Enhanced Enzymatic Activity of OPH in Ammonium-Functionalized Mesoporous Silica: Surface Modification and Pore Effects

Abstract

Organophosphorus hydrolase (OPH) is an enzyme capable of rapidly degrading organophosphorus toxins, such as phosphorus-based nerve agents and pesticides. In these studies, OPH was immobilized within the pores of spherical mesoporous silica particles and the rate of hydrolysis of diethyl-4-nitrophenyl phosphate (paraoxon) was correlated to surface functionalization (acid, amine, or ammonium) and pore diameter. Conversion rates were measured by using a novel 31P NMR method developed by our group. After immobilization within ammonium-modified particles, OPH was more active for paraoxon degradation than free OPH, while amine- or acid-modified particles led to decreased activities. OPH immobilized within the pores of intermediate diameter (6 nm) also showed the highest activities. We also varied the amount of ammonium coverage and found that 14–20% w/w of the ammonium organosilane per particle was sufficient to observe enhancement of OPH activity.