Article

Stereochemistry of Vanadium Peroxido Complexes: The Case of the Quinoline-2-carboxylato Ligand

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Abstract

A new mononuclear vanadium peroxido complex [VO(O2)(phen)(quin)]·H2O (1) exhibiting an unprecedented isomerism of its ligands was isolated from a two-component water–acetonitrile solvent system. DFT computations aimed at inspecting the stability of all possible isomers of complexes [VO(O2)(L1)(L2)], where L1 and L2 are NN+ON, OO+ON, NN+OO, and ON+ON donor atom set ligands, suggested that every complex characterized so far was the one preferred thermodynamically. However, the particular case of complex [VO(O2)(phen)(quin)] reported herein poses a notable exception to this rule, as this complex yielded single crystals of the isomer with total energy above the anticipated isomer, although both of these isomers could be observed concurrently in solution and also in the solid state. 51V NMR spectroscopy suggested these isomers to be present both in the crystallization solution and in the acetonitrile solution of 1. The coexistence of two isomers is a consequence of their small computed energy difference of 2.68 kJ mol–1, while the preferential crystallization favoring the unexpected isomer is likely to be triggered by solvent effects and the effects of different solubility and/or crystal packing. The coordination geometry of the unusual isomer also manifests itself in FT-IR and Raman spectra, which were corroborated with DFT computations targeted at band assignments.

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... Among these, peroxovanadium complexes represent an important class of compounds extensively explored for their wide spectrum of promising biological functions including antidiabetic, antitumor, and catalytic activities. ey also play an inhibitory role in the hydrolysis of phosphoproteins [15][16][17][18][19]. Oxoperoxovanadium (V) complexes mimic the catalytic action of vanadate-dependent haloperoxidases in oxidizing the halides in the presence of hydrogen peroxide. ...
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Vanadium is named after Vanadis, the most aristocratic of Norse goddesses, who symbolises beauty and fertility - essential features of vanadium chemistry. It is a ubiquitous trace element, with a surprising range of biological functions. In Bioinorganic Vanadium Chemistry, Dieter Rehder addresses the major aspects of vanadium chemistry related to living organisms and the mutual impact between biological and inorganic vanadium chemistry. Topics covered include: the history, natural occurrence, distribution and impact of vanadium. Inorganic aspects of the function of vanadium in biological systems. Interaction of aqueous vanadate and vanadyl with biogenic ligands. Vanadium coordination compounds. The vanadium-carbon bond. Methods of characterisation of biogenic and model vanadium systems (EPR and ENDOR for oxovanadium(IV); 51V NMR for vanadium(V); XAS). Vanadium in ascidians and polychaeta worms. The concentration of vanadium in the form of amavadin by Amanita mushrooms. Vanadate-dependent haloperoxidases. Vanadium and the nitrogen cycle. Vanadate as energiser for bacteria, and vanadophores. Medicinal aspectsm including the anti-diabetic potential of vanadium compounds. Interaction of vanadium with proteins and protein substrates. Vanadium and phosphate-metabolising enzymes. Bioinorganic Vanadium Chemistry conveys the essential aspects of vanadium bioinorganic chemistry, making this book a valuable complement to more general bioinorganic chemistry texts and more specialized topical reviews for researchers and students alike.
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The novel heteroleptic complex (gu)2[Nb(O2)3(quin-2-c)]·H2O (1) has been prepared by substituting a peroxo group by quinoline-2-carboxylate ion in the homoleptic complex (gu)3[Nb(O2)4] (2) in the presence of an excess of hydrogen peroxide in aqueous medium (gu+=CN3H6+; quin-2-c=quinoline-2-carboxylate ion). The complexes contain the highly symmetric and planar guanidinium ion as a counter-ion, which exhibits high stability and an extended hydrogen bonding pattern. The crystal structure and the spectral characterization of (gu)2[Nb(O2)3(quin-2-c)]·H2O have been determined. The ground electronic structure of the complex has been calculated with the density functional theory (DFT) method, and TD-DFT calculations have been employed to interpret the UV–Vis transitions. Compilation of the experimental and theoretical results may permit us to produce additional information about binding and catalytic reactivity.
