Temperature Perturbation on Hydrogen Bonding in Aqueous Solutions at Different Amide Concentrations

A series of amides with variation in the number of methyl and amine groups were used as additives of water. Perturbations of water structure by variation of temperature and concentration of urea, formamide, N-methylformamide, and N,N-dimethylformamide was systematically analyzed by vibrational spectroscopy. The water absorption band was critically analyzed by 2D-correlation spectroscopy, its deconvolution and derivative spectra. Degree of perturbation of the water structure was evaluated to provide strong evidence on molecular level interactions, self-aggregation, and modification of the network of water structure. Clusters of water-amides were energetically optimized and consequent theoretical vibrational frequencies of C-N and C=O groups of amide were found to be consistent with experimental frequencies. The water structure underwent disruption through formation of hydrogen bond with amide; while self-aggregated amide and hydrophobic alkyl group assisted formation of ice-like network around them.