Publications from the Lab of Dr. Edwin S. Gould of Kent State University

Inorg Chem 99: Electron Transfer. 140. Reactions of Riboflavin with Metal Center Reductants: "Reactions, under argon, were examined at or near 495 nm, the high-wavelength maximum of the riboflavin radical, using a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Ionic strength was regulated by addition of NaClO4/HClO4

Al-Ajlouni, A. M.,Gould, E. S. Electron Transfer. 139. Reductions with Trioxodinitrate, [N2O3]2-, Inorganic Chemistry; 1999; 38(7); 1592-1595.
Experimental Section
Kinetic Studies. Rates were evaluated from measurements of absorbance changes using a Shimadzu 1601 recording spectrophotometer or a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Most usually, decreases at 250 nm due to loss of trioxodinitrate were followed, but in some cases, the change in a colored coreagent was monitored. Temperatures were kept at 22.0 ± 0.5 ºC. Ionic strength was maintained at 0.20 M by addition of NaClO4. Acidities were regulated by measured quantities of buffering acids and NaOH. For kinetic runs, solutions of the oxidant and the buffering acid were added to solutions of N2O32- in base, thus minimizing the loss of the reductant by acid-catalyzed self-decomposition9 prior to mixing; pH values of the redox mixtures were checked at the conclusion of each reaction. Except as noted below, conversions were first order each in trioxodinitrate and oxidant but were customarily run under pseudo-first-order conditions with one reagent in greater than 10-fold excess. Rate constants were obtained by nonlinear least-squares fitting to the relationship describing exponential decay. Values from replicate runs generally agreed to better than 6%. Rates measured under anaerobic conditions did not differ systematically from those determined in contact with air.

Chandra, S. K., Paul, P. C., Gould, E. S., Electron Transfer. 135. Pendant Carbonyl Groups in the Mediation of the Reactions of Indium(I) with Bound Ruthenium(III)1, Inorganic Chemistry; 1997; 36(21); 4684-4687. (Article)
Experimental Section
Kinetic Experiments. Reactions, under argon, were examined at or near the high-wavelength maximum of the Ru(II) product, using either a Cary 14 instrument or a Durrum-Gibson stopped-flow spectrophotometer12 interfaced with an OLIS computer system. Ionic strength was regulated by addition of NaClO4/HClO4. Reductions with Ti(III) were carried out with the reductant in excess, whereas those with In(I) were run with Ru(III) in excess to avoid formation and precipitation of elementary ruthenium.10 Concentrations of reagents were generally adjusted so that no more of 10% of the reactant in excess was consumed in the reaction. Reductions by Ti(III) yielded simple exponential curves, and rate constants were obtained by nonlinear least-squares fitting to the relationship describing pseudo-first-order decay. These reactions were first order in both redox partners.

Chandra, S. K., Gould, E. S., Electron Transfer. 128. Rate Enhancements by Donor Sulfur in Hexadentate Ligands1, Inorganic Chemistry; 1996; 35(7); 2136-2139. (Article)
Experimental Section
Kinetic Studies. Reactions of Cr(II), V(II), Eu(II), Ti(III), and N-methyldihydrophenazinium cation were carried out under N2, and those of Ru(NH3)62+ were run under argon. Conversions were monitored using a Beckman Model 5260 or Cary 14 recording spectrophotometer or a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Reductions of the Co(III)-N2S2O2 complex were followed at 665 nm, whereas those of the Co(III)-N4O2 oxidant were observed at 584 nm. Ionic strength, which was maintained at 0.10 M for most reactions, was regulated by addition of LiClO4 and HClO4 or, in the case of reductions by Ru(NH3)62+, by addition of HCl. Because the N2S2O2 complex dissolves with difficulty in water, solutions of this oxidant were prepared by dissolving the solid compound in a small volume of CH3CN, then diluting 50-fold with the aqueous supporting medium.24 Excess quantities of the reductant were used in all kinetic runs, and concentrations were generally adjusted so that no more than 10% of the latter was consumed. All reactions yielded simple exponential curves; rate constants were obtained by nonlinear least squares fitting to the relationship describing first order decay. Values calculated from replicate runs agreed to better than 4%. All reactions were first order in both redox partners. Specific rates greater than 50 s-1 were adjusted upward to accommodate the mixing rate associated with the stopped-flow instrument, as described by Dickson.25 Possible rate variations with changes on acidity were examined for reductions with Cr(II), Eu(II), and Ti(III), but not for reductions with V(II) and Ru(NH3)62+; such variation is much less usual with the latter two reductants.17b,20,26 Reactions of both oxidants with Cu+ were immeasurably slow; only upper limits could be obtained for this reductant.

