Nanobiocatalysis for the Synthesis of Pentyl Valerate in Organic Solvents: Characterization, Optimization and Reusability Studies

Background: Biotransformation and enzymatic methods of ester synthesis are more effective when performed in non-aqueous media. The aim of this work was to prepare reusable and more effective biocatalyst to catalyze the synthesis of pentyl valerate by esterification reaction. Method: Silane modified CdS nanoparticles were prepared and used for lipase immobilization. Characterization study was carried out using Infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM), Fluorescence microscopy and Thermal gravimetric analysis (TGA). The effects of the reaction parameters such as pH, temperature, and molar ratio of the substrate to the solvent, acid to alcohol chain length was scrutinized in order to get enhanced esterification activity. Results: Upon optimization, the highest yield obtained for ester synthesis was 86% for immobilized lipase, whereas with free lipase only 52% yield was obtain. The immobilized biocatalyst showed higher catalytic activity (1.6 folds) than crude lipase. Immobilized lipase was recycled for 15 times retaining 80% of its initial activity. Km and Vmax for immobilized lipase are 0.38mM and 205μmoles/mg/min whereas for free lipase Km was 1.4mM and Vmax was 25 μmoles/mg/min. Conclusion: The application of enzyme immobilized on functionalized CdS verifies to be the promising system for ester synthesis in non-aqueous environment. In addition, nanobioconjugant system proves better for improving catalytic performance of lipase when exploited into organic solvents.