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Title: Phosphate Ester Bond Hydrolysis Promoted by Lanthanide- 2 Substituted Keggin-type Polyoxometalates Studied by a Combined 3 Experimental and Density Functional Theory Approach
Authors: Luong, Thi Kim Nga
Mihaylov, Tzvetan
Absillis, Gregory
Shestakova, Pavletta
Pierloot, Kristine
Parac-Vogt, Tatjana # ×
Issue Date: 22-Sep-2016
Publisher: American Chemical Society
Series Title: Inorganic Chemistry vol:55 pages:9898-9911
Abstract: 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.
ISSN: 0020-1669
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
Molecular Design and Synthesis
× corresponding author
# (joint) last author

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