Raman Optical Activity and Raman spectroscopy of carbohydrates in solution

Abstract

This comprehensive study on selected 14 carbohydrates in water solution is an extension of previously published one focused only on solid state analysis. Here, Raman spectroscopy was used as a dedicated method for analysis of carbohydrates in solution, both using a normal effect (RS) and its chiral analogue: Raman Optical Activity spectroscopy (ROA). The compounds were selected as biologically important and representative of all groups: monosaccharides, disaccharides, trisaccharides, cyclodextrines and polysaccharides. RS and ROA spectra are presented together with an expanded discussion on various structures and conformations of studied carbohydrates in the solution taking into account particular regions, i.e. (1) low wavenumber region (250-600 cm^-1), (2) anomeric region (600-950 cm^-1), (3) fingerprint region (950-1200 cm^-1) and (4) CH₂and COH deformations region (1200-1500 cm^-1). So, the following information can be obtained about: (1) the absolute configuration of the anomeric centre; (2) the configuration of the anomeric centre and the orientation of the anomeric hydroxyl group; (3) the ring structures and the relative orientation of substituents and (4) the conformation of the exocyclic CH₂OH (4), respectively. Raman spectroscopy and Raman Optical Activity were shown as unique tools to study complex structures of carbohydrates.

Keywords: Carbohydrates; Optical activity; ROA; Raman spectroscopy; Saccharides; Sugars; Vibrational analysis.