Light-induced multistep redox reactions: The diode-array spectrophotometer as a photoreactor

Fábián, István; Lente, Gábor

doi:10.1351/pac-con-09-11-16

Cited by 38 publications

(40 citation statements)

References 25 publications

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“…The possibility of unwanted photoreactions was tested by using different illumination protocols. 59 Photochemical 7 and recorded with a digitizer at 2 GHz sampling rate. The mass spectra were calibrated using the exact masses of the clusters generated from the electrosprayed solution of sodium trifluoroacetate (NaTFA).…”

Section: Methodsmentioning

confidence: 99%

Decomposition of N-Chloroglycine in Alkaline Aqueous Solution: Kinetics and Mechanism

Szabó

Baranyai

Somsák

et al. 2015

Chem. Res. Toxicol.

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The decomposition kinetics and mechanism of N-chloroglycine (MCG) was studied under very alkaline conditions ([OH(-)] = 0.01-0.10 M). The absorbance change is consistent with two consecutive first-order processes in the 220-350 nm wavelength range. The first reaction is linearly dependent on [OH(-)] and interpreted by the formation of a carbanion from MCG in an equilibrium step (KOH) and a subsequent loss of chloride ion from this intermediate: kobs1 = KOH k1 = (6.4 ± 0.1) × 10(-2) M(-1) s(-1), I = 1.0 M (NaClO4), and T = 25.0 °C. The second process is assigned to the first-order decomposition of N-oxalylglycine, which is also formed as an intermediate in this system: kobs2 = (1.2 ± 0.1) × 10(-3) s(-1). Systematic (1)H and (13)C NMR measurements were performed in order to identify and follow the concentration changes of the reactant, intermediate, and product. It is confirmed that the decomposition proceeds via the formation of glyoxylate ion and produces N-formylglycine as a final product. This compound is stable for an extended period of time but eventually hydrolyses into formate and glycinate ions. A detailed mechanism is postulated which resolves the controversies found in earlier literature results.

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Section: Methodsmentioning

confidence: 99%

Decomposition of N-Chloroglycine in Alkaline Aqueous Solution: Kinetics and Mechanism

Szabó

Baranyai

Somsák

et al. 2015

Chem. Res. Toxicol.

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“…50 Photochemical interference was not observed in this system. Measurements were made in stoppered quartz cells of 10 mm light path.…”

Section: Instruments and Methodsmentioning

confidence: 71%

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

et al. 2015

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The oxidation of pyruvic acid by hypochlorous acid was studied in the pH 1.0 -11.0 range. The main path in the redox process is the reaction between the pyruvate ion and HOCl. It was shown that the reaction is second order in both reactants and kHOCl = 2.14 ± 0.02M −1 s −1 (I = 1.0 M (NaClO4), T = 25.0 °C) with ∆HHOCl ≠ = 34.6 ± 1.2 kJmol −1 and ∆SHOCl ≠ = −120.3 ± 3.6 Jmol −1 K −1 for this reaction step. The relatively large negative entropy of activation is consistent with an O atom-transfer mechanism. DFT calculations support this conclusion by predicting a concerted rearrangement of the activated complex which includes the reactants and the solvent water molecule. It was also confirmed that the hydration of pyruvic acid has significant contribution to the observed kinetic features under acidic condition. The hydration reaction is a proton catalyzed process and the pseudo-first order rate constant can be interpreted by considering theprotolytic and hydration equilibria of pyruvic acid. The rate constants were determined for the non-catalytic and the proton catalyzed path: kh0 = 0.24 ± 0.01 s −1 and kh1 = 5.5 ± 0.2 M −1 s −1 .

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“…The light intensity dependence of the reaction was studied by the variation of the exit slit-width of the monochromator of the stopped-flow apparatus or the integration time of the diode-array photometer. 51 In the case of the stopped-flow measurements, the increase in the spectral bandwidth with increasing slit width was taken into account. Detailed experiments proved that the initial reaction rate at 430 nm ( v 0 430nm ) slightly decreases with the intensity of illumination, and the intermediate at 430 nm decays with a rate proportional to the light intensity (Figure 2).…”

Section: Resultsmentioning

confidence: 99%

Detailed mechanism of the autoxidation of N-hydroxyurea catalyzed by a superoxide dismutase mimic Mn(iii) porphyrin: formation of the nitrosylated Mn(ii) porphyrin as an intermediate

et al. 2012

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The in vitro autoxidation of N-hydroxyurea (HU) is catalyzed by MnIIITTEG-2-PyP5+, a synthetic water soluble Mn(III) porphyrin which is also a potent mimic of the enzyme superoxide dismutase. The detailed mechanism of the reaction is deduced from kinetic studies under basic conditions mostly based on data measured at pH = 11.7 but also including some pH-dependent observations in the pH range 9 – 13. The major intermediates were identified by UV-vis spectroscopy and electrospray ionization mass spectrometry. The reaction starts with a fast axial coordination of HU to the metal center of MnIIITTEG-2-PyP5+, which is followed by a ligand-to-metal electron transfer to get MnIITTEG-2-PyP4+ and the free radical derived from HU (HU•). Nitric oxide (NO) and nitroxyl (HNO) are minor intermediates. The major pathway for the formation of the most significant intermediate, the {MnNO} complex of MnIITTEG-2-PyP4+, is the reaction of MnIITTEG-2-PyP4+ with NO. We have confirmed that the autoxidation of the intermediates open alternative reaction channels, and the process finally yields NO2− and the initial MnIIITTEG-2-PyP5+. The photochemical release of NO from the {MnNO} intermediate was also studied. Kinetic simulations were performed to validate the deduced rate constants. The investigated reaction has medical implications: the accelerated production of NO and HNO from HU may be utilized for therapeutic purposes.

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Light-induced multistep redox reactions: The diode-array spectrophotometer as a photoreactor

Cited by 38 publications

References 25 publications

Decomposition of N-Chloroglycine in Alkaline Aqueous Solution: Kinetics and Mechanism

Decomposition of N-Chloroglycine in Alkaline Aqueous Solution: Kinetics and Mechanism

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

Detailed mechanism of the autoxidation of N-hydroxyurea catalyzed by a superoxide dismutase mimic Mn(iii) porphyrin: formation of the nitrosylated Mn(ii) porphyrin as an intermediate

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