Showing papers by "Bernt Krebs published in 2006"

Thio‐ und Selenoverbindungen von Hauptgruppenelementen ‐ neue anorganische Oligomere und Polymere

Abstract: Moderne praparative und strukturanalytische Methoden haben im letzten Jahrzehnt zu neuen und teilweise unerwarteten oligomeren und polymeren Hauptgruppenelement-Schwefel-Verbindungen mit bemerkenswerten Bindungs-, Struktur- sowie Reaktivitatseigenschaften gefuhrt. Beispiele solcher Entwicklungen sind die Entdeckung von B8S16 und (BS2)n sowie luftbestandiger, ionenleitender Thioborate mit tetraedrisch koordiniertem Bor, die erfolgreiche Verwendung von Borsulfiden in der Anorganischen und Organischen Synthese, weiterhin die gezielte Herstellung polymerhomologer Reihen molekularer mehrkerniger Thio- und Selenoanionen von Ga, In, Si, Ge und Sn, auch neuer mehrkerniger, als reaktive Ausgangsstoffe fur vielseitige Umsetzungen verwendbarer Sulfid- und Selenidhalogenide von Si und Ge, die Synthese von Argyrodit(Ag8GeS6)-artigen Phasen mit interessanten Festkorpereigenschaften, sowie die Charakterisierung des fur das Verstandnis der Wechselwirkungen schwefelhaltiger Biomolekule wichtigen S—H…S-Wasserstoffbruckentyps in Thiokohlen- und Thiophosphinsauren.

Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms.

Abstract: We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.

Alternativ-Liganden, XXXVII. Phosphanliganden mit Bor als Lewis-acidem Zentrum: Synthese und Koordinationseigenschaften / Alternative Ligands, XXXVII. Phosphane Ligands with Boron as Lewis-acidic Centre: Synthesis and Coordinating Properties

Abstract: The complex [Rh(CO)Cl{Me2PC(Me)=C(Me)BMe2}2] (5) has been prepared again in order to prove its structure with weak bonding interactions between the basic rhodium centre and the Lewisacidic Me2B group of the donor/acceptor ligand Me2PC(Me)=C(Me)BMe2 (1). For further investigations additional ligands with P-donor and B-acceptor centres, e. g. Ph2PC(Ph)=C(Ph)BPh2 (2), B(OCH2PMe2)3 (3), and B(CH2CH2PMe2)3 (4), have been prepared and the coordinating properties have been studied by reactions of 1 and 4 with [(π-C5Me5)Rh(CO)2] and Pd(PPh3)4, respectively. Because single crystals of the products [(π-C5Me5)Rh(CO)Me2PC(Me)=C(Me)BMe2] (6), [(π-C5Me5)Rh(CO){Me2PC(Me)=C(Me)BMe2}2] (7) as well as [Pd{B(CH2CH2PMe2)3}] (8) or [(Ph3P)Pd{B(CH2CH2PMe2)3}] (9) could not be generated, quantum chemical calculations have been used to elucidate the coordination geometry expected for 5, 8 and 9. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods and - in spite of the extremely soft coordination sphere of 8 and 9 - are in accord with spectroscopic results for the cage structures.

Altering the Activity of Catechol Oxidase Model Compounds by Electronic Influence on the Copper Core

Abstract: The catecholase activity of the dicopper(II) complexes [Cu2(L1)(μ-OCH3)(NCCH3)2](PF6)2·H2O·CH3CN (1), [Cu2(L2)(μ-OH)(MeOH)(NCCH3)](BF4)2 (2), [Cu2(L3)(μ-OMe)(NCCH3)2](BF4)2·2CH3CN·H2O (3), [Cu2(L2)(μ-OAc)2]BF4·H2O (4), [Cu2(L4)(μ-OAc)2]ClO4 (5) and [Cu2(L5)(μ-OMe)(NCCH3)3(OH2)](ClO4)2·2CH3OH·CH3CN (6) consisting of varying para-substituted phenol ligands HL1 = 4-trifluoromethyl-2,6-bis((4-methylpiperazin-1-yl)methyl)phenol, HL2 = 4-bromo-2,6-bis((4-methyl-1,4-diazepan-1-yl)methyl)phenol, HL3 = 4-bromo-2-((4-methyl-1,4-diazepan-1-yl)methyl)-6-((4-methylpiperazin-1-yl)methyl)phenol, HL4 = 2,6-bis((4-methylpiperazin-1-yl)methyl)-4-nitrophenol and HL5 = 4-tert-butyl-2,6-bis((4-methylpiperazin-1-yl)methyl)phenol was studied. The main difference within the six complexes lies in the individual copper–copper separation that is enforced by the chelating side arms of the phenolate ligand entity and more importantly in the exogenous bridging solvent, hydroxide, methanolate or acetate ions. The distance between the copper cores varies from 2.94A in 1 to 3.29A in 5. The catalytic activity of the complexes 1–6 towards the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5–di-tert-butylquinone characteristic absorption band at about 400 nm over time saturated with O2. The complexes are able to oxidize the substrate 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity (kcat between 92 h−1 and 189 h−1), with an order of decreasing activity 6 > 5 > 1, 2, 4 ≥ 3. A kinetic treatment of the data based on the Michaelis-Menten approach was applied. A correlation of the catecholase activities with the variation of the para- substituents as well as other effects resulting from the copper core distances is discussed. [Cu2(L5)(μ-OMe)(NCCH3)3(OH)2](ClO4)2·2CH3OH·CH3CN (6) exhibited the highest activity of the six complexes as a result of its high turnover rate.