Article
Cadmium(II) complex with quinaldic acid (quinH), [Cd(quin)(2)(H2O)(2)] (1), was prepared by the reaction of cadmium(II) acetate and quinaldic acid in water-ethanol mixture, while another cadmium(II) complex, [Cd(quin)(2)(DMSO)(2)] (2), was prepared by the recrystallization of 1 in DMSO. Both complexes were characterized by IR spectroscopy and TGA/DTA methods. The crystal structure of 2 was determined by X-ray structure diffraction analysis. Cadmium(II) ion is octahedrally coordinated by two N,O-bidentate quinaldate ligands in equatorial and by two DMSO molecules in axial positions. Only weak intermolecular C-H center dot center dot center dot O hydrogen bonds and pi-pi stacking interactions as packing forces are present in the crystal structure of 2. The theoretical investigations included geometry optimizations of both complexes at DFT level (B3LYP and mPW1PW91 functionals) and calculations of vibrational frequencies. Calculated and experimental IR spectra were compared and characteristic bands assigned. The electronic properties of the complexes were investigated by the NBO analysis. Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and of DMSO in 2 and then complete decomposition of quinaldate ligands for both 1 and 2.
Article
The synthesis, structure, and properties, with respect to oxygen transfer to various substrates, of peroxotitanium(IV) derivatives 1-5 are reported. The X-ray crystal structure of 1 essentially revealed that the O-O distance in the peroxo group is short and the HMPT molecule is weakly bonded to titanium. Strong stabilization of the peroxotitanium moiety by picolinato, hydroxyquinolino, or hydroximato ligands precluded oxygen transfer from the titanium compounds to olefins, allylic alcohols, cyclic ketones, or sulfides. Triphenylphosphine and tetracyanoethylene were found to react with 1-5. These results are interpreted in terms of saturation of the metal which only very loosely coordinates strong donors such as HMPT.
Article
The structure of the title compound, K[V0(02)i(C12H7N302)].2H20, was determined. The geometry about the V atom is pentagonal bipyramidal with the pentagonal plane defined by the two peroxo groups and one N atom from the phenanthroline ligand [N(2)]. The oxo ligand lies in the plane vanadium-phenanthroline moiety, trans to the second phenanthroline N atom [N(l)]. The planes formed by the two peroxo groups and the V atom are bent towards each other with a dihedral angle of 22.1 (3)0 and are roughly perpendicular to the phenanthroline ligand. Of the two potential positions for the nitro group, that found puts the greatest possible distance between the nitro group and the oxo ligand.
Article
Komplexe des Vanadium(V) von Typ VO5–nNn (n = 0–2), VO6–nNn (n = 0–3) und VO7–nNn (n = 0–2) mit ein- bis fünfzähnigen, Sauerstoff- und Stickstoff-funktionellen Liganden zeigen chemische Verschiebungen δ(⁵¹V) zwischen – 380 und – 750 ppm (relativ zu VOCl3), wobei die höchsten Abschirmungen in Komplexen mit Dreiringstrukturen (Peroxo- und Hydroxyl-amido-Komplexe) erreicht werden. In den Komplexen V★O(OR)- (LL)2 [LL = N-Phenylbenzylhydroxamat(1–), pbha; 8-Hydroxychinolinat(1–), oxin; 3-Hydroxy-2-methyl-4-pyronat(1–), mal] wird in der Reihe R = CH2R′, CH(R′R″), CR′(R″)2 zunehmende Abschirmung beobachtet. die Komplexe werden durch Umsetzung ein- und mehrwertiger, darunter auch cyclischer Alkohole mit [VO(oxin)2]2(μ-O) bzw. VOCl(pbha)2, oder direkt aus Vanadat und den Liganden erhalten. Chirale Alkohole (R★OH) geben Anlaß zu zwei Kernresonanzsignalen für die beiden diastereomeren Enantiomerenpaare. Die Ergebnisse der Untersuchungen in der Reihe VO(OR)(oxin)2 erlauben eine Beurteilung auch der Koordination einiger Nucleoside (R = Inosin, Uridin und 2′- Desoxyuridin). VOCl(pbha)2 kristallisiert in der monoklinen Raumgruppe P21/n mit den folgenden Zellparametern: a = 1184.3, b = 1564.1, c = 1364.4 pm; β = 91.94°. Die Koordinationsgeometrie ist verzerrt oktaedrisch; der V-O-Doppelbindungsabstand ist mit 180.1 pm bemerkenswert lang.
