POLARIZABILITIES OF PURINE, ALLOPURINOL, HYPOXANTHINE, XANTHINE AND ALLOXANTHINE

Ab initio calculations of the equilibrium geometries, dipole moments a nd static dipole polarizabilities are reported for the 7H and 9H tauto mers of purine, the 1H,8H and 1H,9H tautomers of allopurinol, the 1H,7 H and 1H,9H tautomers of hypoxanthine, the 1H,3H,7H and 1H,3H,9H tauto mers of xanthine, and the 1H,3H,8H and 1H,3H,9H tautomers of alloxanth ine. Our SCF/6-31G* geometries are in significantly better agreement with previous ab initio calculations than with the crystallographic st ructures available for three of these molecules. The latter are influe nced by hydrogen bonding and stacking interactions. Electron correlati on effects are greater than basis set effects for the dipole moments a nd polarizabilities. Our recommended dipole moments and polarizabiliti es are expected to be within 10% of the true values. The qualitative f eatures of the dipole moments and polarizabilities are rationalized wi th the help of additive models and chemical arguments.