Laccase mediated electrosynthesis of heliotropin on mango-kernel derived carbon nanosphere composite: A sustainable approach

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Facile fabrication of enzyme immobilized carbon nanospheres (CNS) based catalysts with high electrical conductivity and catalytic efficiency are of decisive importance for their electrocatalysis. Herein, we report a novel, green and highly efficient synthesis route for the development of an electrode surface with enhanced electrical conductivity and better catalytic activity for the electrochemical synthesis of heliotropin. An important organic intermediate, heliotropin is widely employed in organic synthetic chemistry, perfume, pharmaceutical and dye industries. To design an efficient electrocatalyst, the obtained biowaste (mango seed kernels) was pyrolyzed and subjected to acid treatment to form functionalised CNS (f-CNS). The functionalised CFP electrode was employed as a template for laccase immobilization. This was further treated with free laccase resulting in the formation of Lac-fCNS/CFP electrode. The enzyme based catalytic effect of the developed electrode exhibited excellent electrooxidation of piperonyl alcohol in the presence of TEMPO, which served as the mediator. A high yield (72%) of heliotropin was achieved during the electrooxidation at 0.78 V via bulk electrolysis. The obtained product (heliotropin aka piperonal) was confirmed via 1 H NMR and 13 C NMR. Additionally, computational molecular docking analysis of f-CNS:laccase composite showed strong binding affinity (-6.2 kcal/mol) with TEMPO in comparison with free laccase (-5.1 kcal/mol). The excellent selectivity and efficiency of the developed electrocatalyst aims to surpass all other reported laccase-TEMPO mediated based electrocatalytic oxidation reactions. Effect of porosity obtained from carbon nanospheres might be the reason for the present investigations. • Facile synthesis of mango-seed kernel derived carbon nanospheres (CNS) via pyrolysis. • Laccase immobilization onto functionalized CNS, an effective carbon substrate for electrochemical synthesis. • Laccase-TEMPO mediated electrochemical oxidation of piperonyl alcohol to form heliotropin or piperonal. • A higher binding affinity observed in the interactions between the fabricated composite (Lac-fCNS) and TEMPO was studied by Molecular docking analysis.