Regioselective Esterification of Nitrophenol Isomers Catalyzed by Immobilized Candida rugosa and Porcine Pancreatic Lipases

Regioselectivity of immobilized Candida rugosa lipase (CRL) and porcine pancreatic lipase on esterification of nitrophenol isomers (2-NP, 3-NP, 4-NP) with acetic acid in hexane was investigated. The optimal temperature, activation energy (Ea), and kinetic parameters (Vmax, KM) for each nitrophenol isomers were determined. When esterification activities were evaluated, the highest activities were observed for 3-NP and 4-NP for PPL and CRL, respectively. However, when nitrophenol isomer was 2-NP, both PPL and CRL showed the lowest esterification activity. In simultaneous esterification reactions where 2-NP 3-NP and 4-NP were used together, the regioselectivity tendency was the same, with 2-NP esterification being negligible after 6 hours reaction time. A multi-wavelength UV-Vis method was validated to quantify individual NPs in mixture samples with high accuracy. The study confirms the strong influence of substituent position on lipase activity and highlights the potential of immobilized lipases for regioselective biotransformations.