化学
镧系元素
磷酸盐
水解
密度泛函理论
无机化学
高分子化学
计算化学
有机化学
离子
作者
Thị Kim Nga Lương,Tzvetan Mihaylov,Gregory Absillis,Pavletta Shestakova,Kristine Pierloot,Tatjana N. Parac‐Vogt
出处
期刊:Inorganic Chemistry
[American Chemical Society]
日期:2016-09-22
卷期号:55 (19): 9898-9911
被引量:22
标识
DOI:10.1021/acs.inorgchem.6b01802
摘要
Hydrolytic cleavage of 4-nitrophenyl phosphate (NPP), a commonly used DNA model substrate, was examined in the presence of series of lanthanide-substituted Keggin-type polyoxometalates (POMs) [Me2NH2]11[CeIII(PW11O39)2], [Me2NH2]10[CeIV(PW11O39)2] (abbreviated as (CeIV(PW11)2), and K4[EuPW11O39] by means of NMR and luminescence spectroscopies and density functional theory (DFT) calculations. Among the examined complexes, the Ce(IV)-substituted Keggin POM (CeIV(PW11)2) showed the highest reactivity, and its aqueous speciation was fully determined under different conditions of pD, temperature, concentration, and ionic strength by means of 31P and 31P diffusion-ordered NMR spectroscopy. The cleavage of the phosphoester bond of NPP in the presence of (CeIV(PW11)2) proceeded with an observed rate constant kobs = (5.31 ± 0.06) × 10–6 s–1 at pD 6.4 and 50 °C. The pD dependence of NPP hydrolysis exhibits a bell-shaped profile, with the fastest rate observed at pD 6.4. The formation constant (Kf = 127 M–1) and catalytic rate constant (kc = 19.41 × 10–5 s–1) for the NPP-Ce(IV)-Keggin POM complex were calculated, and binding between CeIV(PW11)2 and the phosphate group of NPP was also evidenced by the change of the chemical shift of the 31P nucleus in NPP upon addition of the POM complex. DFT calculations revealed that binding of NPP to the parent catalyst CeIV(PW11)2 is thermodynamically unlikely. On the contrary, formation of complexes with the monomeric 1:1 species, CeIVPW11, is considered to be more favorable, and the most stable complex, [CeIVPW11(H2O)2(NPP-κO)2]7–, was found to involve two NPP ligands coordinated to the CeIVcenter of CeIVPW11 in the monodentate fashion. The formation of such species is considered to be responsible for the hydrolytic activity of CeIV(PW11)2 toward phosphomonoesters. On the basis of these findings a principle mechanism for the hydrolysis of NPP by the POM is proposed.
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