Silver ion binding to the organophosphorus pesticide diazinon and hydrolytic pathways revealed by mass spectrometric and NMR studies

Abstract

This paper describes the first study of the interactions of Ag + with the organophosphorus (OP) insecticide, diazinon, 1. Electrospray ionization mass spectrometry (ESI-MS) with corroborative collision-induced dissociation-mass spectrometry (CID-MS), demonstrates that 1 forms a bidentate chelate with Ag + . The hydrolysis products of 1, the pyrimidinol (PY) and O,Odiethylphosphorothioic acid (PA), are also found to bind to Ag + via N (PY) and S (PA) Lewis base sites, respectively. 31 P and 1 H nuclear magnetic resonance (NMR) spectra in solution, followed over time with varying ratios of Ag + to 1, confirm the MS evidence and show Ag + catalysis of hydrolysis (e.g. complete hydrolysis of 1 in ca. 5 minutes (first-order half-life = 3 x 10 -4 day; k obs = 2 x 10 3 day -1 ) with equimolar Ag + ; this represents an approximate 150,000-fold enhancement in hydrolysis with Ag + as compared to its absence. A mechanism for the enhanced hydrolysis is proposed in which bidentate binding of Ag + to S of the P=S electrophilic site in tandem with binding to N of the leaving group stabilizes the S N 2(P) transition state relative to the ground state; this effect is described by qualitative energy profiles.Keywords: Electrospray ionization mass spectrometry (ESI-MS), Collision-induced dissociation (CID), P-31 and H-1 nuclear magnetic resonance (NMR) spectrometry, Silver ion catalysis

Multiparameter kinetic analysis of alkaline hydrolysis of a series of aryl diphenylphosphinothioates: models for P=S neurotoxins

“…Therefore, the present results are relevant to our understanding of hydrolytic degradation of OP pesticides and to the thio effect that distinguishes between P=O neurotoxins and their P=S analogues. The present findings, combined with previously published results, suggest that other systems, in which the hydrolytic mechanism for OP neurotoxins was presumed to be concerted, likely do proceed via the S N 2(P) route where the leaving groups are good, ie, p K a (LG‐H, the conjugate acid of the leaving group) < 10.…”

“…Avenues for enhancement of decomposition of OP neurotoxins/simulants have been probed in numerous studies, including the following: use of highly reactive α‐nucleophiles (HOO − and various oximate anions), use of surfactants, the catalytic effects of alkali metal cations, in alcoholic media, the catalysis elicited by metal ions, under environmental conditions, and under optimal degradation conditions . Under such optimal conditions impressive catalytic enhancements for methanolysis of OP pesticides have been reported, ranging from 20,000‐fold to millions‐fold, and to billion‐fold with La 3 + (bridged methoxide lanthanum dimers) and from million‐fold to 100 billion‐fold with Cd 2 + , Mn 2 + , and a Pd 2 + complex .…”

“…For P=O phosphate, phosphonate, and phosphinate esters, both addition‐elimination and S N 2(P) mechanisms have been found or presumed . It has been suggested that for phosphate triesters, depending on the nature of the nucleophile, leaving group, and solvent, there should be a continuum of mechanisms based upon recent computational and kinetic studies …”

Hydrolysis and Photolysis Kinetics, and Identification of Degradation Products of the Novel Bactericide 2-(4-Fluorobenzyl)-5-(Methylsulfonyl)-1,3,4-Oxadiazole in Water

“…Moreover, the hydrolysis of pesticides was reported in some papers. Wyer et al [16] proposed the enhanced hydrolysis of diazinon, in which bidentate binding of Ag + to S of the P = S electrophilic site in tandem with binding to N of the leaving group stabilizes the SN 2 (P) transition state relative to the ground state. Zhang et al [17] investigated the hydrolysis of chlorpyrifos and diazinon in aqueous solution under ultrasonic irradiation.…”

An Au(iii)–amino alcohol complex for degradation of organophosphorus pesticides

“…5,6 The natural degradation of OP pesticides occurs by homogeneous and heterogeneous hydrolysis, 7,8 oxidation, 9 photolysis 10 and biodegradation, 11 whereas thermal, enzymatic or photochemical degradation, as well as chemical treatments through the use of strong oxidants or nucleophiles, are among the methods used for their destruction. [12][13][14][15] Some reports about the use of metal cations as catalysts in the hydrolysis of thionophosphates have been described 16,17 but, to the best of our knowledge, no examples related to dithiophosphates have been reported to date. On the other hand, many of the procedures used for the hydrolysis of dithiophosphates lead to transformation products (TPs), which are even more toxic than the parent compound.…”