Controlled solvothermal synthesis of novel organic functionalized polyoxovanadates

Four novel organic functionalized polyoxovanadates are solvothermally synthesized by altering the reaction temperature and using different organoarsonic acids. These POVs are fully characterized and the phase transitions between different POVs structures are confirmed by X-ray diffraction analyses. Such a transition is temperature-dependent and thus controlled synthesis of new POVs can be achieved.     

Silver(I)-ethynide clusters constructed with phosphonate-functionized polyoxovanadates

Two neutral silver(I)-phenylethynide clusters incorporating the [((t)BuPO(3))(4)V(4)O(8)](4-) unit as an integral shell component, namely {(NO(3))(2)@Ag(16)(C≡CPh)(4)[((t)BuPO(3))(4)V(4)O(8)](2)(DMF)(6)(NO(3))(2)}·DMF·H(2)O and {[(O(2))V(2)O(6)](3)@Ag(43)(C≡CPh)(19)[((t)BuPO(3))(4)V(4)O(8)](3)(DMF)(6)}·5DMF·2H(2)O, have been isolated and characterized by X-ray crystallography. The central cavities of the Ag(16) and Ag(43) clusters are occupied by two NO(3)(-) and three [(O(2))V(2)O(6)](4-) template anions, respectively.     

Self-assembly of hybrid organic-inorganic polyoxovanadates: functionalised mixed-valent clusters and molecular cages

Herein we report the intra- and inter-molecular assembly of a {V(5)O(9)} subunit. This mixed-valent structural motif can be stabilised as [V(5)O(9)(L(1-3))(4)](5-/9-) (1-3) by a range of organoarsonate ligands (L(1)-L(3)) whose secondary functionalities influence its packing arrangement within the crystal structures. Variation of the reaction conditions results in the dodecanuclear cage structure [V(12)O(14)(OH)(4)(L(1))(10)](4-) (4) where two modified convex building units are linked via two dimeric {O(4)V(IV)(OH)(2)V(IV)O(4)} moieties. Bi-functional phosphonate ligands, L(4)-L(6) allow the intramolecular connectivity of the {V(5)O(9)} subunit to give hybrid capsules [V(10)O(18)(L(4-6))(4)](10-) (5-7). The dimensions of the electrophilic cavities of the capsular entities are determined by the incorporated ligand type. Mass spectrometry experiments confirm the stability of the complexes in solution. We investigate and model the temperature-dependent magnetic properties of representative complexes 1, 4, 6 and 7 and provide preliminary cell-viability studies of three different cancer cell lines with respect to Na(8)H(2)[6]·36H(2)O and Na(8)H(2)[7]·2DMF·29H(2)O.     

Formation of high nuclearity mixed-valent polyoxovanadates in the presence of copper amine complexes

Two new Müller-type clusters, a one-dimensional solid [Cu(en)]_{2 4}[Cl ⊂V₁₅O₃₆]−12H₂O1, and a three-dimensional solid [Cu(pn)]_{2 4}[Cl ⊂V₁₈O₄₂]·12H₂O2, have been synthesised by employing identical hydrothermal conditions e_xcept varying the nature of organic diamine.1 crystallised in a chiral space groupP2₁2₁2₁ witha = 12.757(1),b = 18.927(2) andc = 28.590(3) ?, andZ =4.2 crystallised in a tetragonal system with space groupP4/nnc,a = 15.113(1) andc = 18.542(3) ?, andZ = 2. Mixed-valent vanadium ions in structures1 and2 have been established both by magnetisation and bond-length bond-valence measurements. Chemistry of formation of high nuclearity polyoxovanadate clusters is discussed. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.     

Two organic-inorganic poly(pseudo-rotaxane)-like composite solids constructed from polyoxovanadates and silver organonitrogen polymers

Two new composite solids, [Ag(btx)]₄H₂V₁₀O₂₈·2H₂O 1 and [Ag(biim)]₂V₄O₁₁2 (btx=1,4-bis(triazol-1-ylmethyl)benzene, biim=1,1′-(1,4-butanediyl)bis(imidazole)), have been synthesized and characterized by elemental analysis, IR, TGA and single-crystal X-ray diffraction. Compound 1 contains two one-dimensional (1D) polymeric chains, {Ag₂(btx)₂}²⁺ and [Ag₂(btx)₂H₂V₁₀O₂₈]²⁻, that are assembled by supramolecular forces into an intriguing two-dimensional (2D) poly(pseudo-rotaxane) network. Compound 2 comprises cationic {Ag₂(biim)₂}²⁺ three-dimensional (3D) framework penetrated by anionic chains. The electrochemical properties of the two compounds have been studied.     