Chandra, S. K., Gould, E. S., Electron Transfer. 130. Reductions with Indium(I)1, Inorganic Chemistry; 1996; 35(13); 3881-3884. (Article)
Experimental Section
Kinetic Experiments. Reactions, under argon, were examined at the high wavelength maximum of the CoIII complex, using either a Beckman Model 5260 recording spectrophotometer, a Cary 14 instrument, or a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Ionic strength, which was regulated by addition of LiClO4 and HClO4, was maintained at 0.2 M. Excess quantities of oxidant were generally used and concentrations were most often adjusted so that no more than 10% of the latter was consumed in reaction. All rapid reactions yielded simple exponential curves, and rate constants in such cases were obtained by nonlinear least-squares fitting to the relationship describing first-order decay. Values obtained from replicate runs agreed to better than 5%. These reactions were first order in both redox partners. Profiles exhibited no indication of transients formed or destroyed on a time scale comparable to that of the Co(III)-In(I) reaction. For a number of the slower reactions, rate constants were calculated from initial rates, and in many instances only upper limits were estimated.

Chandra, S. K., Gould, E. S., Electron Transfer. 134. Reduction of Bound Ruthenium(III) by Indium(I)1, Inorganic Chemistry; 1997; 36(16); 3485-3487. (Article)
Experimental Procedures
Kinetic Experiments. Reactions, under argon, were examined at the high-wavelength maximum of the Ru(II) product, using either a Cary 14 recording spectrophotometer, a Beckman Model 5260 instrument, or a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Ionic strength, which was regulated by addition of NaClO4/HClO4, was generally maintained at 0.2 M. Concentrations of reagents were customarily adjusted so that no more than 10% of the reactant in excess was consumed in the reaction.14 In no case was kinetic variation with acidity perceived within the range [H+] = 0.030-0.10 M. All reactions in the present series yielded simple exponential curves, and rate constants were obtained by nonlinear least-squares fitting to the relationship describing first-order decay. Values from replicate runs agreed to better than 6%. These reactions were first order in both redox partners. Profiles for reactions in this group showed no indication of transients formed or destroyed on a time scale comparable to that of the principal redox reaction.15

Al-Ajlouni, A. M., Gould, E. S., Electron Transfer. 132. Oxidations with Peroxynitrite1, Inorganic Chemistry; 1996; 35(26); 7892-7896. (Article)
Experimental Section
Kinetic Studies. Rates were evaluated from measurements of absorbance decreases at 300 nm using a Beckman Model 5260 recording spectrophotometer or a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system. Temperatures were kept at 25.0 ± 0.5 ºC. For reductions by As(III), Sb(III), and sulfite, ionic strength was maintained by addition of NaClO4, whereas NaCl was used for reactions of Sn(II). Reductions by Sn(II) were carried out anaerobically, but those by As(III), Sb(III), sulfite, and hypophosphite were not significantly affected by exposure to air under our conditions. Acidities were regulated by measured quantities of the buffering acids and NaOH. For reductions with As(III), kinetic runs using the "biological buffers" ACES, TAPS, and CAPS were more successful than those using phosphate and carbonate systems. For reductions with antimony(III) tartrate, on the other hand, individual buffer-related kinetic effects were observed with the biological buffers, but such complications were minimal with phosphate and borate buffers provided excess tartrate (0.15 M) was present. For kinetic runs, solutions of the reductant and buffering acid were added to peroxynitrite in base, thus minimizing loss of the oxidant by self-decomposition15,18 prior to mixing; pH values of the redox mixtures were checked after completion of the reactions. Conversions were first-order each in peroxynitrite and reductant but were generally carried out under pseudo-first-order conditions with the reductant in greater than 10-fold excess. Rate constants were obtained by nonlinear least-squares fitting to the relationship describing first-order decay. Values calculated from replicate runs agreed to better than 5%.

Electron Transfer. 141. Reactions of Indium(I) with Transition Metal Center Oxidants1 Inorg chem: 2000; "Reactions, under argon, were examined at or near max of the oxidant, using a Durrum-Gibson stopped-flow spectrophotometer interfaced with an OLIS computer system"