Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters to Lysozyme

The high-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [VIVO(acetylacetonato)2] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V15O36(OH2)]5-, which non-covalently interacts with the lysozyme surface, [V15O33(OH2)]+ and [V20O51(OH2)]n- (this latter based on an unusual {V18O43} cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of VIV to VV and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.

Reactivity control of nitrate-incorporating octadecavanadates by changing the oxidation state and metal substitution

Clarification and control of the active sites at the atomic/molecular level are important to develop nanocatalysts. The catalytic performance of two oxidation states of nitrate-incorporating octadecavanadates, [V18O46(NO3)]5- (V18) and [V18O46(NO3)]4- (V18ox), and a copper-substituted one, [Cu2V16O44(NO3)]5- (Cu2V16), in selective oxidation was investigated. Both V18 and V18ox possessed the same double-helical structures and one of two tetravalent vanadium sites of V18 was oxidized in V18ox. The comparison of the mobility of the incorporated nitrate reveals that tetravalent vanadium centres show stronger interaction with the incorporated anions than pentavalent ones. The oxidation reaction with V18ox proceeded more smoothly with tert-BuOOH as an oxidant than that with V18. The reactivity and selectivity of the oxidation of 2-cyclohexen-1-ol were different among the derivatives. V18ox showed the higher reactivity with 72% selectivity to epoxide. With V18, reactivity was lower but higher selectivity to epoxide was achieved. In the presence of Cu2V16, 2-cyclohexen-1-one was selectively obtained with 81% selectivity. The order of the reactivity for cyclooctene was V18ox, V18 and Cu2V16. These results shows that the cap part of the double-helix acts as the active site. Even though the vanadium-oxygen species exhibit the same structures, the catalytic properties can be controlled by changing the valence of vanadium and metal substitution.

Elucidation of Design Criteria for V-based Redox Mediators: Structure-Function Relationships that Dictate Rates of Heterogeneous Electron Transfer

Redox mediators are attractive solutions for addressing the stringent kinetic stipulations required for efficient energy conversion processes. In this work, we compare the electrochemical properties of four vanadium complexes, namely [V(acac)3], [V6O7(OMe)12], [nBu4N]3[V6O13(TRISNO2)2], and [nBu4N]5[V18O46(NO3)] in non-aqueous solutions on glassy carbon electrodes. The goal of this study is to investigate the electron transfer kinetics and diffusivity of these compounds under identical experimental conditions to develop an understanding of structure-function relationships that dictate the physicochemical properties of vanadium oxide assemblies. Complex selection was dictated by two criteria - (1) nuclearity of the transition metal complexes (2) distribution of electron density in the native electronic configuration. Our analyses establish that electronic communication between metal centers significantly impacts charge transfer kinetics of these vanadium-based compounds.

Stabilization and Binding of [V4 O12 ]4- and Unprecedented [V20 O54 (NO3 )]n- to Lysozyme upon Loss of Ligands and Oxidation of the Potential Drug VIV O(acetylacetonato)2

High-resolution crystal structures of lysozyme in the presence of the potential drug VIV O(acetylacetonato)2 under two different experimental conditions have been solved. The crystallographic study reveals the loss of the ligands, the oxidation of VIV to VV and the subsequent formation of adducts of the protein with two different polyoxidovanadates: [V4 O12 ]4- , which interacts with lysozyme non-covalently, and the unprecedented [V20 O54 (NO3 )]n- , which is covalenty bound to the side chain of an aspartate residue of symmetry related molecules.

A General Access Route to High-Nuclearity, Metal-Functionalized Molecular Vanadium Oxides

Molecular metal oxides are key materials in diverse fields like energy storage and conversion, molecular magnetism and as model systems for solid-state metal oxides. To improve their performance and increase the variety of accessible motifs, new synthetic approaches are necessary. Herein, we report a universal, new precursor to access different metal-functionalized polyoxovanadate (POV) clusters. The precursor is synthesized by a novel solid-state thermal treatment procedure. Solution-phase test reactions at room temperature and pressure show that reaction of the precursor with various metal nitrate salts gives access to a range of metal-functionalized POVs. The first nitrate-templated molecular calcium vanadate cluster is reported. We show that this precursor could open new access routes to POV components for molecular magnetism, energy technologies or catalysis.

