Martin Ebel
University of Hamburg
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Dalton Transactions | 2006
Mannar R. Maurya; Shalu Agarwal; Mohammad Abid; Amir Azam; Cerstin Bader; Martin Ebel; Dieter Rehder
Binuclear, mu-bis(oxo)bis{oxovanadium(V)} complexes [(VOL)2(mu-O)2](2 and 7)(where HL are the hydrazones Hacpy-nah I or Hacpy-fah II; acpy = 2-acetylpyridine, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) were prepared by the reaction of [VO(acac)2] and the ligands in methanol followed by aerial oxidation. The paramagnetic intermediate complexes [VO(acac)(acpy-nah)](1) and [VO(acac)(acpy-fah)](6) have also been isolated. Treatment of [VO(acac)(acpy-nah)] and [VO(acac)(acpy-fah)] with aqueous H2O2 yields the oxoperoxovanadium(V) complexes [VO(O2)(acpy-nah)](3) and [VO(O2)(acpy-fah)](8). In the presence of catechol (H2cat) or benzohydroxamic acid (H2bha), 1 and 6 give the mixed chelate complexes [VO(cat)L](HL =I: 4, HL =II: 9) or [VO(bha)L](HL =I: 5, HL =II: 10). Complexes 4, 5, 9 and 10 slowly convert to the corresponding oxo-mu-oxo species 2 and 7 in DMF solution. Ascorbic acid enhances this conversion under aerobic conditions, possibly through reduction of these complexes with concomitant removal of coordinated catecholate or benzohydroxamate. Acidification of 7 with HCl dissolved in methanol afforded a hydroxo(oxo) complex. The crystal and molecular structure of 2.1.5H2O has been determined, and the structure of 7 re-determined, by single crystal X-ray diffraction. Both of these binuclear complexes contain the uncommon asymmetrical {VO(mu-O)}2 diamond core. The in vitro tests of the antiamoebic activity of ligands I and II and their binuclear complexes 2 and 7 against the protozoan parasite Entamoeba histolytica show that the ligands have no amoebicidal activity while their vanadium complexes 2 and 7 display more effective amoebicidal activity than the most commonly used drug metronidazole (IC50 values are 1.68 and 0.45 microM, respectively vs 1.81 microM for metronidazole). Complexes 2 and 7 catalyse the oxidation of styrene and ethyl benzene effectively. Oxidation of styrene, using H2O2 as an oxidant, gives styrene epoxide, 2-phenylacetaldehyde, benzaldehyde, benzoic acid and 1-phenyl-ethane-1,2-diol, while ethyl benzene yields benzyl alcohol, benzaldehyde and 1-phenyl-ethane-1,2-diol.
European Journal of Inorganic Chemistry | 2001
Dongren Wang; Martin Ebel; Carola Schulzke; Cerstin Grüning; Saroj K. S. Hazari; Dieter Rehder
The VO2+ complexes [VOCl(ONS)] (3) and [VO(ONS)′] (4), and the VO3+ complexes [VO(OEt)(ONS)′] (5) {ONS = (R)-salicylaldehyde thiosemicarbazonate(1−) R = 5,6-C4H4 (3a) or 3-OMe (3b); (ONS)′ = (R)-salicylaldehyde[benzylmercaptothiocarbonylhydrazonate(2−)], R = H, (4a/5a) or 3-OMe (4b/5b)} have been prepared and characterised by IR, EPR, 1H-, and 51V-NMR spectroscopy. In (S)-sBuOH, 4a converts to [VO{(S)-OsBu}(ONS)′] (5c) and [VO(OH)(ONS)′] (or a condensation product thereof). Solutions of 5c show three 51V NMR signals, two of which are due to two diastereomers. The EPR spectra of 3 and 4 in THF reveal the presence of octahedral species in solution. The crystal and molecular structures of complexes 3a·OCMe2, 5a, and 5b have been obtained, revealing basically a tetragonal pyramid, and coordination of the sulfur function in the thiocarbonyl (3) or enethiolate mode (5). The relevance of the compounds to bioinorganic aspects is addressed.
Inorganica Chimica Acta | 2003
Martin Ebel; Dieter Rehder
Abstract Four new oxovanadium(IV)-complexes of Schiff-base ligands with tyrosine constituents have been synthesised and characterised. The crystal and molecular structures of [A-VO(nap-R-tyr)(H2O)]·MeOH (nap is derived from 2-hydroxy-naphthalene-1-carbaldhyde) have been determined. The biological significance of vanadium–tyrosine interaction is addressed.
