Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

Abstract

Chiroptical spectroscopy exploring the interaction of matter with polarized light provides many tools for molecular structure and interaction studies. Here, some recent discoveries are reviewed, primarily in the field of vibrational optical activity. Technological advances results in the development of more sensitive vibrational circular dichroism (VCD), Raman optical activity (ROA) or circular polarized luminescence (CPL) spectrometers. Significant contributions to the field also come from the light scattering and electronic structure theories, and their implementation in computer systems. Finally, new chiroptical phenomena have been observed, such as enhanced circular dichroism of biopolymers (protein fibrils, nucleic acids), plasmonic and resonance chirality‐transfer ROA experiments. Some of them are not yet understood or attributed to instrumental artifacts so far. Nevertheless, these unknown territories also indicate the vast potential of the chiroptical spectroscopy, and their investigation is even more challenging.

Pathways to increase the dissymmetry in the interaction of chiral light and chiral molecules

“…As the wavelengths associated with vibrational transitions are about ten times longer than for the electronic transitions of CD in the UV/vis range (electronic CD, ECD), typical VCD g-factors are smaller than those observed in ECD and remain on the order of 10 −4 . 18 Significantly enhancing chiroptical activity requires a breakdown of the electric dipole approximation, which indicates that g-factors that exceed the 'molecular' limit can be achieved either by decreasing the wavelength of light 19 or by exploiting larger molecules and structures. But is there evidence for this?…”

Paving the way to conformationally unravel complex glycopeptide antibiotics by means of Raman optical activity

“…By measuring the difference in intensity between the two polarization states during the ROA experiment, information regarding the molecular absolute conguration (AC) and the conformation can be obtained. [1][2][3][4][5][6][7][8] One of the main applications of ROA is the empirical determination of the structural aspects of proteins, such as their secondary structure. [6][7][8] For small organic (bio)molecules (peptides, carbohydrates, natural products) the ROA spectra have proven to be substantially more difficult to interpret solely based on empirical data.…”

On Raman optical activity sign-switching between the ground and excited states leading to an unusual resonance ROA induced chirality

“…Indeed, chirality accounts for structural and functional diversity of biological molecules, is essential for pharmacy and important in material sciences. Need for characterization of chiral substances motivated fast development of Vibrational Circular Dichroism (VCD) and Raman Optical Activity (ROA) 1,2 which have become complementary to much more sensitive Electronic Circular Dichroism (ECD). This is due to the distinctiveness and specificity of weak but abundant vibrational bands contrasting with a low number of intense but broad electronic ones.…”