Polyoxometalate-metal organic framework-lipase: An efficient green catalyst for synthesis of benzyl cinnamate by enzymatic esterification of cinnamic acid.

Iron-carboxylate (MIL-100(Fe)) and HKUST-1 (Cu(BTC), BTC=1,3,5-benzenetricarboxylic acid) as nanoporous metal organic framework supports were compared for immobilization of porcine pancreatic lipase (PPL). These immobilizations improved thermal, pH and operational stability of PPL compared to the soluble enzyme. Stability of MIL-100(Fe) was better than HKUST-1 as support. MIL-100(Fe) encapsulated Keggin phosphotungstic acid HPWO (PW) (PW@MIL-100(Fe)) was synthesized to develop novel enzyme immobilized system and characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and Barrett Joyner Halenda (BJH) analysis. Relative activity for immobilized lipase on PW@MIL-100(Fe) was more than MIL-100(Fe) in pH range of 3-9. At the elevated temperature of 70°C, the PW@MIL-100(Fe) was the most stable one. PW@MIL-100(Fe)/PPL substrate exhibited the higher stability at 4°C and 25°C, along with other supports. Moreover, PW@MIL-100(Fe) was chosen as the best support for immobilization of PPL and was also applied for the synthesis of benzyl cinnamate by enzymatic esterification of cinnamic acid. The immobilized enzyme retained 90.4% of its initial activity during synthesis of benzyl cinnamate after 5 successive catalytic rounds and reached 80.0% yield after 8 reuses.