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

Abstract

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 440 K 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.