Wolfgang Priebsch

Vanadate-dependent bromo/iodoperoxidase from ascophyllum nodosum also contains unspecific low-affinity binding sites for vanadate (V): A 51V NMR investigation, including the model peptides Phe-Glu and Gly-Tyr

Abstract The interaction of vanadate(V) with bromo/iodoperoxidase from the cell wall of knobbed wrack (Ascophyllum nodosum), A.n.I, has been investigated by 51 V NMR. With excess vanadate, the holoenzyme (E*) forms unspecific associates. The main component is a complex (VE*) A with K A = 16(7)M −1 (250(25)M −1 in the presence of KBr, pH = 7.3)) and a chemical shift δ( 51 V) = −498 to −512 ppm relative to VOCl 3 . The enhancement of binding by substrate bromide is discussed in terms of a stepwise incorporation of vanadate into the active site of the enzyme. Additional, very weak complexes have been detected, among these a tetrahedral one (possibly hydrogen bonded monovanadate) in exchange with free monovanadate at medium exchange rates. Characteristics similar to those for (VE*) A have been observed for complexes of vanadate with the dipeptides Phe-Glu and Gly-Tyr, suggesting similar coordination modes. Phe-Glu, at pH 7.5, forms a mono- and dinuclear, monoligate complex (δ = −515 ppm; K for the mononuclear species is 322 M −1 ). The complexes obtained from the interaction between vanadate and Gly-Tyr (K = 128 M −1 , δ = −510 at pH = 7.2; δ = −500 and −506 ppm at pH = 8.2) are mononuclear and monoligate. Tentative formulations for the coordination compounds consider side chain functions, the peptide linkage, and the terminal amino group.

Synthesis, structure and reactions of seven-coordinate, phosphine-supported, halide-activated carbonyl-and alkyne-complexes of niobium(I)

The complexes (Hal)Nb(CO)3(PR3)3 (PR3  PEt3, Hal  I; PR3  PMe2Ph, Hal  Cl, Br, I) and (Hal)Nb(CO)4/2(dppe)1/2 (Hal  Br, I) have been prepared by oxidative halogenation of carbonylniobate with pyridinium halides (Hal  Cl, Br) or iodine (Hal  I). In the tricarbonyls, one CO and one PR3 are labile and can be displaced by a four-electron donating alkyne to give all-trans-[(Hal)Nb(CO)2(RCCR′)(PR3)2] (PR3 = PMe2Ph; Hal  Cl, Br, I: R, R′  H, Et, Ph; R  H, R′  Ph. PR3  PEt3, Hal  I: R, R′  Pr; R  H, R′  Bu, Ph; R  Me, R′  Et). In the case of acetylene, INb(CO)(HCCH)2(PEt3)2 is also formed. PR3 can be displaced by P(OMe) 3. In the tetracarbonyls, two CO ligands are replaced by two isonitriles to form INb(CO)2(CNR)2dppe (R  tBu, Cy), or by one alkyne to form (Hal)Nb(CO)2(PhCCPh)dppe (Hal  Br, I). In these complexes, the remaining CO ligands occupy cis positions. The structure of BrNb(CO)2(dppe)2·THF, INb(CO)2(dppe)2·hexane and INb(CO)2(PEt3)2(MeCCEt) have been determined by a single crystal X-ray diffraction study. The alkyne complexes are best regarded as octahedral with the centre of the alkyne ligand occupying the positions trans to the halide and the CC axis aligned with the OCNbCO axis. The complexes (Hal)Nb(CO)2(dppe)2 adopt a trigonal prismatic structure with the halide capping the tetragonal face spanned by the four phosphorus functions. The crystal structure of a by-product, Br2Nb(CO)(H2CPhPCH2CH2PPh2)2·1/2THF has also been determined. The geometry is pentagonal bipyramidal, with one of the bromine atoms and the CO on the axis. Some 93 Nb NMR data for the NbI complexes are presented, and preliminary observations on the reactions between the π-alkyne complexes and H2 or H− are reported.

