Abstract
NMR spectroscopy and molecular dynamics (MD) simulation analyses of the chiral molecular micelles poly-(sodium undecyl-(L,L)-leucine-valine) (poly-SULV) and poly-(sodium undecyl-(L,L)- valine-leucine) (poly-(SUVL)) are reported. Both molecular micelles are used as chiral selectors in electrokinetic chromatography and each consists of covalently linked surfactant chains with chiral dipeptide headgroups. To provide experimental support for the structures from MD simulations, NOESY spectra were used to identify protons in close spatial proximity. Results from the NOESY analyses were then compared to radial distribution functions from MD simulations. In addition, the hydrodynamic radii of both molecular micelles were calculated from NMR-derived diffusion coefficients. Corresponding radii from the MD simulations were found to be in agreement with these experimental results. NMR diffusion experiments were also used to measure association constants for polar and non-polar binaphthyl analytes binding to both molecular micelles. Poly(SUVL) was found to bind the non-polar analyte enantiomers more strongly, while the more polar analyte enantiomers interacted more strongly with poly(SULV). MD simulations in tum showed that poly(SUL V) had a more open structure that gave greater access for water molecules to the dipeptide headgroup region.
Highlights
The specificity and efficacy of many biologically important reactions are based on chiral interactions, a fundamental phenomenon that is observed in all biological systems
In order to further assess the validity of these structures, Molecular Dynamics (MD) simulation results were compared to experimental NOESY and diffusion coefficient analyses from NMR spectroscopy
Results from the MD simulations were compared to these analyte binding results by examining the number of water molecules in each Molecular Micelles (MM) core and dipeptide headgroup region
Summary
The specificity and efficacy of many biologically important reactions are based on chiral interactions, a fundamental phenomenon that is observed in all biological systems. While significant progress has been made, from both a fundamental and application-oriented perspective, a complete understanding of chiral recognition has yet to materialize. This research has lead to the development of many chiral separation media for the enantiomeric resolution of chiral compounds including chiral cyclodextrins, surfactants, and polymers [1]. The focus of this investigation is two chiral polymers formed by covalently linking amino acid based surfactant monomers. These materials are known as Molecular Micelles (MM) because they contain a hydrophobic hydrocarbon core and hydrophillic amino acid headgroups. MD simulations and NMR spectroscopy were used to investigate the structures of MM with headgroups containing the amino acids leucine and valine
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