Effects of Headgroup Structure on Dephosphorylation of <i>p</i>-Nitrophenyl Diphenyl Phosphate by Functional Oximate Comicelles

Bunton, Clifford A.; Foroudian, Houshang J.; Gillitt, Nicholas D.

doi:10.1021/la981138m

Langmuir

1999

DOI: 10.1021/la981138m

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Effects of Headgroup Structure on Dephosphorylation of p-Nitrophenyl Diphenyl Phosphate by Functional Oximate Comicelles

Clifford A. Bunton

Houshang J. Foroudian

Nicholas D. Gillitt

Abstract: Rate constants of reaction of n-dodecyl [2-(hydroximino)-2-phenylethyl]dimethylammonium bromide (DHDBr) with p-nitrophenyl diphenyl phosphate in comicelles with inert surfactants, at pH such that the oximate zwitterion (DHD) is formed quantitatively, depend on the mole fraction of DHD to total surfactant. Second-order rate constants of reaction in the micellar pseudophase decrease in the following sequence of inert surfactant headgroups: phosphine oxide ≈ sulfoxide ≈ pyrrolidinone > Me3N+ > sulfobetaine > Bu3… Show more

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Cited by 24 publications

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“…(5) and (6), while the k 2 m values were obtained on the assumption that V m = 0.40 L/mol [7]. If, however, it is assumed that V m = 0.37 L/mol, as in the case of the cationic micelles of CTAB [12], the differences in the k 2 m values compared with those presented in Table 1 do not exceed 10%. The reactivity of the functional detergents follows the acid ionization constants of the a-nucleophilic group.…”

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Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

et al. 2008

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Functional detergents (FD) based on pyridine and containing aldoximate, ketoximate, and hydroxamate groups were synthesized. Their reactivity in FD/CTAB comicelles toward 4-nitrophenyl 4-toluenesulfonate (NPTS), diethyl phosphate (NPDEP), and diethylphosphonate (NPDEPS) in weakly alkaline media was investigated. Functional detergents based on pyridine are effective in the decomposition of ecotoxicants; the half-lives for the transformation of the substrates into the reaction products in the presence of a functional detergent containing, for example, a ketoximate group amounts to~40 s (NPTS),~120 s (NPDEP), and~5 s (NPDEPS). By analyzing the results it was possible to establish the paths to further modification of the head group of the surfactant, i.e., by varying the structure of the oximate group at various positions of the pyridinium ring aimed at the production of low-basicity functional detergents.Functional detergents containing a heterocycle (pyridinium, imidazolium, etc.) and a fragment of an a-nucleophile in the head group are effective supernucleophilic reagents in the decomposition of phosphate esters -model analogs of pesticides, toxic warfare agents, etc. [1][2][3][4][5][6][7][8][9]. Modifications of the surfactants and the creation of new compounds were directed at the production of substances that make it possible to achieve the highest observable rates of decomposition of ecotoxicants under "mild" experimental conditions and in particular in media with acidity close to neutral. It is such compounds that are of particular interest from the practical point of view -the production of antidotes and supernucleophilic reagents that form the basis of degassing systems [1][2][3]5]. By varying the structure of the a-nucleophilic fragment it is possible to synthesize detergents in which the functional group will be fully ionized at pH £ 10.0.The present work examines the reactivity, the micellar effects of functional detergents (I)-(III), and the nucleophilicity of their methyl analogs (Ia)-(IIIa) in relation to 4-nitrophenyl diethylphosphonate (NPDEPS), diethyl phosphate (NPDEP), and 4-toluenesulfonate (NPTS). The functional detergents (II) and (III) were obtained for the first time.The direction of the investigation was chosen for the following reasons: The oximate and hydroxamate anions are typical a-nucleophiles that react anomalously quickly with organophosphorus compounds (OPC) [1][2][3][4][5][6][7][8]; oximes are widely used as antidotes, and the creation and investigation of inhibited cholinesterase reactivators based on them are currently being 292 0040-5760/08/4405-0292

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Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

et al. 2008

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“…Second, on the basis of the k ob -C 0 relationship the limiting rate of decomposition of NPDEP is reached at C 0 » (4-6)·10 -4 M. In view of the value of CMC = 1.6·10 -4 , determined in [1], and the fraction of bonded substrate a S ³ 0.9 the bonding constant of NPDEP must be~10 4 L/mol, which seems unlikely. Such a bonding constant is typical of very hydrophobic substances and of 4-nitrophenyl diphenyl phosphate in particular [3]. For NPDEP the value of K S hardly exceeds~5·10 2 L/mol [7][8][9], and the fraction of bonded substrate a S £ 0.2 (with C 0 = 4·10 -4 M).…”

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confidence: 94%

“…Starting from the molecular weight of II and the density of the surfactant, which is taken as equal to 0.9 ± 1.1 g/mL [12], the value of V m for II will amount to~0.43 L/mol. The partial molar volume for CTAB is usually assumed to be equal to~0.37 L/mol [3]. Taking account of the foregoing, we used the value V m » 0.4 L/mol during determination of the k 2 m values presented in Table 2.…”

