The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO2 and dithiothreitol

1986 ◽  
Vol 64 (1) ◽  
pp. 67-70 ◽  
Author(s):  
Parminder S. Surdhar ◽  
David A. Armstrong ◽  
Vincent Massey
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Radical Anion ◽  
Pulse Radiolysis ◽  
Continuous Production ◽  
Radical Anions ◽  
Reduction Step ◽  
Equivalence Point ◽  
Electron Reduction ◽  
The One

The one- and two-electron reductions of 2-thioriboflavin with[Formula: see text] and cyclic disulphide anion of dithiothreitol [Formula: see text] have been studied by the steady state γ and pulse radiolysis techniques. The [Formula: see text] radical reacted with 2-thioriboflavin to give the neutral semiquinone (•FlH) and the radical anion (•Fl−) at pH 5 and 10 respectively. The pK of the •FlH radical was determined to be 7.4. In the case of the anion, the 2-thioriboflavin spectrum is similar in shape to that of FAD radical anion, but red shifted by 40–50 nm. Red shifts are also seen in the neutral •FlH form for the 370-nm peak and 580-nm shoulder. However, in addition, there is strong enhancement of the absorbance at 500 nm. The spectrum of 2-thioriboflavin semiquinone produced in the presence of 2–5 mM dithiothreitol was perturbed, as was observed previously for unsubstituted flavin semiquinones in the presence of sulphydryls. The rate constants for the initial one-electron reduction step viz: [Formula: see text] were 4.0 ± 0.5 × 109 M−1 s−1 and 1.3 ± 0.2 × 109 M−1 s−1 at pH 7 and 10 respectively. The corresponding rate for the reaction of [Formula: see text] with 2-thioriboflavin at pH 7 was determined to be 2.4 ± 0.2 × 109 M−1 s−l. The continuous production of [Formula: see text] radicals by γ radiolysis reduced 2-thioriboflavin to the dihydro form, and the flavin was regenerated on the addition of air. The[Formula: see text] radical also effected a two-electron reduction. However, in this case, if the process was taken beyond the equivalence point, the dihydroflavin spectrum was bleached and the oxidized flavin could not be recovered.

The one-electron reduction of a multi-centred iron(III) polyoxometallate. A pulse radiolysis study

2011 ◽  
Vol 14 (9) ◽  
pp. 1390-1392 ◽  
Author(s):  
Inna Popivker ◽  
Israel Zilbermann ◽  
Eric Maimon ◽  
Haim Cohen ◽  
Dan Meyerstein
Keyword(s):  
Pulse Radiolysis ◽  
Electron Reduction ◽  
The One

scholarly journals Biomimetic Ketone Reduction by Disulfide Radical Anion

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5429
Author(s):  
Sebastian Barata-Vallejo ◽  
Konrad Skotnicki ◽  
Carla Ferreri ◽  
Bronislaw Marciniak ◽  
Krzysztof Bobrowski ◽  
...  
Keyword(s):  
Radical Anion ◽  
Radical Mechanism ◽  
Cyclic Ketones ◽  
High Concentration ◽  
Radical Chain ◽  
Ketyl Radical ◽  
Electron Reduction ◽  
The One ◽  
Key Steps ◽  
Radical Chain Reaction

The conversion of ribonucleosides to 2′-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3′-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR•−) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys)•− in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys)•− transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys)•−at λmax = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 104–105 M−1s−1 at ~22 °C.

Reactions of lumiflavin with amine radicals

1985 ◽  
Vol 63 (7) ◽  
pp. 1357-1364 ◽  
Author(s):  
Parminder S. Surdhar ◽  
Douglas E. Bader ◽  
David A. Armstrong
Keyword(s):  
Quantum Yield ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Primary Amine ◽  
Pulse Radiolysis ◽  
Ethylene Diamine ◽  
Secondary Amines ◽  
Diamine Tetraacetate ◽  
Effects Of Ph ◽  
Electron Reduction