Supramolecular assembly of a hierarchically structured 3D potassium vanadate framework

The hierarchical assembly of 3D-polyoxovanadate frameworks using host–guest interactions is reported.

Atomic and electronic structure of solids of Ge2Br2PN, Ge2I2PN, Sn2Cl2PN, Sn2Br2PN and Sn2I2PN inorganic double helices: a first principles study

We report the results of density functional theory calculations on the atomic and electronic structure of solids formed by assembling A₂B₂PN (A = Ge and Sn, B = Cl, Br, and I) inorganic double helices.

Halide encapsulation by dicarboxylate oxido-vanadium cage complexes

Compounds [Bu₄N]₂[V₈O₁₆(oda)₄⊂2Cl], 1, [Bu₄N]₂[V₈O₁₆(glut)₄⊂2Cl], 2, and [Bu₄N][V₄O₈(glut)₂⊂F], 3, (oda = oxydiacetate, O(CH₂COO)₂^2-; glut = glutarate, CH₂(CH₂COO)₂^2-) were obtained by a stepwise reaction of in situ prepared [Bu₄N]VO₃ with HCl (or HF for 3) and then with the dicarboxylic acid X(CH₂COOH)₂ (X = O and CH₂), under appropriate reaction conditions. Multinuclear magnetic resonance (¹H, ¹³C{¹H}, ³⁵Cl, ¹⁹F and ⁵¹V), electrochemical studies, X-ray structural determinations (single crystal and powder), thermogravimetric analyses (TGA) and Density Functional Theory (DFT) calculations were employed to characterise these polyoxovanadate complexes 1-3. They included encapsulated halide anions, two chloride ions in 1 and 2 and one fluoride ion in 3, where the shape and dimensions of the cage were governed by the halide size. The stabilizing template effect of the chloride ion towards the bowl-shaped [V₄O₈(OOCR)₄] fragment (i.e. the half part of 1 and 2), containing a crown-shaped {V₄O₈} subunit, or that of the fluoride ion towards the planar {V₄O₈} moiety in 3, was definitively demonstrated by DFT calculations. The HOMO composition of 1 prompted us to study the possible oxidation of the two encapsulated chloride ions toward a chlorine molecule. The electrochemical behaviors of 1-3 were thus investigated. However, the chlorine molecule in the model [V₈O₁₆(oda)₄⊂(Cl₂)], 6c, was not capable to stabilise the polyoxovanadate cage [V₈O₁₆(oda)₄], 4c, according to DFT calculations.

A Bowl-Type Dodecavanadate as a Halide Receptor

The dodecavanadate framework, [V₁₂O₃₂]^4-, exhibits a unique bowl-type structure with an open molecular oxide cage having a cavity diameter of 4.4 Å, and different synthetic paths were required to construct the bowl-type structure with a different guest. A new dodecavanadate, {(n-C₄H₉)₄N}₄[V₁₂O₃₂(CH₃NO₂)] (1), is synthesized with a nitromethane guest, which is stacked above the entrance of the hemisphere rather than fully occupying the cavity, and it enables a guest-capturing reaction, while retaining the anionic cage structure. Compound 1 is a good precursor for halide-centered dodecavanadates, {(C₂H₅)₄N}₅[V₁₂O₃₂(X)] (X = Cl^- (2), Br^- (3), and I^- (4)). The position of the halide inside the cavity correlates with the ionic radius of the guest; the small chloride ion sat at the far bottom, and the large iodide floated at the entrance. The inclusion reaction rates were estimated through ⁵¹V NMR time-course measurements in nitromethane. The reaction rates increase in the order I^- < Br^- < Cl^-.