Environmentally Friendly Enzyme Immobilization on MOF Materials

Metal-organic framework (MOF) materials have revolutionized the applications of nanoporous materials. They can be potentially used in separation, storage, and catalysis, among other applications. Since their discovery in 1999 (Li et al. Nature 402:276-279, 1999; Chui Science 283:1148-1150, 1999), more than 20,000 new structures have been synthesized thanks in part to their high compositional versatility. However, only some of them are really stable in water (both in liquid and vapor phase), which limits their employment in other applications. Furthermore, biocatalysis field has been demanding a "universal support" able to encapsulate/immobilize any type of enzyme in a straightforward methodology and, simultaneously, capable of keeping the enzymatic catalytic activity. This requisite set has been a big challenge considering the drastic synthesis conditions required for most of the MOF materials. Thus, a compromise between the development of a well-formed material support and an acceptable enzymatic activity had to be achieved in order to obtain active biocatalysts, ideally prepared in just one step and under sustainable conditions. In this chapter, we describe the protocols about how to synthesize MOF materials in water, under mild conditions and almost instantaneously in the presence of enzymes. The most successful support of these sustainable MOFs was the semicrystalline Fe-BTC MOF material (like the commercial Basolite F300) allowing the development of efficient active biocatalysts (97% with respect to the free enzyme in the case of CALB lipase). Particularly, this enzyme support improves the benefits given by some other MOF-based supports also described in this chapter, like NH2-MIL-53(Al). Furthermore, we present the post-synthesis immobilization approach, which consists firstly in the synthesis or preparation of the respective MOF material (Fe-BTC or NH2-MIL-53(Al)), followed by an enzyme immobilization protocol. As reported in bibliography, MOFs as enzyme supports combine together more active biocatalysts with lower enzyme leaching when compared to other conventional materials. Moreover, MOFs prepared in non-aqueous media (for instance, N,N-dimethylformamide) can also trap enzymes in an otherwise adverse media. These facts bring these biocatalysts closer to industrial employment in even more demanding applications.