Insights into the Structures of Bilirubin and Biliverdin from Vibrational and Electronic Circular Dichroism: History and Perspectives

Testing the Simplified Molecular Dynamics Approach to Improve the Reproduction of ECD Spectra and Monitor Aggregation

A simplified molecular-dynamics-based electronic circular dichroism (ECD) approach was tested on three condensed derivatives with limited conformational flexibility and an isochroman-2H-chromene hybrid, the ECD spectra of which could not be precisely reproduced by the conventional ECD calculation protocol. Application of explicit solvent molecules at the molecular mechanics (MD) level in the dynamics simulations and subsequent TDDFT-ECD calculation for the unoptimized MD structures was able to improve the agreements between experimental and computed spectra. Since enhancements were achieved even for molecules with limited conformational flexibility, deformations caused by the solvent molecules and multitudes of conformers produced with unoptimized geometries seem to be key factors for better agreement. The MD approach could confirm that aggregation of the phenanthrene natural product luzulin A had a significant contribution to a specific wavelength range of the experimental ECD. The MD approach has proved that dimer formation occurred in solution and this was responsible for the anomalous ECD spectrum. The scope and limitations of the method have also been discussed.

Pfeiffer effect on configurationally labile dyes within ternary complexes with metal ions and enantiopure macrocycles

A configurationally-labile helical dye, 2,4,5,7-tetranitrofluorenone oximate, is used to probe complexes made of enantiopure macrocycles and mono/divalent metal ions. Induced electronic circular dichroism (ECD) and 1H NMR responses are amplified at room temperature only in the presence of K+ and Na+ ions despite larger binding efficiency with alkaline earth metal ions.

Vibrational circular dichroism study and gas chromatographic analysis of chiral epichlorohydrin

In recent years, there have been numerous incidents of serious accidents related to impurities of optical isomers, particularly in pharmaceutical treatment, environmental problems, and pesticide application. Among these impurities, chiral epichlorohydrin (ECH) is an important C3 synthon and a potentially genotoxic impurity. The enantiopure forms of S-ECH and R-ECH are key raw materials for synthesizing many drugs, which make it important to accurately quantify the specific conformation of chiral epichlorohydrin in pharmaceuticals. In this paper, we achieved the separation of chiral ECH by gas chromatography (GC) and based on the combination of vibrational circular dichroism (VCD) experiments and theoretical calculations, the qualitative method of chiral ECH was achieved without relying on a single enantiomeric standard.