Conformational equilibrium of 2-deoxyadenosine molecules isolated in inert Ar matrices.

The FTIR spectra of 2-deoxyadenosine (dA) molecules isolated in low-temperature Ar matrices were obtained in the range of 3800-180 cm^-1 with a resolution of 0.3 cm^-1. The population analysis of the major structural isomers of dA was carried out by MP2 and DFT quantum-mechanical calculation methods. It was established that dA can sustain prolonged evaporation at 440K without undergoing thermal decomposition. For the first time, it was shown that the populations of dA syn-conformers with the intramolecular hydrogen bond O5'H-N3 is close to (76 ± 5)% in the gas phase and matrix. Upon freezing in the matrix the syn-conformers with the intramolecular hydrogen bond O5'H-N3 and C3'-endo structure of the deoxyribose ring were fully transformed into the subset of syn-conformers with the C2'-endo structure of the deoxyribose ring. Only two structures from this subset with different rotation angles of the O3'H-group can be stabilized in the matrix. Unlike pyrimidine nucleosides, the dA conformers with the intramolecular hydrogen bonds O3'H-O5 or O5'H-O3 were not found. [ABSTRACT FROM AUTHOR]