Kinetic studies on oxidation of l-cysteine and 2-mercaptoethanol by a trinuclear Mn(IV) species in aqueous acidic media

Shallangwa

et al. 2020

Heliyon

The redox kinetics involving the reaction of N, N 0 -phenylenebis(salicyalideneiminato)cobalt(III) ([CoSalophen] þ ) and l-cysteine (LSH) was studied using pseudo-first order approach under the following conditions,The redox reaction was 1 st order in both [CoSalophen þ ] and [LSH], with the overall 2 nd order. Hydrogen ion concentration effect revealed the activeness of both the protonated and deprotonated form of the reductant, positive Brønsted-Debye salt effect and was also ion catalyzed. There was no evidence suggesting an intermediate complex of significant stability in the reaction. Free radical was detected to take part and as such the reasonable mechanistic pathway for the reaction is suggested to be outer-sphere, hence proposed.

Section: Introductionmentioning

confidence: 99%

Reaction of N, N-phenylenebis(salicyalideneiminato)cobalt(III) and l-cysteine in mixed aqueous medium: kinetics and mechanism

Abdulsalam

Shallangwa

et al. 2020

Heliyon

“…The contributions of unstable molecules in the redox process were studied by introducing 0.4 cm 3 acrylamide to the reacting mixture with surplus methanol 30,31 . Thermodynamic parameters were investigated by varying the temperature of the reaction mixture with Grant JB1 thermostated H 2 O immersion, and the data generated was evaluated with Eyring approach to evaluating activated parameters [32][33][34] . The surfactant effect on the reaction rate was explored quantitatively by using the Piszkiewicz equation (Eq.…”

Section: Methodsmentioning

confidence: 99%

Application of Piszkiewicz model on the electron transfer reaction of dithionite ion and bis-(2-pyridinealdoximato)dioxomolybdate(IV) complex

Nkole

Abdulkadir

et al. 2022

Sci Rep

The need to better understand the binding mode of antioxidants (sulfur oxyanions) kinetically is a concern in medicine. Hence, a spectrophotometric method was used to study the application of the Piszkiewicz model on the electron transfer reaction of dithionite ion (S2O42−) and bis-(2-pyridinealdoximato)dioxomolybdate(IV) complex at 303 K and an absorption maxima of 560 nm. It follows an acid dependent reductive pathway that is medium sensitive. Charge distribution from the reaction species contributes to the redox efficiency of the system, resulting in a primary salt effect (NaCl) with an enhanced reaction rate. Alteration of the reaction medium with ethanol led to an elevation of reduction time as the charge catalysis was distorted by a drop in the system permittivity. Likewise, sodium dodecyl sulfate in the system decreased the reduction rate of the complex due to the low impact of hydrophobic and ion interaction between the micelle and substrates. First order reaction kinetics was observed in the concentration of the redox partners and a 2:1 (complex: S2O42−) stoichiometry was obtained with the involvement of hydrogenated sulfite radical which resulted in the formation of sulfur dioxide and a Mo2+ deactivated complex. The occurrence of counterion catalysis is pronounced in the reaction system owing to the participation of like-charged substrates in the rate-controlling phase. The standard enthalpy (69.12 $$\pm$$ ± 0.05 kJ mol−1) and Gibbs energy (80.10 $$\pm$$ ± 0.07) kJ mol−1 suggest that the process is endothermic dependent. The investigation of the anionic surfactant effect on the reaction medium was quantitatively ascertained from the Piszkiewicz model of the complex interaction sequence.

“…Its thiol group (–SH), thiolate ion (CS − ), and thiyl radical species (CS * ) are capable of initiating reduction reaction in acidic, aqueous, or buffer media [ 11 – 13 ]. The electron transfer reactions of l-cysteine have been investigated in a good number of researches such as reduction of trinuclear Mn(IV) species in which the rate was found to increase in aqua media [ 14 ], [Mn 4 O 6 ] 4+ core resulted in a significant decrease in the observed second-order rate constants in aqua media enriched with deuterium water and a proton-mixed single electron transfer reaction was proposed [ 15 ], 11-tungstophosphovanate(V) resulted in a first order with respect to [redox species] [ 16 ], Hexacyanoferrate(III) showed an increased reaction rate with increase in hydroxide ion concentration and the product was found to be sulfenic acid [ 17 ], and [CoSalophen] + complex established the importance of deprotonated and protonated form of l-cysteine in the electron transfer process [ 18 ]; in the view to gain more understanding of the character of enzymes containing thiol group in bio-systems.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics and Kinetic Investigation of Reaction of Acriflavine with L-cysteine in Aqueous Medium

Nkole

2021

Chemistry Africa

Graphic abstract The kinetic investigation of reaction of 3,6-diamino-10-methylacridin-10-ium chloride (acriflavine) with l-cysteine in aqueous acidic medium at maximum absorption = 460 nm, ionic strength (I) = 0.1 mol dm −3 and temperature (T) = 307 K has been carried out spectrophotometrically. Using a pseudo first order approach, the rate of the redox reaction resulted to first order with respect to the [acriflavine, (AF)] and [l-cysteine, (CSH)] and second order total. Stoichiometric determination confirms that a mole of the acriflavine is consumed by a mole of l-cysteine at a time for the attainment of product formation. The reaction followed a one-way acid independence path. The adjustment in ionic strength (NaCl) and solvent polarity (water/acetone mixture) of the reaction system showed no reasonable effect and there was a fairly decrease in the reaction rate, respectively. The reaction rate is also characterised by neither catalysis nor inhibition of added ions. The negative magnitude of entropy of activation, S ‡ , (− 151.39 ± 031 J mol −1 K −1 ) and positive value of enthalpy of activation, H ‡ , (+ 31.378 ± 030 kJ mol −1 ) suggest that the reaction proceeds via an associative pathway and reasonable energy are needed to lower the activation energy for a tangible products formation. Two acridine unit products polymerised afterward forming a dimer as a result of an intramolecular coupling. A determinable intermediate has been observed through a spectroscopic test and confirmed by Michaelis–Menten’s plot. Based on Taube’s inorganic electron transfer reaction, an inner-sphere mechanistic pathway is implicated with a stable intermediate complex formation as shown below;