[2010年03月01日]

手性拉曼光谱首次应用于手性催化反应研究

     手性催化反应中绝对构型的变化监测长期以来一直是光谱研究的挑战。手性拉曼光谱(ROA)由于其具有样品无需结晶、微量检测、对样品非破坏性、生物亲和性等优势近年来被认为是研究手性分子立体构型和构象,特别是水溶液中生物分子行为的有效手段。

 我组首次利用手性拉曼光谱,结合理论计算方法研究了手性催化中的典型反应:(-)-α-蒎烯环氧化生成环氧蒎烯及之后生成(-)-蒎二醇的水解反应。详细讨论了新增加的手性中心对双环化合物手性拉曼光谱的影响,考察了环氧蒎烯中取代氧原子和(-)-蒎二醇中羟基基团对于手性信号的贡献,并比较了电偶极矩-磁偶极矩各向异性不变量和电偶极矩-电四极矩各向异性不变量在产生手性拉曼信号中的权重,验证了键极化模型。结果表明手性拉曼光谱能够提供手性催化反应中手性环境改变的信息,可以广泛应用于化学和生物学体系。

Article

Chirality transition in the epoxidation of (-)-α-pinene and successive

hydrolysis studied by Raman optical activity and DFT      

Shi Qiua, Guanna Lia, Peng Liu, Changhao Wang, Zhaochi Feng* and Can Li*

aThese authors contributed equally to this work.

Phys. Chem. Chem. Phys., 2010, DOI: 10.1039/b919993d

http://www.rsc.org/publishing/journals/CP/article.asp?doi=B919993D

Abstract

  Characterization of the chirality evolution involved in chemical and biochemical reaction processes is extremely important to the understanding of the chiral catalysis mechanism. In this work, the chiral transition from the epoxidation of (-)-α-pinene to α-pinene oxide and successive hydrolysis to (-)-pinanediol has been studied as an archetype of the asymmetric catalysis by Raman optical activity (ROA) and the DFT calculation. Minor changes of the absolute configuration of the chiral products from (-)-α-pinene to (-)-pinanediol lead to the dramatic variation in ROA spectra indicating that the chirality is delocalized in the whole molecule rather than only concentrated on the chiral centers. The oxygen atom of α-pinene oxide contributes strong ROA signals while the two hydroxyl groups of (-)-pinanediol give no apparent contribution to the chirality in terms of ROA signals. Isolation of the two symmetric anisotropic invariants shows that the predominant contribution to the ROA signals stems from the electric dipole–magnetic dipole invariant, and the bond polarizability model is indeed found to be a good approximation for molecules composed of entirely axially-symmetric bonds in α-pinene oxide and (-)-pinanediol. This study demonstrates the feasibility of using ROA to sensitively monitor the variation of the chirality transition during the chiral reactions either in the chemical or biological system.

 

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