Study of <i>N</i>-Acetylamino Saccharides with Synchrotron-Based Ultraviolet Resonance Raman Spectroscopy: In Combination with ATR Far-Ultraviolet Spectroscopy

We investigate resonance (true resonance and pre-resonance) Raman (RR) effects in glucose, galactose, <i>N</i>-acetylglucosamine, and <i>N</i>-acetylgalactosamine with ultraviolet resonance Raman (UVRR) and far-ultraviolet (FUV) spectroscopies. Electronic transitions in the FUV region are attributed to electronic orbitals due to σ and π electrons. Their geometric orientations that participate in the resonance effect have not yet been well studied, unlike those for visible and near-infrared RR spectroscopies. In this study, we have employed monosaccharides and their derivatives with an amino group, which has strong FUV absorption near 190 nm. Quantum chemical calculation indicates that the band at 190 nm consists of multiple electric transitions. Their UVRR spectra measured with 213, 226, and 250 nm excitation suggest that Raman bands due to the amino group are enhanced via multiple electronic transitions, but those due to the saccharide groups are enhanced slightly. The results demonstrate that a combined study with UVRR and FUV spectroscopies provides new insights into the geometry and symmetry of the electronic transitions in σ and π orbitals.