Infrared spectroscopy and molecular simulations of a polymeric sorbent and its enantioselective interactions with benzoin enantiomers
Journal
Journal of Physical Chemistry B
Journal Volume
115
Journal Issue
44
Date Issued
2011-11-10
Author(s)
Abstract
Retention factors, kR and kS, and enantioselectivities, S - kR/kS, of amylose tris[(S)-α-methylbenzylcarbamate] (AS) sorbent for benzoin (B) enantiomers were measured for various isopropyl alcohol (IPA)/n-hexane compositions of the high-performance liquid chromatography (HPLC) mobile phase. Novel data for pure n-hexane show that kR = 106, kS = 49.6, and S = 2.13. With some IPA from 0.5 to 10 vol %, with S = 1.8-1.4, the retention factors were smaller. Infrared spectra showed evidence of substantial hydrogen bonding (H-bonding) interactions in the pure polymer phase and additional H-bonding interactions between AS and benzoin. Density functional theory (DFT) was used to model the chain-chain and chain-benzoin H-bonding and other interactions. DFT was also used to predict fairly well the IR wavenumber shifts caused by the H-bonds. DFT simulations of IR bands of NH and C=O allowed for the first time the predictions of relative intensities and relative populations of H-bonding strengths. Molecular dynamics (MD) simulations were used to model a single 12-mer polymer chain. MD simulations predicted the existence of various potentially enantioselective cavities, two of which are sufficiently large to accommodate a benzoin molecule. Then "docking" studies of benzoin in AS with MD, Monte Carlo (MC), and MC/MD simulations were done to probe the AS-B interactions. The observed enantioselectivities are predicted to be primarily due to two H-bonds, of the kind AS CO•••HO (R)-benzoin and AS NH•••OC (R)-benzoin, and two π-π (phenyl-phenyl) interactions for (R)-benzoin and one H-bond, of type AS CO•••HO (S)-benzoin, and one π-π interaction for (S)-benzoin. The MC/MD predictions are consistent with the HPLC and IR results. © 2011 American Chemical Society.
SDGs
Type
journal article