Celebration of Scholars
NMR Investigation of the Effect of pH on Micelle Formation of the Surfactant L-Undecyl Phenylalaninate
Name:
Gabriel Rothbauer
Major: Chemistry
Hometown: Mondovi
Faculty Sponsor:
Kevin Morris
Other Sponsors:
Type of research: SURE
Funding: National Science Foundation
Abstract
NMR spectroscopy was used
to study the amino acid-base surfactant L-undecyl phenylalanine (und-Phe).
Amino acid-based surfactants like und-Phe are used in the pharmaceutical, food,
and cosmetic industries because they are biodegradable, biocompatible, have a
low toxicity, and can be produced using renewable materials. They are also used
as pseudostationary phases in capillary electrophoresis separations. NMR
measurements of the surfactant’s critical micelle concentration (CMC) showed
that und-Phe micelles began to form at approximately 6.0 mM in solutions
containing the anionic surfactant and sodium counterions. However, micelles
formed in the 3.5-4.0 mM range in solutions containing either arginine or
lysine counterions. In addition, NMR diffusion experiments showed that arginine
and lysine counterions bound to und-Phe micelles below pH 9.0, but dissociated
from the micelle surface at high pH. Finally, two-dimensional NMR experiments
suggested that the mechanism of arginine and lysine binding to und-Phe micelles
was different and that when the und-Phe micelles formed, their aromatic rings
rotated toward the non-polar micelle core.