(331e) Engineering a PVDF-Based Biocatalytic Membrane for Caffeine Upcycling

Xanthine derivatives are a group of compounds derived from the purine base xanthine. They include caffeine, theobromine, and theophylline, which are found in coffee, tea, and chocolate, respectively. Xanthine derivatives have a variety of medical applications, including as stimulants, bronchodilators, diuretics, and anti-inflammatory agents. Caffeine (1,3,7-trimethylxanthine) is one of the most abundant sources of methylxanthines, but it has low value, while other compounds such as paraxanthine and 7-methylxanthine cost up to 31,000-times the cost of caffeine. Using an enzyme immobilization technique, biocatalytic membranes can detect and convert low price caffeine to high value paraxanthine and 7-methylxanthine in an enzymatic reaction process. For this project, a CDE protein is covalently attached to a PVDF membrane to give the membrane biocatalytic properties. The CDE protein can catalyze the transformation of 7-methylxanthine into xanthine, which is the second step in the process of caffeine upcycling. There are two different approaches in the chemical grafting of polymer brushes: “grafting to” and “grafting from” methods. We use the “grafting to” approach where polymer molecules react with complementary functional groups located on the membrane surface to form tethered chains. We used a branched polyethylenimine to graft to the solid substrate of PVDF membrane. Subsequently, the primary amine functionalities on the PVDF surface were modified with glutaraldehyde, a coupling agent commonly used for enzyme attachment. The water contact angle (WCA), ATR-FTIR, and BET tests all support that the membrane was modified. Following this, CDE enzymes were attached to the membrane surface to create an enzyme-immobilized membrane. The SEM, WCA, BET, and ATR-FTIR techniques were used to characterize the membranes, and a mass balance was conducted to determine the amount of enzyme attached. Additionally, Bradford reagents tests provided qualitative evidence that enzyme attachment had taken place. The activity of CDE enzyme on the membrane surface can be determined by assessing the capacity of the active immobilized enzymes on the membrane to demethylate 7-methylxanthine to xanthine, detectable by HPLC.