A Quantitative Treatment of Dephosphorylation by an Amphiphilic Hydroxamate Ion. The Role of Micellar Charge

Abstract

Comicelles of (Z)-dodecano-N-phenylhydroxamate ion (1b) with cationic and sulfobetaine surfactants effectively accelerate the hydrolysis of p-nitrophenyl diphenyl phosphate (pNPDPP). The surfactants are cetyl trimethyl-and tributylammonium bromide (CTABr and CTBABr respectively), and (tetradecyldimethylammonio)propanesulfonate (SB3-14). Reaction is slower in comicelles with Brij-35, 23-dodecyl ether (C12E23), and much slower in comicelles with sodium dodecyl sulfate (SDS). In all conditions, the hydroxamic acid was fully deprotonated and pNPDPP was fully micellar-bound and, on the basis of NMR data (Langmuir 1997, 13, 6439), it appears that the rate effects are due to differences in the relative locations of pNPDPP and the hydroxamate residue in the interfacial region, which are related to micellar charge. Inhibition of reaction in SB3-14 on addition of ClO4 -, and acceleration in SDS by weakly hydrophilic cations, are understandable in these terms, as are effects of n-dodecyldimethylphosphine oxide and n-decylmethyl sulfoxide on reactivity in SDS. The propiono-N-phenylhydroxamate ion (1a) is an E-Z mixture in water, which complicates comparisons of rate constants of this reaction with pNPDPP in water with those of 1b in micelles.

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

“…At the same time it is not impossible that for the S N 2 reactions taking place in the co-micelles of cationic SFAs with functional detergents a substantial change in the structure of the head group of the inert SFA may lead to a change in the nucleophilicity of the functional fragment. 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].…”

“…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].…”

In silico study on the mechanism of formation of hydrazine and nitrogen in the reactions of excess hydroxylamine with 2,4-dinitrophenyl diethyl phosphate

“…2 The use of a-nucleophiles such as hydrazine, oximes and hydroxylamine as effective dephosphorylating agents is well documented. [3][4][5][6] Being an ambident a-effect nucleophile, hydroxylamine has been studied extensively with phosphate esters. 7 The unique property of hydroxylamine is that the nitrogen is alkylated and acylated, however, in general phosphorylated on oxygen with reaction through the oxygen atom.…”

Enhanced nucleophilic reactivity of hydroxamate ions in some novel micellar systems for the cleavage of Parathion

“…It has been proved that hydroxamate ions are α-nucleophiles [12][13][14]; i.e., they are better nucleophiles than Brønsted relations between nucleophilicity and basicity. Moreover, in the presence of cationic micelles the reactivity of α-nucleophile considerably enhanced.…”