Observation and calculation of vibrational circular birefringence: A new form of vibrational optical activity

Abstract

We report the first mid-infrared observation of vibrational circular birefringence (VCB) arising from individual chiral molecules. VCB can also be called vibrational optical rotatory dispersion (VORD) and is the Kramers-Kronig transform of vibrational circular dichroism (VCD). The method of measurement involves a simple change in the optical set-up and electronic processing of a VCD spectrometer such that the VCB spectrum appears at twice the polarization modulation frequency as a pseudo vibrational linear dichroism (VLD) spectrum. VCB spectra are also calculated with density function theory (DFT) for the first time using a commercially available program for rotational strengths where the calculated intensities are convolved with the real, dispersive part of a normalized complex Lorentzian lineshape rather than the imaginary, absorptive part, normally used for IR and VCD intensity calculations. Comparison of the measured and calculated VCB, VCD, and IR spectra of (1)-R-limonene and (2)-S-apinene show close agreement and confirm the validity of the new VCB measurements. Chirality 21:E277-E286, 2009. V

Vibrational optical activity

“…Such approaches could open the way to time-resolved VCD studies of, inter alia, dynamic processes in proteins in solution that are too fast for NMR investigations [134]. In another recent VOA instrument development, the first observation of infrared vibrational circular birefringence (VCB) was reported [135], this being the Kramers-Kronig transform of VCD. VCB may also be called vibrational optical rotatory dispersion (VORD), which is in fact the observable measured in the IR femtosecond ellipsometric experiment [132].…”

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

“…69 Other monoterpenes whose VCD spectra were investigated in both mid-IR and near-IR regions include (+)-(R)limonene (5), (À)-(R)-carvone (6) and its antipode (7), (+)-(R)pulegone (8), (À)-(1S)-b-pinene (9), and both enantiomers of menthol (10 and 11). 74 Regarding ROA, compound 1 was used in the rst simultaneous acquisition of all four forms of circular polarization ROA. 73 The S enantiomer of compound 1 along with compound 5 were used in the rst mid-IR observation of vibrational optical rotatory dispersion.…”

Intrinsic Chirality and Prochirality at Air/R‐(+)‐ and S‐(–)‐Limonene Interfaces: Spectral Signatures With Interference Chiral Sum‐Frequency Generation Vibrational Spectroscopy

“…31,32 In this work, we report using high-resolution SFG spectroscopy to capture the details of achiral, chiral, and prochiral spectral signatures of the S-(-)-limonene and R-(+)-limonene molecules at their air/liquid interfaces. Our interest in the limonene molecules is not only because it has been a benchmark choice for studying molecular chirality with various chiroptical and spectroscopic techniques in the bulk, 10,15,[33][34][35][36] but also because of the importance of a class of chiral isoprene and monoterpene molecules, such as limonene and pinene, etc., in the global secondary organic aerosol (SOA) formation and impact on climate changes. [37][38][39][40][41][42] It has been shown that chirality is not only an important component in the SOA, 39,40 the surface structure and reactivity of these SOA particles are also crucial for understanding the transformation and impact of the SOAs.…”