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Mixed micelles based on amphiphilic gadolinium(III)-DOTA and europium(III)-DTPA complexes were synthesized and evaluated for their paramagnetic and optical properties as potential bimodal contrast agents. Amphiphilic folate molecule for targeting the folate receptor protein, which is commonly expressed on the surface of many human cancer cells, was used in the self-assembly process in order to create nanoaggregates with targeting properties. Both targeted and nontargeted nanoaggregates formed monodisperse micelles having distribution maxima of 10 nm. The micelles show characteristic europium(III) emission with quantum yields of 2% and 1.1% for the nontargeted and targeted micelles, respectively. Fluorescence microscopy using excitation at 405 nm and emission at 575-675 nm was employed to visualize the nanoaggregates in cultured HeLa cells. The uptake of folate-targeted and nontargeted micelles is already visible after 5 h of incubation and was characterized with the europium(III) emission, which is clearly observable in the cytoplasm of the cells. The very fast longitudinal relaxivity r

Estrogen deficiency induces bone loss by increasing bone resorption, in part through upregulation of receptor activator of nuclear factor-κB ligand (RANKL). RANKL is secreted by osteoblasts and osteocytes, but more recently bone marrow (pre)adipocytes have also been shown to express RANKL. Estrogen deficiency increases bone marrow adipose tissue (BMAT). The aim of this study was to determine the effect of ovariectomy (OVX) on RANKL protein expression by bone marrow adipocytes in C3H/HeJ mice. Fourteen-week-old female C3H/HeJ mice ( n = 20) were randomized to sham surgery (Sham) or OVX. After 4 wk animals were euthanized. BMAT volume fraction (BMAT volume/marrow volume) was quantified by polyoxometalate-based contrast-enhanced nano-computed tomography. The percentage of RANKL-positive bone marrow adipocytes (RANKL-positive bone marrow adipocytes/total adipocytes) and the percentage of RANKL-positive osteoblasts covering the bone surface (bone surface covered in RANKL-positive osteoblasts/total bone surface) were quantified in the distal metaphysis of immunohistochemically stained sections of the left femur. The effects of OVX were analyzed by Student’s t test or Mann–Whitney U test. RANKL was detected in osteoblasts, osteocytes, and bone marrow adipocytes. OVX significantly increased mean percentage of RANKL-positive bone marrow adipocytes [mean (SD): Sham 42 (18)%; OVX 64 (12)%; P = 0.029] as well as BMAT volume/marrow volume [median (interquartile range): Sham 1.4 (4.9)%; OVX 7.2 (7.3)%; P = 0.008] compared with Sham. We show that OVX increased both the percentage of RANKL-positive bone marrow adipocytes and the total BMAT volume fraction in C3H/HeJ mice. Therefore, RANKL produced by bone marrow adipocytes could be an important contributor to OVX-induced bone loss in C3H/HeJ mice.

The discovery of nanozymes for selective fragmentation of proteins would boost the emerging areas of modern proteomics, however, the development of efficient and reusable artificial catalysts for peptide bond hydrolysis is challenging. Here we report the detailed catalytic properties of a microporous zirconium carboxylate metal-organic framework, MIP-201, in promoting peptide bond hydrolysis in a simple dipeptide, as well as in horse-heart myoglobin (Mb) protein that consists of 153 amino acids. We demonstrate that MIP-201 features an excellent catalytic activity and selectivity, a good tolerance toward reaction conditions covering a wide range of different pH values, and importantly, an exceptional recycling ability associated with easy regeneration process. Taking into account the excellent catalytic performance of MIP-201 and its other advantages such as 6-connected Zr6 cluster active sites, the green, scalable and cost-effective synthesis, and an outstanding chemical and architectural stability, our finding suggests that MIP-201 may be a promising and practical alternative to the current commercially available catalysts for peptide bond hydrolysis.

The catalytic activity of metal–organic frameworks (MOFs) toward peptides and proteins provides an attractive route for the development of nanozymes for applications in biotechnology and proteomics...

Understanding the stability and speciation of metal-oxo clusters in solution is essential for many of their applications in different areas. In particular, hybrid organic-inorganic polyoxometalates (HPOMs) have been attracting increasing attention as they combine the complementary properties of organic ligands and metal-oxygen nanoclusters. Nevertheless, the speciation and solution behavior of HPOMs have been scarcely investigated. Hence, in this work, a series of HPOMs based on the archetypical Anderson-Evans structure, δ-[MnMo6O18{(OCH2)3C-R}2]3-, with different functional groups (R = -NH2, -CH3, -NHCOCH2Cl, -N═CH(2-C5H4N) {pyridine; -Pyr}, and -NHCOC9H15N2OS {biotin; -Biot}) and countercations (tetrabutylammonium {TBA}, Li, Na, and K) were synthesized, and their solution behavior was studied in detail. In aqueous solutions, decomposition of HPOMs into the free organic ligand, [MoO4]2-, and free Mn3+ was observed over time and was shown to be highly dependent on the pH, temperature, and nature of the ligand functional group but largely independent of ionic strength or the nature of the countercation. Furthermore, hydrolysis of the amide and imine bonds often present in postfunctionalized HPOMs was also observed. Hence, HPOMs were shown to exhibit highly dynamic behavior in solution, which needs to be carefully considered when designing HPOMs, particularly for biological applications. ispartof: INORGANIC CHEMISTRY vol:60 issue:14 pages:10215-10226 ispartof: location:United States status: published

A simple and cost-effective method based on multi-photon microscopy is presented for the preliminary screening of the general morphology, size range and heterogeneity of Ir(III) nano-aggregate formulations. ispartof: RSC Advances vol:11 issue:2 pages:657-661 ispartof: location:England status: published

Materials which synergistically combine Lewis and Bronsted acid properties hold potential for applications as efficient heterogeneous catalysts for preparation of biofuels and biolubricants. Herein we report new heterogeneous catalysts based on grafting the intact Lewis metal (ZrIV) substituted Keggin polyoxometalate (POM) on mesoporous silica support. A new approach for immobilization of the POM in MCM-41 silica was developed by co-condensation of Si source (tetraethyl orthosilicate, TEOS) with POM salt in the presence of a template molecule as an alternative to the commonly used acidic POM form and impregnation procedure for catalyst preparation. The proposed synthesis method in combination with extraction of the template proceeded with preservation of the intact POM structure and resulted in hybrid catalysts with in situ generated Bronsted acid sites in addition to the Lewis acidity provided by the metal centers. Textural properties of the catalysts were characterized by X-ray diffraction, N2 physisorption and transmission electron microscopy (TEM). Insight into POM stability and structural transformations during synthesis, template removal and impregnation was provided by solid state 31P and 29Si NMR spectroscopy. Catalytic activity was studied in esterification reactions of levulinic acid with ethanol or octanol to value-added esters. The directly synthesized POM-functionalized hybrid catalysts exceeded the post synthesis impregnated ones, demonstrating significantly higher catalytic activity, recyclability and resistance against leaching. The proposed approach for immobilization of Lewis metal POMs in MCM-41 silica framework with in situ generation of the active Bronsted acid sites opens prospects for the development of efficient hybrid catalysts for esterification reaction, which overcomes the main limitations of common POM based catalysts such as low stability of the acid sites during the synthesis and the catalytic reaction, low surface area, agglomeration of the catalytically active phase and low stability of the Lewis metal center in presence of water.

