Microencapsulation of Enzymes and Cells for Nonaqueous Biotransformations

Jeffrey A. Khan and Evgeny N. Vulfson 1. Introduction

The use of biocatalysts in nonaqueous organic solvents is now a well-established method for the preparation of pharmaceutical products (1-2), food ingredients (3-5), and intermediates used in the fine chemicals industry (6-10). One of the advantages of this approach is that it enables the bioprocess operation at much higher concentrations of poorly water-soluble substrates, thus making both the synthesis and product recovery more attractive from a practical standpoint (11,12). However, many enzymes, and certainly microorganisms, still require a substantial amount of water present to maintain their catalytic activity at synthetically useful levels. In these cases, conventional aqueous-organic two-phase systems are still widely used, although the rates of mass transfer and inactivation of biocatalysts at the interface can be a serious drawback (13-16).

An alternative approach to biotransformations in aqueous-organic two-phase systems involves the entrapment of enzymes and whole cells within permeable polymeric microcapsules containing an aqueous phase. This is achieved using mild methods of interfacial polymerization developed in our laboratory to maintain biocatalyst activity/viability during the immobilization step (Fig. 1A,B) followed by the resuspension of these biocatalyst preparations in an organic solvent to perform the required reactions (Fig. 1D,E).

Microencapsulation offers certain advantages over more conventional methods of cell and enzyme immobilization (e.g., calcium alginate gels, k-carra-geenan beads, hydrogels), including (1) improved mass transfer of the substrate and product between the organic and aqueous cell-containing phase resulting from the smaller size of the microcapsules and higher surface-to-volume ratio;

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0,75M MOPS. pH 7.8

biocatalyst

aqueous phase aqueous phase

organic phase b organic phase

stirrer encapsulated biocatalyst

biotransformation solvent

exchange of organic solvent stirrer encapsulated biocatalyst

polymerization solvent exchange of organic solvent polymerization solvent

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