Chemie der Carbonylniobverbindungen. X. Neue Hydridocarbonylkomplexe des Vanadiums, Niobs und Tantals

Abstract Complexes of the general formula HM(CO) n (oligophos) (M = V, n = 2; M = Nb, n = 3 and 2; M = Ta, n = 3) have been prepared by ion exchange on silica gel from their ionic precursors [Et 4 N][M(CO) 4,3 (oligophos)] ( n = 3) or by UV irradiation of HM(CO) n +1 (oligophos) ( n = 2). The new compounds, including fac -[Et 4 N]-[Nb(CO) 3 PPh(CH 2 CH 2 PPh 2 ) 2 ] and cis -[Et 4 N][Ta(CO) 4 PPh(CH 2 CH 2 PPh 2 ) 2 ], are characterized by their IR (ν(CO)), 1 H (hydride), 31 P and metal ( 51 V and 93 Nb) NMR spectra.

Aspects of carbonyltantalum chemistry

Abstract UV irradiation of [Et 4 N][Ta(CO) 6 ] in the presence of 2- to 4-dentate phosphines, P n , yields [Et 4 N][Ta(CO) 4 p 4 ]. Ion exchange

Zur Reaktivität von Hydridocarbonylvanadium-Komplexen: Darstellung und Charakterisierung von Alkylvanadium-Komplexen, und die Molekülstruktur von trans-[V(CO)2(Ph2PCH2CH2PPh2)2]☆

Abstract Various σ-alkylvanadium complexes of the general formula RV(CO) n p m ( n = 4, 3; p m is an m -dentate phosphine coordinating through (6 – n P-functions) have been prepared by photo-reaction between the hydrido precursors HV(CO) n p m and alkenes, and characterized by IR- and 51 V NMR spectroscopy. The preparation of the new phosphines Me 2 P(CH 2 ) 3 P( i Pr) 2 and i PrP(CH 2 CH 2 CH 2 PMe 2 ) 2 is described. trans -[V(CO) 2 (dppe) 2 ] crystallizes in the space group P l with the following cell parameters: a = 1012.1(9), b = 1012.9(6), c = 1224.7(9) pm, α = 105.780(6), β = 102.601(7)°.

Bis[tetraethylammonium]-meso-bis[dichloro-μ-chloro-oxo-aquavanadat(IV)], [(C2H5)4N]2[{VOCl2(OH2)}2(μ-Cl)2]: Molekülstruktur und spektroskopische Charakteristika/ Tetraethylammonium raeso-Bis[dichloro-μ-chloro-oxo-aquavanadate(IV)], [(C2H5)4N]2[{VOCl2(OH2)}2(μ-Cl)2]: Molecular Structure and Spectroscopic Characteristics

Abstract The title compound crystallizes in the monoclinic space group P21/c with a = 822.0(1), b = 1126.4(2), c = 1629.0(2) pm and β = 103.54(1)°. The two vanadium centers of the anion, which is an edge-bridged bioctahedron, are asymmetrically connected by bridging chloroligands; V -(μ -Cl) bond lengths are 238.4 und 278.3 pm , respectively. ESR and IR characteristics are discussed.

trans-[Na(thf)][V(N2)2(Ph2PCH2CH2PPh2)2]: structural characterization of a dinitrogenvanadium complex, a functional model for vanadiumnitrogenase

Reduction of VCl3(thf)3(thf = tetrahydrofuran) by Na in the presence of bis(phosphines) and N2 yields the complexes trans-[V(N2)2L2]–, which have been structurally characterized by X-ray crystallography for L = Ph2PCH2CH2PPh2, and in solution by 51V NMR spectroscopy for L = Me2PCH2CH2PMe2; 25% of the coordinated N2 is reductively protonated to NH3 and a small amount of N2H4 by HBr.