[Ho5(H2O)16(OH)2As6W64O220]25−, ein großes neuartiges Polyoxoanion aus trivakanten Keggin-Fragmenten

Abstract: [Ho5(H2O)16(OH)2As6W64O220]25−, a Large Novel Polyoxoanion from Trivacant Keggin Fragments The novel polyoxotungstate Na7K18[Ho5(H2O)16(OH)2As6W64O220] · 56 H2O (1) was synthesized in aqueous solution and characterized by X-ray structure analysis, elemental analysis and IR spectroscopy. The anion in 1 represents one of the largest polyoxoanions known yet and exhibits an unusual arrangement of six Keggin units. It consists of six trivacant lacunary α-B-(AsW9O33)9− Keggin fragments which are connected by a bridging [Ho5W10(H2O)16(OH)2O22]29+ unit. The five HoIII atoms are coordinated by eight oxygen atoms, forming a square-antiprism.

Recombinant purple acid phosphatase isoform 3 from sweet potato is an enzyme with a diiron metal center

Abstract: Purple acid phosphatases (PAPs) from sweet potato (sp) have been classified on the basis of their primary structure and the dinuclear metal center into isoforms spPAP1 [Fe(III)-Zn(II)] and spPAP2 [Fe(III)-Mn(II)]; for spPAP3 only the cDNA is known. With the aim of unraveling the character of the dinuclear metal center we report here the characterization of this isoform at the protein level. We cloned spPAP3 cDNA in a baculovirus and overexpressed this enzyme in Sf9 insect cells. Preparation of recombinant spPAP3 in two steps afforded pure enzyme with yields of 4.5 mg.L(-1) culture medium. This enzyme is a dimeric, disulfide-linked PAP of 110 kDa, similar to known PAP isoforms from higher plants. Enzymatic studies and spectroscopic properties (max. absorption at 550-565 nm) indicated a diiron enzyme; quantitative and semiquantitative metal analysis using ICP-OES and TOF-SIMS, respectively, revealed the presence of only iron in purified spPAP3. Metal replacement in the second metal-binding site upon preparation of the semiapo-enzyme with Fe(II), Zn(II), or Mn(II) showed highest activities with Fe(II). The data show that recombinant spPAP3 has a diiron metal center. Site-directed mutagenesis was conducted to check catalytic efficiency at the atomic level. Tyr291 at the substrate-binding site in spPAP3 was mutated to His and Ala, the respective residues found in spPAP1 and spPAP2. Kinetic analysis showed that conversion of Tyr291 to His further optimized the performance of this protein as a diiron enzyme, whereas the Ala mutation weakened the catalytic efficiency regardless of the metal present in the second binding site.

The First Structurally Characterized Mn(III) Substituted Sandwich-type Polyoxotungstates

Abstract: The new polyoxotungstates $$((\hbox{CH}_{3})_{4}\hbox{N})_{2}\hbox{Na}_{7}[(\hbox{Mn}^{{\rm III}}(\hbox{H}_{2}\hbox{O}))_{3}(\hbox{SbW}_{9}\hbox{O}_{33})_{2}]\cdot 24.5$$ H2O (1), $$\hbox{Na}_{8.25}[(\hbox{Mn}^{\rm III}(\hbox{H}_{2}\hbox{O}))_{2.25}(\hbox{WO}(\hbox{H}_{2}\hbox{O}))_{0.75} (\hbox{AsW}_{9}\hbox{O}_{33})_{2}]$$ · 28H2O (2) and $$\hbox{Na}_{3}\hbox{K}_{9}[\hbox{Mn}^{\rm II}(\hbox{H}_{2}\hbox{O})\hbox{Mn}_{2}(\hbox{AsW}_{9}\hbox{O}_{33})_{2}]\ \cdot 16$$ H2O (3) were synthesized in aqueous solution and characterized by IR and Raman spectroscopy, energy dispersive X-ray fluorescence and single-crystal X-ray analysis. The anions in 1 and 2 are the first structurally characterized sandwich-type polyoxoanions which contain trivalent manganese atoms. The manganese atoms are coordinated by four oxygen atoms of two $$(\hbox{XW}_{9}\hbox{O}_{33})^{9-}$$ Keggin fragments and one water molecule, forming a square pyramid. The manganese(II) containing anions in 3 are linked via Mn–O–W-bonds, forming a two-dimensional network.

