Ar-Matrix IR Spectra of 5-Halouracils Interpreted by Means of DFT Calculations

Abstract

The infrared low-temperature Ar-matrix spectra of 5-halouracils and unsubstituted uracil were measured and interpreted in terms of the spectra calculated at the DFT/B3PW91/6-311G level followed by a potential energy distribution (PED) analysis. For the PED analysis, the sets of halouracil mode definitions were constructed so that dissimilarities in the interpretations of the different spectra were minimized. Anharmonic frequency calculations enabled more light to be shed on the Fermi resonance (FR) phenomena occurring in the nu(C=O) stretching vibrations region. For each halouracil vibrational spectrum, several FRs manifest themselves in the nu(C=O) stretching vibrations region. We show that the most frequent components participating in these resonances are the nu(C(4)=O(10)) frequency, a beta(N-H) mode frequency, and a beta(C=O) mode frequency. The experimental nu(N-H) frequencies are reproduced by the calculated anharmonic frequencies better than by the scaled harmonic ones, and the nu(C=O) frequencies respond in the opposite manner. The experimental frequencies located below 1500 cm(-1) are reproduced equally well by the two kinds of calculations.

FTIR and FT‐Raman spectra and density functional computations of the vibrational spectra, molecular geometry and atomic charges of the biomolecule: 5‐bromouracil

“…23 -25 From spectroscopy point of view, 5-BrU in the gas phase has been studied by several experimental techniques, such as dissociative electron attachment (DEA), 26 electronic absorption and fluorescence emission spectra, 27,28 NMR 29,30 and ESR. 41 However, the present work on 5-BrU remarkably improves upon the earlier results, identifying all the bands for the first time and reviewing the assignments of several bands. 38,39 In our previous work, IR and Raman studies on this molecule have also been reported, but again without theoretical support.…”

Loading and release of 5-fluorouracil from HY zeolites with varying SiO2/Al2O3 ratios

“…The peaks at 1771 and 1723 cm À1 are assigned to the carbonyl vibrational bands for the C2 and C4 carbonyl groups, respectively, through a comparison with the FTIR spectrum of 5-FU in an Ar-matrix [35]. The peak at 1665 cm À1 is assigned to the C5@C6 stretching mode of 5-FU and the peak at 1245 cm À1 is assigned to the C-F bending vibration according to the literature [29,[35][36][37]. The HY samples loaded with 5-FU have characteristic vibrations at 1756, 1717, 1690 and 1247 cm À1 .…”

Computational studies of vibrational spectra and molecular properties of 6-methyluracil using HF, DFT and MP2 methods

“…Uracil derivatives exhibit significant pharmacological activity, thereby attracting many workers for vibrational studies [1][2][3][4][5][6]. 6-Methyluracil (6MU) has been found to accelerate healing of burn wounds [7] and effects the regulation of lipid peroxidation [8].…”

“…(Ring), Q (C 6 -CH3 ), Q (C 4 -C5 ) experimental spectrum have been assigned to Q (N 1 -H 15 ) and Q (N 3 -H 14 ) respectively. These characteristic vibrational frequencies are shifted from the vapour spectrum and calculated frequencies, which may be due to the occurrence of intermolecular hydrogen bonding in solid state sample of 6MU.…”