A kinetic study of the oxidation of the tetrakisoxalatouranate(IV) ion by the hexacyanoferrate(III) ion in an oxalate buffer medium

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

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 (S₂O₄^2-) 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: S₂O₄^2-) 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 [Formula: see text] 0.05 kJ mol^-1) and Gibbs energy (80.10 [Formula: see text] 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.

The study of Piszkiewicz’s and Berezin’s models on the redox reaction of allylthiourea and bis-(2-pyridinealdoximato)dioxomolybdate(IV) complex in an aqueous acidic medium

Background

The study of Piszkiewicz’s and Berezin’s models on the redox reaction of allylthiourea and bis-(2-pyridinealdoximato)dioxomolybdate(IV) complex ([MoIVO2(paoH)2]2−) in an aqueous acidic medium is suggested. The Piszkiewicz’s and Berezin’s models are applied, and their parameters are used to explain the redox behaviour of allylthiourea with Mo(IV) complex in the presence of surfactants.

Results

The reaction followed a high cooperativity pattern that reflects a strong interaction between the two redox partners in the presence of cetyltrimethylammonium bromide (CTAB) which is reinforced by a notable binding constant at the Stern layer of the micelle. The effect of cationic counter-ion (Ca2+) on the reaction rate further confirmed the effectiveness of the interaction at the rate-limiting step. The presence of sodium dodecyl sulphate (SDS) in the reaction medium resulted in reaction inhibition which reveals the interplay of electrostatic repulsion at the electrophilic polar head of the surfactant and the redox species. The effect of ionic strength on the reaction rate shows that one of the reacting species is not charged (neutral) which kept the rate of the reaction uniform at different salt concentrations studied. The change in the medium polarity buttressed the effect of ionic strength on the reaction which is explained better by Piszkiewicz’s and Berezin’s models. Free radical was actively engaged in the reductive process of the Mo(IV) complex, and this revealed that the hydrophobic region is a possible location for the interaction of the redox partner in the presence of SDS micelle.

Conclusions

The models depict well the microenvironments of enzymatic reactions involving bimolecular interactions with significant binding constants and cooperativity indexes that show the strength of the interaction between the substrates and surfactant molecules.

Graphical Abstract