The enol-keto tautomerism of 2-(2’-hydrophenyl)benzoxazole (HBO) in its metastable triplet states has been studied in fluid, non-polar solution. After laser flash excitation the keto triplet state is populated with high efficiency. The establishment of a ketoenol equilibrium was observed between 55 and 220 K. At low temperatures the rate of this reaction is determined by tunnel effects. The bar...

Several possible mechanisms underlying isoguanine formation when OH radical attacks the C(2) position of adenine (A C 2) are investigated theoretically for the first time. Two steps are involved in this process. In the first step, one of two low-lying A C 2⋅⋅⋅OH reactant complexes is formed, leading to C(2)-H(2) bond cleavage. Between the two reactant complexes there is a small isomerization ba...

A series of new tautomeric azonaphthols are synthesized and the possibilities for molecular switching are investigated using molecular spectroscopy, X-ray analysis and density functional theory quantum chemical calculations. Two opposite effects that influence switching are studied: attaching a piperidine sidearm, and adding substituents to the phenyl ring. On the one hand, the attached piperid...

We theoretically investigate the mechanism of tautomerism in the gas-phase acetylacetone molecule. The minimum energy path between the enolone and diketo forms has been computed using the Nudged-Elastic Band (NEB) method within the density-functional theory (DFT) using the projector augmented-wave method and generalized gradient approximation in Perdew-Wang (PW91) parametrization. The lowest tr...

Mass spectrometric analysis of proteolysis products of haloenol lactone-modified glutathione S-transferase isozyme mGSTP1 indicates that the haloenol lactone 3-cinnamyl-5(E)-bromomethylidenetetrahydro-2-furanone is covalently attached to the protein at Cys-47. Comparisons of the extent of adduct formation with losses in enzymatic activity indicate that mGSTP1 exhibits greatest reactivity toward...

The structures of l-phenyl-3-methyl-pyrazolone-5 and its benzoyl derivatives have been investigated by means of IR, UV, NMR, and mass spectral spectroscopy. 1-Phenyl 3-methyl-pyrazolone-5 is found to exist as a zwitter ion in the solid state, in the 5-keto form in chloroform and dioxane, and in the 5-hydroxy form in pyridine. The 4-benzoyl derivative of l-phenyl-3-methyl-pyrazolone-5 is shown t...

In their Review (article number 2001952), Ling Chen, Peng-Yan Fu, Mei Pan and co-workers give a summary introduction of ESIPT (excited state intramolecular proton transfer) materials in the solid including small organic molecules, metal-organic frameworks covalent-organic frameworks. The four-leveled energy cycle based keto-enol emissions these respond to temperature, pressure, solvent, ions, l...

The wobble hypothesis does not discriminate between uracil and thymine. Methylation could favor further stabilization of uracil in the keto form. Thymine is present in keto form only and can pair up but with adenine. Uracil can easily construct the enol form; that is why it forms the U-G pair. In previous E-print I proposed an alternative to the wobble hypothesis [1]. According to my reviewers ...