Glutaraldehyde-crosslinked Rhizopus oryzae whole cells show improved catalytic performance in alkene epoxidation

Existing methods for alkene epoxidation are based on lipase-catalysed perhydrolysis. However, the inactivation of the expensive lipase enzyme is problematic for enzymatic epoxidation at large scales due to the use of hydrogen peroxide and peracids at high concentrations in the reaction. The immobilisation of whole cells appears to be a promising approach to alleviate this problem.

A green oxidation system containing hydrogen peroxide, Na₃C₆H₅O₇, an acyl donor, and glutaraldehyde (GA)-crosslinked cells of Rhizopus oryzae was developed for the epoxidation of alkenes. GA-crosslinked cells of Rhizopus oryzae were adopted as a biocatalyst into the epoxidation system. A variety of alkenes were oxidised with this system, with a 56-95% analytical yield of the corresponding epoxides. The catalytic performance of the crosslinked treated cells was substantially improved compared to that of the untreated cells and the initial reaction rate increased from 126.71 to 234.72 mmol/L/h, retaining 83% yields even after four batches of reactions. The addition of 3.5 mmol Na₃C₆H₅O₇ not only acts as an acid-trapping reagent to eliminate the negative effect of the carboxylic acid on the alkene oxide but also forms a saturated salt solution with the aqueous phase, affecting the concentration of H₂O₂ in the three phases and thus the epoxidation reaction. Organic solvents with a logP value > 0.68 were good at producing hydroxy peracids; however, this method is only suitable for oxidation in a two-liquid phase.

Compared with other lipase biocatalysts, the GA-crosslinked whole-cell biocatalyst is inexpensive, readily available, and highly stable. Therefore, it can be considered promising for industrial applications.