Vanadium Centers Research Articles

Synthesis and Characterisation of Polymer‐Anchored Oxidovanadium(IV) Complexes and Their Use for the Oxidation of Styrene and Cumene

AbstractThe Schiff bases H2fsal‐ea (I), H2fsal‐pa (II) and H2fsal‐amp (III), derived from 3‐formylsalicylic acid and 2‐aminoethanol, 3‐aminopropanol and 2‐amino‐2‐methylpropanol, respectively, have been connected, by means of covalent bonds, to chloromethylated polystyrene cross‐linked with 5 % divinylbenzene. On treatment with [VO(acac)2] in dimethylformamide (DMF), these polymer‐anchored ligands PS‐H2fsal‐ea (IV), PS‐H2fsal‐pa (V) and PS‐H2fsal‐amp (VI) gave the oxidovanadium(IV) complexes, PS‐[VO(fsal‐ea)·DMF] (4), PS‐[VO(fsal‐pa)·DMF] (5) and PS‐[VO(fsal‐amp)·DMF] (6), respectively. The corresponding neat complexes [VO(fsal‐ea)]2 (1), [VO(fsal‐pa)]2 (2) and [VO(fsal‐amp)]2 (3) have also been similarly prepared. These complexes all exhibit a medium intensity band between 964 and 993 cm–1 in their IR spectra resulting from the V=O stretch. The EPR spectra of the polymer‐anchored complexes are characteristics of monomeric VIV centres with a simple S = ${1 \over 2}$ electronic spin and with an axial pattern typical of square pyramidal geometry. Broad features for the neat complexes along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interactions between two vanadium centres in close proximity. These catalysts have been tested for the oxidation of styrene and cumene and were found to be efficient. Styrene gives five reaction products namely styrene epoxide, benzaldehyde, 1‐phenylethane‐1,2‐diol, benzoic acid and phenylacetaldehyde, whereas cumene gives acetophenone, 2‐phenylpropanal, α‐methyl styrene epoxide, 2‐phenyl‐2‐propanol, 2‐isopropyl‐1,4‐benzoquinone and α‐methyl styrene. The polymer‐anchored heterogeneous catalysts are recyclable. The catalytic activities of the neat complexes have also been examined and compared with the corresponding anchored analogues. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Inside Cover: An Isolable and Monomeric Phosphorus Radical That Is Resonance‐Stabilized by the Vanadium(IV/V) Redox Couple (Angew. Chem. Int. Ed. 17/2007)

Bulky redox‐active metalloligands stabilize the phosphorus radical [.P{NV[N(Np)Ar]3}2] (Np=neopentyl) to the extent that it exists as a monomer even in the solid state. C. C. Cummins and co‐workers describe in their Communication on page 3111 ff. the EPR spectrum of the radical (see picture; P orange, N blue, V yellow), which reveals delocalization of the unpaired electron onto both vanadium centers. Radical bond formation at the phosphorus atom leads to diamagnetic products.

Synthesis and Characterization of Vanadium(IV) Complexes with cis-Inositol in Aqueous Solution and in the Solid-State

The complex formation of vanadium(IV) with cis-inositol (ino) and the corresponding trimethyl ether 1,3,5-trideoxy-1,3,5-trimethoxy-cis-inositol (tmci) was studied in aqueous solution and in the solid-state. With increasing pH, the formation of [VO(H-2L)], [(VO)2L2H-5]-, [VO(H-3L)]- (L = ino) or [(VO)2L2H-6]2- (L = tmci), [V(H-3L)2]2-, and [VO(H-3L)(OH)2]3- was observed. For the vanadium(IV)/ino system, [(VO)2L2H-7]3- was observed as an additional dinuclear species. The formation constants of these complexes were determined by potentiometric titrations (25 degrees C, 0.1 M KCl). In addition, the vanadium(IV)/ino system was investigated by means of UV-vis spectrophotometric methods. EPR spectroscopy and cyclic voltammetry confirmed this complexation scheme. EPR measurements indicated the formation of three distinct isomers of the non-oxo complex [V(H-3ino)2]2- in weakly basic solution. This type of isomerism, which is not observed for the vanadium(IV)/tmci system, was assigned to the ability of ino to bind the vanadium(IV) center with three alkoxo groups having either a 1,3,5-triaxial or an 1,2,3-axial-equatorial-axial arrangement. The structures of [V(H-3ino)2][K2(ino)2].4H2O (1) and [Na6V(H-3ino)2](SO4)2.6H2O (2) were determined by single-crystal X-ray analysis. In both compounds, the coordination of each ino molecule to the vanadium(IV) center via three axial deprotonated oxygen donors was confirmed. The centrosymmetric structure of the coordination spheres corresponds to an almost regular octahedral geometry with a twist angle of 60 degrees. The crystal structure of the potassium complex 1 represents an unusual 1:1 packing of [V(H-3ino)2]2- dianions and [K2(ino)2]2+ dications, in which both K+ ions have a coordination number of nine and are bonded simultaneously to a 1,3,5-triaxial and an 1,2,3-axial-equatorial-axial site of ino. In 2, the [V(H-3ino)2]2- complexes are surrounded by six Na+ counterions that are bonded to the axial alkoxo oxygens and to the equatorial hydroxy oxygens of the cis-inositolato moieties. The six Na+ centers are further interlinked by bridging sulfate ions. According to EPR spectroscopy, the D3d symmetric structure of the [V(H-3ino)2]2- anion is retained in H2O, in dimethylformamide, and in a mixture of CHCl3/toluene 60:40 v/v.

