FTIR ATR spectral and theoretical based vibrational studies of uracil in dimethylsulfoxide or diethylsulfoxide solutions

Abstract

In this work the solutions of uracil in pure dimethylsulfoxide (DMSO) and diethylsulfoxide (DESO) have been studied by both FTIR ATR spectroscopy and quantum-chemical calculations. The remarkable changes were observed in the C=O, N—H (1745—1630 cm–1) and in S=O stretching region (1100—970 cm–1). The changes of the aforementioned frequencies are explained by the destruction of self-associates of sulfoxides in the presence of uracil and formation of uracil/DMSO (DESO) complexes via hydrogen-bond of the uracil N—H group with the S=O group of sulfoxides. Structural, energetic and vibrational characteristics for the hydrogen-bonded molecular complex of uracil/DMSO (DESO) in the gas phase and in solution have been studied by DFT and ab initio MO theory. It revealed, that the uracil/DMSO complex is more compact compared with uracil/DESO complex due to additional hydrogen bonds via C=O group of uracil and —CH group of DMSO. The observed wavenumbers are in good agreement with calculated wavenumbers.