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Dissertation Information for Bessie Nneka Arufolonye Mbadugha

NAME:
- Bessie Nneka Arufolonye Mbadugha

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (2002)

ADVISORS:
- Fred M. Menger

COMMITTEE MEMBERS:
- Frank E. McDonald
- Lanny S. Liebeskind

MPACT Status: Fully Complete

Title: I. Gemini surfactants with a disaccharide spacer. II. Synthesis and bilayer interactions of neosaponins

Abstract: Part I . Two related families of gemini surfactants have been synthesized, both with trehalose, a disaccharide, as a polar spacer. One family, Series A , is non-ionic and has amide groups separating the long chains from the trehalose spacer. The other family, Series B , has quaternary ammonium ions connecting the long chains to the trehalose spacer. It was found that Series A geminis are water-insoluble despite the two amides and multiple hydroxyls. When hydrated or extruded, these geminis form bilayer vesicles above their transition temperatures, which were determined calorimetrically, Insoluble monomolecular films, constructed from these geminis, have interfacial areas that are dominated by the sugar spacer although intermolecular chain/chain interactions seem to stabilize the films. Thus the behavior of Series A geminis in many ways parallels that of phospholipids and simple double-chain surfactants. In contrast, cationic Series B geminis are water soluble and form micelles with critical micelle concentrations an order of magnitude lower than that of corresponding conventional surfactants. Molecular modeling using the Amber* force field explains the difference in properties between the two families of geminis. Series A are tubular in shape and thus prefer bilayer packing as do other amphiphiles in which the headgroups are similar in width to the sum of the tail diameters. Series B geminis are conical shaped and pack more readily into spherical micelles. This work entails synthesis, tensiometry, conductance, microscopy, surface balance studies, calorimetry, light scattering, and molecular modeling. In colloid chemistry, a balanced perspective cannot be achieved by one methodology alone but only through the pursuit of consilience among multiple approaches.

Part II . Saponins, found in a number of plants and in some marine organisms, are amphiphilic conjugates containing one or more carbohydrate groups covalently bound to a steroid or triterpene aglycone. Monodesmosidic saponins, featuring sugar substitution at a single position on the aglycone, generally exhibit more potent biological activities than their bidesmosidic cousins, which possess sugar attachments at two positions on the aglycone. Although the exact mechanisms of action of the numerous biological activities possessed by saponins are unknown, membrane interactions are speculated to be a determining factor. As such, the relative inactivity of bidesmosides has been attributed to an inability to intercalate into bilayers due to their bipolar disposition. Herein a group of bidesmosidic neosaponins and a monodesmosidic control containing different monosaccharide units and steroid aglycones have been synthesized and their interactions with model phospholipid membranes probed by differential scanning calorimetry. Incorporation of the bidesmosidic models was indicated, with an observed dependence on the structure and of the specific monosaccharide unit and nature of attachment to the aglycone. A plausible model to explain bilayer insertion of the bipolar neosaponins has been proposed.

MPACT Scores for Bessie Nneka Arufolonye Mbadugha

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-03-23 20:47:02

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