Evidence of Enhanced Reactivity of DAAP Nucleophiles toward Dephosphorylation and Deacylation Reactions in Cationic Gemini Micellar Media

Bhattacharya, Santanu and Kumar, Praveen V (2004) Evidence of Enhanced Reactivity of DAAP Nucleophiles toward Dephosphorylation and Deacylation Reactions in Cationic Gemini Micellar Media. In: Journal of Organic Chemistry, 69 (2). pp. 559-562.

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Abstract

4,4'-(Dialkylamino)pyridine (DAAP)-based compounds 1-4 catalytically cleave hydrophobic organophosphate and carboxylate esters in various host micellar aggregates at mildly alkaline pH. The role of the micellar reaction medium in such esterolytic reactions has been carefully examined in this work. The cationic gemini surfactant based micellar aggregates provide more than 1 order of magnitude better reaction medium for the above reactions than their conventional single-chain, single-charge, cationic cetyl trimethylammonium bromide (CTABr) micelles. The catalytic turnover behavior of DAAP nucleophiles in the presence of excess substrates is also retained in Gemini micellar media. Realization of a green chemical process in solution involves appropriate choice of a safe, nontoxic, and inexpensive solvent. Despite solubility limitations, water remains the most obvious choice for this purpose. However,the use of water as a medium for promoting organic reactions has been rather neglected in the development of organic reactions and synthesis, although it is the solvent in which almost all biochemical processes take place. When the chemistry involves conversion of large stockpiles of toxic molecules into nontoxic end products (decontamination), the use of aqueous media is even more appropriate. For instance, many chemical warfare and persistent agents (Chart S1, Supporting Information), such as paraoxon, parathion, VX, or sarin, etc., are hydrophobic phosphorus(V) esters, and their decontamination often involves dephosphorylation or hydrolysis. Phosphotriesters and their derivatives are toxic to both target and nontargeted organisms. Paraoxon and parathion are most often responsible for the poisoning of agricultural workers. Remediation of such contamination is therefore an urgent goal. However,the extreme toxicity of such compounds often mandates that most laboratory research employ simulants instead of the actual compounds. Since these esters or their standard simulant,p-nitrophenyl diphenyl phosphate (PNPDPP), are not water-soluble, aqueous solutions of surfactants (micelles or other aggregates) are generally employed as a reaction medium for the cleavage of such organophosphate esters. In such a medium, organic reactants are partitioned into the surfactant aggregates by electrostatic and hydrophobic interactions, and the observed rate accelerations are largely due to the increased localization of the reactants and also of the typical physiochemical properties of micellar environment, which are significantly different from those of the bulk solvents. Chemical means of achieving efficient destruction of such toxic organophosphate esters remains an active area of much research, with attention focused recently on peroxides, iodosoarene carboxylates, and metallomicelles employed in cetyltrimethylammonium (CTA) surfactant micelles as a medium.Recently, syntheses of surfactants of several other molecular architectures have been reported which upon solubilization in water form different types of micelles. Among the new synthetic surfactants, gemini surfactants appear quite attractive as hosts, in that the aqueous solutions of such systems often display unique properties that can result in improved performance. However, most papers on gemini surfactants have focused on the investigation of their specific aggregation properties, with a very few studies on reaction rates.

Item Type:	Journal Article
Publication:	Journal of Organic Chemistry
Publisher:	American Chemical Society
Additional Information:	The copyright belongs to American Chemical Society.
Department/Centre:	Division of Chemical Sciences > Organic Chemistry
Date Deposited:	25 Aug 2008
Last Modified:	19 Sep 2010 04:28
URI:	http://eprints.iisc.ac.in/id/eprint/7294

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