Theoretical study of the tautomerism of 8-azaadenine

Abstract

The prototropic tautomerism of 8-azaadenine (azaade) was studied theoretically by means of ab initio methods, in both the gas phase and aqueous solution. A number of tautomeric forms were not included in the calculations after applying a stepwise elimination procedure based on both AM1 and HF/6-31G* energy values. The tautomers 9H-azaade, 8H-azaade and 7H-azaade survived to this elimination and their optimized geometries and energies were calculated at the MP2/6-31*//HF/6-31G* level. To include the solvent effects, two self-consistent reaction field method were used: (1) Onsager's SCRF with multipolar expansion up to the hexadecapolar term and (2) the isodensity polarizable continuum method (IPCM). Both methods produce similar results, although the latter represents better the situation in aqueous solution. The stability order in solution, 8H-b 9H-b 7H-azaade, differs slightly from that found in the gas phase, implying that in general the electrostatic effects in solution are important, but the intrinsic stability of these species in the gas phase overcomes the solvent effect.

Adsorption orientation of 8‐azaadenine on silver nanoparticles determined by SERS and DFT

“…Accordingly, it is reasonable that similar tautomerization could occur for 8AA. Because 9H‐ and 8H‐8AA are both stable in aqueous solution, the 9H‐, 8H‐, and 7H‐8AA tautomers were all taken into consideration in our calculations, for which adsorption via all available nitrogen atoms was considered. After the optimization step, nine Ag + /8AA complexes were obtained and are shown from lowest to highest energy (Figure ).…”

2-r-(4-Chlorophenyl)-6-c-phenyl-3,4,5,6-tetrahydro-2H-thiopyran-4-one 1-oxide

“…For a related crystal structure, see: Thiruvalluvar et al (2007). For applications of sulfoxides, see: Contreras et al (1998); Hutton et al (2002); Okada & Tanaka (2002). For the conformational analysis of substituted thian-1-oxides, see: Freeman et al (2001); Nagao et al (1995).…”

“…Increasing interest has been focused on the stereochemical aspects of sulphoxides. The conformational analysis of cyclic sulphoxides is an area of attraction for many groups (Okada & Tanaka, 2002;Hutton et al, 2002;Contreras et al, 1998).…”

Tautomeric equilibrium and hydrogen shifts in tetrazole and triazoles: Focal-point analysis and ab initio limit

“…28 A number of theoretical studies on the triazole/tetrazole system have been conducted in the past few decades. 4,12,17,24,[29][30][31][32][33][34][35][36][37][38][39][40][41][42] Unfortunately, there is much inconsistency among these published results, even in the gas phase ͑see below͒. 17,24,29,[31][32][33][34][35]38,[40][41][42] Focal-point analysis [43][44][45] ͑FPA͒ is one of the most effective methods of modern high-accuracy ab initio theory.…”