Intrinsic Chirality and Prochirality at Air/R‐(+)‐ and S‐(–)‐Limonene Interfaces: Spectral Signatures With Interference Chiral Sum‐Frequency Generation Vibrational Spectroscopy. Issue 9 (4th June 2014)

• Record Type: Journal Article
• Authors: Fu, Li; Zhang, Yun; Wei, Zhe‐Hao; Wang, Hong‐Fei
• Is Part Of: Chirality. Volume 26:Issue 9(2014:Sep.)
• Page Start: 149
• Page End: 160
• Publication Date: 2014-06-04
• Subjects: Chirality -- Periodicals; Pharmaceutical chemistry -- Periodicals; 541.22
• DOI: 10.1002/chir.22337
• Languages: English
• ISSNs: 0899-0042

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>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<sup>‐1</sup>) of the air/liquid interfaces of <italic>R‐(+)‐limonene</italic> and <italic>S‐(−)‐limonene</italic>, using the recently developed high‐resolution broadband sum‐frequency generation <named-content content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">vibrational spectroscopy</named-content> (HR‐BB‐SFG‐VS). The achiral SFG spectra of <italic>R‐limonene</italic> and <italic>S‐limonene</italic>, 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 Cα‐H stretching mode, and a spectral signature from the prochiral response of the CH<sub>2</sub> asymmetric stretching mode, respectively. The chiral spectral feature of the Cα‐H stretching mode changes sign from <italic>R‐(+)‐limonene</italic> to <italic>S‐(–)‐limonene</italic> surfaces, and disappears for the RS racemic mixture surface. While the prochiral spectral feature of the CH<sub>2</sub> asymmetric stretching mode is the same for <italic>R‐(+)‐limonene</italic> and <italic>S‐(–)‐limonene</italic> surfaces, and also surprisingly remains the same for the RS racemic mixture surface. Therefore, the structures of the <italic>R‐(+)‐limonene</italic> and the <italic>S‐(–)‐limonene</italic> 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 <italic>R‐(+)‐limonene</italic> and the <italic>S‐(–)‐limonene</italic> 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 for chirality characterization and <named-content content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">chiral recognition</named-content> at the molecular interface. <italic>Chirality 26:149–160, 2014.</italic> © 2014 Wiley Periodicals, Inc.</p> </abstract>