Fizika Nizkikh Temperatur: Volume 45, Number 9 (September 2019), p. 1181-1191 ( to contents , go back )
Nucleoside conformers in the low-temperature argon matrices: FTIR spectroscopy of isolated thymidine, deuterothymidine molecules and quantum mechanical calculations
A.Yu. Ivanov, S.G. Stepanian, V.A. Karachevtsev
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Nauki Ave., Kharkiv 61103, Ukraine
University of Arizona, Tucson, 85721, Arizona, USA
Received March 14, 2019, published online July 26, 2019
The conformational equilibrium of thymidine and deutero-thymidine molecules in low-temperature Ar matrices was investigated with using low-temperature Fourier transform infrared spec-troscopy of the matrix isolation and quantum chemical calculations by the DFT/B3LYP and MP2 methods. It was established that two anticonformers ta2_0, ta3_0 with different structures of the sugar ring: C2′-endo and C3′-endo dominate in low-temperature matrices. In the gas phase, each of these conformers has several low-barrier satellites that can be completely transformed into more stable structures when molecules are frozen in matrices. The main syn-conformer ts2_0 is stabilized by the intramolecular hydrogen bond O5′H∙∙∙O2, and the dominant conformation of the deoxyribose ring is C2′-endo. The significant loss in the population of ts2_0 structure to the anti-conformers ta2_0, ta3_0 can be explained by a smaller occupation of low-barrier conformer satellites. It is shown that the absorption band of the valence vibration νN3D may be split by the Fermi resonance. https://doi.org/10.1063/1.4904426
Key words: FTIR spectroscopy, low-temperature matrix isolation, quantum-mechanical calculations, nucleosides.