Phosphate Ester Bond Hydrolysis Promoted by Lanthanide-Substituted Keggin-type Polyoxometalates Studied by a Combined Experimental and Density Functional Theory Approach.

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) [MeNH][Ce(PWO)], [MeNH][Ce(PWO)] (abbreviated as (Ce(PW)), and K[EuPWO] by means of NMR and luminescence spectroscopies and density functional theory (DFT) calculations. Among the examined complexes, the Ce(IV)-substituted Keggin POM (Ce(PW)) showed the highest reactivity, and its aqueous speciation was fully determined under different conditions of pD, temperature, concentration, and ionic strength by means of P and P diffusion-ordered NMR spectroscopy. The cleavage of the phosphoester bond of NPP in the presence of (Ce(PW)) proceeded with an observed rate constant k = (5.

Probing Polyoxometalate-Protein Interactions Using Molecular Dynamics Simulations.

The molecular interactions between the Ce -substituted Keggin anion [PW O Ce(OH ) ] (CeK) and hen egg-white lysozyme (HEWL) were investigated by molecular dynamics simulations. The analysis of CeK was compared with the Ce -substituted Keggin dimer [(PW O ) Ce] (CeK ) and the Zr -substituted Lindqvist anion [W O Zr(OH )(OH)] (ZrL) to understand how POM features such as shape, size, charge, or type of incorporated metal ion influence the POM⋅⋅⋅protein interactions. Simulations revealed two regions of the protein in which the CeK anion interacts strongly: cationic sites formed by Arg21 and by Arg45 and Arg68.

Detailed Mechanism of Phosphoanhydride Bond Hydrolysis Promoted by a Binuclear Zr(IV)-Substituted Keggin Polyoxometalate Elucidated by a Combination of (31)P, (31)P DOSY, and (31)P EXSY NMR Spectroscopy.

A detailed reaction mechanism is proposed for the hydrolysis of the phosphoanhydride bonds in adenosine triphosphate (ATP) in the presence of the binuclear Zr(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (ZrK 2:2). The full reaction mechanism of ATP hydrolysis in the presence of ZrK 2:2 at pD 6.4 was elucidated by a combination of (31)P, (31)P DOSY, and (31)P EXSY NMR spectroscopy, demonstrating the potential of these techniques for the analysis of complex reaction mixtures involving polyoxometalates (POMs).

Reactivity of Dimeric Tetrazirconium(IV) Wells-Dawson Polyoxometalate toward Dipeptide Hydrolysis Studied by a Combined Experimental and Density Functional Theory Approach.

Detailed kinetic studies on the hydrolysis of glycylglycine (Gly-Gly) in the presence of the dimeric tetrazirconium(IV)-substituted Wells-Dawson-type polyoxometalate Na14[Zr4(P2W16O59)2(μ3-O)2(OH)2(H2O)4] · 57H2O (1) were performed by a combination of (1)H, (13)C, and (31)P NMR spectroscopies. The catalyst was shown to be stable under a broad range of reaction conditions. The effect of pD on the hydrolysis of Gly-Gly showed a bell-shaped profile with the fastest hydrolysis observed at pD 7.

Hydrolysis of the RNA model substrate catalyzed by a binuclear Zr(IV)-substituted Keggin polyoxometalate.

The reactivity and solution behaviour of the binuclear Zr(IV)-substituted Keggin polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (ZrK 2 : 2) towards phosphoester bond hydrolysis of the RNA model substrate 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP) was investigated at different reaction conditions (pD, temperature, concentration, and ionic strength). The hydrolysis of the phosphoester bond of HPNP, followed by means of (1)H NMR spectroscopy, proceeded with an observed rate constant, kobs = 11.5(±0.

Highly Amino Acid Selective Hydrolysis of Myoglobin at Aspartate Residues as Promoted by Zirconium(IV)-Substituted Polyoxometalates.

SDS-PAGE/Edman degradation and HPLC MS/MS showed that zirconium(IV)-substituted Lindqvist-, Keggin-, and Wells-Dawson-type polyoxometalates (POMs) selectively hydrolyze the protein myoglobin at Asp-X peptide bonds under mildly acidic and neutral conditions. This transformation is the first example of highly sequence selective protein hydrolysis by POMs, a novel class of protein-hydrolyzing agents. The selectivity is directed by Asp residues located on the surface of the protein and is further assisted by electrostatic interactions between the negatively charged POMs and positively charged surface patches in the vicinity of the cleavage site.

Eu(III) luminescence and tryptophan fluorescence spectroscopy as a tool for understanding interactions between hen egg white lysozyme and metal-substituted Keggin type polyoxometalates.

