Vibrational circular dichroism theoretical predictions

Abstract The Vibrational Circular Dichroism (VCD) spectroscopy has been developing rapidly in both experimental and theoretical aspects. Currently, the VCD has become one of the most effective and reliable spectroscopic technique to determine the absolute configuration of chiral molecules. Its success is related to the availability of instrumentation and software for quantum-chemical calculation of the spectra. Nowadays, large parts of the VCD spectra can be trustfully predicted by theory and critically verified by confiding experiment, and vice versa. In the last decade, several theoretical and experimental VCD studies reported on VCD chirality transfer phenomenon occurring when an achiral molecule becomes VCD active as a result of intermolecular interactions with a chiral one. There are still some theoretical and experimental uncertainties about the VCD chirality transfer, however, benefits from an comprehensive use of the phenomenon can push our ability to diversify the intermolecular complexes and deepen our understanding of intermolecular interactions. This chapter is a review of the computational studies on VCD chirality transfer phenomenon supported by the experimental references, and ended by perspectives. 

Circular dichroism (CD) can be observed in the vibrational transitions of chiral molecules vibrational circular dichroism (VCD). An example of a VCD spectrum is shown in Figure 1, together with the corresponding unpolarized absorption spectrum. The sample is a 0.6 M solution of (lR,4jR)-(-i-)-cam-phor in CCI4. Here, we discuss the theoretical analysis of VCD spectra. The current state-of-the-art is illustrated in Figure 1, where VCD and absorption spectra of camphor, predicted within the harmonic approximation (HA) using ab initio density functional theory (DFT), are shown. 

Vibrational spectroscopy is an important tool to obtain information about the secondary structure of proteins [827]. The ability to relate protein conformations to infrared vibrational bands was established very early in the pioneering work of Elhot and Ambrose before any detailed X-ray results were available [828]. Vibrational circular dichroism (VCD) provides sensitive data about the main chain conformation [829, 830]. The Raman optical activity (ROA) signal results from sampling of different modes but is especially sensitive to aromatic side chains [831, 832]. A theoretical prediction for the ROA phenomenon was developed by Barron and Buckingham [833, 834], and the first ROA spectra were measured by Barron, Bogaard and Buckingham [835, 836]. First ab initio predictions were provided by Polavarapu [837]. In 2003, Jalkanen et al. showed that DPT approaches in combination with explicit water molecules and a continuum model reproduce the experimental spectra much better [838]. DFT-based approaches to VCD spectra were, for example, pioneered by Stephens et al. [839]. To extract the local structural information provided by ROA, Hudecova et al. [721] developed multiscale QM/MM simulation techniques. 

The information required for predicting and/or analyzing spectra in the field of vibrational spectroscopy are vibrational frequencies and the corresponding intensities. While the former are univocally defined, the definition of the latter depends on the technique considered (infrared, vibrational circular dichroism, and Raman). For the extended theoretical background of the various spectroscopies, we refer interested readers to well-established textbooks [59, 60, 205,... 

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