DFT and Raman study of all-trans astaxanthin optical isomers

Abstract

Astaxanthin (AST) is a xanthophyll carotenoid widely distributed in aquatic animals, which has many physiological functions such as antioxidant, anti-inflammatory, anti-hypertensive and anti-diabetic activities. Astaxanthin has three optical isomers, including a pair of enantiomers (3S,3 S and 3R,3 R) and a meso form (3R,3 S). Different optical isomers have differences in a variety of physiological functions. Traditionally, High Performance Liquid Chromatography (HPLC) can be used to distinguish these isomers. In this work, its found that Raman spectroscopy can be employed to distinguish the three optical isomers. Because the intensities of two Raman bands at 1190 cm-1 and 1215 cm-1 of three isomers are different. DFT calculations are performed and used to analyze the spectral differences. The calculation results show that the structures of these chiral isomers are not strictly mirror-symmetrical to each other, which leads to the difference in their Raman spectra. HighlightsO_LIRaman spectroscopy can be utilized to distinguish three optical isomers of all-trans astaxanthin. C_LIO_LIThe DFT-calculated spectrum is used to explain why the Raman bands of optical isomers at 1190 and 1215 cm-1 are different. C_LIO_LIThe structural parameters of the three optical isomers have been identified. C_LI