Article
To understand and calculate the interactions of a solute with a solvent, a good method of computing the molecular surface is needed. Three kinds of surfaces may be used: the van der Waals Surface, the Accessible Surface, and the Molecular Surface. The latter is redefined in this article as the Solvent-Excluding Surface. The new algorithm for computing the Solvent-Excluding Surface included in the GEPOL93 program is described. GEPOL93 follows the same concept as former versions of GEPOL but with a full new algorithm. Thus, it computes the Solvent-Excluding Surface by filling the spaces not accessible to the solvent with a set of new spheres. The computation is controlled by three parameters: the number of triangles per sphere, controlled by NDIV; the maximum overlap among the new spheres (OFAC); and the size of the smallest sphere that can be created (RMIN). The changes introduced for the computation of the ESURF make GEPOL93 not just a new version but a new program. An estimation is made of the error in the area and volume obtained in the function of the parameters. © 1994 by John Wiley & Sons, Inc.
Article
The majority of 51V NMR studies on V(V) complexes have been reported in water, which currently limits the usefulness of 51V NMR in identifying V(V) species in non-aqueous solvents. In this report, the 51V NMR spectra have been obtained for vanadate and peroxovanadate complexes that exist at pH ≤ 7 in solutions containing 2–90% water in acetonitrile. Millimolar vanadate and peroxovanadate solutions in acetonitrile containing as little as 2% water were prepared by diluting a conc. aq. solution of vanadate (Bu4N+ salt) with acetonitrile. As with simple oxovanadate oligomers and peroxovanadate complexes in aqueous solutions, the species present in acetonitrile solution are a function of vanadium, acid and peroxide concentrations. The 51V resonances for several species can be assigned by correlating changes in chemical shifts as a function of water concentration. Species definitively characterized include VO2+, HxVO4x−3, HV2O73−, V4O124−, V5O155−, V10O286−, VO(O2)+, VO(O2)2− and V2O2(O2)3. While the chemical shift for every assigned species moves downfield as water concentration is decreased, the magnitude of the downfield shift is highly dependent on the vanadium species. The assignments provided herein from the foundation for establishing the reactivity patterns for peroxovanadate in non-aqueous media.
Article
The discovery of vanadium's insulin-like behaviour in vitro, and later of the orally available glucose- and lipid-lowering capability of these same compounds in vivo, has stimulated renewed interest in vanadium coordination chemistry. Besides the anti-diabetic effects for which it is now so well known, vanadium also exhibits a number of other therapeutic effects including anti-tumour and anti-inflammatory activities. In this review, emphasis will be on the most recent developments in the coordination chemistry of vanadium(III), (IV) and (V), as related to development of these compounds for pharmaceutical use. How best to measure bioactivity and the pharmaceutical relevance of accompanying increased oxidative stress will also be considered.
Article
A method is presented which utilizes the calculation of the molecular electrostatic potential or the electric field at a discrete number of preselected points to evaluate the environmental effects of a solvent on the properties of a molecular system. No limitations are imposed on the composition and dimension of the solute, on the goodness of the corresponding wavefunction, or on the shape of the cavity in the dielectric. Several levels of approximation, which evidence the effect of self-polarization of the system of surface charges, the influence of the tails of the solute charge distribution going beyond the limits of the cavity, and the effect of the polarization of the solute, are examined and discussed.