The interaction between the lacunary Keggin K7PW11O39, the Eu(III)-substituted Keggin K4EuPW11O39 (Eu-Keggin) and the Ce(IV)-substituted Keggin [Me2NH2]10[Ce(PW11O39)2] (Ce-Keggin) polyoxometalates (POMs), and the proteins hen egg white lysozyme (HEWL) and the structurally homologous α-lactalbumin (α-LA) was studied by steady state and time-resolved Eu(III) luminescence and tryptophan (Trp) fluorescence spectroscopy. The excitation spectrum of Eu-Keggin at lower concentrations ([Eu-Keggin]<100 μM) is dominated by a ligand-to-metal charge transfer band (291 nm). For higher concentrations ([Eu-Keggin]>250 μM) the (5)L6←(7)F0 transition becomes the most intense peak.

Multinuclear diffusion NMR spectroscopy and DFT modeling: a powerful combination for unraveling the mechanism of phosphoester bond hydrolysis catalyzed by metal-substituted polyoxometalates.

A detailed reaction mechanism is proposed for the hydrolysis of the phosphoester bonds in the DNA model substrate bis(4-nitrophenyl) phosphate (BNPP) in the presence of the Zr(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]⋅7 H2O (ZrK 2:2) at pD 6.4. Low-temperature (31)P DOSY spectra at pD 6.

Selective hydrolysis of oxidized insulin chain B by a Zr(IV)-substituted Wells-Dawson polyoxometalate.

We report for the first time on the selective hydrolysis of a polypeptide system by a metal-substituted polyoxometalate (POM). Oxidized insulin chain B, a 30 amino acid polypeptide, was selectively cleaved by the Zr(IV)-substituted Wells-Dawson POM, K15H[Zr(α2-P2W17O61)2]·25H2O, under physiological pH and temperature conditions in aqueous solution. HPLC-ESI-MS, LC-MS/MS, MALDI-TOF and MALDI-TOF MS/MS data indicate hydrolysis at the Phe1-Val2, Gln4-His5, Leu6-Cys(SO3H)7, and Gly8-Ser9 peptide bonds.

Molecular origin of the hydrolytic activity and fixed regioselectivity of a Zr(IV) -substituted polyoxotungstate as artificial protease.

A multitechnique approach has been applied in order to identify the thermodynamic and kinetic parameters related to the regioselective hydrolysis of human serum albumin (HSA) promoted by the Wells-Dawson polyoxometalate (POM), K15 H[Zr(α2 -P2 W17 O61 )2 ]. Isothermal titration calorimetry (ITC) studies indicate that up to four POM molecules interact with HSA. While the first interaction site is characterized by a 1:1 binding and an affinity constant of 2×10(8)  M(-1) , the three remaining sites are characterized by a lower global affinity constant of 7×10(5)  M(-1) .

Integrating 31P DOSY NMR spectroscopy and molecular mechanics as a powerful tool for unraveling the chemical structures of polyoxomolybdate-based amphiphilic nanohybrids in aqueous solution.

Novel organic-inorganic hybrids of various sizes were generated by reaction of 1,8-octanediphosphonic acid (ODP) and (NH4)6Mo7O24 in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH4)6Mo7O24 concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by (1)H, (31)P, and (95)Mo NMR spectroscopy.

Regioselective hydrolysis of human serum albumin by Zr(IV)-substituted polyoxotungstates at the interface of positively charged protein surface patches and negatively charged amino acid residues.

Complexes comprising the Lewis acidic Zr(IV) metal and protein binding polyoxotungstate ligands of Lindqvist-, Keggin- and Wells-Dawson-type were found to region selectively hydrolyze human serum albumin at four distinct positions. Higher reactivities were found for structures with higher polyoxometalate charges and the cleavage positions were found in protein regions of mixed charge. Both findings suggest an electrostatic nature of the observed reactivity.

Molecular interactions between serum albumin proteins and Keggin type polyoxometalates studied using luminescence spectroscopy.

The interaction between the plenary Keggin H3PW12O40, lacunary Keggin K7PW11O39 and the Eu(III)-substituted Keggin K4EuPW11O39 (Eu-Keggin) type polyoxometalates (POMs), and the proteins human and bovine serum albumin (HSA and BSA) was studied using steady state and time-resolved Eu(III) luminescence and tryptophan (Trp) fluorescence spectroscopy. The excitation spectrum of the Eu-Keggin POM is dominated by a ligand-to-metal charge transfer band at 291 nm. In the absence of proteins, the number of water molecules coordinated in the first coordination sphere of the Eu(III) center of Eu-Keggin was determined to be 4, indicating that Eu(III) occurs as a 1 : 1 isomer in solution.

Amino acid side chain induced selectivity in the hydrolysis of peptides catalyzed by a Zr(IV)-substituted Wells-Dawson type polyoxometalate.

In this paper the reactivity of K15H[Zr(α2-P2W17O61)2]·25H2O (1), a Zr(IV)-substituted Wells-Dawson polyoxometalate, is examined towards a series of Gly-Aa, Aa-Gly or Aa-Ser dipeptides, in which the nature and the size of the Aa amino acid side chain were varied. The rate of peptide bond hydrolysis, determined by (1)H NMR experiments, in Gly-Aa dipeptides is strongly dependent on the molecular volume and the chemical structure of the Aa side chain. When the volume of the aliphatic side chain of the Aa residue in Gly-Aa increased, a clear decrease in the hydrolysis rate was observed.