The controlled formation of protein supramolecular assemblies is challenging but it could provide an important route for the development of hybrid biomaterials. In this work, we demonstrate formation of well-defined complexes formed between the 8-fold symmetrical designer protein Tako8 and soluble metal-oxo clusters from the family of Anderson-Evans, Keggin and ZrIV- substituted Wells-Dawson polyoxometalates. A combination of x-ray crystallography and solution studies showed that metal-oxo clusters are able to serve as linker nodes for the bottom-up creation of protein based supramolecular assemblies. Our findings indicate that clusters with larger size and negative charge are capable of modulating the crystal packing of the protein, highlighting the need for a size and shape complementarity with the protein node for optimal alteration of the crystalline self-assembly.

Efficient and selective hydrolysis of inert peptide bonds is of paramount importance. MOF-808, a metal-organic framework based on Zr6 nodes, can hydrolyze peptide bonds efficiently under biologically relevant conditions. However, the details of the catalyst structure and of the underlying catalytic reaction mechanism are challenging to establish. By means of DFT calculations we first investigate the speciation of the Zr6 nodes and identify the nature of ligands that bind to the Zr6O8H4-x core in aqueous conditions. The core is predicted to strongly prefer a Zr6O8H4 protonation state and to be predominantly decorated by bridging formate ligands, giving Zr6(μ3-O)4(μ3-OH)4(BTC)2(HCOO)6 and Zr6(μ3-O)4(μ3-OH)4(BTC)2(HCOO)5(OH)(H2O) as the most favorable structures at physiological pH. The GlyGly peptide can bind MOF in several different ways, with the preferred structure involving coordination through the terminal carboxylate analogously to the binding mode of formate ligand. The pre-reactive binding mode in which the amide carbonyl oxygen coordinates the metal core lies 7 kcal higher in free energy. The preferred reaction pathway is predicted to have two close-lying transition states, either of which could be the rate-determining step: nucleophilic attack on the amide carbon atom and C-N bond breaking, with calculated relative free energies of 31 and 32 kcal mol-1, respectively. Replacement of formate by water and hydroxide at the Zr6 node is predicted to be possible, but does not appear to play a role in the hydrolysis mechanism. ispartof: PHYSICAL CHEMISTRY CHEMICAL PHYSICS vol:22 issue:43 pages:25136-25145 ispartof: location:England status: published

The development of artificial proteases is challenging, but important for many applications in modern proteomics and biotechnology. The hydrolysis of hydrophobic or unstructured proteins is particularly difficult due to their poor solubility, which often requires the presence of surfactants. Herein, it is shown that a zirconium(IV)-substituted Keggin polyoxometalate (POM), (Et2 NH2 )10 [Zr(α-PW11 O39 )2 ] (1), is able to selectively hydrolyze β-casein, which is an intrinsically unstructured protein at pH 7.4 and 60 °C. Four surfactants (sodium dodecyl sulfate (SDS), N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12), 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), and polyethylene glycol tert-octylphenyl ether (TX-100)), which differ in the nature of their polar groups, were investigated for their role in influencing the selectivity and efficiency of protein hydrolysis. Under experimental conditions, β-casein forms micellar structures in which the hydrophilic part of the protein is water accessible and able to interact with 1. Identical fragmentation patterns of β-casein in the presence of 1 were observed through SDS poly(acrylamide) gel electrophoresis both in the presence and absence of surfactants, but the rate of hydrolysis varied, depending on the nature of surfactant. Whereas TX-100 surfactant, which has a neutral polar head, caused only a slight decrease in the hydrolysis rate, stronger inhibition was observed in the presence surfactants with charges in their polar heads (CHAPS, ZW3-12, SDS). These results were consistent with those of tryptophan fluorescencequenching studies, which showed that the binding between β-casein and 1 decreased with increasing repulsion between the POM and the polar heads of the surfactants. In all cases, the micellar structure of β-casein was not significantly affected by the presence of POM or surfactants, as indicated by circular dichroism spectroscopy. ispartof: CHEMISTRY-A EUROPEAN JOURNAL vol:26 issue:49 pages:11170-11179 ispartof: location:Germany status: published

The reactivity of a range of Keggin and Wells-Dawson type heteropolyacids (HPAs): H3 PW12 O40 H4 SiW12 O40 , H3 PMo12 O40 , K6 P2 W18 O62 , and NaH2 W12 O4 , towards the heavily glycosylated α-1-acid glycoprotein (AGP) is reported. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) show that after incubation of the protein with HPAs at 80 °C and pH 2.8 complete hydrolysis of terminal glycosidic bond has been achieved, resulting in the removal of sialic acids with no observed destruction of the protein core or the residual glycan chains. The 1 H NMR spectroscopy confirmed that the released sialic acids preserve intact structure upon their excision from the protein, which makes the reported method suitable for the analysis of sialic acid modifications which play an important role in numerous biological processes. The presence of other sugars was not detected by 1 H NMR and HPAEC-PAD, suggesting that HPAs hydrolyze only the terminal glycosidic bond in the glycoprotein, resulting in the selective release of sialic acid from AGP. The kinetic results have shown that under equal temperature and pH conditions, the hydrolysis of the terminal glucosidic bond occurred faster in the presence of HPAs compared to conventional mineral acids. The observed rate constants were in the range 6,7×10-2 -11,9×10-2 min-1 and the complete and selective excision of sialic acids could be achieved within 60 min of incubation. The Trp fluorescence and CD spectroscopy show that non-covalent interaction between HPA and protein takes place in solution which could lead to stabilization of the sialosyl cation that is formed during the glycosidic bond hydrolysis by anionic HPA cluster.

Redox reactions between polyoxometalates (POMs) and biologically relevant molecules have been virtually unexplored but are important, considering the growing interest in the biological applications of POMs. In this work we give a detailed account on the redox behavior of CeIV-substituted polyoxometalates (CeIV-POMs) toward a range of amino acids and peptides. CeIV-POMs have been shown to act as artificial proteases that promote the selective hydrolysis of peptide bonds. In presence of a protein, a concomitant reduction of CeIV to CeIII ion is frequently observed, leading us to examine the origins of this redox reaction by first using amino acid building blocks as simple models. Among all of the examined amino acids, cysteine (Cys) showed the highest activity in reducing CeIV-POMs to CeIII-POMs, followed by the aromatic amino acids tryptophan (Trp), tyrosine (Tyr), histidine (His), and phenylalanine (Phe). While the redox reaction with Cys afforded the well-defined product cystine, no oxidation products were detected for the Trp, His, Tyr, and Phe amino acids after their reaction with CeIV-POMs, suggesting a radical pathway in which the solvent likely regenerates the amino acid. In general, the rate of redox reactions increased upon increasing the pD, temperature, and ionic strength of the reaction. Moreover, the redox reaction is highly sensitive to the type of polyoxometalate scaffold, as complexation of CeIV to a Keggin (K) or Wells-Dawson (WD) polyoxotungstate anion resulted in a large difference in the rate of redox reaction for both Cys and aromatic amino acids. The reduction of CeIVK was at least 1 order of magnitude faster in comparison to CeIVWD, in accordance with the higher redox potential of CeIVK in comparison to CeIVWD. The reaction of CeIVPOMs with a range of peptides containing redox-active amino acids revealed that the redox reaction is influenced by their coordination mode with CeIV ion, but in all examined peptides the redox reaction is favored in comparison to the hydrolytic cleavage of the peptide bond. ispartof: INORGANIC CHEMISTRY vol:59 issue:15 pages:10569-10577 ispartof: location:United States status: published