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confidence: 99%

Structure of the head group, nucleophilicity, and micellar effects of functional detergents in acyl transfer reactions

et al. 2008

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The micellar effects of 1-cetyl-2-methyl-3-(2-hydroxyiminopropyl)imidazolium and 1-cetyl-3-hydroxyiminomethylpyridinium halides in acyl transfer reactions (phosphoryl, phosphonyl, and toluenesulfonyl) were investigated. Variation of the nature of the head group does not lead to change in the reactivity of the oximate group, while the nucleophilicity follows the basicity of the functional fragment. The increase of the observed reaction rates during transfer of the disintegration of the substrates from water to the micellar pseudophase is due both to concentration of the reagents and to change in the reactivity of the oximate group. The new detergent 1-cetyl-2-methyl-3-(2-hydroxyiminopropyl)imidazolium chloride is one of the most effective functional surfactants in the decomposition of organophosphorus compounds. Key words: functional surfactants based on pyridine and imidazole, nucleophilicity, micellar effects.Functional surfactants containing an a-nucleophilic fragment in the head group are usually characterized both by high nucleophilic reactivity and by effective solubilization of electrically neutral polar substrates, including excotoxicants of organophosphorus type [1-10]. During the design of new functional detergents an important role is played by the true solubility of the surfactant in water, the basicity of the functional group, and its reactivity. However, the introduction of the functional fragment often leads to a decrease in the solubility of the surfactant in water [1,2,5,8]. Therefore, during study of the micellar effects of such detergents, as during their use in systems for the decomposition of excotoxicants, it is necessary to introduce an inert surfactant -a co-detergent, and this makes the system multicomponent and less attractive from the practical standpoint. The nucleophilicity of functional detergents can be predicted on the basis of the reactivity of analogs not forming micelles [1,2,[7][8][9][10]. This opens up the possibility of specific modification of the structure of the surfactant with the aim of producing compounds with the required level of nucleophilicity. This is the approach that we used during the creation of functional detergents based on imidazole [7][8][9]. With variation of the position of the oximate group in the series of hydroxyiminomethyl-1-cetylpyridinium halides the variation of the observed rates of decomposition of 4-nitrophenyl diethyl phosphate corresponds likewise to the variation of the basicity of the a-nucleophilic fragment in hydroxyimino-1-methylpyridinium halides [1]. It is important to note that for oximes that are not micelle-forming compounds there is a single Brönsted relationship onto which the points for oximes containing both an imidazole ring and a pyridinium ring fit [11]. In so far as analysis of the experimental results in [1] in terms of the existing models for description of micellar effects was not made 0040-5760/08/4402-0093

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“…Thus, the k 2 m value remains practically constant for the reaction with 4-nitrophenyldiphenylphosphate in the IV/cationic SFA co-micelles [9]. However, k 2 m increases by almost twice in the transition from the IV/CTAB co-micelles to the V/cetyltributylammonium bromide co-micelles [10]. [7] 36.5 b [7] 18 260 (520) [7] 360 b [7] 180 [7] 250 ( [7] 14 d [7] 100 d [7] Thus, analysis of the experimental results indicates that the nucleophilicity of the specific functional groups of SFAs I-III does not undergo substantial changes with variation in the nature of the head group of the inert (cationic) SFA and the fraction of the functional detergent in the co-micelle.…”

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confidence: 92%

“…In the case of the reactions of the anionic nucleophile (or anionic specific fragment of the functional SFA [7,9,10]) with an uncharged substrate the choice of a cationic SFA was more reasonable [1]. CTAC and CTAB (cetyltrimethylammonium chloride and bromide, commercially available detergents) are widely used for studying micellar effects [2].…”

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The effect of the nature of the head group on the micellar effects of functional/cationic co-micelles in acyl transfer reactions

et al. 2007

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toluenesulfonic acids was investigated. It was shown that the nucleophilicity of the functional groups in the surfactant does not undergo substantial changes with variation in the nature of the head group of the cationic surfactant and the fraction of functional detergent in the co-micelle. This makes it possible to create systems that decompose organophosphorus substrates unusually quickly even with small contents of the functional surfactant. The use of organized molecular systems, including micelles and microemulsions based on surfactants (SFA) opens up wide possibilities for the control of reaction rates [1-3]. Most of the examples of the effect of micelles on the rate of chemical processes relate to the reactions of anionic nucleophiles with organic substrates in the presence of cationic micelles [2]. One of the important regions of application of the micellar effects of surfactants is the problem of the decomposition and utilization of ecotoxicant substrates of the organophosphorus type. It requires the search for and construction of effective systems characterized by high nucleophilicity and solubilizing power in relation to organophosphorus compounds (OPC) [3][4][5]. A promising method of modifying a surfactant involves the creation of functional SFAs by introducing functional groups with given properties into the head group [2,4]. As the basis of highly effective micellar systems in the decomposition of organophosphorus compounds we proposed [5-7] a new class of functional detergents, containing an imidazole ring and typical fragments of a-nucleophiles -oximate (I), hydroxamate (II), and amidoximate (III) groups.Earlier we had shown that the micelles of functional surfactants I-III and their co-micelles with cationic surfactantscetyltrimethylammonium chloride (CTAC) -decompose the 4-nitrophenyl esters of diethylphosphoric (NPDEP), 0040-5760/07/4301-0035

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Effects of Headgroup Structure on Dephosphorylation of p-Nitrophenyl Diphenyl Phosphate by Functional Oximate Comicelles

Cited by 24 publications

References 64 publications

Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

Structure of the head group, nucleophilicity, and micellar effects of functional detergents in acyl transfer reactions

The effect of the nature of the head group on the micellar effects of functional/cationic co-micelles in acyl transfer reactions

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