Kinetic Studies and Free-Radical Mechanisms of the Alkaline Permanganate Oxidation of L-Tryptophan

International Journal of Chemistry | Vol. 15, No. 2, February 2024 | pp. 9–16

DOI: 10.46882/2024/IJC/000184

Article Type: Original Research Paper

Title: Kinetic Studies and Free-Radical Mechanisms of the Alkaline Permanganate Oxidation of L-Tryptophan

Names of Authors: T. M. Usman¹, F. M. Al-Rasheed²*

Authors’ Affiliations:
¹Department of Chemistry, Bayero University, Kano, Nigeria.
²Department of Chemistry, King Saud University, Riyadh, Saudi Arabia.

Abstract: The kinetics of transition metal electron transfer reactions involving basic amino acids yield essential data required to map biochemical oxidation paths and structural intermediate transformations. The oxidation of L-tryptophan by permanganate ions (MnO₄⁻) was investigated spectrophotometrically in an aqueous sodium hydroxide medium at a constant ionic strength of 0.20 M (NaClO₄). The reaction progress was monitored under pseudo-first-order conditions by following the absorbance decay of MnO₄⁻ at its absorption maximum of 525 nm. The empirical rate law showed a first-order dependence on [permanganate] and a fractional-first-order dependence on [L-tryptophan]. The reaction rate increased with rising hydroxyl ion concentration, revealing a base-catalyzed pathway driven by the active unprotonated amine species. Variations in ionic strength produced positive kinetic shifts, indicating a rate-determining step involving two similarly charged ionic species. Stoichiometric determinations confirmed that 1 mole of L-tryptophan consumed 2 moles of permanganate, producing indole-3-acetaldehyde and Mn(II) species as the primary end products. Thermodynamic activation constants calculated from temperature-dependence datasets using the Eyring equation yielded an enthalpy of activation (delta H*) of 45.8 kJ/mol and an entropy of activation (delta S*) of -112.4 J/mol K, supporting an inner-sphere mechanism.

Keywords: Reaction kinetics; Spectrophotometry; Permanganate oxidation; L-tryptophan; Activation parameters; Reaction mechanisms

Manuscript Timeline: Received: July 10, 2022; Revised: August 20, 2022; Accepted: September 15, 2022; Published: February 07, 2024.

Citation: Usman, T. M., & Al-Rasheed, F. M. (2024). Kinetic Studies and Free-Radical Mechanisms of the Alkaline Permanganate Oxidation of L-Tryptophan. International Journal of Chemistry, 15(2), 9–16.

Subscribe to read the full article: https://internationalscholarsjournals.org/subscribe-to-read