Metal Cation Micelle Mediated Hydrolysis of Phosphonic Acid Esters

Abstract

p-Nitrophenyl methylphosphonate (PNPMP, 3) and p-nitrophenyl phenylphosphonate (PNPPP, 4) are rapidly hydrolyzed in acidic solutions (pH 3.5−6.0) at 37 °C by excess Zr4+, Ce4+, or Th4+ cations. Brij-35 micelles are employed in the Ce4+ and Th4+ cases. Second-order rate constants (M-1 s-1) with PNPMP are 115 (Zr4+), 53.9 (Ce4+), and 16.9 (Th4+), while for PNPPP they are, respectively, 76.8, 16.1, and 13.1. Relative to water (k 2 = 3.6 × 10-11 M-1 s-1 at 30 °C, pH 7.6), kinetic advantages with Zr4+ or Ce4+ exceed 1012.

Cleavage of phosphate diesters mediated by Zn(II) complex in Gemini surfactant micelles

“…Thus, the true cause of the higher reactivity of HPNP catalytic cleavage in cationic micelles is attributed to the formation of plentiful substrate-catalyst complexes via a supposed "sandwich absorptive mode" (micelle-HPNP-catalyst mode), in which the negative HPNP molecule is sandwiched in the interlayer between the positive micelle and the catalyst. Despite that this proposed sandwich absorptive mode is not like those traditional metallomicelle models [13][14][15][16][17], it is still consistent with a pseudo-intramolecular reaction mechanism described in Section 3.2. Ultimately, the rate of HPNP cleavage mediated by ZnL shows 29.5 times and 12 times the magnitude rate acceleration in Gemini 16-2-16 micelles and CTAB micelles over that in the pure buffer solution, respectively.…”

Comparative studies on reaction of bis(p‐nitrophenyl) phosphate and α‐nucleophiles in cationic micellar media

“…It is in agreement with similar work presenting 2‐hydroxypropyl p ‐nitrophenyl phosphate (HPNP) cleavage in the presence of cationic micelles . They observed ‘sandwich absorptive mode’ (micelle‐HPNP‐catalyst mode), in which the negative HPNP molecule is sandwiched in the interlayer between the positive micelle and the catalyst …”

“…[6] They observed 'sandwich absorptive mode' (micelle-HPNP-catalyst mode), in which the negative HPNP molecule is sandwiched in the interlayer between the positive micelle and the catalyst. [5,[42][43][44][45][46] Effect of head group, chain length, and counter ion…”

Properties of surface-cross-linked micelles probed by fluorescence spectroscopy and their catalysis of phosphate ester hydrolysis

“…HPNPP is often studied as a model compound for RNA hydrolysis. Although the hydrolysis of this and other activated phosphate esters has been studied in micelles, metal ions were generally responsible for the rate acceleration [43][44][45]. Fig.…”