engleski

Infrared Optical Constants of Liquid Water-Formamide, Water-N-Methylformamide, and Water-N, N-Dimethylformamide Mixtures

Due to their crucial importance for the living systems, peptide bond in acqueous medium is for decenies under very vivid investigation. Being the smallest molecules containing peptide bond motif, simple amides are very useful as model systems of peptide bond. The real and imaginary refractive index spectra of mixtures of water and three simple amides, namely formamide, N-methylformamide, and N, N-dimethylformamide, over the full composition range at 25°C, were determined between 4000 and 1000 cm-1 by calibrated multiple attenuated total reflection FTIR spectroscopy. Under the assumption of the Lorentz local field, the corresponding molar polarisability spectra were calculated and used to investigate the structure of the mixtures. The concentrations of water-bonded, amide-bonded, and non-hydrogen-bonded O-H groups, and of water-bonded and non-hydrogen-bonded amide molecules, were obtained from the integrated intensities CO-H and CC=O, the areas under the O-H and C=O stretching bands in the molar polarisability spectra. The present results are compared with the results of MD simulations of these systems.

Amide; Water; FTIR; ATR; Optical Constants

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