Electron transfer and agglomeration in the systems phenanthrenequinone, acenaphthenequinone, their dianions, radical ions, and dimers

Staples, Thomas L.; Szwarc, M.

doi:10.1021/ja00720a003

Cited by 21 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The change in the absorption spectrum of PQ ⋅‐ due to the complex formation with Y 3+ is shown in Figure 7 a, where the absorption band due to the PQ ⋅‐ −(Y 3+ ) 2 complex ( λ max =630 nm) is significantly red shifted as compared to the absorption band of PQ ⋅‐ ( λ max =484 nm). The absorbance change at 630 nm observed by changing concentration of Fc* with a fixed concentration of PQ (1.7×10 −3 M ) agrees with the concentration of the PQ ⋅‐ −(Y 3+ ) 2 complex, determined by double integration of the ESR signal in reference to a known amount of the stable radical, 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH) (see Experimental Section) 43. Thus, the absorption band at 630 nm is assigned to the PQ ⋅‐ −(Y 3+ ) 2 complex, which is stable under the present experimental conditions.…”

Section: Resultssupporting

confidence: 66%

Binding Modes in Metal Ion Complexes of Quinones and Semiquinone Radical Anions: Electron‐Transfer Reactivity

2006

View full text Add to dashboard Cite

9,10-Phenanthrenequinone (PQ) and 1,10-phenanthroline-5,6-dione (PTQ) form 1:1 and 2:1 complexes with metal ions (M (n+)=Sc (3+), Y (3+), Mg (2+), and Ca (2+)) in acetonitrile (MeCN), respectively. The binding constants of PQ--M (n+) complexes vary depending on either the Lewis acidity or ion radius of metal ions. The one-electron reduced species (PTQ(-)) forms 1:1 complexes with M (n+), and PQ(-) also forms 1:1 complexes with Sc(3+), Mg(2+), and Ca(2+), whereas PQ(-) forms 1:2 complexes with Y(3+) and La(3+), as indicated by electron spin resonance (ESR) measurements. On the other hand, semiquinone radical anions (Q(-) and NQ(-)) derived from p-benzoquinone (Q) and 1,4-naphthoquinone (NQ) form Sc(3+)-bridged pi-dimer radical anion complexes, Q(-)--(Sc(3+))(n)--Q and NQ(-)--(Sc(3+))(n)-NQ (n=2 and 3), respectively. The one-electron reduction potentials of quinones (PQ, PTQ, and Q) are largely positively shifted in the presence of M (n+). The rate constant of electron transfer from CoTPP (TPP(2-)=dianion of tetraphenylporphyrin) to PQ increases with increasing the concentration of Sc(3+) to reach a constant value, when all PQ molecules form the 1:1 complex with Sc(3+). Rates of electron transfer from 10,10'-dimethyl-9,9'-biacridine [(AcrH)(2)] to PTQ are also accelerated significantly by the presence of Sc(3+), Y(3+), and Mg(2+), exhibiting a first-order dependence with respect to concentrations of metal ions. In contrast to the case of o-quinones, unusually high kinetic orders are observed for rates of Sc(3+)-promoted electron transfer from tris(2-phenylpyridine)iridium(III) [Ir(ppy)(3)] to p-quinones (Q): second-order dependence on concentration of Q, and second- and third-order dependence on concentration of Sc(3+) due to formation of highly ordered radical anion complexes, Q()--(Sc(3+))(n)--Q (n=2 and 3).

show abstract

Section: Resultssupporting

confidence: 66%

Binding Modes in Metal Ion Complexes of Quinones and Semiquinone Radical Anions: Electron‐Transfer Reactivity

2006

View full text Add to dashboard Cite

show abstract

“…Spectral measurements of mixtures of pyrrolo-quinoline quinone and pyrroloquinoline quinol in solutions with alkali hydroxides from Li to Cs having equal cation concentrations, show a shift of the absorption maximum to higher wavelengths ( Fig.4) and a decrease of the ESR signal with a change of the hyperfine structure spectrum to that of a 'powder spectrum'. A similar behaviour has been reported for several o-quinones and the shift to higher wavelengths has been attributed to the formation of a diamagnetic radical complex in which the alkali-metal ion is included as a counterion [13].…”

Section: Discussionsupporting

confidence: 80%

Characterization of the Second Prosthetic Group in Methanol Dehydrogenase from Hyphomicrobium X