Synthesis and Characterization of Vanadium(IV) and (V) Complexes with 2‐Hydroxy‐acetophenone‐semicarbazone (H2hasc) as Ligand. X‐Ray Crystal Structures of [VO2(H2hasc)] and [VO2(Hhasc)

AbstractThree novel vanadium complexes with pharmacologically active ligands were synthesized and characterized: [VIVO(acac)(Hhasc)], [VIVO2(H2hasc)], and [VVO2(Hhasc)], where H2hasc = 2‐Hydroxy‐acetophenone‐semicarbazone. The analytical methods used included FTIR, 1H‐, 13C‐, 51V‐NMR and EPR spectroscopies, elemental analysis and X‐ray diffractometry from single crystals. The crystal and molecular structures of [VIVO2(H2hasc)] and [VVO2(Hhasc)] were determined. [VIVO2(H2hasc)] crystallizes monoclinic [P21/c, Z = 4, a = 783.4(2), b = 1024.9(2), c = 1365.5(3) pm, β = 99.506(14)°]. The (VO2)2+ core is coordinated to a neutral O,N,O‐tridentate unit of the H2hasc ligand, with the vanadium atom showing a square pyramidal coordination sphere. In the crystal of [VVO2(Hhasc)], triclinic [${\rm P}{\bar 1}$, Z = 4, a = 858.73(11), b = 967.39(5), c = 1318.63(12) pm, α = 97.423(5), β = 101.590(6), γ = 98.144(5)°], two symmetry independent (VO2)+ cores are observed. Each of them coordinates to a monodeprotonated Hhasc− unit, in a O,N,O‐tridentate mode. One assumes a square pyramidal geometry for the pentacoordinate vanadium(V) center. An additional interaction is observed for the other one, involving the phenolate oxygen atom from a symmetry related unit, resulting in a [5+1]‐coordination number for the transition metal atom.

Synthesis and characterization of some oxovanadium(V) complexes with internally functionallized oximes. Crystal and molecular structure of heptacoordinated [VOCl{ON=C(CH3) (C4H3S-2)}2] · CH3OH

New heteroleptic oxovanadium(V) chloro oximato complexes of the type [VO{Cl}3-n{ON=C(CH3)(Ar)}n] (where Ar = C4H3O-2, C4H3S-2, C5H4N-2 and n = 1 or 2) have been synthesized in excellent yields by the reaction of VOCl3 with the sodium salts of corresponding internally functionallized oximes in refluxing anhydrous benzene. The complexes are characterized by elemental analyses and spectroscopic techniques (FT-IR, 1H-, 13C{1H}- and 51V-NMR). FAB mass spectral analysis of one of the derivatives, [VOCl{ON=C(CH3)C4H3S}2] indicates the monomeric nature of the complex. 51V-NMR spectral studies of these complexes suggest tetra-coordination around the vanadium atom in solution. However, the single crystal X-ray diffraction study of a redistribution product [VOCl{ON=C(CH3)(C4H3S-2)}2] · CH3OH obtained on recrystallization of [VOCl2{ON=C(CH3)(C4H3S-2)}] from a methanol-hexane mixture shows the vanadium(V) atom is hepta-coordinated with distorted pentagonal bipyramidal geometry. The oxo-atom occupies the axial position while the weakly coordinated CH3OH group is trans to the V=O atom. The two oximato ligands in the approximate pentagonal plane are bonded to the central vanadium atom in dihapto (η2-N, O) manner with the formation of three-membered rings. The V–Cl bond occupies the fifth position in the approximate plane.

