title: How many conformers determine the thymidine low-temperature matrix infrared spectrum? DFT and MP2 quantum chemical study.
abstract: A comprehensive conformational analysis of isolated 2'-beta-deoxy-thymidine (T), canonical DNA nucleoside, has been performed by means of ab initio calculations at the MP2/6-311++G(d,p)//DFT B3LYP/6-31G(d,p) level of theory. At 298.15 K, all 92 conformers of isolated dT are within a 7.49 kcal/mol Gibbs energy range. Syn orientation for the base and South (S) conformers for the sugar dominate at this temperature: syn/anti = 61.6%:38.4% and S/N = 74.5%:25.5%. However, at 420 K, the majority of conformers contain anti base and the population of North (N) sugars increases: syn/anti = 38.0%:62.0% and S/N = 59.5%:40.5%. The whole conformational parameters (P, chi, gamma, delta, beta, epsilon, nu max) were analyzed as well as the energies of the OH...O intramolecular H-bonds on the basis of nu(OH) stretching vibrations. Convolution of calculated IR spectra of all of the T conformers appears consistent with its low-temperature matrix spectrum (Ivanov et al. Low Temp. Phys. 2003, 29, 809). The maximal discrepancy in frequencies between calculated and experimental spectra is less than 1%. A conclusion was made that for reliable reconstruction of the isolated nucleoside IR spectrum the quasi whole set of conformers should be taken into consideration. In essence, this result opens up a possibility to reconstruct IR spectra of isolated nucleosides at physiological temperatures with rather satisfactory probability.
authors.affiliation: Department of Molecular and Quantum Biophysics, Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, vul. Zabolotnoho 150, 03143 Kyiv, Ukraine.
authors.forename: Yevgen P
authors.initials: YP
authors.lastname: Yurenko
authors.forename: Roman O
authors.initials: RO
authors.lastname: Zhurakivsky
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Ghomi
authors.forename: Svitlana P
authors.initials: SP
authors.lastname: Samijlenko
authors.forename: Dmytro M
authors.initials: DM
authors.lastname: Hovorun
mesh_terms: D000465:Algorithms; D008968:Molecular Conformation; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics; D013936:Thymidine / Q000737:chemistry*
chemical_list: D013936:Thymidine