Doctor of Philosophy (PhD)
The research presented in this dissertation involves the synthesis, modification, characterization, and the application of polymeric surfactants in micellar electrokinetic chromatography (MEKC). Sodium undecenoyl-L-Leucinate (L-SUL) was synthesized and modified by use of alkali metal counterions, alcohols, and Triton X-102. Characterization of the modified poly-L-SUL was performed in order to elucidate the structural changes on the surfactants by use of four techniques. While surface tensiometry was used for the determination of the critical micelle concentration (cmc), fluorescence measurements were used for the determination of the polarity of the modified polymeric surfactants. The information about the size of the polymeric surfactants was obtained by use of pulsed field gradient-NMR (PFG-NMR). A superior chromatographic performance in MEKC was demonstrated by the modified polymeric surfactants as compared to the non-modified polymeric surfactants. A correlation between the polarity and the size of the polymeric surfactants was used to explain the observed enhanced enantiomeric recognition of analytes. The effect of polydispersity of poly-L-SUL on chiral separation of compounds was also examined. Centrifugal filtration was used to fractionate the polymeric surfactant into different molecular weight distribution. The resulting fractions were characterized by use fluorescence, PFG-NMR, densitometry, and analytical ultracentrifugation (AUC). The partial specific volumes of the fractionated and non-fractionated surfactant were determined by use of a densitometer. The molecular weights were determined by use of sedimentation equilibrium mode in AUC. Examination of the separation data obtained from MEKC experiments indicated that fractionated polymeric surfactants yielded a better chiral separation. In addition, increase in molecular weight of the fractionated surfactants resulted in a concomitant increase in enantiomeric resolution.
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Tarus, Jepkoech, "Tuning polymeric chiral surfactants for enhanced enantiomeric recognition in micellar electrokinetic chromatography" (2004). LSU Doctoral Dissertations. 1340.
Isiah M. Warner