Pulsed-field gradient NMR study of sodium dodecyl sulfate micelle-peptide association

Pulsed-field gradient (PFG) NR-IR spectroscopy was used to characterize the interactions between a series of small peptides and sodium dodecyl sulfate (SDS) micelles. The study was undertaken because peptide-micelle interactions are often exploited in the chromatographic analysis of complex mixtures, and therefore an accurate knowledge of peptide-micelle association constants is essential for a thorough understanding of the separation mechanism in these techniques. In the PFG-NMR experiment, diffusion coefficients for each peptide were measured in free solution and in the presence of SDS micelles. These diffusion coefficients allowed the mole fraction of peptide molecules associated with SDS micelles and the peptide-micelle association constants, K-eq, to be calculated. In a study of dipeptides derived from the leucine enkephalin (YGGFL) and D-(Ala)(2)-leucine enkephalin (YAGFL) amino acid sequences, only Phe-Leu was found to associate strongly with the micellar aggregates. The equilibrium constant for this dipeptide was found to be 69 +/- 6 M-1. The dipeptides Tyr-Gly, Tyr-Ala, Gly-Gly and Gly-Phe exhibited little to no micelle binding, whereas Tyr-Leu had an association constant that was a factor of four less than the Phe-Leu value. Furthermore, the association constants for the pentapeptides leucine enkephalin and D-(Ala)(2)-leucine enkephalin (130 +/- 8 and 564 +/- 38, respectively) were both higher than the K-eq values for all dipeptides investigated. These results suggest that micelle-induced changes in peptide conformation and peptide hydrophobicity both play important roles in governing peptide-micelle binding. Copyright (C) 2001 John Wiley & Sons, Ltd.