Stability of protein-coated microcrystals in organic solvents

Previously we reported a new high activity biocatalyst for use in organic media, termed protein-coated microcrystals (PCMC) [M. Kreiner, B.D. Moore, M.C. Parker, Chem. Commun. 12 (2001) 1906]. These novel biocomposites consist of water-soluble micron-sized crystalline particles coated with the given biocatalyst(s). Here we have looked at the stability of PCMC and their catalytic behaviour as a function of temperature in different organic media. PCMC show very good long-term stability at room temperature, when stored as suspensions in 1-propanol/I wt.% H2O. Candida antarctica lipase B and subtilisin Carlsberg (SC) in PCMC form retained nearly 90% of their initial activity after 1 year at room temperature (RT). The effects of temperature on the catalytic activity of SC-PCMC are solvent-dependant. In 1-propanol/1 wt.% H2O, the initial rate increased when the temperature was elevated from 25 to 60 degrees C, whereas in acetonitrile/1 wt.% H2O, SC-PCMC lost activity. The operational stability of PCMC is also solvent-dependant. In 1-propanol/I wt.% H2O, SC-PCMC lost only 16% of the initial activity after five batch cycles. Rather poor stability was found for SC-PCMC in THF/1% (v/v) H2O and acetonitrile/1% (v/v) H2O, with a rapid loss of activity within 4h in a continuous flow reactor. However, during the next 4 days only a slow further deactivation was observed.