A study on the electronic effect of para substituents in the aryloxy ring of the hydrazone ligands on the vanadium centre in a family of mixed-ligand [VVO(ONO)(OO)] complexes

[VIVO(acac)2] reacts with the methanolic solutions of tridentate dibasic ONO donor hydrazone ligands derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone (H2L1) or its para-substituted derivatives (H2L2–4) (general abbreviation H2L), in the presence of vanillin (Hvan) in equimolar ratio under aerobic conditions generating the mixed-ligand oxovanadium(V) complexes of the type [VVO(L)(van)], (1)–(4) in good yield. All the complexes are diamagnetic and exhibit only ligand-to-metal charge transfer (l.m.c.t.) band near 510 nm in addition to intra-ligand (π → π*) transition band near 330 nm in CH2Cl2 solution. 1H-n.m.r. spectra of the complexes in CDCl3 solution indicate the presence of two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios, which is explained by the interchange of the two binding sites of van− motif between its coordinated equatorial and axial positions. Complexes display two quasi-reversible one electron reduction peaks near +0.10 V and near +0.30 V versus s.c.e. in CH2Cl2 solution which are attributed to the successive reduction of VV→ VIV and the VIV→ VIII motifs, respectively. λmax (for l.m.c.t. transition), and the two reduction potential values (E1/2)I (average of the first step anodic and first step cathodic peak potentials) and (E1/2)II (average of the second step anodic and second step cathodic peak potentials) of the complexes, are found to be linearly related to the Hammett constants (σ) of the substituents in the aryloxy ring of the hydrazone ligands. λmax, (E1/2)I and (E1/2)II values show large dependence: dλmax/dσ = 37.29 nm, d(E1/2)I/dσ = 0.21 V and d(E1/2)II/dσ = 0.21 V, respectively, on σ.

(L-Histidinato-κ3N,N,O)(L-histidine-κ2N,O)oxidovanadium(IV) perchlorate monohydrate

The first homoleptic oxovanadium(IV)–histidine complex {systematic name: [(S*)-α-amino-4-imidazole­propionato-κ3N,N,O][(S*)-α-amino-3-(1H-imidazol-3-ium-5-yl)propionato-κ2N,O]oxovanadium(IV) perchlorate monohydrate}, [VIVO(C6H8N3O2)(C6H9N3O2)]ClO4·H2O, adopts a distorted octa­hedral structure where one l-histidine ligand coordinates to the vanadium(IV) center in a tridentate fashion as a monoanion and the other in a bidentate fashion leaving a protonated imidazole group as a pendent group.

Time-resolved studies on correlations between dynamic electronic structure and selectivity of a H 5[PV 2Mo 10O 40] partial oxidation catalyst

Time-resolved in situ X-ray absorption spectroscopy studies on an activated H 5[PV 2Mo 10O 40] oxidation catalyst were performed to obtain correlations between the dynamic structure and the catalytic selectivity of the material. Both the geometric and electronic structures of the vanadium and molybdenum metal centers of the catalyst change dynamically under the reaction conditions used. Moreover, the selectivity of the catalyst exhibits a pronounced correlation with the degree of reduction and the solid-state kinetics of the reoxidation process. The corresponding extent of reoxidation curve can be simulated with a solid-state kinetic model assuming three-dimensional diffusion as the rate-limiting step. Thus, the partially reduced catalyst exhibits a rate constant of the bulk-diffusion limited reoxidation, coinciding with the temporal evolution of the selectivity of the catalyst.

