Protonation of Nucleic Acid Bases. A Comprehensive Post-Hartree−Fock Study of the Energetics and Proton Affinities

摘要: The results of an ab initio post-Hartree−Fock study the protonation all nucleic acid bases are reported. Rare tautomers guanine and cytosine, which coexist in gas phase with major forms, were also included study. geometries local minima transition states optimized without symmetry restrictions by gradient procedure at HF MP2 levels theory verified energy second-derivative calculations. standard 6-31+G(d,p) basis set was used. single-point calculations have been performed MP4(SDTQ)/6-31+G(d,p)//MP2/6-31+G(d,p) MP2/6-311++G(d,p)//MP2/6-31+G(d,p) approximations. relative stabilities different protonated forms values proton affinities (PA) for each base including contributions rare cytosine calculated. We shown that calculated very close to expe...