Redox Mechanisms and Detection and Quantification of Kynurenic Acid and Kynurenine on Carbon Electrodes

This work, for the first time, investigated and compared electrochemical and thermodynamic properties of kynurenic acid (KYNA) and kynurenine (KYN) in aqueous electrolytes, on glassy carbon electrodes (GCE) and disposable screen‐printed carbon electrodes (SPCEs). Both GCE and SPCEs were electrochemically pretreated to activate and functionalize their surfaces. The experiments were performed using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). Overall, the voltammetric data for KYNA on GCE and SPCE were convergent and indicated an irreversible, pH‐dependent anodic process, associated with the withdrawal of one electron from the hydroxy group at C4, with the formation of a KYNA • radical. The KYNA • radical can polymerize on the electrode, causing passivation of its surface, and/or react with water, leading to the formation of quinone derivatives. The electrooxidation of KYNA occurred at high potentials, and its process was most easily identified by pulse voltammetric techniques. An electrooxidation mechanism of KYNA in aqueous media on carbon electrodes was proposed. The oxidation of KYN at SPCE occurred in a single, irreversible, pH‐dependent step, with the removal of one electron from the 2‐aminobenzoyl group, forming a cation radical intermediate. The radicals combined to form electroactive dimers. Establishing and comparing the electrochemical properties of KYNA and KYN are important data for understanding their redox reactions, redox stability, and metabolism in biological systems. Electroanalytical methods have been proposed for the detection and quantification of KYNA and KYN on SPCEs. For KYNA, the proposed method used SWV at pH = 7.00 and presented limit of detection (LOD) = 0.782 µmol L −1 . For the proposed method for detection and quantification of KYN, DPV was used at pH = 0.30, and a LOD = 0.304 µmol L −1 was obtained.