Hybrid polyoxovanadates: anion-influenced formation of nanoscopic cages and supramolecular assemblies of asymmetric clusters

Two novel hybrid polyoxovanadates that are functionalized by (4-aminophenyl)arsonic acid ligands form upon the reduction of vanadates(V) in aqueous systems, whereby the underlying condensation reactions are influenced by the nature of the employed acid. In the presence of Cl(-) ions that derive from hydrochloric acid, a tetradecanuclear cage structure [V(IV)(14)O(16)(OH)(8)-(O(3)AsC(6)H(4)-4-NH(2))(10)](4-), whose cavity contains stabilizing halide ions and water molecules, is obtained. When nitric acid is used, a decanuclear [V(10)O(18)(O(3)AsC(6)H(4)-4-NH(2))(7)(DMF)(2)](5-) cluster can be isolated. The latter organizes into a hexagonal packing arrangement in the solid state.     

The challenges of trafficking hydrolysis prone metals and ascidians as an archetype

Some of the metal ions that are required, exploited, or simply managed in biological systems are susceptible to hydrolysis and to hydrolytic precipitation in the aqueous, aerobic environment of much of biology. Organisms have evolved exquisite mechanisms for handling these metal ions, offering striking examples of biological control over inorganic coordination chemistry. This year marks the one hundredth anniversary of the discovery of remarkably high vanadium concentrations in the blood cells of the ascidian. In the ensuing years, these marine invertebrates were established as masters of the biological chemistry of very hydrolysis-prone metals, with various ascidian species accumulating high concentrations of iron, vanadium, and titanium, among others. These three metals have very different histories of biological relevance, and many questions remain about how, and ultimately why, these organisms sequester them. This Perspective addresses the aqueous coordination chemistry that organisms like ascidians must control if they are to manipulate hydrolysis-prone metal ions, and describes some of the ascidian biomolecules that have been implicated in this phenomenon. The recently available genome sequence for one ascidian species offers a glimpse into its metal-management arsenal. It offers the opportunity to map the relatively well-studied paradigm of iron management onto the genome of an organism that is intermediate in evolution between invertebrates and vertebrates. The ascidians have much to teach us about how to manage metals like iron, titanium, and vanadium and how that ability evolved.     

From chain to network: design and analysis of novel organic-inorganic assemblies from organically functionalized zinc-substituted polyoxovanadates and zinc organoamine subunits

A series of novel organic-inorganic assemblies, [Zn(Meen)2]2[(4,4'-bipy)Zn2As8V12O40(H2O)] (1), [Zn(en)2(H2O)][Zn(en)2(4,4'-bipy)Zn2As8V12O40(H2O)].3H2O (2), [[Zn(en)3]2[Zn2As8V12O40(H2O)]].4H2O.0.25bipy (3) and [Zn2(en)5][[Zn(en)2][(bpe)HZn2As8V12O40(H2O)]2].7H2O (4) [en = ethylenediamine, Meen = 1,2-diaminopropane, 4,4'-bipy = 4,4'-bipyridine, and bpe = 1,2-bis(4-pyridyl)ethane] constructed from organically modified Zn-substituted polyoxovanadates and zinc organoamine subunits have been synthesized. Each anion cluster of compound 1 is directly linked by the 4,4'-bipy ligand into a one-dimensional (1D) straight chain. The secondary metal complex [Zn(Meen)2]2+ acts as an isolated countercation. The 1D chain structure of 2 is similar to that of 1 but sinuate because of the secondary metal complex [Zn(en)2]2+ decorated on the anion cluster. The en ligands covalently bonding to the surface anion of 3 not only support the secondary metal complex [Zn(en)2]2+ but also coordinate to another anion through the secondary metal complex [Zn(en)2]2+ bridge to form an "eight-shaped" chiral helix. The unprecedented 2D layer of compound 4 with large nanosized inner rectangular cavities [33.669(6) x 14.720(8) A] is successfully achieved through the anion clusters polymerized first into chains by flexible organic ligands and then secondary metal complexes bridged between the chains. The different coordination abilities and geometries of the bidentate organodiamine ligands used in the four-reaction systems play important roles in the formation of the final structures: from straight chains to sinuate chains, to helical chiral chains, and finally to a 2D layer with helices.     

