Catalytic Application of 3-D Macroporous Materials

A new route to preparing 3-D ordered macroporous materials through polymer latex templating has been reported. Fig. 1 Electron micrograph of an ordered polymer template

While enzyme immobilisation using mesoporous materials (ca. 6 nm) has been developed in our research group it is unfortunate that the dimensions of many enzymes are too large to fit inside the mesopores: materials with larger pore dimensions (macropores) are needed for this area of research to proceed.

A new route to preparing 3-D ordered macroporous materials through polymer latex (PS or PMMA) templating has been reported (see Fig. 2). These materials possess a pore size ranging from 100-300 nm, which is suitable for supporting biological molecules such as proteins and enzymes. These materials are mainly inorganic oxide-based solids such as SiO₂, TiO₂, Al₂O₃, ZrO₂ etc. but it is the SiO₂ member which is our main interest.

Fig. 2 Scheme illustrating the route to new macroporous solids

The primary problem of enzyme immobilisation is leaching of active enzyme molecules during reactions. Pure siliceous mesoporous materials suffer badly from this problem. Surface functionalised silica shows huge improvement in enzyme retention. Moreover, changing the surface properties can also promote the catalytic activity of the enzyme. For example, impregnation of titanium and vanadium into silica the framework has been shown to improve the catalytic activity of the fusarium solani pisi cutinase enzyme from E-coli WK-6 (an alcoholase) in alcoholysis of butyl acetate. This is accounted for by the change in hydrophilcity of the support surface. A mixed-oxide with 3-D ordered macroporous structure can therefore be useful in enzyme immobilisation.

3-D macroporous silica templated with these PS latex samples, prepared in our laboratory (see Fig. 3), is currently being prepared for testing in protein and enzyme immobilisation.

Fig. 3 Cubic packed polymer latex