The selective hydrolysis of proteins by non-enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal-oxo cluster [Hf

The selective hydrolysis of proteins by non‐enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal‐oxo cluster [Hf18O10(OH)26(SO4)13⋅(H2O)33] (Hf18), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of HfIV Lewis acidic sites and the Brønsted acidic surface of Hf18. X‐ray scattering and ESI‐MS revealed that Hf18 is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf18 cluster, and not from smaller, soluble Hf species that could leach into solution. This is the peer-reviewed version of the following article: Moons, J.; de Azambuja, F.; Mihailović, J.; Kozma, K.; Smiljanić, K.; Amiri, M.; Ćirković-Veličković, T.; Nyman, M.; Parac-Vogt, T. Discrete Hf18 Metal‐oxo Cluster as a Heterogeneous Nanozyme for Site‐Specific Proteolysis. Angewandte Chemie (International Edition) 2020, 59 (17), 1–9. [https://doi.org/10.1002/anie.202001036]. Supplementary material: [https://cherry.chem.bg.ac.rs/handle/123456789/4851]

The development of modular platforms that can undergo postfunctionalization reactions permits coupling of inorganic clusters with different organic functionalities, thereby expanding the range of key physicochemical properties that are relevant for applications in different areas of science. In this work, a novel hybrid Wells-Dawson polyoxometalate (POM) platform was developed and successfully used for postfunctionalization via a nucleophilic substitution reaction. Two new halogen-functionalized bis-organosilyl Wells-Dawson POMs TBA6[α2-P2W17O61{O(SiC3H6-X)2}] (X = Cl or I) were synthesized, and their coupling with amine substrates was explored in a one-step postfunctionalization reaction. The iodide form of the POM has proven to be much more reactive, and its reaction with a range of primary and secondary amines resulted in a series of new bis-substituted Wells-Dawson POMs with the general formula TBA6[α2-P2W17O61{O(SiC3H6-NR1R2)2}]. Coupling of 18 amines with R1 and R2 groups, which exhibited a wide variety in terms of both chemical nature and bulkiness, was achieved under mild conditions via a catalyst-free approach. Using Na2CO3 as a base in acetonitrile solutions at 55 °C resulted in hybrid products that were obtained in high purity and good yields, after a simple isolation and purification procedure. ispartof: INORGANIC CHEMISTRY vol:59 issue:14 pages:10146-10152 ispartof: location:United States status: published

Acetylcholinesterase (AChE) inhibitors are important in the treatment of neurodegenerative diseases. Two inhibitors, 12-tungstosilicic acid (WSiA) and 12-tungstophosphoric acid (WPA), which have polyoxometalate (POM) type structure, have been shown to inhibit AChE activity in nM concentration. Circular dichroism and tryptophan fluorescence spectroscopy demonstrated that the AChE inhibition was not accompanied by significant changes in the secondary structure of the enzyme. The molecular docking approach has revealed a new allosteric binding site, termed β-allosteric site (β-AS), which is considered responsible for the inhibition of AChE by POMs. To the best of our knowledge, this is the first study reporting a new allosteric site that is considered responsible for AChE inhibition by voluminous and negatively charged molecules such as POMs. The selected POMs were further subjected to genotoxicity testing using human peripheral blood cells as a model system. It was shown that WSiA and WPA induced a mild cytostatic but not genotoxic effects in human lymphocytes, which indicates their potential to be used as medicinal drugs. The identification of non-toxic compounds capable of binding to an allosteric site that so far has not been considered responsible for enzyme inhibition could be fundamental for the development of new drug design strategies and the discovery of more efficient AChE modulators. ispartof: EUROPEAN JOURNAL OF PHARMACEUTICAL SCIENCES vol:151 ispartof: location:Netherlands status: published

MOF-808, a Zr(IV)-based metal-organic framework, has been proven to be a very effective heterogeneous catalyst for the hydrolysis of the peptide bond in a wide range of peptides and in hen egg white lysozyme protein. The kinetic experiments with a series of Gly-X dipeptides with varying nature of amino acid side chain have shown that MOF-808 exhibits selectivity depending on the size and chemical nature of the X side chain. Dipeptides with smaller or hydrophilic residues were hydrolyzed faster than those with bulky and hydrophobic residues that lack electron rich functionalities which could engage in favorable intermolecular interactions with the btc linkers. Detailed kinetic studies performed by 1H NMR spectroscopy revealed that the rate of glycylglycine (Gly-Gly) hydrolysis at pD 7.4 and 60 °C was 2.69 × 10-4 s-1 ( t1/2 = 0.72 h), which is more than 4 orders of magnitude faster compared to the uncatalyzed reaction. Importantly, MOF-808 can be recycled several times without significantly compromising the catalytic activity. A detailed quantum-chemical study combined with experimental data allowed to unravel the role of the {Zr6O8} core of MOF-808 in accelerating Gly-Gly hydrolysis. A mechanism for the hydrolysis of Gly-Gly by MOF-808 is proposed in which Gly-Gly binds to two Zr(IV) centers of the {Zr6O8} core via the oxygen atom of the amide group and the N-terminus. The activity of MOF-808 was also demonstrated toward the hydrolysis of hen egg white lysozyme, a protein consisting of 129 amino acids. Selective fragmentation of the protein was observed with 55% yield after 25 h under physiological pH.

Biological tissues have a complex and heterogeneous 3D structure, which is only partially revealed by standard histomorphometry in 2D. We here present a novel chemical compound for contrast-enhanced microfocus computed tomography (CE-CT), a Hafnium-based Wells-Dawson polyoxometalate (Hf-POM), which allows simultaneous 3D visualization of mineralized and non-mineralized skeletal tissues, such as mineralized bone and bone marrow vasculature and adipocytes . We validated the novel contrast agent, which has a neutral pH in solution, by detailed comparison with (immuno)histology on murine long bones as blueprint , and showed that Hf-POM-based CE-CT can be used for virtual 3D histology. Furthermore, we quantified the 3D structure of the different skeletal tissues, as well as their spatial relation to each other, during aging and diet-induced obesity. We discovered, based on a single CE-CT dataset per sample, clear differences between the groups in bone structure, vascular network organization, characteristics of the adipose tissue and proximity of the different tissues to each other. These findings highlight the complementarity and added value of Hf-POM-based CE-CT compared to standard histomorphometry. As this novel technology provides a detailed 3D simultaneous representation of the structural organization of mineralized bone and bone marrow vasculature and adipose tissue, it will enable to improve insight in the interactions between these three tissues in several bone pathologies and to evaluate the in vivo performance of biomaterials for skeletal regeneration.

