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 similar to 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.