Chiral molecules computational studies

A common finding of computational PECD studies is that a relatively large partial wave expansion, typically running to niax > 15 is required. Chiral molecules necessarily are of very low, or no, symmetry, and hence are quite... 

In Section IV the computer simulation is extended to describe the effects of excitation in chiral molecules and racemic mixtures of enantiomers. The modification of the dynamical properties brought about by mixing two enantiomers in equimolar proportion may be explained in terms of rotation-translation coupling. The application of an external field in this context ai iplifies the difference between the field-on acf s and cross-correlation of enantiomer and racemic mixture and provides a method of studying experimentally the fundamental phenomenon of rotation-translation coupling in the molecular liquid state of matter. 

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. 

An understanding of the recognition of chirality at a molecular level has become of interest in many fields of chemistry and biology. In the past decade, many attempts to clarify the mechanism of chiral recognition on CSPs for liquid chromatography have been made by means of chromatography, NMR spectroscopy,199 202 X-ray analysis, and computational methods.203 - 206 The successful studies have been mostly carried out for the small-molecule CSPs, especially cyclodextrin-based CSPs and Pirkle-type (brush-type) CSPs. In contrast, only a few mechanistic studies on chiral discrimination at the molecular... 

In the early 1990s, several studies were published on the computation of selector-selectand interactions in chiral CE. This relates basically to the interactions between CDs and their chiral guests, which seem to be caused by the fact that CDs are rather rigid molecules of medium size and therefore calculations for these molecules are easier and faster and may be rather precise. In addition, many CDs are well studied by alternative techniques for structure elucidation. Among these, X-ray crystallographic data are of the highest interest. 

Since there is only a small energy difference between the different conformational states depending upon the presence or absence of a Pro, Gly or N-alkylated amino acid residue, and upon the chirality of the constituent amino acid residues and also to a lesser extent upon the side-chain functionalities, it is not possible to unambiguously predict the conformation of a cyclic pentapeptide. These molecules have often been studied in different solvents and solvent effects were neglected, and/or the methodology to handle such conformational equilibrium was not available. It is only recently that modem NMR techniques and computational procedures have become available to treat this complex problem of fast exchanging conformational equilibria. 36,269,270 ... 

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