The amino radicals (•AH) formed by the 60Co radiolysis of N2O-saturated 0,05 M solutions of ethylene diamine tetraacetate (EDTA) at pH 7 and 11.2 and of glycine at pH 11.2 brought about an efficient two-electron reduction of lumiflavin (Fl). The spectra of the products were identical to those formed by photolysis of the same solutions and by reduction of the lumiflavin with •CO2− radicals. The products were reoxidised to flavin by oxygen. The quantum yield for flavin disappearance was 0.52 ± 0.07 and 0.17 ± 0.01 in the presence of EDTA at pH 7 and 11.2 and 0.065 ± 0.008 and 0.17 ± 0.01 for glycine at the same pHs, respectively.The overall two-electron reduction can be explained by the mechanism:[Formula: see text]The rate constants of reaction [4] were found by pulse radiolysis to be 1.8 ± 0.3 × 109 and 1.5 ± 0.3 × 109 M−1s−1 for the radicals of glycine and EDTA at pH 7 and 3.6 ± 0.3 × 108 M s−1 for glycine radicals at pH 11.2. The spectrum of •FlH formed by glycine radicals at pH 7 is similar to that produced by•CO2−, but there was some perturbation, which is apparently due to interaction with the amine.The radicals formed from the secondary amines piperazine and diethylamine at pH 11.8 also effected reversible two-electron reduction. However, the radicals from glycine anhydride and the primary amine ethylamine yielded significant amounts of non-oxidisable products. The reaction mechanisms are discussed and effects of pH are considered.

Correlation of the first reduction potential of selected radiosensitizers determined by cyclic voltammetry with theoretical calculations

2011 ◽  
Vol 76 (8) ◽  
pp. 937-946 ◽  
Author(s):  
Miroslav Gál ◽  
Viliam Kolivoška ◽  
Marta Ambrová ◽  
Ján Híveš ◽  
Romana Sokolová
Keyword(s):  
Experimental Study ◽  
Cyclic Voltammetry ◽  
Radical Anion ◽  
Reduction Potential ◽  
Theoretical Calculations ◽  
Dft Method ◽  
Basis Set ◽  
Radical Anions ◽  
Electron Affinities ◽  
Electron Reduction

Radiosensitizers are drugs that make cancer cells more sensitive to radiation therapy. The cytotoxic properties of such compounds are due to the fact that in the cell these compounds undergo one-electron reduction to generate radical anions. Therefore, their theoretical and/or experimental study is of high interest. To determine the correlation between reduction potential determined by cyclic voltammetry measurements and some physicochemical properties of selected radiosensitizers theoretical calculations of electron affinities based on the DFT method with B3LYP functional at the level of 6-311++G** basis set in vacuum were utilized. Very good correlation was found between electron affinities of radiosensitizers and their reduction potential and so called E71 potential that account for the energy necessary to transfer the first electron to an electroactive group at pH 7 in aqueous medium to form a radical anion.

Electrochemistry of Ruthenium Ammine Complexes

1975 ◽  
Vol 53 (19) ◽  
pp. 2922-2929 ◽  
Author(s):  
C. M. Elson ◽  
I. J. Itzkovitch ◽  
J. McKenney ◽  
John A. Page
Keyword(s):  
Cyclic Voltammetry ◽  
Rate Constants ◽  
Reduction Step ◽  
Methane Sulfonate ◽  
Ammine Complexes ◽  
Chloro Complexes ◽  
First Order ◽  
Order Rate ◽  
Electron Reduction ◽  
Hydrolysis Of

The electrochemistry of ruthenium(III) penta- and tetraammine chloro complexes has been investigated. In each case, the ruthenium(III) species was found to undergo an initial one electron reduction step, followed by hydrolysis of the chloride(s) in the ruthenium(II) product. The rate constants for the substitution steps were evaluated by cyclic voltammetry. An aqueous 0.30 M methane sulfonate electrolyte of pH 2.0 was used at 25 °C.Values for the reversible "E1/2" (V υs. SCE) and first order rate constants for the (stepwise) replacement of the Cl− are: Ru(NH3)5Cl+, −0.282 V and 17 s−1; cis-Ru(NH3)4Cl2+, −0.328 V, 80 s−1, and 5 s−1; trans-Ru(NH3)4Cl2+, −0.412 V, 2 s−1, and 0.4 s−1.The electrochemistry of Ru(NH3)5SO22+was also investigated. In a 0.10 M CH3SO3H – 0.20 M CH3SO3Na electrolyte the ruthenium(II) species was found to undergo an initial one electron oxidation step with "E1/2" = +0.50 V, followed by a slow hydrolysis of the SO2 in the ruthenium(III) product with k = 2.4 × 10−2 s−1 at 25 °C.

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