An NMR Investigation of the Effect of pH on the Aggregation of Amino Acid Surfactants — Presentation Detail — Celebration of Scholars

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Jun Wang
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An NMR Investigation of the Effect of pH on the Aggregation of Amino Acid Surfactants

Name: Mark Flanigan
Major: Chemistry
Hometown: Saint Charles, IL
Faculty Sponsor: Kevin Morris
Other Sponsors:
Type of research: SURE
Funding: National Science Foundation

Abstract

NMR Spectroscopy was used to investigate the physical properties of micelles formed by molecules containing a long hydrocarbon chain terminated with the amino acid leucine. Since the a-carbon atom in the leucine headgroup is chiral, these micelles can be used as stationary phases in chiral separations. NMR spectroscopy was used to study the effect of solution pH on the sizes, viscosities, and structures of the micelles. NMR diffusion experiments showed that the micelles were largest at acidic and very basic pH levels and smaller in the pH range of 7-9. NMR titrations revealed that the leucine amide proton disappeared from the NMR spectra around pH 10. Variable temperature NMR experiments showed this effect was most likely due to an increase in amide proton exchange rate with solvent at high pH. Two-dimensional NMR spectra suggested that in the micelles the surfactant molecules underwent minimal folding. Finally, both the (S) and (R) enantiomers of a chiral compound were found to bind to micelles at mole fractions above 0.80.

Poster file