Enzymes are highly selective and active biocatalysts that can catalyze reactions at much milder conditions than heterogeneous catalysts. However, in solution enzymes are not reusable, can not be used in a flow cell, and can be difficult to separate from the products. By immobilizing enzymes onto a solid support, it is possible to create a catalytic system that combines the activity and selectivity of enzymes with the reusability and ease of separation of heterogeneous catalysis. This immobilization process also allows for enzymes to be studied with surface-specific techniques.
One method to immobilize enzymes is through DNA directed immobilization (DDI). This method uses the selective binding of complementary DNA strands to immobilize enzymes in an ordered and selective manner. The activity of aldolase—an enzyme in the glycolysis pathway that catalyzes the C-C bond breaking step—was found to be significant after conjugation to DNA and subsequent immobilization onto functionalized glass surfaces. These immobilized enzyme surfaces were found to be reusable for multiple reaction cycles and regeneratable by dehybridizing the DNA strands.
These DNA and enzyme modified surfaces were studied by using sum frequency generation (SFG) vibrational spectroscopy. This showed that quartz modified with double-stranded DNA has an ordered structure, while single-stranded DNA surfaces are more disordered due to the lack of rigidity.
Alcohol dehydrogenase, which catalyzes the conversion of a primary or secondary alcohol into an aldehyde or ketone, can be immobilized onto the mesoporous silica material SBA-15 through non-specific physical adsorption. These immobilized enzymes are active upon adsorption but are prone to significant leaching. The specificity of immobilized alcohol dehydrogenase towards longer alcohols was found to be slightly diminished.
This dissertation builds on existing knowledge of enzyme immobilization methods and surface science characterization techniques. This research shows that immobilized enzymes are a promising method for creating novel catalytic systems. The results show the importance of limiting the leaching of enzymes off of the support for potential catalytic applications.