Probing the vibrational dynamics of amide bands of N-methylformamide, N, N-dimethylacetamide, and N-methylacetamide in water

We report the vibrational dynamics of amide modes of N-methylformamide (NMF), N-methylacetamide (NMA), and N, N-dimethylacetamide (DMA) in water using first principles molecular dynamics simulations. The solvent-mediated dynamics and stretching profile of C=O, N-H, and C-N modes of amide molecules were analyzed in terms of vibrational spectral and second-order reorientational dynamical properties. The maximum redshift is observed for the amide I band of DMA due to stronger DMA-water hydrogen bonding interaction; a blue shift is observed for NMF. The calculations also reveal that the amide-A band of NMF exhibits a redshift as compared to NMA. Multiple peaks are located for the C-N band of DMA, and this feature gradually decreases for NMA and NMF. Spectral dynamics of amide bands were investigated by calculating the frequency-frequency correlation functions. Slowest spectral diffusion is found for the C=O band of DMA. However, NMA shows slower dynamics for N-H band than that of NMF.