Article
A recently proposed procedure for introducing solvent effects in the molecular hamiltonian of a solute is here re-elaborated to get approximate solutions of the corresponding classical electrostatic problem. The basic feature of the original procedure, i.e. the direct utilization of a quantum-mechanical ab initio description of the solute charge distribution in the “continuum” solution model, with cavities of arbitrary shape, is maintained. The meaning of supplementary assumptions introduced in classical calculation 0is discussed, and a comparison is made with analogous evaluations obtained with other approaches
Article
Polarization functions are added in two steps to a split-valence extended gaussian basis set: d-type gaussians on the first row atoms C. N, O and F and p-type gaussians on hydrogen. The same d-exponent of 0.8 is found to be satisfactory for these four atoms and the hydrogen p-exponent of 1.1 is adequate in their hydrides. The energy lowering due to d functions is found to depend on the local symmetry around the heavy atom. For the particular basis used, the energy lowerings due to d functions for various environments around the heavy atom are tabulated. These bases are then applied to a set of molecules containing up to two heavy atoms to obtain their LCAO-MO-SCF energies. The mean absolute deviation between theory and experiment (where available) for heats of hydrogenation of closed shell species with two non-hydrogen atoms is 4 kcal/mole for the basis set with full polarization. Estimates of hydrogenation energy errors at the Hartree-Fock limit, based on available calculations, are given.
Article
Two extended basis sets (termed 5–31G and 6–31G) consisting of atomic orbitals expressed as fixed linear combinations of Gaussian functions are presented for the first row atoms carbon to fluorine. These basis functions are similar to the 4–31G set [J. Chem. Phys. 54, 724 (1971)] in that each valence shell is split into inner and outer parts described by three and one Gaussian function, respectively. Inner shells are represented by a single basis function taken as a sum of five (5–31G) or six (6–31G) Gaussians. Studies with a number of polyatomic molecules indicate a substantial lowering of calculated total energies over the 4–31G set. Calculated relative energies and equilibrium geometries do not appear to be altered significantly.
Article
The present work deals with the isomeric complexes of the molecular composition [Ru(II)(trpy)(L)Cl] in 1 and 2 (trpy = 2,2':6',2''-terpyridine, L = deprotonated form of quinaldic acid, HL). Isomeric identities of 1 and 2 have been established by their single-crystal X-ray structures, which reveal that under the meridional configuration of trpy, O(-) and N donors of the unsymmetrical L are in trans, cis and cis, trans configurations, respectively, with respect to the Ru-Cl bond. Compounds 1 and 2 exhibit appreciable differences in bond distances involving Ru-Cl and Ru-O1/Ru-N1 associated with L on the basis of their isomeric structural features. In relation to isomer 2, the isomeric complex 1 exhibits a slightly lower Ru(II)-Ru(III) oxidation potential [0.35 (1), 0.38 (2) V versus SCE in CH(3)CN] as well as lower energy MLCT transitions [559 nm and 417 nm (1) and 533 nm and 378 nm (2)]. This has also been reflected in the DFT calculation where a lower HOMO-LUMO gap of 2.59 eV in 1 compared to 2.71 eV in 2 is found. The isomeric structural effect in 1 and 2 has also been prominent in their (1)H NMR spectral profiles. The relatively longer Ru-Cl bond in 1 (2.408(2) Å) as compared to 2 (2.3813(9) Å) due to the trans effect of the anionic O(-) of coordinated L makes it labile, which in turn facilitates the transformation of [Ru(II)(trpy)(L)(Cl)] (1) to the solvate species, [Ru(II)(trpy)(L)(CH(3)CN)](Cl) (1a) while crystallizing 1 from the coordinating CH(3)CN solvent. The formation of 1a has been authenticated by its single-crystal X-ray structure. However, no such exchange of "Cl(-)" by the solvent molecule occurs in 2 during the crystallization process from the coordinating CH(3)CN solvent. The labile Ru-Cl bond in 1 makes it a much superior precatalyst for the epoxidation of alkene functionalities. Compound 1 is found to function as an excellent precatalyst for the epoxidation of a wide variety of alkene functionalities under environmentally benign conditions using H(2)O(2) as an oxidant and EtOH as a solvent, while isomer 2 remains almost ineffective under identical reaction conditions. The remarkable differences in catalytic performances of 1 and 2 based on their isomeric structural aspects have been addressed.