The surface and catalytic properties of titania-supported mixed PMoV heteropoly compounds for total oxidation of chlorobenzene

Heteropoly catalysts based on the mixed PMoV heteropoly compounds (HPC) with Keggin structure were prepared. The behaviors of the samples (in bulk and in titania-supported form) as a function of temperature treatment in the range of 343-923 K and the number of introduced V atoms into the heteropoly anions were studied. The catalytic activity of titania-supported catalysts was evaluated in the reaction of total oxidation of Cl-benzene at 473 K. The samples were characterized by S-BET method, thermogravimetric analysis (TGA), Fourier transform infrared,spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The XRD, IR and Raman results provided clear evidence that V indeed is incorporated into the Keggin unit. Introduction of one V atom into heteropolyanion leads to a significant increase of its thermal stability. On the other hand, the presence of the vanadium centers appears to be responsible for the increased activity of the titania-supported samples in the reaction of total oxidation of chlorobenzene. (c) 2006 Elsevier B.V. All rights reserved.

Preparations, Structures, and Properties of Sulfato-Bridged Dinuclear and Tetranuclear Vanadium(III) Complexes with a Dinucleating Ligand, 2-Oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate

Abstract New dinuclear and tetranuclear vanadium(III) complexes with sulfato bridge(s), [{VIII(H2O)}2(μ-hpnbpda)(μ-OH)(μ-SO4)]·5.25H2O (1) and [VIII4(μ-hpnbpda)2(μ-OH)2(μ-SO4)2]·12H2O (2), where hpnbpda is an alkoxo-bridging dinucleating ligand, 2-oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate, were prepared, and their structures were determined by X-ray crystallography. The vanadium(III) center in 1 adopts heptacoordinate structure while that in 2 has a hexacoordinate structure. In 2, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two hydroxo and two sulfato bridging groups, resulting in a dimer-of-dimers structure. Measurement of the temperature dependence of the magnetic susceptibility of 1 revealed that the two vanadium(III) ions are antiferromagnetically coupled with J = −5.9 cm−1 and g = 1.90.

Characteristics of vanadium-substituted mesoporous silica with wormhole framework structure: effects of vanadium content

Vanadium-substituted wormhole framework structure (V-WMS) mesoporous silicas (V-WMS) with various Si/V ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfactant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), N2 adsorption–desorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy. V-WMS samples shown characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. These mesoporous V-WMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. An absorption band of FT-IR at ca. 960 cm−1 was assigned to the vibration of Si–O–V linkages. These samples also showed one strong UV–visible absorbance with overlapping maxima at about 255 nm. The results show that vanadium was incorporated into the structure of wormhole mesoporous silica (WMS). However, for V-WMS with high vanadium content (Si/V < 25), a broad shoulder in XRD pattern was observed at about 3–4°, suggesting the presence of impurity phase of vanadium species in the sample. The efforts in preparing V-WMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active vanadium centers.

Vielseitige Koordinationschemie von Vanadium(V): Substitutionsreaktionen, Umlagerungen und Kondensationsreaktionen von Oxovanadium(V)‐Komplexen des tripodalen Sauerstoffliganden LOMe− = [η5‐(C5H5)Co{P(OMe)2(O)}3]−

AbstractMultifaceted Coordination Chemistry of Vanadium(V): Substitution, Rearrangement Reactions, and Condensation Reactions of Oxovanadium(V) Complexes of the Tripodal Oxygen Ligand LOMe− = [η5‐(C5H5)Co{P(OMe)2(O)}3]−The octahedral oxovanadium(V) complex [V(O)F2LOMe] of the tripodal oxygen ligand LOMe− = [η5‐(C5H5)Co{P(OMe)2(O)}3]− reacts with alcohols and phenol with substitution of one fluoride ligand to form alkoxo complexes [V(O)F(OR)LOMe], R = Me, Et, i‐Prop, Ph. In the presence of water, however, both fluoride ions are substituted and a complex with the composition VO2LOMe can be isolated. The crystal structure shows that the oxo‐bridged trimer [{V(O)(LOMe)O}3] was synthesized. In the presence of BF3 the fluoride ligand in the alkoxo‐complex [V(O)F(OEt)LOMe] can be exchanged for pyridine to yield [V(O)(OEt)pyLOMe]BF4. Analogous attempts to exchange the fluoride ligand for tetrahydrofuran and acetonitrile induces a rearrangement reaction that leads to the vanadium complex [V(O)(LOMe)2]BF4. The crystal structure of this compound has been determined. Its 1H and 31P‐NMR spectra show that it is a highly fluxional vanadium complex at ambient temperature in solution. The two tripodal ligands LOMe− coordinate the vanadium centre as bidentate or tridentate ligands. The exchange bidentate/tridentate becomes slow on the NMR time scale below about 200 K.