Push–Pull archetype of reduced graphene oxide functionalized with polyfluorene for nonvolatile rewritable memory

A solution‐processable PFTPA‐convalently grafted reduced graphene oxide (RGO‐PFTPA) was synthesized by the 1,3‐dipolar cycloaddition of azomethine ylide. Bistable electrical switching and nonvolatile rewritable memory effects were demonstrated in a sandwich structure of indium tin oxide/RGO‐PFTPA/Al. The switch‐on voltage of the as‐fabricated device was around ?1.4 V, and the ON/OFF‐state current ratio was more than 10³. The ON–OFF transition process is reversible because the application of a high enough positive voltage can induce the reverse transfer of electrons, reducing the conductivity back to its initial OFF state. Both the OFF and ON states are accessible and very stable under a constant voltage stress of ?1 V for up to 3 h, or under a pulse voltage stress of ?1 V for up to 10⁸ continuous read cycles (pulse period = 2 μs, pulse width = 1 μs). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Lanthanide complexes of macrocyclic polyoxovanadates by VO4 units: synthesis, characterization, and structure elucidation by X-ray crystallography and EXAFS spectroscopy

Reactions of a tetravanadate anion, [V(4)O(12)](4-), with a series of lanthanide(III) salts yield three types of lanthanide complexes of macrocyclic polyoxovanadates: (Et(4)N)(6)[Ln(III)V(9)O(27)] [Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6)], (Et(4)N)(5)[(H(2)O)Ho(III)(V(4)O(12))(2)] (7), and (Et(4)N)(7)[Ln(III)V(10)O(30)] [Ln = Er (8), Tm (9), Yb (10), Lu (11)]. Lanthanide complexes 1-11 are isolated and characterized by IR, elemental analysis, single-crystal X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS). Lanthanide complexes 1-6 are composed of a square-antiprism eight-coordinated Ln(III) center with a macrocyclic polyoxovanadate that is constructed from nine VO(4) tetrahedra through vertex sharing. The structure of 7 is composed of a seven-coordinated Ho(III) center, which exhibits a capped trigonal-prism coordination environment by the sandwiching of two cyclic tetravanadates with a capping H(2)O ligand. Lanthanide complexes 8-11 have a six-coordinated Ln(III) center with a 10-membered vanadate ligand. The structural trend to adopt a larger coordination number for a larger lanthanide ion among the three types of structures is accompanied by a change in the vanadate ring sizes. These lanthanide complexes are examined by EXAFS spectroscopies on lanthanide L(III) absorption edges, and the EXAFS oscillations of each of the samples in the solid state and in acetonitrile are identical. The Ln-O and Ln···V bond lengths obtained from fits of the EXAFS data are consistent with the data from the single-crystal X-ray studies, reflecting retention of the structures in acetonitrile.     

Optical biochemical sensor for determining hydroperoxides in nonpolar organic liquids as archetype for sensors consisting of amphiphilic conetworks as immobilisation matrices

This paper reports the successful design of a prototype of an optical biochemical sensor for the determination of hydroperoxides in nonpolar organic liquids. The sensor consists of a matrix of an amphiphilic polymer conetwork (APCN), a novel class of very promising polymeric materials for easy preparation of biochemical sensor matrices. APCNs are characterised by nanoscopic phase separation between the hydrophilic and the hydrophobic phases. For medium ratios of conetwork composition, the domains of both phases are interconnected both on the surface of the conetworks and throughout the bulk. The APCNs have peculiar swelling properties—the hydrophilic phase swells in hydrophilic media and the hydrophobic phase swells in hydrophobic media. In both types of media dissolved reagents can diffuse from the solution into the swollen phase of the polymeric conetwork. This enables loading of the hydrophilic phase of the APCNs with enzymes and indicator reagents by simple impregnation. Hydrophobic analytes can diffuse into the polymeric conetwork via its hydrophobic phase and react with indicator reagents immobilised in the hydrophilic phase at the huge internal interface between the two opposite phases. To prepare the described hydroperoxide-sensitive biosensors, we used APCN films consisting of 58% (w/w) poly(2-hydroxyethyl acrylate) (PHEA) as hydrophilic chains and 42% (w/w) polydimethylsiloxane (PDMS) as hydrophobic linkers. Horseradish peroxidase (HRP) and diammonium 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as indicator reagent were co-immobilised in this optically clear and transparent matrix. In this feasibility study the conditions investigated were principally those relevant to characterisation of the innovative matrix material and the disposable biosensor produced from it; the biosensor was not optimised. Sensitivity toward tert-butylhydroperoxide (tBuOOH) dissolved in n-heptane was acceptable, between approximately 1 and at least 50 mmol L⁻¹, even in the dry state. The response time was 1.7 to 5.0 min. No leaching of immobilised reagents was observed during a period of at least one hour. Pre-swelling the sensors with water increased the reaction rate and the total turnover number of the enzyme. In a dry atmosphere at 4 °C the sensors were found to be stable for at least two weeks.     