Article
The complexation of V(IV)O(2+) ion with 10 picolinate and quinolinate derivatives, provided with the donor set (N, COO(-)), was studied in aqueous solution and in the solid state through the combined application of potentiometric (pH-titrations), spectroscopic (EPR, UV/vis and IR spectroscopy), and computational (density functional theory (DFT) calculations) methods. Such derivatives, that form potent insulin-enhancing V(IV)O(2+) compounds, are picolinic (picH), 6-methylpicolinic (6-mepicH), 3-methylpicolinic (3-mepicH), 5-butylpicolinic or fusaric (fusarH), 6-methyl-2,3-pyridindicarboxylic (6-me-2,3-pdcH(2)), 2-pyridylacetic (2-pyacH), 2-quinolinecarboxylic or quinaldic (quinH), 4-hydroxyquinoline-2-carboxylic or kynurenic (kynurH), 1-isoquinolinecarboxylic (1-iqcH) and 3-isoquinolinecarboxylic (3-iqcH) acid. On the basis of the potentiometric, spectroscopic, and DFT results, they were divided into the classes A, B, and C. The ligands belonging to class A (3-mepicH, 1-iqcH, 2-pyacH) form square pyramidal complexes in aqueous solution and in the solid state, and those belonging to class B (picH, fusarH, 3-iqcH) form cis-octahedral species, in which the two ligands adopt an (equatorial-equatorial) and an (equatorial-axial) arrangement and one water molecule occupies an equatorial site in cis position with respect to the V═O bond. Class C ligands (6-mepicH, 6-me-2,3-pdcH(2), quinH, kynurH) yield bis chelated species, that in water are in equilibrium between the square pyramidal and trans-octahedral form, where both the ligand molecules adopt an (equatorial-equatorial) arrangement and one water is in trans position with respect to the V═O group. The trans-octahedral compounds are characterized by an anomalous electron paramagnetic resonance (EPR) response, with A(z) value being reduced by about 10% with respect to the prediction of the "additivity rule". DFT methods allow to calculate the structure, (51)V hyperfine coupling constant (A(z)), the stretching frequency of V═O bond (ν(V═O)), the relative stability in aqueous solution, and the electronic structure and molecular orbital composition of bis chelated complexes. The results were used to explain the biotransformation of these potent insulin-enhancing compounds in blood serum.
Article
Two new mononuclear peroxo complexes of tungsten of the formula (gu)(2)[WO(2)(O(2))(2)] (1) and (gu)[WO(O(2))(2)(quin-2-c)] (2a) (where gu(+)=guanidinium ion, CN(3)H(6)(+) and quin-2-c=quinoline-2-carboxylate ion) have been synthesized and characterized by elemental analysis, infrared, Raman, UV-visible and (1)H NMR spectroscopies. The crystal structure of (gu)[WO(O(2))(2)(quin-2-c)].H(2)O (2b) determined by X-ray diffraction indicates that the side-on peroxo groups and the bidentate quinaldate ligand bind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a counterion and the hydrogen-bound interactions stabilize the complexes. The in vitro insulin-mimetic effect of the complexes has been evaluated by the inhibitory effect on free fatty acid release in isolated fat adipocytes treated with epinephrine. Moreover the niobate analogues, synthesized and characterized previously, (gu)(3)[Nb(O(2))(4)] and (gu)(2)[Nb(O(2))(3)(quin-2-c)].H(2)O have been tested for the insulin-like activity.
Article
The metal-carbon bond-dissociation energies (D0) and geometries for the first- and second-row transition-metal methyl neutrals and positive ions are determined. The computed D0 values for the positive ions compare favorably with experiment, except for RuCH3(+), RhCH3(+), and PdCH3(+), where the experimental values are 10-15 kcal/mol larger. The computed D0 values for the hydride and methyl positive ions are similar for all metals in both transition rows, except for Cu and Ag. However, for the neutral systems, the D0 values for the methyls are smaller, especially on the right-hand side of both transition rows, where the differences approach 15 kcal/mol.
