Esterification between amyl alcohol isomers and n-caprylic acid under microwave irradiation-enzyme coupling catalysis (MIECC)

The enzymatic esterification between amyl alcohol isomers and n-caprylic acid was investigated in the following three ways to reveal the potential coupling mechanism of microwave irradiation-enzyme coupling catalysis (MIECC). That is, (1) MI manner: on-line microwave irradiation with 2450 MHz emission frequency and constant output power, (2) CH manner: conventional isothermal heating and (3) pre-MI + CH manner: enzyme pre-treated by microwave irradiation followed by catalysis under conventional heating. The obvious MIECC effect on increasing initial reaction rate 2.5-4.5 times but less influence on shifting reaction equilibrium was observed. The structure of amyl alcohol affects both the initial reaction rate and the ultimate yield of amyl n-caprylate in the following sequence: primary alcohol > secondary alcohol > tertiary alcohol. Increment of microwave power shows some effect on the initial reaction rate of esterification but the short intermittence of MI/cooling seems more favorable to MIECC in reaction rate. The experimental results show that no matter how MI or pre-MI + CH manner can activate enzymes and especially the enzyme that undergoes pre-MI can keep the stimulated activity during following reaction due to some memory function of enzyme to pre-MI.