472471 Complex Coacervate Core Micelles for the Dispersion and Stabilization of Organophosphate Hydrolase in Organic Solvents

Thursday, November 17, 2016: 5:00 PM
Golden Gate 2 (Hilton San Francisco Union Square)
Carolyn Mills, Allie Obermeyer, Xuehui Dong and Bradley D. Olsen, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA

Complex coacervation is a liquid-liquid phase separation that occurs in solutions of oppositely charged polyelectrolytes. This phenomenon can be exploited to from complex coacervate core micelles (C3Ms) that can be used in a variety of applications in aqueous media, including nanoparticle growth, gene delivery, and MRI contrast agent formulation; however, little work has been done to study the behavior of these C3M systems in hydrophobic environments. Here, we investigate the formation of C3Ms between a positively charged-neutral block copolymer, poly(oligo(ethylene glycol) methacrylate))-b-poly(4-vinyl N-methylpyridyl iodide) (POEGMA-b-qP4VP), and an oppositely charged homopolymer, poly(acrylic acid) (PAA) in two organic solvents—ethanol, a water miscible solvent, and dimethyl methylphosphonate (DMMP), a solvent that is marginally miscible with water. We also investigate the ability of these C3Ms to both disperse and protect the organophosphate hydrolase (OPH) enzyme for use in decontamination of bulk chemical warfare agents.

The formation of C3Ms was first studied in aqueous solution, where dynamic light scattering (DLS) was used to determine the ideal buffer concentration and polymer mixing ratio for micelle formation. Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) confirmed the formation of micellar structures approximately 40 nm in diameter. The same techniques showed formation of similar structures after addition of OPH. C3Ms formed by POEGMA-b-qP4VP and PAA were then transferred into two organic solvents, ethanol and DMMP (which has similar density, water miscibility, molecular weight, chemical structure, and atomic content to chemical warfare agents of interest). The structures formed by the C3M system were compared to those formed by the POEGMA-b-qP4VP block copolymer alone were compared in both solvents using DLS. In both solvents, the structures formed by the block copolymer alone were different from those formed by C3Ms. Interestingly, while the structures formed by the block copolymer alone in DMMP were smaller than those formed by the block copolymer alone in ethanol, the C3Ms formed in DMMP were several nm larger than those formed in ethanol. Fits to SANS data taken in ethanol confirmed the formation of 14.4 ± 0.4 nm diameter structures by the block copolymer alone, and 40.0 ± 0.4 nm diameter structures by the C3M system. TEM was used to confirm the formation of C3Ms in DMMP. Similarly sized structures were observed after the addition of the OPH enzyme. To evaluate the ability of C3Ms to chemostabilize the OPH enzyme, activity against methyl paraoxon was assayed after incubation in both organic solvents. In ethanol, OPH in C3Ms retained 26 ± 1% of its activity, and in DMMP, OPH in C3Ms retained 35 ± 3% of its activity. This is a dramatic improvement over the activity retained by OPH alone after incubation in both of these solvents, which was less than 5%.

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