Article
A selected set of 14 V(V) complexes was tested for toxicity and antitumor activity against L1210 murine leukemia, to examine the biological properties of peroxoheteroligand vanadates(V) of the formula (NH4)4[O(VO(O2)2)2], M3I[VO(O2)2C2O4], and MI[VO(O2)L], L = malate, citrate, iminodiacetate, nitrilotriacetate, and EDTA. The x-ray structure is known for five of these compounds. A relationship has been found between the chemical composition and the biological activity (antitumor activity-toxicity) of these complexes. Activity in the L1210 system is defined as greater than or equal to 25% increase in life span, and this was seen with (NH4)4[O(VO(O2)2)2]; M3[VO(O2)2(C2O4)]2H2O, M = K, NH4; and NH4[VO(O2)Malato]H2O. These observations are important for the biochemistry of vanadium. The special nature of electron transfer within the V(V)-peroxo moiety is proposed to be responsible for this phenomenon. Peroxo heteroligand vanadates(V) therefore represent a model system for studying some biochemical interactions of vanadium in living matter.
Article
Current gradient-corrected density-functional approximations for the exchange energies of atomic and molecular systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy density. Here we report a gradient-corrected exchange-energy functional with the proper asymptotic limit. Our functional, containing only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more.
Article
Langreth and Mehl (LM) and co-workers have developed a useful spin-density functional for the correlation energy of an electronic system. Here the LM functional is improved in two ways: (1) The natural separation between exchange and correlation is made, so that the density-gradient expansion of each is recovered in the slowly varying limit. (2) Uniform-gas and inhomogeneity effects beyond the randomphase approximation are built in. Numerical results for atoms, positive ions, and surfaces are close to the exact correlation energies, with major improvements over the original LM approximation for the ions and surfaces.
Article
Halogenated natural products are frequently reported metabolites in marine seaweeds. These compounds span a range from halogenated indoles, terpenes, acetogenins, phenols, etc., to volatile halogenated hydrocarbons that are produced on a very large scale. In many cases these halogenated marine metabolites possess biological activities of pharmacological interest. Given the abundance of halogenated marine natural products found in marine organisms and their potentially important biological activities, the biogenesis of these compounds has intrigued marine natural product chemists for decades. Over a quarter of a century ago, a possible role for haloperoxidase enzymes was first suggested in the biogenesis of certain halogenated marine natural products, although this was long before haloperoxidases were discovered in marine organisms. Since that time, FeHeme- and Vanadium-haloperoxidases (V-HPO) have been discovered in many marine organisms. The structure and catalytic activity of vanadium haloperoxidases is reviewed herein, including the importance of V-HPO-catalyzed bromination and cyclization of terpene substrates.
Article
Monoperoxovanadium(V) complexes, [NH3(CH2)2NH3][VO(O2)(ox)(pic)]·2H2O (1) and [NH3(CH2)2NH3][VO(O2)(ox)(pca)] (2) [NH3(CH2)2NH3 = ethane-1,2-diammonium(2+), ox = oxalate(2−), pic = pyridine-2-carboxylate(1−), pca = pyrazine-2-carboxylate(1−)], were synthesized and characterized by X-ray analysis, IR and Raman spectroscopies. The five equatorial positions of the pentagonal bipyramid around the vanadium atoms are occupied by the η2-peroxo ligand, two oxygen atoms of the ox, and the nitrogen atom of the pic or pca ligands, respectively. The oxo ligand and the oxygen atom of pic or pca are in the axial positions. Networks of X–H⋯O (X = C, N or O) hydrogen bonds, and π–π interactions between aromatic rings in 1 and anion–π interactions in 2, determine the molecular packings and build up the supramolecular architecture. Three stereochemical rules for occupation of the donor sites in two-heteroligand [VO(O2)(L1)(L2)] complexes (L1, L2 are bidentate neutral or differently charged anionic heteroligands providing an OO, NN or ON donor set) are discussed. 1 and 2 crystallize as racemic compounds. The 51V NMR spectra proved that the parent complex anions of 1 and 2 partially decompose on dissolution in water to the monoperoxo–ox, –pic or –pca complexes.