Paul F. Heelis

The pH dependence of the reactions of flavin triplet states with amino acids: A laser flash photolysis study

The pH dependence of the rate constants of reaction of several amino acids with the triplet states of flavin mononucleotide in aqueous solution has been determined. In addition, the relative contributions of hydrogen atom transfer, electron transfer and physical deactivation to the overall process of triplet quenching by amino acids have been estimated. Analogous experiments to those with amino acids were carried out with EDTA as the substrate. The results indicate that the flavin triplet state abstracts an electron from EDTA but does not form an excited state flavin-EDTA complex as suggested in a previous study.

One-electron oxidation of the flavin triplet state as studied by laser-flash photolysis

One-electron oxidation of the flavin triplet state occurs in its reaction with tetranitromethane.

Low-temperature electron paramagnetic resonance studies reveal the structure of thymine dimer radical anions

Electron addition at 77 K to cis-syn pyrimidine dimers yields the monomer radical anion directly, whereas the trans-syn dimer does not split, thus allowing the first observation of the undissociated dimer anion radical species.

Spectral and redox properties of benzodipteridine. A pulse radiolysis,laser flash photolysis and semi-empirical molecular orbital study

The properties of the flavin enzyme mimic benzodipteridine (BDP) have nbeen studied by pulse radiolysis, laser flash photolysis and nsemi-empirical molecular orbital (AM1) methods. The redox, protolytic nand tautomeric equilibria in the ground state and excited triplet state nwere compared to the parent flavin molecule (FL). Pulse radiolysis was nused to detect the one-electron reduced form of BDP which was found to nbe less basic than flavins, in agreement with the prediction of nsemi-empirical calculations. BDP is more electrophilic than FL in the nground state, but not in the excited triplet state, due to the lower ntriplet energy of the former as predicted by semi-empirical ncalculations. In contrast to FL, the triplet state of BDP does not nappear to be more basic than the ground state, in agreement with the ncalculated shift in electron density upon excitation.

One-electron reduction of 1,5-dihydroflavins in aqueous solution: a pulse radiolysis study

One-electron reduction of 1,5-dihydroflavins with e(aq)– yields a three-electron reduced flavin species (FIH2˙–), which protonates with an associated pKa value of 6.1, whereas the reaction of 1,5-dihydroflavins with CO2˙– yields a similar, but not identical flavin species, which may be an adduct radical.