Физика Низких Температур: Том 47, Выпуск 3 (Март 2021), c. 201-218 ( к оглавлению , назад )
Molecular structure and vibrational spectra of isolated nucleosides at low temperatures (Review Article)
A.Yu. Ivanov and S. G. Stepanian
B.Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of UkraineKharkiv 61103, Ukraine
Received November 16, 2020, published online January 26, 2021
The application of various action spectroscopy and absorption spectroscopy methods for studying the structure of biological molecules and their constituent fragments in an isolated state is considered. The main attention is paid to the results achieved in the study of the nucleosides which are the structural units of DNA and RNA. It has been demonstrated that modern low-temperature spectroscopy methods allow registration the vibrational spectra of isolated nucleosides in neutral or ionized form. It was shown that most of the nucleosides can be converted into the gas phase by prolonged evaporation from the Knudsen cell without thermal decomposition. Cooling molecules to cryogenic temperatures plays an important role in these studies. The conformational equilibrium of the gas phase between syn and anti subsets of nucleosides is maintained due to fast cooling when frozen in inert matrices. Within these subsets, interconversion processes between conformers can occur during cooling if the conformers are separated by low energy barriers. In inert gas matrices at 6 K, subsets of the syn-conformers of deoxyribonucleosides are mainly frozen with the C2′-endo structure of the deoxyribose ring. The structures of molecular ions of nucleosides are very different from their neutral forms. In particular protonation leads to the domination of the enol forms of thymidine, as well as syn-conformations of adenosine, stabilized by the intramolecular hydrogen bond N3H+•••O5.
Key words: FTIR spectroscopy, low-temperature matrix isolation, nucleosides, ab initio calculations.