Efficient Catalysis of Phosphate Ester Hydrolysis by Bare Silica

This work reports the catalysis of bare silica materials (MCM-41, SBA-15, and silica gel) for the complete hydrolyses of bis(2,4-nitrophenyl)­phosphate (BDNPP) and bis(4-nitrophenyl)­phosphate (BNPP), which share the same phosphate diester chemical core with important biological molecules, DNA and RNA, and toxic substances like EA2192 and anatoxin-a(s). Catalytic effects above 7000-fold were observed for the hydrolysis of BNPP, which were consistent with a concerted SN2­(P) mechanism under the action of siloxide and silanol groups that provide water activation by general base catalysis and leaving-group departure stabilization by general acid catalysis, respectively. We also observed that product formation follows a sigmoidal behavior as a result of catalytic effect enhancement following an induction period. This effect is discussed considering cooperative effects caused by silica hydration, which is unchanged upon material reuse affording strong catalytic effects for phosphate diester hydrolyses and no induction periods.