Introducing organosilicone source into the synthetic system of polyoxovanadates: two novel {V15Si6O48}-based extended chains

Two novel extended chains based on rare {V(IV)(15)Si(6)O(48)} have been prepared under hydrothermal conditions by introducing an organosilicone source into the synthetic system of the polyoxovanadates. Single-crystal X-ray diffraction analyses show that the neighboring {V(IV)(15)Si(6)O(48)} clusters are linked by a pair of V(V)O(2) fragments via the coordination bonds of (Si-)O-V-O(-Si) to give rise to a zig-zag chain in compound 1, which is the first example of V(iv,v) mixed valence states successfully synthesized in {V(15)Si(6)O(48)}-containing POMs. While in 2 the linkages are changed to [Co(pdn)(2)(H(2)O)](2+) (pdn = 1,3-propanediamine) cations instead of {V(V)O(2)} fragments, to generate another comparable 1-D infinite chain, which demonstrates the first organic-inorganic vanadosilicon hybrid linked by a second transition-metal complex. The possible hydrolysis mechanism of tetraethyl orthosilicate as the Si source is postulated to afford a feasible protocol to synthesize a new type of vanadosilicate cluster. The magnetic properties of the two compounds have also been investigated.     

Studying functional dynamics in bio-molecules using accelerated molecular dynamics

Many biologically important processes such as enzyme catalysis, signal transduction, ligand binding and allosteric regulation occur on the micro- to millisecond time-scale. Despite the sustained and rapid increase in available computational power and the development of efficient simulation algorithms, molecular dynamics (MD) simulations of proteins and bio-machines are generally limited to time-scales of tens to hundreds of nano-seconds. In this perspective article we present a comprehensive review of Accelerated Molecular Dynamics (AMD), an extended biased potential molecular dynamics approach that allows for the efficient study of bio-molecular systems up to time-scales several orders of magnitude greater than those accessible using standard classical MD methods, whilst still maintaining a fully atomistic representation of the system. Compared to many other approaches, AMD affords efficient enhanced conformational space sampling without any a priori understanding of the underlying free energy surface, nor does it require the specific prior definition of a reaction coordinate or a set of collective variables. Successful applications of the AMD method, including the study of slow time-scale functional dynamics in folded proteins and the conformational behavior of natively unstructured proteins are discussed and an outline of the different variants and extensions to the standard AMD approach is presented.     

Establishment of the C(2)H(5)+O(2) reaction mechanism: a combustion archetype

The celebrated C(2)H(5)+O(2) reaction is an archetype for hydrocarbon combustion, and the critical step in the process is the concerted elimination of HO(2) from the ethylperoxy intermediate (C(2)H(5)O(2)). Master equation kinetic models fitted to measured reaction rates place the concerted elimination barrier 3.0 kcal mol(-1) below the C(2)H(5)+O(2) reactants, whereas the best previous electronic structure computations yield a barrier more than 2.0 kcal mol(-1) higher. We resolve this discrepancy here by means of the most rigorous computations to date, using focal point methods to converge on the ab initio limit. Explicit computations were executed with basis sets as large as cc-pV5Z and correlation treatments as extensive as coupled cluster through full triples with a perturbative inclusion of quadruple excitations [CCSDT(Q)]. The final predicted barrier is -3.0 kcal mol(-1), bringing the concerted elimination mechanism into precise agreement with experiment. This work demonstrates that higher correlation treatments such as CCSDT(Q) are not only feasible on systems of chemical interest but are necessary to supply accuracy beyond 0.5 kcal mol(-1), which is not obtained with the "gold standard" CCSD(T) method. Finally, we compute the enthalpy of formation of C(2)H(5)O(2) to be Delta(f)H degrees (298 K)=-5.3+/-0.5 kcal mol(-1) and Delta(f)H degrees (0 K)=-1.5+/-0.5 kcal mol(-1).     

