Hyper-Raman Spectroscopic Investigation of Amide Bands of N-Methylacetamide in Liquid/Solution Phase

We have demonstrated hyper-Raman (HR) spectroscopy of N-methylacetamide (NMA) for the first time. Fundamental knowledge of amide bands in HR spectra has been obtained. HR spectra of NMA exhibit various amide bands with different intensity patterns from Raman and IR spectra. The amide III and II signals were strongly observed, suggesting the possible application of HR spectroscopy to analyze secondary structures, complementary to IR and Raman spectroscopy. The peak positions of HR amide bands sharply reflect the hydrogen-bonding environment around the molecule. The depolarization ratios of the amide II and III bands at 532 nm excitation suggest the resonance HR effect via the pi-pi* transition. In contrast, that of the amide I band of neat NMA indicates the contribution of high energy transitions to its signal enhancement. This work proposes that HR spectroscopy can be a powerful tool for studying the molecular structure and environment of biomolecules with peptide bonds.

Automated summary

This work demonstrates hyper-Raman spectroscopy of N-methylacetamide for the first time and provides fundamental knowledge of amide bands in HR spectra. The HR spectra of NMA show various amide bands with different intensity patterns and can be a powerful tool for studying the molecular structure and environment of biomolecules with peptide bonds.