Lanthanides, holmium(iii), dysprosium(iii), and terbium(iii), were coordinated to an amphiphilic DOTA bis-coumarin derivative and then further assembled with an amphiphilic europium(iii) DTPA bis-coumarin derivative into mono-disperse micelles. The self-assembled micelles were characterized and assessed for their potential as bimodal contrast agents for high field magnetic resonance and optical imaging applications. All micelles showed a high transverse relaxation (r2) of 46, 34, and 30 s-1 mM-1 at 500 MHz and 37 °C for Dy(iii), Ho(iii) and Tb(iii), respectively, which is a result of the high magnetic moment of these lanthanides and the long rotational correlation time of the micelles. The quantum yield in aqueous solution ranged from 1.8% for Tb/Eu to 1.4% for Dy/Eu and 1.0% for the Ho/Eu micelles. Multi-photon excited emission spectroscopy has shown that due to the two-photon absorption of the coumarin chromophore the characteristic Eu(iii) emission could be observed upon excitation at 800 nm, demonstrating the usefulness of the system for in vivo fluorescence imaging applications. To the best of our knowledge, this is the first example reporting the potential of a holmium(iii) chelate as a negative MRI contrast agent. ispartof: DALTON TRANSACTIONS vol:47 issue:31 pages:10646-10653 ispartof: location:England status: published

A novel, reversible redox-active MRI probe, GdNR1, has been developed for the study of redox changes associated with diseased states. This system exhibits switching in relaxivity upon reduction and oxidation of the appended nicotinimidium. Relaxivity studies and cyclic voltammetry confirmed the impressive reversibility of this system, at a biologically-relevant reduction potential. A 2.5-fold increase in relaxivity was observed upon reduction of the complex, which corresponds to a change in the number of inner-sphere water molecules, as confirmed by luminescence lifetimes of the Eu(iii) analogue and NMRD studies. This is the first example of a redox-responsive MRI probe utilising the biologically-inspired nicotinimidium redox switch. In the future this strategy could enable the non-invasive identification of hypoxic tissue and related cardiovascular disease. ispartof: CHEMICAL COMMUNICATIONS vol:54 issue:92 pages:12986-12989 ispartof: location:England status: published

The reactivity of polyoxovanadates towards adenosine-5′-triphosphate (ATP) hydrolysis at pH 2, 4, 6 and 7 is reported. Detailed kinetic investigation of ATP hydrolysis in the presence of polyoxovanadates was performed through multinuclear nuclear magnetic resonance (NMR) spectroscopy. In general, rate acceleration of up to five orders of magnitude was observed in the presence of vanadates compared to spontaneous ATP hydrolysis, with the greatest acceleration observed for reactions carried out at pH 2. Interestingly, the effectiveness of vanadates in promoting ATP hydrolysis decreased as the pH of the reaction solution increased, nevertheless, at pH = 7, the rate increase of one order of magnitude in comparison to blank reactions was still observed. Interactions between vanadate species in solution and ATP were investigated by means of 31P and 51V NMR spectroscopy, and this pointed towards the preferential interaction of vanadium with the phosphate groups rather than other regions of the ATP molecule.

Group (IV) metal oxo clusters are a diverse class of compounds with rapidly growing applications in catalysis, materials chemistry, electronics and optics. They possess unique structural stability, reactivity and electronic properties; however, their potential remains underexplored due to the gaps in fundamental understanding about their structure, intrinsic features, and nuances in their synthesis that overall would allow for great tunability of their properties. In this context, here we review the chemistry of discrete zirconium, hafnium, and titanium metal oxo clusters reported in the literature in order to provide a critical overview of the structural features, properties and reactivity disclosed to date. While a comprehensive summary of Zr and Hf clusters is presented, only the most recent Ti oxo clusters are discussed in addition to some key compounds that have been revised elsewhere. Envisioning the growing relevance group (IV) metal oxo clusters for the synthesis of nanostructure materials and in catalysis, we also summarize key principles of their surface chemistry, and the photoactivity of Ti oxo clusters, given the paramount importance of these properties for the development of future applications.

This study represents the first example of protein hydrolysis at pH = 7.4 and 60 °C by a metal-substituted polyoxometalate (POM) in the presence of a zwitterionic surfactant. Edman degradation results show that in the presence of 0.5% w/v 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) detergent, a Zr(IV)-substituted Wells-Dawson-type POM, K15H[Zr(α2-P2W17O61)2]·25H2O (Zr1-WD2), selectively hydrolyzes human serum albumin exclusively at peptide bonds involving Asp or Glu residues, which contain carboxyl groups in their side chains. The selectivity and extent of protein cleavage are tuned by the CHAPS surfactant by an unfolding mechanism that provides POM access to the hydrolyzed peptide bonds. ispartof: ACS Omega vol:2 issue:5 pages:2026-2033 ispartof: location:United States status: published

Na/K-ATPase is emerging as an important target for a variety of anticancer metal-based drugs. The interactions of Na/K-ATPase (in its E1 state) with three representative and structurally related cytotoxic gold(III) complexes, i.e. [Au(bipy)(OH)(2)][PF6], bipy = 2,2'-bipyridine; [Au(py(dmb)-H)(CH3COO)(2)], py(dmb)-H = deprotonated 6-(1,1-dimethylbenzyl)-pyridine and [Au(bipy(dmb)-H)(OH)][PF6], bipy(c)-H = deprotonated 6-(1,1-dimethylbenzyl)-2,20-bipyridine, are investigated here in depth using a variety of spectroscopic methods, in combination with docking studies. Detailed information is gained on the conformational and structural changes experienced by the enzyme upon binding of these gold(III) complexes. The quenching constants of intrinsic enzyme fluorescence, the fraction of Trp residues accessible to gold(III) complexes and the reaction stoichiometries were determined in various cases. Specific hypotheses are made concerning the binding mode of these gold(III) complexes to the enzyme and the likely binding sites. Differences in their binding behaviour toward Na/K-ATPase are explained on the ground of their distinctive structural features. The present results offer further support to the view that Na/K-ATPase may be a relevant biomolecular target for cytotoxic gold(III) compounds of medicinal interest and may thus be involved in their overall mode of action.

A mild post-functionalization method, based on a copper(i) catalyzed azide-alkyne cycloaddition, was developed for the fragile [P2W15V3]9- (PWV). PWV was functionalized with an azide and used as a platform to attach various alkyne functionalized compounds.

A highly negatively charged binuclear ZrIV-substituted Keggin polyoxometalate [{α-PW11O39Zr(μ-OH)(H2O)}2]8- (ZrK 2 : 2) has been shown to promote the hydrolytic cleavage of phosphoester bonds in the supercoiled plasmid pUC19 DNA under physiological pH and temperature, giving relaxed and linear forms of pUC19 as hydrolysis products. The interaction between ZrK 2 : 2 and DNA was experimentally proven by circular dichroism (CD) spectroscopy and 31P diffusion ordered NMR spectroscopy. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: T. N. Parac-Vogt (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 24 October 2016; Accepted 9 December 2016; Accepted Manuscript published 9 December 2016; Advance Article published 16 December 2016; Version of Record published 3 January 2017 ispartof: Chemical Communications vol:53 issue:3 pages:617-620 ispartof: location:England status: published

