Phospholipid‐Based Catalytic Nanocapsules

The encapsulation and catalytic efficiency of organophosphate hydrolyzing enzymes in polymer‐stabilized nanocapsules is reported. Polymerized vesicles—derived from a headgroup‐polymerizable phospholipid, 1,2‐dipalmitoyl‐sn‐glycero‐3‐phospho‐N‐(2‐hydroxymethyl)‐3,5‐divinylbenzamide (DPPE‐DVBA)—containing enzymes were used as catalytic nanocapsules. Three enzymes, organophosphorus hydrolase (OPH), phosphotriesterase (PTE), and organophosphorus acid anhydrolase (OPAA), were encapsulated in vesicles by incubating them with freeze‐dried vesicles at 55 °C, followed by intermittent vortex‐mixing. Enzyme‐containing vesicles, collected after gel‐filtration, were stabilized by photopolymerization at 254 nm to yield crosslinked catalytic nanocapsules. The nanocapsules containing OPH and PTE showed specific activities of 0.36 and 1.74 μmol mg–1 min–1, respectively, against methyl parathion (MPT), and OPAA‐containing nanocapsules showed a specific activity of 57.1 μmol mg–1 min–1 against diisopropylfluorophosphate. Freeze‐dried, OPH‐ and PTE‐containing nanocapsules showed retentions of 83 % and 85 % specific activity, respectively, upon redispersion in buffer solution. Three‐week, room‐temperature storage of OPH‐containing nanocapsules showed a retention of 18 % enzyme activity. Hydrolysis of MPT in crosslinked DPPE‐DVBA/OPH vesicles showed that hydrophobic MPT permeated through the bilayer membrane of the freeze‐dried nanocapsules, releasing the hydrolysis product para‐nitrophenol, which permeated back to the exogenous dispersion medium leaving the enzymes free to react with freshly permeated MPT in the interior of the nanocapsules.