Esterification of R/S-ketoprofen with 2-propanol as reactant and solvent catalyzed by Novozym® 435 at selected conditions

Abstract

Abstract The enzymatic esterification of R/S-ketoprofen with 2-propanol catalyzed with the commercial biocatalyst Novozym® 435 is addressed in this investigation. The low reaction rate registered in this reaction was investigated in terms of the effect of the alcohol on the physicochemical–enzymatic stability of the biocatalyst and the interaction of the substrates with the catalytic triad at a molecular level. The effect of contacting 2-propanol:H2O mixture on Novozym® 435 was investigated at 45 °C for an extended period of time (8 days). The mixture dissolves the polymethylmethacrylate (PMMA) that constitutes the support of the Candida antarctica B lipase (CALB). Additionally, the alcohol diffuses into the biocatalyst's beads remaining strongly adsorbed (the alcohol desorption is evidenced only upon heating at 187 °C) and altering the inner texture of the biocatalyst's beads. Additionally, 2-propanol modifies the secondary structure of the enzyme by decreasing the β-sheet contribution and increasing the β-turn structure. The molecular modeling of the interaction of R/S-ketoprofen and 2-propanol with the catalytic triad of the lipase provides evidences that the secondary alcohol exerts an important steric hindrance for the reaction to proceed.