Amide bond hydrolysis in peptides and cyclic peptides catalyzed by a dimeric Zr(IV)-substituted Keggin type polyoxometalate.

Detailed kinetic studies on the hydrolysis of glycylserine (Gly-Ser) and glycylglycine (Gly-Gly) in the presence of the dimeric zirconium(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (1) were performed by a combination of (1)H, (13)C and (31)P NMR spectroscopy. The observed rate constants for the hydrolysis of Gly-Ser and Gly-Gly at pD 5.4 and 60 °C were 63.

Peptide bond hydrolysis catalyzed by the Wells-Dawson Zr(α2-P2W17O61)2 polyoxometalate.

In this paper we report the first example of peptide hydrolysis catalyzed by a polyoxometalate complex. A series of metal-substituted Wells-Dawson polyoxometalates were synthesized, and their hydrolytic activity toward the peptide bond in glycylglycine (GG) was examined. Among these, the Zr(IV)- and Hf(IV)-substituted ones were the most reactive.

Hydrolysis of DNA model substrates catalyzed by metal-substituted Wells-Dawson polyoxometalates.

In this study we report the first example of phosphoester bond hydrolysis in 4-nitrophenyl phosphate (NPP) and bis-4-nitrophenyl phosphate (BNPP), two commonly used DNA model substrates, promoted by metal-substituted polyoxometalates (POMs). Different transition metal and lanthanide ions were incorporated into the Wells-Dawson polyoxometalate framework and subsequently screened for their hydrolytic activity towards the cleavage of the phosphoester bonds in NPP and BNPP. From these complexes, the Zr(iv)-substituted POM showed the highest reactivity.

Polyoxomolybdate promoted hydrolysis of a DNA-model phosphoester studied by NMR and EXAFS spectroscopy.

Hydrolysis of (p-nitrophenyl)phosphate (NPP), a commonly used phosphatase model substrate, was examined in molybdate solutions by means of (1)H, (31)P, and (95)Mo NMR spectroscopy and Mo K-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. At 50 °C and pD 5.1 the cleavage of the phosphoester bond in NPP proceeds with a rate constant of 2.

Direct observation of molecular-level template action leading to self-assembly of a porous framework.

The molecular steps involved in the self-assembly of Cu(3)(BTC)(2) (BTC=1,3,5-benzenetricarboxylic acid) metal-organic frameworks that enclose Keggin-type H(3)PW(12)O(40) heteropolyacid molecules were unraveled by using solution (17)O, (31)P, and (183)W NMR spectroscopy, small-angle X-ray scattering, near-IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu(2+) ions with Keggin-type heteropolyacids was observed. Cu(2+) ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu(3)(BTC)(2) MOF structure HKUST-1.

Hydrolytic cleavage of DNA-model substrates promoted by polyoxovanadates.

Hydrolysis of 4-nitrophenyl phosphate (NPP) and bis-4-nitrophenyl phosphate (BNPP), two commonly used DNA model substrates, was examined in vanadate solutions by means of (1)H, (31)P and (51)V NMR spectroscopy. The hydrolysis of the phosphoester bond in NPP at 50 degrees C and pH 5.0 proceeds with a rate constant of 1.

Hydrolytic cleavage of an RNA-model phosphodiester catalyzed by a highly negatively charged polyoxomolybdate [Mo7O24]6- cluster.

Hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP), a commonly used RNA model substrate, was examined in molybdate solutions by means of (1)H, (31)P, and (95)Mo NMR, Raman, and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. (1)H and (31)P NMR spectroscopy indicate that at 50 degrees C and pD 5.9 the cleavage of the phosphodiester bond in HPNP proceeds with a rate constant of 6.

Phosphoesterase activity of polyoxomolybdates: diffusion ordered NMR spectroscopy as a tool for obtaining insights into the reactivity of polyoxometalate clusters.

Diffusion ordered NMR spectroscopy (DOSY NMR) is shown to be an excellent tool for observing reactive transients in the hydrolysis of the phosphatase model substrate (p-nitrophenyl)phosphate (NPP) promoted by polyoxomolybdate.

Questioning the paradigm of metal complex promoted phosphodiester hydrolysis: [Mo7O24](6-) polyoxometalate cluster as an unlikely catalyst for the hydrolysis of a DNA model substrate.

The first example of a phosphodiester bond cleavage promoted by a highly negatively charged polyoxometalate cluster has been discovered: the hydrolysis of the phosphodiester bond in a DNA model substrate bis(p-nitrophenyl)phosphate (BNPP) is promoted by the heptamolybdate anion [Mo7O24](6-) with rates which represent an acceleration of nearly four orders of magnitude compared to the uncatalyzed cleavage.