Hydrolysis of carboxylate and phosphate esters using monopyridinium oximes in cationic micellar media

Abstract

The reactions of p-nitrophenyl acetate (PNPA) with a series of monopyridinium oximes, viz. 2-PAM (2-hydroxyiminomethyl-1-methylpyridinium iodide), 3-PAM (3-hydroxyiminomethyl-1-methylpyridinium iodide), and 4-PAM (4-hydroxyiminomethyl-1-methylpyridinium iodide) have been studied in the presence of cationic surfactants of same hydrophobic chain length (C 16 ) within the concentration range of 0.5-6.0 mM at pH 8.0 under the pseudo-first-order condition. The observed rate constant (k obs ) increases with increasing surfactant concentration culminating into a maximum, and this has been analyzed in detail following the concepts of micellar catalysis. The structure-activity relationship of the investigated oximes has been discussed, and 2-PAM was found to be the most reactive among all the three investigated oximes for the cleavage of PNPA. Esterolytic decomposition of pnitrophenyldiphenyl phosphate with oximate ions ( CH NO − ) was followed in cetyltrimethylammonium bromide micelles at pH 9.0, and 4-PAM was the most reactive oxime for the micellar hydrolysis of phosphate ester. The apparent acid dissociation constants (pK a ) of the investigated oximes have been determined spectrophotometrically. C

Oxime functionality in surfactant self-assembly: An overview on combating toxicity of organophosphates

“…We have studied hydrolysis of carboxylate and phosphate esters with mono-pyridinium oximes (8), in mixed micelles with cationic surfactants of same hydrophobic chain length (C 16 ) at pH 8.0 (NPA) and 9.0 (NPDPP) [65]. The observed rate constant (k obs ) increases with increasing surfactant concentration culminating into a maximum, and this has been analyzed in detail following the concepts of micellar catalysis.…”

“…Since last few years, our research group has been engaged in physicochemical and kinetic studies of various oximes and oxime based functionalized surfactants for the hydrolysis of carboxylate, phosphate and sulfonate esters [45,65,66,85,86].…”

Acid Dissociation Constants and Molecular Descriptors of Some Xylene Linked Bispyridinium Oximes

“…The toxicity of organophosphorus (OP) compounds in mammals results from the inhibition of enzyme acetylcholinesterase (AChE, EC 3.1.1.7) which leads to the accumulation of neurotransmitter acetylcholine (ACh) in the synaptic junction of neurons in both the central and peripheral nervous systems (CNS and PNS). This phenomenon triggers the over-rstimulation of nervous system which can be lethal if not timely controlled [2][3][4].…”

O‐Nucleophilicity of Hydroxamate Ions for Cleavage of Carboxylate and Phosphate Esters in Cationic Micelles

“…Hydrolysis and nucleophilic reactions of carboxylate and phosphate esters are involved in many biological processes . The nucleophile‐aided hydrolysis is the most preferred reaction for the detoxification organophosphorus toxic compounds . In this regard, many α‐effect nucleophiles such as o‐ iodosylcarboxylate , peroxides , oximates , hypochlorites , and hydroxamates have been investigated alone or as functionalized surfactants.…”