as the oxidizing agent in water (Chapter 2). The method presented here is safe and cost effective compared to other conventional methods that use metal catalysts or organic solvents for bromine generation. As an illustration, in situ generated bromine has been employed as a brominating agent for cholesterol and methyl styrene; and as an oxidizing agent for benzyl alcohol and 1,4-bis(hydroxymethyl)benzene. The partial oxidation of the aromatic alcohols form aldehydes and is significant since the typical oxidation product of primary alcohols in water is their corresponding acid. However, the partial oxidation of 1,4-bis(hydroxymethyl)benzene in CPB micelle gives a regioselective oxidation product monoaldehyde, as the sole product, while CTAB micelles give both mono and dialdehyde as the product. In order to understand the differences in the oxidation of diol in CPB and CTAB micelle, molecular dynamics (MD) simulations have been performed using GROMACS package (Chapter 3). A united atom force field for CPB molecule has been developed for the first time to assist in the molecular dynamics studies. Based on the results from MD simulations, it is concluded that the preferential orientation of substrate in CPB micelle, compared to CTAB micelle, results in the difference in product distribution (Chapter 4). In Chapter 5, a pH responsive catanionic system has been developed from CTAT, SDBS and TDA mixture that can sequester drug such as doxorubicin at higher pH (7.4) and is released at maximal rate at lower pH (< 6.0).