#33: NMR Spectroscopy of Glutamic Acid Containing Surfactant Micelles — Presentation Detail — Celebration of Scholars

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Jun Wang
Kim Instenes
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Nora Nickels
Andrew Pustina
James Ripley

#33: NMR Spectroscopy of Glutamic Acid Containing Surfactant Micelles

Name: Jacob Mayer
Major: Biology and Chemistry
Hometown: Kenosha, WI
Faculty Sponsor:
Other Sponsors:
Type of research: SURE
Funding: REU-NSF

Abstract

Surfactant molecules contain a charged headgroup bound to a hydrocarbon tail. In aqueous solution, surfactants aggregate into spherical structures called micelles by placing their headgroups at the micelle surface and their non-polar tails in the micelle core. This project used nuclear magnetic resonance (NMR) spectroscopy to study micelle formation by an amino acid-based surfactant (glutamic acid headgroup) which is naturally derived and a green alternative to the surfactants used in cosmetics, pharmaceuticals, and detergents. Our goal was to characterize how the properties of micelles formed by this surfactant changed with solution pH and with different counterions. Our hypothesis was that since the surfactant contained multiple carbocyclic acid functional groups, the physical properties of micelles formed by the surfactant should depend on solution pH. NMR spectroscopy was used to measure diffusion coefficients to determine micelle properties. Titration measurements showed that the pKa of the side-chain carbocyclic acid in the glutamic acid surfactant’s headgroup was 6.4. Diffusion experiments showed that when counterions with a +1 charge were in solution, micelles only formed below pH 6 while +2 counterions micelles formed between pH 5 and 10.5. Our conclusions were that unfavorable electrostatic repulsion between the negative headgroups prevented micelle formation when +1 counterions were in solution beyond pH 6.4. However, +2 counterions were better able to balance the surfactant’s negative charge, therefore micelles formed above pH 6 in solutions containing +2 counterions. Future work will investigate different amino acid headgroups and counterions.

Poster file