Synthesis, structure, solution chemistry and the electronic effect of para substituents on the vanadium center in a family of mixed-ligand [V VO(ONO)(ON)] complexes

Four tridentate dibasic ONO donor hydrazone ligands derived from the condensation of benzoylhydrazine with either 2-hydroxyacetophenone or its para substituted derivatives (H 2L 1–4, general abbreviation H 2L) have been used as primary ligands and 8-hydroxyquinoline (Hhq, a bidentate monobasic ON donor species) has been used as auxiliary ligand. The reaction of [V IVO(acac) 2] with H 2L in methanol followed by the addition of Hhq in equimolar ratio under aerobic condition afforded the mixed-ligand oxovanadium(V) complexes of the type [V VO(L)(hq)] ( 1– 4) in excellent yield. The X-ray structure of the compound [V VO(L 4)(hq)] ( 4) indicates that the H 2L 4 ligand is bonded with vanadium meridionally in a tridentate dinegative fashion through its deprotonated phenolic-O, deprotonated enolic-O and imine-N atoms. The V–O bond length order is: oxo < phenolato < enolato. 1H NMR spectra of 4 in CDCl 3 solution indicates that it’s solid-state structure is retained in solution. Complexes are diamagnetic and exhibit only ligand to metal charge transfer (LMCT) transition band near 530 nm in CH 2Cl 2 solution in addition to intra-ligand π → π ∗ transition band near 335 nm and they display quasi-reversible one electron reduction peak near − 0.10 V versus SCE in CH 2Cl 2 solution. λ max (for LMCT transition) and the reduction peak potential ( E p c ) values of the complexes are found to be linearly related with the Hammett ( σ) constants of the substituents in the aryloxy ring of the hydrazone ligands. λ max and E p c values show large dependence d λ max/d σ = 32.54 nm and d E p c / d σ = 0.19 V, respectively, on the Hammett constant.

Characterization of SiC Wafers by Photoluminescence Mapping

The effectiveness of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of structural defects, such as dislocations, micropipes and stacking faults, in SiC wafers. PL spectra of bulk wafers were dominated by deep-level emissions due to Si vacancies, vanadium and undefined centers like UD-1 at room temperature, while those from epitaxial wafers involved near band-edge emission. We developed a whole-wafer PL intensity mapping system with a capability of zooming in on the area of interest with a spatial resolution as high as 1 μm, and showed that the mapping patterns agree well with the etch-pit patterns originating from the structural defects both on a wafer scale and on a microscopic scale. The intensity contrast around the defects varied depending on the emission band, suggesting differences in their interactions with impurities and point defects.

Synthesis and characterization of two oxovanadium (IV) Schiff base complexes derived from amino acids and pyridoxal

Two N-pyridoxylideneamino acidato complexes of oxovanadium (IV), [VO(pyr-D,L-Met)(bipy)] and [VO(pyr-D,L-Thr)(bipy)]⋅H 2O with Schiff bases, made from amino acids (DL-methionine and DL-threonine) and pyridoxal, were prepared by an amine-diffusion reaction and characterized by single crystal X-ray diffraction. Both [VO(pyr-D,L-Met)(bipy)] and [VO(pyr-D,L-Thr)(bipy)]⋅H 2O crystallize in triclinic P - 1 with cell parameters a = 9.2605 ( 19 ) Å , b = 12.851 ( 3 ) Å , c = 19.079 ( 4 ) Å , α = 92.34 ( 3 ) ° , β = 93.20 ( 3 ) ° , γ = 91.03 ( 3 ) ° , V = 2264.7 ( 8 ) Å 3 , Z = 2 , and a = 9.4513 ( 8 ) Å , b = 11.9026 ( 13 ) Å , c = 12.7589 ( 12 ) Å , α = 66.836 ( 6 ) ° , β = 87.171 ( 6 ) ° , γ = 67.214 ( 6 ) ° , V = 1207.6 ( 2 ) Å 3 , Z = 2 , respectively. They contain two diastereomers, donating the chiral vanadium centers as A or C, e.g., [A(pyr-D-Met)(bipy)], [C(pyr-L-Met)(bipy)] and [A(pyr-D-Thr)(bipy)]⋅H 2O, [C(pyr-L-Thr)(bipy)]⋅H 2O. The complexes were also characterized by elemental analysis, IR and EPR spectroscopy. The EPR spectra illustrate well-resolved coupling of the unpaired electron with V 51 nucleus ( I = 7 / 2 ).

