Crystal structures of polymorphs and solvatomorphs of the potential anxiolytic drug fenobam exhibit an exclusive preference for one of the two possible tautomeric structures. A novel methodology based on nonlinear optical response has been successfully employed to detect the presence of a polymorphic impurity in a mixture of polymorphs.

The shape of the barrier for the H transfer between the normal and tautomeric forms have been determined for the adenine and thymine molecules. The correlations for several singlet and triplet states has been calculated using the CNDO/2-CI method. The relative stability between both conformations and the agreement with some experimental values is also discussed.

The title compound, C(18)H(21)NO(3), crystallizes in the phenol-imine tautomeric form, with the H atom attached to oxygen rather than on nitro-gen. This H atom is involved in a strong intra-molecular O-H⋯N hydrogen bond. A C-H⋯π inter-action is also present. The dihedral angle between the aromatic rings is 12.23 (7)°.

A quantum spin model representing tautomeric mutation is proposed for any DNA molecule. Based on this model, the quantum mechanical calculations for mutational rate and complementarity restoring repair rate in the replication processes are carried out. A possible application to a real biological system is discussed.

Two polymorphs of 2,6-dichloropurine, C(5)H(2)Cl(2)N(4), have been crystallized and identified as the 9H- and 7H-tautomers. Despite differences in the space group and number of symmetry-independent molecules, they exhibit similar hydrogen-bonding motifs. Both crystal structures are stabilized by intermolecular N-H···N interactions that link adjacent molecules into linear chains, and by some non...

A remarkable temperature dependence on the 13C NMR and 15N NMR chemical shifts of pyridoxine in water (pH = 7.0) has been observed. C-3, C-6, and N-1 were the most sensitive nuclei to the temperature effect. This dependence has been explained on the basis of an equilibrium shift thermally induced between the neutral and the dipolar form of this molecule. The thermodynamic characterization of ta...

Infrared absorption spectra, in the vapour phase, have been recorded in the regions of NH, OH and carbonyl stretching frequencies, for a series of 1-substituted uracils and 9-substituted adenine and hypoxanthine, formal analogues of the natural nucleosides of uracil, adenine and hypoxanthine found in DNA and/or RNA. A number of related analogues was also examined, including the N-methyl derivat...

Binding of metal cations to the nucleobases can influence base pairing, base stacking and nucleobase tautomerism. Gas-phase condensation of dc discharge generated alkali metal cations and thermally vaporized cytosine (DC/FT) has been found to produce kinetically trapped excited tautomeric conformations of the M(+)(cytosine) complexes, which influences the threshold collision-induced dissociatio...

Methods for establishing the absolute configuration of sulfur-stereogenic aza-sulfur derivatives are scarce, often relying on cumbersome protocols and a limited pool enantioenriched starting materials. We have addressed this by exploiting, first time, feature sulfonimidamides in which it is possible tautomeric structures to also be enantiomeric. Such can readily generate prochiral ions, we expl...