382321 Bridging the Gap Between Chemical and Biological Catalysis to Produce Biorenewable Chemicals
Biomass is a renewable source of carbon that has the potential to replace fossil-based resources as the feedstock for producing fuels and chemicals. An attractive option for obtaining biorenewable chemicals from biomass leverages the high efficiency of traditional heterogeneous chemical catalysts to upgrade highly functionalized molecules produced via recent advances in metabolic and enzyme engineering. By such coupling of chemical and biological catalysis it is possible to access molecules not easily obtainable by either discipline alone.
My doctoral research has focused on the challenges and opportunities associated with bridging the gap between chemical and biological catalysis. One key aspect of such strategies is to elucidate reaction networks that stem from a particular biologically-derived intermediate. For example, cortalcerone, which can be derived enzymatically from glucose, can be dehydrated over a Brønsted acid catalyst, such as HCl, to yield furylglyoxal hydrate (FH). In turn, FH has appropriate functionality to be converted to furylglycolic acid (FA), a hydroxy-acid amenable for co-polymerization with lactic acid to yield biorenewable polymers reported to have polystyrene-like properties. FA can be produced from FH via an intramolecular Meerwein-Ponndorf-Verley-Oppenauer hydride shift using a Lewis acid catalyst, such as a Sn-containing beta zeolite. Furthermore, FA can be produced in one pot from cortalcerone using a bifunctional Al-containing Sn-beta zeolite possessing both Brønsted and Lewis sties. In another example, triacetic acid lactone (TAL), a highly functionalized molecule obtained via polyketide biosynthesis, can be upgraded to 11 potential end products and intermediates, including bifunctional ketones via decarboxylation of TAL or its hydrogenated analogue, lactones via dehydration of hydrogenated TAL, and unsaturated acids, including the common food preservative sorbic acid, via ring opening of these lactones.
Another key aspect of coupling chemical and biological catalysis is to elucidate the influence of biogenic impurities on heterogeneous catalysts. For example, amino acids can result in deactivation of the metal catalysts used for TAL hydrogenation. This effect can, however, be mitigated by appropriate catalyst design. Overcoating a traditional Pd catalyst with poly(vinyl alcohol) (PVA) results in the formation of microenvironments surrounding the metal nanoparticles that prevent adsorption of such species. For example, the Pd catalyst used in TAL hydrogenation loses 83% of its activity after 14 hours of exposure to methionine (a representative, sulfur-containing amino acid), but a PVA-overcoated catalyst is stable under the same conditions. Indeed, combining the use of a PVA overcoat to prevent adsorption of amino acids with the use of PdAu bimetallic nanoparticles to prevent deposition of carbonaceous residues from TAL decomposition, it is possible to decrease the deactivation rate constant by an order of magnitude when upgrading TAL recovered from spent cell culture medium. My future research will continue to focus on these types of challenges and opportunities that are associated with integrating chemical and biological catalysis, with the ultimate goal of efficiently producing high-value chemicals from biomass.