Polyoxometalates (POMs) represent an important group of metal-oxo nanoclusters, typically comprised of early transition metals in high oxidation states (mainly V, Mo and W). Many plenary POMs exhibit good pH, solvent, thermal and redox stability, which makes them attractive components for the design of covalently integrated hybrid organic-inorganic molecules, herein referred to as hybrid-POMs. Until now, thousands of organic hybrid-POMs have been reported; however, only a small fraction can be further functionalized using other organic molecules or metal cations. This emerging class of 'post-functionalizable' hybrid-POMs constitute a valuable modular platform that permits coupling of POM properties with different organic and metal cation functionalities, thereby expanding the key physicochemical properties that are relevant for application in (photo)catalysis, bioinorganic chemistry and materials science. The post-functionalizable hybrid-POM platforms offer an opportunity to covalently link multi-electron redox responsive POM cores with virtually any (bio)organic molecule or metal cation, generating a wide range of materials with tailored properties. Over the past few years, these materials have been showcased in the preparation of framework materials, functional surfaces, surfactants, homogeneous and heterogeneous catalysts and light harvesting materials, among others. This review article provides an overview on the state of the art in POM post-functionalization and highlights the key design and structural features that permit the discovery of new hybrid-POM platforms. In doing so, we aim to make the subject more comprehensible, both for chemists and for scientists with different materials science backgrounds interested in the applications of hybrid (POM) materials. The review article goes beyond the realms of polyoxometalate chemistry and encompasses emerging research domains such as reticular materials, surfactants, surface functionalization, light harvesting materials, non-linear optics, charge storing materials, and homogeneous acid-base catalysis among others. ispartof: CHEMICAL SOCIETY REVIEWS vol:49 issue:2 pages:382-432 ispartof: location:England status: published

To advance clinical translation of regenerative medicine, there is, amongst others, still need for better insights in tissue development and disease. For this purpose, more precise imaging of the 3D microstructure and spatial interrelationships of the different tissues within organs is crucial. Despite being destructive towards the sample, conventional histology still is the gold standard for structural analysis of biological tissues. It is, however, limited by 2D sections of a 3D object, prohibiting full 3D structural analysis. MicroCT has proven to provide full 3D structural information of mineralized tissues and dense biomaterials. However, the intrinsic low X-ray absorption of soft tissues requires contrast-enhancing staining agents (CESAs). In a previous study, we showed that hafnium-substituted Wells-Dawson polyoxometalate (Hf-WD POM) allows simultaneous contrast-enhanced microCT (CE-CT) visualization of bone and its marrow vascularization and adiposity. In this study, other POM species have been examined for their potential as soft tissue CESAs. Four Wells-Dawson POMs, differing in structure and overall charge, were used to stain murine long bones and kidneys. Their staining potential and diffusion rate were compared to those of Hf-WD POM and phosphotungstic acid (PTA), a frequently used but destructive CESA. Monolacunary Wells-Dawson POM (Mono-WD POM) showed similar soft tissue enhancement as Hf-WD POM and PTA. Moreover, Mono-WD POM is less destructive, shows a better diffusion than PTA, and its synthesis requires less time and cost than Hf-WD POM. Finally, the solubility of Mono-WD POM was improved by addition of lithium chloride (LiCl) to the staining solution, enhancing further the soft tissue contrast. Statement of Significance To advance clinical translation of regenerative medicine, there is, amongst others, still need for better insights in tissue development and disease. For this purpose, more precise imaging of the 3D microstructure and spatial interrelationships of the different tissues within organs is crucial. Current standard structural analysis techniques (e.g. 2D histomorphometry), however, do not allow full 3D assessment. Contrast-enhanced X-ray computed tomography has emerged as a powerful 3D structural characterization tool of soft biological tissues. In this study, from a library of Wells Dawson polyoxometalates (WD POMs), we identified monolacunary WD POM together with lithium chloride, dissolved in phosphate buffered saline, as the most suitable contrast-enhancing staining agent solution for different biological tissues without tissue shrinkage.

Creating efficient and residue-directed artificial proteases is a challenging task due to the extreme inertness of the peptide bond, combined with the difficulty of achieving specific interactions between the catalysts and the protein side chains. Herein we report strictly site-selective hydrolysis of a multi-subunit globular protein, hemoglobin (Hb) from bovine blood, by a range of ZrIV -substituted polyoxometalates (Zr-POMs) in mildly acidic and physiological pH solutions. Among 570 peptide bonds in Hb, selective cleavage was observed at only eleven sites, each occurring at Asp-X peptide bonds located in the positive patches on the protein surface. The molecular origins of the observed Asp-X selectivity were rationalized by means of molecular docking, DFT-based binding, and mechanistic studies on model peptides. The proposed mechanism of hydrolysis involves coordination of the amide oxygen to ZrIV followed by a direct nucleophilic attack of the side chain carboxylate group on the C-terminal amide carbon atom with formation of a cyclic anhydride, which is further hydrolyzed to give the reaction products. The activation energy for the cleavage of the structurally related Glu-X sequence compared to Asp-X was calculated to be higher by 1.4 kcal mol-1 , which corresponds to a difference of about one order of magnitude in the rates of hydrolysis. The higher activation energy is attributed to the higher strain present in the six-membered ring of glutaric anhydride (Glu-X), as compared to the five-membered ring of the succinic anhydride (Asp-X) intermediate. Similarly, the cleavage at X-Asp and X-Glu bonds are predicted to be kinetically less likely as the corresponding activation energies were 6 kcal mol-1 higher, explaining the experimentally observed selectivity. The synergy between the negatively charged polyoxometalate cluster, which binds at positive patches on protein surfaces, and selective activation of Asp-X peptide bonds located in these regions by ZrIV ions, results in a novel class of artificial proteases with aspartate-directed reactivity, which is very rare among naturally occurring proteases. ispartof: CHEMISTRY-A EUROPEAN JOURNAL vol:25 issue:63 pages:14370-14381 ispartof: location:Germany status: published

Hydrolysis of Transferin (Tf), a glycoprotein consisting of 679 amino acids and three glycan chains, has been examined in the presence of Ce(IV)-substituted Keggin polyoxometalate [CeIV(α-PW11O39)2]10− (Ce-K POM). Incubation at pH = 7.4 and at 37 °C resulted in selective fragmentation of the Tf after 24 h, which was followed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE). After 5 days of incubation nearly 90% of Tf was hydrolyzed, giving 9 fragments with molecular weight (Mw) in the range between 13.7 and 69.5 kDa. Under the same conditions, the sample of Tf which did not contain the Ce-K POM, showed only 7% of background hydrolysis. The interactions between Ce-K and Tf were studied by tryptophan fluorescence, circular dichroism (CD) and 31P Nuclear magnetic resonance (NMR) spectroscopy. The association constant (Ka) for the interaction was calculated to be 3.2 × 104 M−1 from tryptophan quenching studies. CD spectroscopy revealed that binding of Ce-K to Tf resulted in significant secondary structure changes, mainly affecting the alpha-helical content of the protein. 31P NMR spectroscopy showed that in the presence of the Tf partial reduction of Ce(IV) to Ce(III) occurred, which did not affect the overall structure of the Keggin POM. ispartof: Polyhedron vol:170 pages:570-575 status: published

