Infrared Spectroscopy and Molecular Simulations of a Polymeric Sorbent and Its Enantioselective Interactions with Benzoin Enantiomers

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• 作者：Hung-Wei Tsui ; Jonathan N. Willing ; Rahul B. Kasat ; Nien-Hwa Linda Wang ; Elias I. Franses
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：November 10, 2011
• 年：2011
• 卷：115
• 期：44
• 页码：12785-12800
• 全文大小：1375K
• 年卷期：v.115,no.44(November 10, 2011)
• ISSN：1520-5207

文摘

Retention factors, k_R and k_S, and enantioselectivities, S 鈮?k_R/k_S, of amylose tris[(S)-伪-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 k_R = 106, k_S = 49.6, and S = 2.13. With some IPA from 0.5 to 10 vol %, with S = 1.8鈥?.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鈥揷hain and chain鈥揵enzoin 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鈺怬 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 鈥渄ocking鈥?studies of benzoin in AS with MD, Monte Carlo (MC), and MC/MD simulations were done to probe the AS鈥揃 interactions. The observed enantioselectivities are predicted to be primarily due to two H-bonds, of the kind AS CO路路路HO (R)-benzoin and AS NH路路路OC (R)-benzoin, and two 蟺鈥撓€ (phenyl鈥損henyl) interactions for (R)-benzoin and one H-bond, of type AS CO路路路HO (S)-benzoin, and one 蟺鈥撓€ interaction for (S)-benzoin. The MC/MD predictions are consistent with the HPLC and IR results.