Duine

Frank

Jzn

et al. 1981

European Journal of Biochemistry

View full text Add to dashboard Cite

Procedures are described for preparing 2,7,9‐tricarboxy‐1H‐pyrrolo[2,3‐ƒlquinoline‐4,5‐diol (pyrrolo‐quinoline quinol) from 2,7,9‐tricarboxy‐1H‐pyrrolo[2,3‐ƒ]quinoline‐4, 5‐dione (pyrrolo‐quinoline quinone). When methanol dehydrogenase is denatured, two compounds are liberated which have the same properties as the quinone and quinol mentioned above. On analysing the extract by high‐performance liquid chromatography, one molecule of the quinone and one molecule of the quinol per enzyme molecule are found. Mixtures of pyrrolo‐quinoline quinone and pyrrolo‐quinoline quinol at high pH produce the semiquinone form and, under certain conditions, a diamagnetic complex. Since electron spin resonance (ESR) shows that methanol dehydrogenase contains the semiquinone and the absorption spectrum suggests the presence of a diamagnetic dimer, it is tentatively concluded that the two prosthetic group molecules in the enzyme interact with each other. NMR experiments of pyrrolo‐quinoline quinone in 2H2O demonstrate that it is partly hydrated, most prohably at the C‐5 position. Although methanol adds in the same way, it is still questionable whether the product of this addition plays a role in the mechanism of the enzymic reaction. Potentiometric titrations show a midpoint potential of the quinone/quinol couple of + 90 mV at pH 7.0 and the information of the semiquinone as an intermediate in the titration at pH 13.0.

show abstract

“…It has strong absorptions at 276 and 360 nm together with a broad band at 570 nm. This spectrum is relatively similar to those of a monomeric phenanthrene semiquinone radical anion (PQ rad - ) (λ max = 331 and 499 nm) and a monomeric semiquinone radical anion of 9-decarboxy-PQQ (9-decarboxy-PQQ rad - ) (λ max = 395 and ∼580 nm), but quite different from those of the corresponding diamagnetic dimers ([PQ rad - ] 2 : λ max = 440 and 670 nm, [9-decarboxy-PQQ rad - ] 2 : λ max = 460 and ∼670 nm). , Thus, 1 rad Me - exists as a paramagnetic monomer in CH 2 Cl 2 . Bulk electrolysis of the resulting solution of 1 rad Me - at 0.0 V vs Ag/Ag + regenerated quinone 1 ox Me quantitatively (Figure B), agreeing well with the reversibility observed in the cyclic voltammetric measurement (Figure A).…”

Section: Resultsmentioning

confidence: 85%

Electrochemical Behavior and Characterization of Semiquinone Radical Anion Species of Coenzyme PQQ in Aprotic Organic Media

1998

View full text Add to dashboard Cite

Electrochemical behavior of coenzyme PQQ has been investigated in aprotic organic solvents using the trimethyl ester of PQQ (1 ox H, trimethyl 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylate) and its 1-methylated derivative (1 ox Me, trimethyl 4,5-dihydro-4,5-dioxo-1-methylpyrrolo[2,3-f]-quinoline-2,7,9-tricarboxylate). 1 ox H shows a complicated cyclic voltammogram in organic media (CH 2 Cl 2 , MeCN, and DMSO); there are at least three reduction peaks and four oxidation peaks. The first irreversible reduction peak of 1 ox H around -0.9 V vs ferrocene/ferricenium (Fc/Fc + ) is very close to that of the reversible reduction peak of 1 ox Me. Addition of an equimolar amount of acetic acid into the solution of 1 ox Me results in a change of the reversible one-electron redox couple of 1 ox Me/1 rad Me -to an irreversible one as observed in 1 ox H. This phenomenon indicates that protonation of the semiquinone radical anion causes disproportionation of the resulting neutral semiquinone 1 rad H 2 into (1/2) 1 ox H (quinone) and (1/2) 1 red H 3 (quinol). In this case, 1 ox H itself in bulk solution acts as the proton source to be converted into 1 ox -. This is confirmed by the observation of reversible redox peaks due to a 1 ox -/1 rad 2-couple at -1.30 vs Fc/Fc + in DMSO and by the 2:1 formation of 1 ox -and 1 red H 3 in the thin layer UV-vis spectrum of 1 ox H electrolyzed at -0.8 V Ag/Ag + . Solution ESR spectra of electrochemically generated semiquinone radical anion species, 1 rad H -, 1 rad Me -, and 1 rad 2-, as well as the UV-vis spectrum of 1 rad Me -are also reported to explore the electronic structures of the semiquinone radical anion species of coenzyme PQQ. Addition of Ca 2+ , which is another cofactor of quinoprotein alcohol dehydrogenases, into the solution of 1 ox Me causes ca. 0.57 V positive shift of the oneelectron reduction potential of 1 ox Me, showing the enhancement of the oxidation power of 1 ox Me by a strong interaction between Ca 2+ and 1 rad Me -. The ESR spectrum of 1 rad Me --Ca 2+ complex is successfully detected and compared with that of the free semiquinone radical anion 1 rad Me -.

show abstract

Electron transfer and agglomeration in the systems phenanthrenequinone, acenaphthenequinone, their dianions, radical ions, and dimers

Cited by 21 publications

References 0 publications

Binding Modes in Metal Ion Complexes of Quinones and Semiquinone Radical Anions: Electron‐Transfer Reactivity

Binding Modes in Metal Ion Complexes of Quinones and Semiquinone Radical Anions: Electron‐Transfer Reactivity

Characterization of the Second Prosthetic Group in Methanol Dehydrogenase from Hyphomicrobium X

Electrochemical Behavior and Characterization of Semiquinone Radical Anion Species of Coenzyme PQQ in Aprotic Organic Media

Contact Info

Product

Resources

About