RationaleStroke patients lose bone mass and experience fracture at an elevated rate. Although functional intraosseous vasculature is necessary for skeletal maintenance, the effect of stroke on osteovasculature is unknown.ObjectiveTo characterize changes to osteovascular function, structure, and composition following mild-to-moderate-severity ischemic stroke in mice, both with and without exercise therapy.Methods and ResultsTwelve-week-old male mice (n=27) received either a stroke (middle cerebral artery occlusion) or sham procedure, followed by four weeks of daily treadmill or sedentary activity. Intraosseous perfusion, measured weekly in the proximal tibial metaphysis, was reduced by stroke for two weeks. In the second week of recovery, exercise nearly restored perfusion to sham levels, and perfusion tended to be lower in the stroke-affected limb. At the conclusion of the study, osteovascular structure was assessed with contrast-enhanced computed tomography in the distal femoral metaphysis. Stroke significantly increased osteovascular volume and branching but reduced the relative number of blood vessels close to bone surfaces (6-22 µm away) and increased the relative number more than 52 µm away. These differences in vessel proximity to bone were driven by changes in the stroke-exercise group, indicating compounded effects of stroke and exercise. Exercise, but not stroke, nearly reduced the amount of osteogenic Type H blood vessels in the proximal tibial metaphysis, quantified with immunofluorescence microscopy.ConclusionsThis study is the first to examine the effects of stroke on osteovasculature. Stroke increased the amount of osteovasculature, but since blood vessels close to bone are associated with bone remodeling, the shift in osteovascular structure could play a role in bone loss following stroke. The exercise-induced reduction in the amount of Type H vessels and the stroke-exercise effect on osteovascular structure suggest moderate aerobic activity may have detrimental effects on bone remodeling during early stroke recovery.

© 2019 American Chemical Society and Division of Chemical Education, Inc. Single-type, 8-fold-grooved, commercially accessible interlocking disks (ILDs) have been used for modeling of complex polyhedral and reticular topologies with relevance to inorganic and hybrid materials. The assembly of complex topologies relies on the preparation of secondary building units (SBUs), which exhibit different connectivity than that of the primary ILDs. All ILD-based models are light, scalable, programmable, and suitable for discovery-based learning and classroom demonstrations of stereochemistry and complex chemical concepts. ispartof: Journal Of Chemical Education vol:96 issue:3 pages:601-605 status: published

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Four Wells–Dawson type metal-substituted polyoxometalates (MSPs), 1:2 ZrIV-Wells–Dawson [ZrIV(α2-P2W17O61)]8– (1), 1:1 CoII-Wells–Dawson [CoII(α2-P2W17O61)]10– (2), 1:1 NiII-Wells–Dawson [NiII(α2-P2W17O61)]10– (3) and 1:1 CuII-Wells–Dawson [CuII(α2-P2W17O61)]10– (4), which differ in the nature of the imbedded metal ion, were examined in co-crystallization experiments with a protein Hen Egg White Lysozyme (HEWL). Single crystal X-ray structures of four noncovalent complexes between POMs and HEWL have been determined, and the influence of the type of substituted metal on the mode of POM binding to a protein was investigated. All crystal structures exhibited a high degree of similarity, suggesting that the interaction is largely independent on the nature of substituted metal within the same polyoxometalate (POM) archetype. The main driving force for the formation of the noncovalent complex is electrostatic attraction between POM and HEWL surface regions. Stabilization is further provided by direct and water mediated hydrogen bonding between terminal oxygen atoms of the POM framework and flexible HEWL residues. ispartof: EUROPEAN JOURNAL OF INORGANIC CHEMISTRY vol:2019 issue:3-4 pages:506-511 status: published

In this study, mechanisms of hydrolysis of all four chemically diverse cleavage sites of human serum albumin (HSA) by [Zr(OH)(PW11 O39 )]4- (ZrK) have been investigated using the hybrid two-layer QM/MM (ONIOM) method. These reactions have been proposed to occur through the following two mechanisms: internal attack (IA) and water assisted (WA). In both mechanisms, the cleavage of the peptide bond in the Cys392-Glu393 site of HSA is predicted to occur in the rate-limiting step of the mechanism. With the barrier of 27.5 kcal/mol for the hydrolysis of this site, the IA mechanism is found to be energetically more favorable than the WA mechanism (barrier = 31.6 kcal/mol). The energetics for the IA mechanism are in line with the experimentally measured values for the cleavage of a wide range of dipeptides. These calculations also suggest an energetic preference (Cys392-Glu393, Ala257-Asp258, Lys313-Asp314, and Arg114-Leu115) for the hydrolysis of all four sites of HSA. © 2018 Wiley Periodicals, Inc. ispartof: JOURNAL OF COMPUTATIONAL CHEMISTRY vol:40 issue:1 pages:51-61 ispartof: location:United States status: published

The hydrolysis of horse heart cytochrome c (cytC) protein by two isostructural Keggin-type polyoxometalates (POMs), (Me2NH2)10[Ce(α-PW11O39)2] (Ce1–K2) and (Et2NH2)10[Zr(PW11O39)2] (Zr1–K2), which differ in the nature of the embedded Lewis acid metal ion, has been investigated. In the presence of Ce1–K2, selective hydrolysis of cytC was observed at the Trp60-Lys61 and Gly78-Thr79 peptide bonds at pH 7.4 and 37 °C. However, the isostructural Zr1–K2 exhibited a lower reactivity and different selectivity, cleaving cytC at the Asp3-Val4, Asp51-Ala52 and Gly78-Thr79 peptide bonds. Different spectroscopic techniques were used to verify the molecular interactions between cytC and each metal-substituted Keggin POM to elucidate the role of the Lewis acid metal ion in directing the selectivity of protein hydrolysis. ispartof: European Journal of Inorganic Chemistry vol:2016 issue:32 pages:5098-5105 status: published

A new prototype consisting of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles decorated with europium(III) ions encapsulated in a DO3A organic scaffold was designed as a platform for further development of bimodal contrast agents for MRI and optical imaging. The USPIO nanoparticles act as negative MRI contrast agents, whereas the europium(III) ion is a luminophore that is suitable for use in optical imaging detection. The functionalized USPIO nanoparticles were characterized by TEM, DLS, XRD, FTIR, and TXRF analysis, and a full investigation of the relaxometric and optical properties was conducted. The typical luminescence emission of europium(III) was observed and the main red emission wavelength was found at 614 nm. The relaxometric study of these ultrasmall nanoparticles showed r2 values of 114.8 mM(-1) Fes(-1) at 60 MHz, which is nearly double the r2 relaxivity of Sinerem(®).

The interaction between the 1:2 Zr(IV) :Wells-Dawson complex, K15 H[Zr(α2 -P2 W17 O61 )2] (1), and a range of surfactants was studied in detail with the aim of developing metal-substituted POMs as potential artificial proteases for membrane proteins. The surfactants include the positively charged cetyl(trimethyl)ammonium bromide (CTAB), the negatively charged sodium dodecyl sulfate (SDS), the neutral Triton X-100 (TX-100), and zwitterionic 3-[dodecyl(dimethyl)ammonio]-1-propanesulfonate (Zw3-13) and 3-[dimethyl(3-{[(3α,5β,7α,12α)-3,7,12-trihydroxy-24-oxocholan-24-yl]amino}propyl)ammonio]-1-propanesulfonate (CHAPS). A combination of multinuclear (1)H, (13)C, and (31) P NMR spectroscopy, (1)H diffusion-ordered NMR spectroscopy ((1)H DOSY), and nuclear Overhauser effect spectroscopy (NOESY) was used to examine the interaction between 1 and each surfactant on the molecular level. Cationic surfactant CTAB caused precipitation of 1 due to strong electrostatic interactions, while the anionic SDS and neutral TX-100 surfactants did not exhibit any interaction at neutral pD. (1)H DOSY NMR spectroscopy indicated an interaction between 1 and zwitterionic surfactants Zw3-12 and CHAPS, which occurs via the positively charged ammonium group in the surfactant molecule. In the presence of anionic, neutral, and zwitterionic surfactants, 1 preserves its catalytic activity towards the hydrolysis of the peptide bond in the dipeptide glycyl-l-histidine (GH). The fastest hydrolysis was observed at pD 7.0 and could be rationalized by taking into account pD-dependent speciation of 1 and coordination properties of GH.