Spatio-temporal dynamics in glycolysis

During the glycolytic degradation of sugar in a thin layer of yeast extract, travelling waves of NADH and protons can be generated that carry a state of high enzymatic activity through the system. The controlled initiation of such waves with an activator of the enzyme phosphofructokinase (PFK) and the influence of various salts and co-factors on the propagation dynamics are investigated. Furthermore a first study of the dispersion of waves is presented. The experimental characterisation of this in vitro system contributes to unravelling the possible role of glycolysis for biological information processing. In this context, the provision of chemically available energy in the absence of compartmentation by glycolysis is of primary importance.     

Coupling of an advanced tri-functional building block by reductive amination leads to a protected backbone of a new archetype of foldamer

In order to advance our project to explore a new archetype of foldamer that preferentially folds in water, we designed two types of tri-functional building blocks with increasingly favorable ketone deprotection properties. Both were selected for their ease of synthetic access and the availability of bulk starting material. While the first building block proved unsuitable for efficient coupling by reductive amination, the second gave rise to almost quantitative yields according to mass spectral monitoring. It was thus effectively turned into a protected dimer and a tetramer. Although their subsequent purification prior to exhaustive ketone deprotection was preparatively impractical in view of their high polarity/water solubility, the stage is now set for transfer of the oligomer synthesis onto the solid phase on resin in view of the efficient five-step synthetic access from affordable bulk material, the favorable deprotection properties, the perspective for introduction of a variety of backbone substituents, and the possibility to protect the amine terminus by Boc or Fmoc protection.     

Synthetically persistent, self assembled [V(IV)2V(V)4] polyoxovanadates: facile synthesis, structure and magnetic analysis

Slow diffusion in a H-tube at room temperature of a methanolic solution of [VO(acac)(2)] (Hacac = acetylacetone) and 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy) into an aqueous solution of sodium pyrophosphate (Na(4)P(2)O(7)) resulted in the serendipitous formation of X-ray quality crystals of mixed-valent, hexameric oxovanadates of general formula [V(6)O(12)(OCH(3))(4)(L)(4)]·solv [L = 1,10-phenanthroline (phen) for 1· 2CH(3)OH · 4H(2)O (1a), and 2,2'-bipyridine (bipy) for 2· 4H(2)O (2a)]. These were characterized by single-crystal X-ray diffraction, IR, elemental and thermogravimetric analysis (TGA). A facile, rationalized synthetic route for the isolation of 1a and 2a could be established following structural determination, involving NaOH in place of Na(4)P(2)O(7) as pH modulator. The use of distilled water (pH 7) as methanolic co-solvent also resulted in crystallization of the two complexes, proving the presence of a base in the reaction scheme is not vital, with slightly pH-depended yields noted for 2a only. A survey of the literature revealed the occurrence of several other procedures, from classical methods to hydrothermal routes, leading to different solvates of 1, the crystal structure of 2 being unreported in any form to date. The precise nature of the molecular assembly in these type of hybrid organic-inorganic poly-vanadates is contradictory in published reports. On the basis of newly acquired high resolution crystal data and supported by magnetic investigation of the samples, we propose herein a formulation as [(V(IV)O)(2)(V(V)O(2))(4)(μ(3)-O)(2)(μ-OCH(3))(4)(L)(4)], with two oxovanadyl(IV) and four dioxovanadyl(V) units per molecule. A net ferromagnetic coupling between the two isolated V(IV) metal centers was measured with literature-consistent J values of +16.1(1) and +19.7(1) cm(-1) for 1a and 2a, respectively [H = -JS(A)·S(B) + S(A)·D·S(B) + βH (g(A)S(A) + g(B)S(B))], suggesting that crystal packing forces do not significantly influence the magnetic properties of this class of materials. A facile route toward the synthesis of the fully-oxidized [V(V)(4)O(8)(CH(3)O)(4)(bipy)(2)] and [V(V)(4)O(6)(CH(3)O)(6)(acac)(2)] tetraoxovanadates is also reported.