Inorganic Chemistry Communications | 2002
Wenjian Zhang; Xintao Wu; Martin Ebel; Dongren Wang; Dieter Rehder
Abstract Two mixed molybdenum–copper–sulfur clusters containing two or three {E=MoS3Cu2} (E=O, S) fragments have been assembled around the nucleophiles μ2-Sn2S64− or μ3-S2−, viz. [(MoES3Cu2)2(μ-Sn2S6)]4− (E=0.7 O + 0.3 S) and [(MoS4Cu2)3(μ3-S)2]4−.
Dalton Transactions | 2005
Mannar R. Maurya; Shalu Agarwal; Cerstin Bader; Martin Ebel; Dieter Rehder
Reaction between [VO(acac)2] and H2L (H2L are the hydrazones H2sal-nah I or H2sal-fah II; sal = salicylaldehyde, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) in methanol leads to the formation of oxovanadium(IV) complexes [VOL.H2O](H2L = I: 1, H2L = II: 4). Aerial oxidation of the methanolic solutions of 1 and 4 yields the dinuclear oxo-bridged monooxovanadium(V) complexes [{VOL}2mu-O](H2L = I: 2, H2L = II: 5). These dinuclear complexes slowly convert, in excess methanol, to [VO(OMe)(MeOH)L](H(2)L = I: 9, H(2)L = II: 10), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of the dianionic ligands in their enolate form. Reaction of aqueous K[VO3] with the ligands at pH ca. 7.5 results in the formation of [K(H2O)][VO2L](H2L = I: 3, H2L = II: 6). Treatment of 3 and 6 with H2O2 yields (unstable) oxoperoxovanadium(v) complexes K[VO(O2)L], the formation of which has been monitored spectrophotometrically. Acidification of methanolic solutions of 3 and 6 with HCl affords oxohydroxo complexes, while the neutral complexes [VO2(Hsal-nah)] 7 and [VO2(Hsal-fah)] 8 were isolated on treatment of aqueous solutions of 3 and 6 with HClO4. These complexes slowly transform into 9 and 10 in methanol, as confirmed by 1H, 13C and 51V NMR. The anionic complexes 3 and 6 catalyse the oxidative bromination of salicylaldehyde in water in the presence of H2O2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. They are also catalytically active for the oxidation of benzene to phenol and phenol to catechol and p-hydroquinone.
Pure and Applied Chemistry | 2005
Dieter Rehder; Martin Ebel; Cornelia Wikete; Gabriella Santoni; Jessica Gätjens
The active center of vanadate-dependent peroxidases (VPOs) is represented by vanadate covalently attached to a histidine, with vanadium in a trigonal-bipyramidal environment. Protein phosphatases and kinases are inhibited by the phosphate analog vanadate [VVO2(OH)2- and VIVO(OH)3-], which can be related to the coordination of vanadium to histidine or a hydroxide function as provided by tyrosinate or serinate. The vanadium centers in these proteins have been modeled by employing chiral ONO ligands. The penta-coordinated chiral complexes [VO(OMe)(L1)] (H2L1 = substituted diethanolamine) are distorted trigonal-bipyramidal with the methoxy group and the amine-N in the axial positions. These structural models of VPO also mimic the sulfide-oxidation activity of the peroxidases. The complexes [VO(H2O)L3] (H2L3 = Schiff-base ligands based on salicylaldehyde derivatives (o-vanillin; 2-hydroxy-naphthylaldehyde) and L- or D,L-tyrosine, or D,L-serine are tetragonal-pyramidal; the OH functions of the amino acid moieties are not directly coordinated to vanadium; they are involved, however, in complex hydrogen-bonding networks. The oxo/peroxo anion [VO(O2)(L2)2]3- (H2L2 = 2,5-dipicolinic acid) contains a slightly asymmetrically bonded O22-, featuring structural characteristics of the peroxo/hydroperoxo intermediates of the peroxidases. XD structure results are reported for the following complexes: R,S- and R,R-[VO(OMe)(L1)], K3[VO(O2)(L2)2].4.5H2O, the Tyr derivatives L-[VO(H2O)L3].MeOH and D,L-[VO(H2O)L3].H2O, and the Ser derivative D,L-[VO(H2O)L3].2H2O.
Inorganic Chemistry | 2006
Mannar R. Maurya; Amit Kumar; Martin Ebel; Dieter Rehder
Inorganic Chemistry | 2003
Neela Pooransingh; Ekaterina Pomerantseva; Martin Ebel; Sven Jantzen; Dieter Rehder; Tatyana Polenova
Inorganic Chemistry | 2006
Martin Ebel; Dieter Rehder
Inorganic Chemistry | 2004
Wenjian Zhang; Axel Behrens; Jessica Gätjens; Martin Ebel; Xintao Wu; Dieter Rehder