Dysprosium(iii) was coordinated to four 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) bisamide derivatives functionalized with amphiphilic p-dodecylaniline and p-tetradecylaniline in a differing cis- and trans-orientation. The complexes were assembled into mono-disperse micelles having size distribution maxima ranging from 10 to 15 nm and the magnetic and optical properties of the micelles were examined in detail. The micelles show characteristic Dy(iii) emission with quantum yields reaching 0.8%. The transverse relaxivity r2 per Dy(iii) ion at 500 MHz and 310 K reaches maximum values of ca. 20 s(-1) mM(-1) which is a large increase when compared to a value of 0.8 s(-1) mM(-1) observed for Dy(III)-DTPA. The micelles were stable in water when incubated at 37 °C for 1 week and showed no relaxivity decrease when measured in the presence of 4% (w/v) human serum albumin. The efficient T2 relaxation, especially at strong magnetic fields, is sustained by the high magnetic moment of the dysprosium(iii) ion, the coordination of water molecules and long rotational correlation times.

Peptide bond hydrolysis of 18 different dipeptides, divided into four groups depending on the nature of the amino acid side chain, by the dimeric Zr(IV)-substituted Keggin type polyoxometalate (POM) (Et2NH2)8[{α-PW11O39Zr-(μ-OH)(H2O)}2]·7H2O (1) was studied by means of kinetic experiments and 1H/13C NMR spectroscopy. The observed rate constants highly depend on the bulkiness and chemical nature of the X amino acid side chain. X-Ser and X-Thr dipeptides showed increased reactivity due to intramolecular nucleophilic attack of the hydroxyl group in the side chain on the amide carbon, resulting in a reactive ester intermediate. A similar effect in which the amino acid side chain acted as an internal nucleophile was observed for the hydrolysis of Gly-Asp. Interestingly, in the presence of 1 deamidation of Gly-Asn and Gly-Gln into Gly-Asp and Gly-Glu was observed. Dipeptides containing positively charged amino acid side chains were hydrolyzed at higher rates due to electrostatic interactions between the negatively charged POM surface and positive amino acid side chains.

The catalytic hydrolysis of a phosphoester bond in the DNA-model substrate 4-nitrophenyl phosphate (NPP) promoted by Zr(iv)-substituted Wells-Dawson Na14[Zr4(P2W16O59)2(μ3-O)2(OH)2(H2O)4]·57H2O polyoxometalate (ZrWD 4 : 2) was followed by means of (1)H and (31)P NMR spectroscopy. The hydrolytic reaction proceeded with a rate constant of 8.44 (±0.36) × 10(-5) s(-1) at pD 6.4 and 50 °C, representing a 300-fold rate enhancement in comparison with the spontaneous hydrolysis of NPP (kobs = 2.81 (±0.25) × 10(-7) s(-1)) under the same reaction conditions. The ZrWD 4 : 2 was also active towards hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) and the RNA model substrate 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP). The pD dependence of kobs shows that the rate constants for NPP hydrolysis decrease significantly when the pD values of the reaction mixtures increase. The formation constant (Kf = 190 M(-1)) and catalytic rate constant (kc = 6.40 × 10(-4) s(-1)) for the NPP-ZrWD 4 : 2 complex, activation energy (Ea) of 110.15 ± 7.06 kJ mol(-1), enthalpy of activation (ΔH(‡)) of 109.03 ± 6.86 kJ mol(-1), entropy of activation (ΔS(‡)) of 15.20 ± 2.49 J mol(-1) K(-1), and Gibbs activation energy (ΔG(‡)) of 104.32 ± 6.09 kJ mol(-1) at 37 °C were calculated from kinetic studies. The recyclability of ZrWD 4 : 2 was examined by adding an extra amount (5.0 mM) of NPP twice to a fully hydrolyzed mixture of 5.0 mM NPP and 1.0 mM ZrWD 4 : 2. The interaction between ZrWD 4 : 2 and the P-O bond of NPP was evidenced by a change in the (31)P chemical shift of the (31)P atom in NPP upon addition of ZrWD 4 : 2. Based on (31)P NMR experiments and the kinetic studies, a mechanism for NPP hydrolysis promoted by ZrWD 4 : 2 has been proposed. ispartof: Dalton Transactions vol:45 issue:30 pages:12174-12180 ispartof: location:England status: published

The hydrolysis of the iron-binding blood plasma glycoprotein transferrin (Tf) has been examined at pH = 7.4 in the presence of a series of Zr-substituted polyoxometalates (Zr-POMs) including Keggin (Et2NH2)10[Zr(PW11O39)2]∙7H2O (Zr-K 1:2), (Et2NH2)8[{&alpha, PW11O39Zr-(&mu, OH) (H2O)}2]∙7H2O (Zr-K 2:2), Wells-Dawson K15H[Zr(&alpha, 2-P2W17O61)2]&middot, 25H2O (Zr-WD 1:2), Na14[Zr4(&alpha, P2W16O59)2(&mu, 3-O)2(&mu, OH)2(H2O)4]&middot, 57H2O (Zr-WD 4:2) and Lindqvist (Me4N)2[ZrW5O18(H2O)3] (Zr-L 1:1), (nBu4N)6[(ZrW5O18(&mu, &ndash, OH))2]∙2H2O (Zr-L 2:2)) type POMs. Incubation of transferrin with Zr-POMs resulted in formation of 13 polypeptide fragments that were observed on sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), but the hydrolysis efficiency varied depending on the nature of Zr-POMs. Molecular interactions between Zr-POMs and transferrin were investigated by using a range of complementary techniques such as tryptophan fluorescence, circular dichroism (CD), 31P-NMR spectroscopy, in order to gain better understanding of different efficiency of investigated Zr-POMs. A tryptophan fluorescence quenching study revealed that the most reactive Zr-WD species show the strongest interaction toward transferrin. The CD results demonstrated that interaction of Zr-POMs and transferrin in buffer solution result in significant secondary structure changes. The speciation of Zr-POMs has been followed by 31P-NMR spectroscopy in the presence and absence of transferrin, providing insight into stability of the catalysts under reaction condition.

