Intrinsic Chirality and Prochirality at Air/R-(+)- and S-(-)-Limonene Interfaces: Spectral Signatures With Interference Chiral Sum-Frequency Generation Vibrational Spectroscopy
Intrinsic Chirality and Prochirality at Air/R-(+)- and S-(-)-Limonene Interfaces: Spectral Signatures With Interference Chiral Sum-Frequency Generation Vibrational Spectroscopy
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DOI：
10.1002/chir.22337
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发表时间：
2014-09-01
期刊：
影响因子：
2
通讯作者：
Wang, Hong-Fei
中科院分区：
文献类型：
--
作者：
Fu, Li;Zhang, Yun;Wang, Hong-Fei
本文报道了利用新近发展的高分辨宽带和频振动光谱仪（HR-BB-SFG-VS）对R-（+）-柠檬烯和S-（-）-柠檬烯气/液界面C-H伸缩振动区（2800-3050 cm（-1））的手性和非手性和频振动光谱的详细测量。R-柠檬烯和S-柠檬烯以及RS外消旋混合物（50/50等量混合物）的非手性SFG光谱表明，R和S对映体的相应分子基团具有相同的界面取向。柠檬烯对映体的干涉手性SFG光谱分别表现出来自C α-H伸缩模式的手性响应的光谱特征和来自CH 2不对称伸缩模式的前手性响应的光谱特征。C α-H伸缩模式的手性光谱特征从R-（+）-柠檬烯表面到S-（-）-柠檬烯表面改变符号，并且对于RS外消旋混合物表面消失。而CH 2不对称伸缩模式的前手性光谱特征对于R-（+）-柠檬烯和S-（-）-柠檬烯表面是相同的，并且对于RS外消旋混合物表面也令人惊讶地保持相同。因此，R-（+）-柠檬烯和S-（-）-柠檬烯在液体界面处的结构仍然不是彼此的镜像，即使相应的基团相对于界面法线具有相同的倾斜角，即。例如，表面的R-（+）-柠檬烯和S-（-）-柠檬烯是非对映体而不是对映体。这些结果为理解分子界面的结构和手性提供了详细的信息，并证明了SFG-VS作为一种独特的光谱工具或分子界面手性表征和手性识别的灵敏度和潜力。(C)2014 Wiley Periodicals，Inc.
We report in this work detailed measurements of the chiral and achiral sum-frequency vibrational spectra in the C-H stretching vibration region (2800-3050 cm(-1)) of the air/liquid interfaces of R-(+)-limonene and S-(-)-limonene, using the recently developed high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS). The achiral SFG spectra of R-limonene and S-limonene, as well as the RS racemic mixture (50/50 equal amount mixture), show that the corresponding molecular groups of the R and S enantiomers are with the same interfacial orientations. The interference chiral SFG spectra of the limonene enantiomers exhibit a spectral signature from the chiral response of the C alpha-H stretching mode, and a spectral signature from the prochiral response of the CH2 asymmetric stretching mode, respectively. The chiral spectral feature of the C alpha-H stretching mode changes sign from R-(+)-limonene to S-(-)-limonene surfaces, and disappears for the RS racemic mixture surface. While the prochiral spectral feature of the CH2 asymmetric stretching mode is the same for R-(+)-limonene and S-(-)-limonene surfaces, and also surprisingly remains the same for the RS racemic mixture surface. Therefore, the structures of the R-(+)-limonene and the S-(-)-limonene at the liquid interfaces are nevertheless not mirror images to each other, even though the corresponding groups have the same tilt angle from the interfacial normal, i. e., the R-(+)-limonene and the S-(-)-limonene at the surface are diastereomeric instead of enantiomeric. These results provide detailed information in understanding the structure and chirality of molecular interfaces and demonstrate the sensitivity and potential of SFG-VS as a unique spectroscopic tool or chirality characterization and chiral recognition at the molecular interface. (C) 2014 Wiley Periodicals, Inc.