7Li NMR and Two‐Dimensional Exchange Study of Lithium Dynamics in Monoclinic Li3V2(PO4)3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

An oxovanadium(IV) complex derived from l-histidine, [V 2O 2( l-his) 2(2,2′-bipy) 2] · [C 2H 6O 2 · (2,2′-bipy)]: Hydrothermal synthesis, crystal structure and magnetic properties

A dinuclear oxovanadium compound [V 2O 2( l-his) 2(2,2′-bipy) 2] · [C 2H 6O 2 · (2,2′-bipy)] was synthesized under hydrothermal condition and characterized by single-crystal X-ray diffraction. X-ray crystallography revealed that each vanadium center is six coordinated and adopts a distorted octahedral structure. IR spectroscopy, ESR spectrum and magnetic susceptibility data for this compound are given. X-band ESR spectroscopy of the sample indicated the existence of vanadium(IV) ions in the compound. The temperature dependent magnetic susceptibility data showed the presence of a ferromagnetic coupling between the two V(IV) ions in the range 4–180 K.

Binuclear Mixed Valence Oxovanadium(IV/V) Complexes Containing a [OVIV(μ‐Ooxo)(μ‐Ophen)VVO]2+ Core: Synthesis, EPR Spectra, Molecular and Electronic Structure

AbstractBinuclear mixed valence oxovanadium(IV/v) complexes of general formula [V2O3L] containing a [OVIV(μ‐Ooxo)(μ‐Ophen)VVO]2+ core have been synthesised using conformationally labile N4O3‐coordinating heptadentate ligands (H3L). The X‐ray structure of one complex has been examined. Solution EPR spectra revealed that the unpaired electron of the complexes is delocalised between the two vanadium centres. The simulated EPR spectrum of one complex confirms this experimental observation. DFT studies have been performed using crystallographic coordinates in order to obtain further insight into the electronic structure of this type of molecule. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

51V Solid-State Magic Angle Spinning NMR Spectroscopy of Vanadium Chloroperoxidase

We report 51V solid-state NMR spectroscopy of the 67.5-kDa vanadium chloroperoxidase, at 14.1 T. We demonstrate that, despite the low concentration of vanadium sites in the protein (one per molecule, 1 mumol of vanadium spins in the entire sample), the spinning sideband manifold spanning the central and the satellite transitions is readily detectable. The quadrupolar and chemical shift anisotropy tensors have been determined by numerical simulations of the spinning sideband envelopes and the line shapes of the individual spinning sidebands corresponding to the central transition. The observed quadrupolar coupling constant C(Q) of 10.5 +/- 1.5 MHz and chemical shift anisotropy delta(sigma) of -520 +/- 13 ppm are sensitive reporters of the geometric and electronic structure of the vanadium center. Density functional theory calculations of the NMR spectroscopic observables for an extensive series of active site models indicate that the vanadate cofactor is most likely anionic with one axial hydroxo- group and an equatorial plane consisting of one hydroxo- and two oxo- groups. The work reported in this manuscript is the first example of 51V solid-state NMR spectroscopy applied to probe the vanadium center in a protein directly. This approach yields the detailed coordination environment of the metal unavailable from other experimental measurements and is expected to be generally applicable for studies of diamagnetic vanadium sites in metalloproteins.

7Li NMR and Two-Dimensional Exchange Study of Lithium Dynamics in Monoclinic Li3V2(PO4)3

High-resolution solid-state (7)Li NMR was used to characterize the structure and dynamics of lithium ion transport in monoclinic Li(3)V(2)(PO(4))(3). Under fast magic-angle spinning (MAS) conditions (25 kHz), three resonances are clearly resolved and assigned to the three unique crystallographic sites. This assignment is based on the Fermi-contact delocalization interaction between the unpaired d-electrons at the vanadium centers and the lithium ions. One-dimensional variable-temperature NMR and two-dimensional exchange spectroscopy (EXSY) are used to probe Li mobility between the three sites. Very fast exchange, on the microsecond time scale, was observed for the Li hopping processes. Activation energies are determined and correlated to structural properties including interatomic Li distances and Li-O bottleneck sizes.