The catalytic fragmentation of hydrophobic proteins by polyoxometalates (POMs) requires the presence of surfactants in order to increase the solubility of the protein. Depending on the nature of the surfactant, different effects on the kinetics of protein hydrolysis are observed. As the molecular interactions between the POMs and surfactants in solutions have been scarcely explored, in this study, the interaction between the catalytically active Keggin polyoxometalate [Zr(&alpha, PW11O39)2]10&minus, and four different surfactants&mdash, sodium dodecyl sulfate (SDS), dodecyldimethyl(3-sulfopropyl)ammonium (Zw3-12), dodecyldimethyl(3-sulfopropyl) ammonium (CHAPS), and polyethylene glycol tert-octylphenyl ether (TX-100)&mdash, have been studied in aqueous media. The effect of polyoxometalate on the self-assembly of surfactant molecules into micelles and on the critical micellar concentration (CMC) has been examined by fluorescence spectroscopy and diffusion ordered NMR spectroscopy (DOSY).

The successful cocrystallization of the noncovalent complex formed between (Et2NH2)8[{α-PW11O39Zr-(μ-OH)(H2O)}2]·7H2O Keggin polyoxometalate (2) and Hen Egg White Lysozyme (HEWL) protein is reported. The resulting structural model revealed interaction between monomeric [Zr(PW11O39)]4−(1), which is a postulated catalytically active species, and the protein in two positions in the asymmetric unit. The first position (occupancy 36%) confirms the previously observed binding sites on the protein surface, whereas the second position (occupancy 14%) provides novel insights into the hydrolytic mechanisms of ZrIV-substituted polyoxometalates. The new interaction site occurs at the Asn65 residue, which is directly next to the Asp66–Gly67 peptide bond that was identified recently as a cleavage site in the polyoxometalate-catalysed hydrolysis of HEWL. Furthermore, in this newly discovered binding site, the monomeric polyoxometalate 1 is observed to bind directly to the side chain of the Asn65 residue. This binding of ZrIV as a Lewis-acid metal to the carbonyl O atom of the Asn65 side chain is very similar to the intermediate state proposed in density functional theory (DFT) studies in which ZrIV activates the peptide bond via interaction with its carbonyl O atom, and can be thus regarded as a model for interaction between ZrIV and a peptide bond.

In this paper we investigate the effect of three different types of surfactants, on the hydrolysis of Cytochrome c (Cyt c), a predominantly α helical protein containing a heme group, promoted by [Ce(α PW11O39)2]10- (CeK) and [Zr(α PW11O39)2]10- (ZrK) polyoxometalates. In the presence of SDS, Zw3 12, or CHAPS surfactants, which are commonly used for solubilizing hydrophobic proteins, the specificity of CeK or ZrK toward hydrolysis of Cyt c does not change. However, the hydrolysis rate of Cyt c by CeK was increased in the presence of SDS, but decreased in the presence of CHAPS, and was nearly inhibited in the presence of Zw3 12. The Circular dichroism and Tryptophan fluorescence spectroscopy have shown that the structural changes in Cyt c caused by surfactants are similar to those caused by POMs, hence the same specificity in the absence or presence of surfactants was observed. The results also indicate that for Cyt c hydrolysis to occur, large unfolding of the protein is needed in order to accommodate the POMs. While SDS readily unfolds Cyt c, the protein remains largely folded in the presence of CHAPS and Zw3 12. Addition of POMs to Cyt c solutions in CHAPS results in unfolding of the structure allowing the interaction with POMs to occur and results in protein hydrolysis. Zw3 12, however, locks Cyt c in a conformation that resists unfolding upon addition of POM, and therefore results in nearly complete inhibition of protein hydrolysis. ispartof: FRONTIERS IN CHEMISTRY vol:6 issue:AUG ispartof: location:Switzerland status: published

In this study, a combined molecular docking (rigid and flexible) and all-atom molecular dynamics simulations technique have been employed to investigate interactions of 1:1 Zr-containing Keggin polyoxometalate (ZrK) with four chemically distinct cleavage sites [Arg114-Leu115 (site 1), Ala257-Asp258 (site 2), Lys313-Asp314 (site 3), and Cys392-Glu393 (site 4)] of human serum albumin (HSA). The ZrK-HSA complexations were analyzed using electrostatic potentials, the chemical nature of amino acid residues, binding free energies, and secondary structures as parameters. They suggested that ZrK binds in a rather distinct manner to different cleavage sites, and its association was dominated by hydrogen bonding, both direct and solvent mediated, and electrostatic interactions, as suggested experimentally. The computed binding free interaction energies (-57.5, -24.2, -50.8, and -91.2 kJ/mol for sites 1, 2, 3, and 4, respectively) predicted the existence of one major binding site (site 4) and three minor binding sites (site 1, site 2, and site 3). The strong exothermicity of the binding was also supported by isothermal calorimetry experiments. Additionally, the binding of ZrK did not alter the overall α-helical secondary structure of HSA, which was in line with experimental observation. Furthermore, hydrolysis of the peptide bonds of the substrate was found to retain its overall structure. These results have provided a deeper understanding of the complex ZrK interactions with proteins, and they will lead to the design of the next generation of catalytically active polyoxometalates with improved hydrolytic activities. ispartof: JOURNAL OF PHYSICAL CHEMISTRY B vol:122 issue:29 pages:7219-7232 ispartof: location:United States status: published

Bone marrow adipose tissue (BMAT) increases after menopause, and increased BMAT is associated with osteoporosis and prevalent vertebral fractures. Peroxisome proliferator-activated receptor-γ (PPARγ) activation promotes adipogenesis and inhibits osteoblastogenesis; therefore, PPARγ is a potential contributor to the postmenopausal increase in BMAT and decrease in bone mass. The aim of this study is to determine if PPARγ inhibition can prevent ovariectomy-induced BMAT increase and bone loss in C3H/HeJ mice. Fourteen-week-old female C3H/HeJ mice ( n = 40) were allocated to four intervention groups: sham surgery (Sham) or ovariectomy (OVX; isoflurane anesthesia) with either vehicle (Veh) or PPARγ antagonist administration (GW9662; 1 mg·kg-1·day-1, daily intraperitoneal injections) for 3 wk. We measured BMAT volume, adipocyte size, adipocyte number. and bone structural parameters in the proximal metaphysis of the tibia using polyoxometalate-based contrast enhanced-nanocomputed topogaphy. Bone turnover was measured in the contralateral tibia using histomorphometry. The effects of surgery and treatment were analyzed by two-way ANOVA. OVX increased the BMAT volume fraction (Sham + Veh: 2.9 ± 2.7% vs. OVX + Veh: 8.1 ± 5.0%: P < 0.001), average adipocyte diameter (Sham + Veh: 19.3 ± 2.6 μm vs. OVX + Veh: 23.1 ± 3.4 μm: P = 0.001), and adipocyte number (Sham + Veh: 584 ± 337cells/μm3 vs. OVX + Veh: 824 ± 113cells/μm3: P = 0.03), while OVX decreased bone volume fraction (Sham + Veh: 15.5 ± 2.8% vs. OVX + Veh: 7.7 ± 1.9%; P < 0.001). GW9662 had no effect on BMAT, bone structural parameters, or bone turnover. In conclusion, ovariectomy increased BMAT and decreased bone volume in C3H/HeJ mice. The PPARγ antagonist GW9662 had no effect on BMAT or bone volume in C3H/HeJ mice, suggesting that BMAT accumulation is regulated independently of PPARγ in C3H/HeJ mice. ispartof: AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM vol:316 issue:1 pages:E96-E105 ispartof: location:United States status: published