title: Kinetics of photoinduced electron transfer between DNA bases and triplet 3,3',4,4'-benzophenone tetracarboxylic acid in aqueous solution of different pH's: proton-coupled electron transfer?
abstract: The kinetics of triplet state quenching of 3,3',4,4'-benzophenone tetracarboxylic acid (BPTC) by DNA bases adenine, adenosine, thymine, and thymidine has been investigated in aqueous solution using time-resolved laser flash photolysis. The observation of the BPTC ketyl radical anion at λ(max) = 630 nm indicates that one electron transfer is involved in the quenching reactions. The pH-dependence of the quenching rate constants is measured in detail. As a result, the chemical reactivity of the reactants is assigned. The bimolecular rate constants of the quenching reactions between triplet BPTC and adenine, adenosine, thymine, and thymidine are k(q) = 2.3 × 10(9) (4.7 < pH < 9.9), k(q) = 4.0 × 10(9) (3.5 < pH < 4.7), k(q) = 1.0 × 10(9) (4.7 < pH < 9.9), and k(q) = 4.0 × 10(8) M(-1) s(-1) (4.7 < pH < 9.8), respectively. Moreover, it reveals that in strong basic medium (pH = 12.0) a keto-enol tautomerism of thymine inhibits its reaction with triplet BPTC. Such a behavior is not possible for thymidine because of its deoxyribose group. In addition, the pH-dependence of the apparent electrochemical standard potential of thymine in aqueous solution was investigated by cyclic voltammetry. The ΔE/ΔpH ≈ -59 mV/pH result is characteristic of proton-coupled electron transfer. This behavior, together with the kinetic analysis, leads to the conclusion that the quenching reactions between triplet BPTC and thymine involve one proton-coupled electron transfer.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria. nxt-fct@mail.hut.edu.vn
authors.forename: Truong X
authors.initials: TX
authors.lastname: Nguyen
authors.forename: Daniel
authors.initials: D
authors.lastname: Kattnig
authors.forename: Asim
authors.initials: A
authors.lastname: Mansha
authors.forename: Günter
authors.initials: G
authors.lastname: Grampp
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Yurkovskaya
authors.forename: Nikita
authors.initials: N
authors.lastname: Lukzen
mesh_terms: D001577:Benzophenones / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D055668:Photochemical Processes; D011522:Protons; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: C580652:3,3',4,4'-benzophenone tetracarboxylic acid; D001577:Benzophenones; D002264:Carboxylic Acids; D011522:Protons; D012996:Solutions; D014867:Water; D004247:DNA