Iron(III) complexes with the ligand N',N'-bis[(2-pyridyl)-methyl]ethylenediamine (uns-penp) and its amide derivative N-acetyl-N',N'-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp)

Abstract: Synthesis and structural characterization of the iron(III) complexes of the tripodal ligands N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (uns-penp), [Fe(uns-penp)Cl2]ClO4·CH3CN, [{Fe(uns-penp)Cl}2O](ClO4)2·2CH3CN and the amide derivative N-Acetyl-N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp), [Fe2(acetyl-uns-penp)2O](ClO4)2·H2O, [Fe(acetyl-uns-penp)(tcc)Br]·(C2H5)2O (tcc = tetrachlorocatecholate), and [{Fe(acetyl-uns-penp)(tcc)}2O]·(C2H5)2O·CH3OH are reported. Catechol dioxygenase reactivity of in situ prepared complex solutions was tested and showed that all complexes reacted slower compared with the iron tmpa system described in the literature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Verbindungen mit zweifach metalliertem Kohlenstoff durch metallinduzierte Vinyl‐Ethyliden‐Umlagerung

Abstract: Das vollstandige Manuskript dieser Zuschrift erscheint in: Angew. Chem. Suppl. 1982, 506. DOI: 10.1002/ange.198205060

Synthese und Charakterisierung neuer fünf‐ und sechsfach koordinierter Mangan(II)‐Komplexe als Modellsysteme für manganabhängige Catecholdioxygenasen

Abstract: Synthesis and Characterization of Novel Five- and Six-coordinate Manganese Complexes as Catechol Dioxygenase Models The five- and six-coordinate manganese complexes [Mn(tphhp)Cl2] {tphhp = N,N′-bis(2-pyridylmethyl)-2-(2-pyridyl)hexahydropyrimidine} (1), [Mn(bpma)Cl](ClO4) {bpma = bis((2-pyridylmethyl)((1-methylbenzimidazol-2-yl)-methyl)amine} (2) and [Mn(L)TCC] {HL = (1-hydroxy-4-nitrobenzyl)((1-methylimidazol-2-yl)methyl)(2-pyridylmethyl)amine} (3) were synthesized and characterized by various techniques such as single crystal X-ray structure analysis, mass spectrometry, IR and UV/vis spectroscopy, cyclic voltammetry, and elemental analysis. 1 and 2 crystallize in the monoclinic space group P21/n (No. 14) (1) and P21/c (No. 14) (2). The ligand and the chlorine ions provide the N3Cl2-donorset in 1 and the N3Cl2-donorset in 2, respectively. Compounds 1 and 2 show catalytic activity regarding the oxidation of 3,5-di-tertbutylcatechol to 3,5-di-tert-butylchinon. To our knowledge, 1 and 2 are the first five-coordinate manganese complexes that show catecholase activity. 3 crystallize in the orthorhombic space group P212121 (No. 19) and the ligand and tetrachlorocatechol (TCC) build the N3O3-donorset in 3.

Cycloarsanes (AsCF3)n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F3CAs=AsCF3

Abstract: Tetrakis(trifluoromethyl) cyclotetraarsane (F3CAs)4 (2) was used to repeat the UV initiated [4+2]-cycloaddition reaction of the diarsene F3CAs=AsCF3 (1) with cyclohexa-1,3-diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X-ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E-configuration. 2 was also applied for [2+2]-cycloaddition reactions of 1 with tBuC≡P and MeC≡CNiPr2, but in contrast to positive results with (F3CP)4 the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π-donor ligand to the Pd(PPh3)2 complex fragment yielding η2-bis(trifluoromethyl)diarsene-bis(triphenylphosphane)-palladium(0) 5, which was characterized by X-ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1, generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]-cycloadduct with 1-di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3-dimethyl-1,3-butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F3CP=PCF3.

Alternativ-Liganden, XXXVIII [1]. Phosphanliganden mit Bor als Lewis-acidem Zentrum : Synthese und Koordinationseigenschaften

Abstract: The complex [Rh(CO)Cl{Me2PC(Me)=C(Me)BMe2}2] (5) has been prepared again in order to prove its structure with weak bonding interactions between the basic rhodium centre and the Lewis-acidic Me 2 B group of the donor/acceptor ligand Me 2 PC(Me)=C(Me)BMe 2 (1). For further investigations additional ligands with P-donor and B-acceptor centres, e.g. Ph 2 PC(Ph)=C(Ph)BPh 2 (2), B(OCH 2 PMe 2 ) 3 (3), and B(CH 2 CH 2 PMe 2 ) 3 (4), have been prepared and the coordinating properties have been studied by reactions of 1 and 4 with [(π-C 5 Me 5 )Rh(CO) 2 ] and Pd(PPh 3 ) 4 , respectively. Because single crystals of the products [(π-C 5 Me 5 )Rh(CO)Me 2 PC(Me)=C(Me)BMe 2 ] (6), [(π-C 5 Me 5 )Rh(CO){Me 2 PC(Me)=C(Me)BMe 2 } 2 ] (7) as well as [Pd{B(CH 2 CH 2 PMe 2 ) 3 }] (8) or [(Ph3P)Pd{B(CH2CH2PMe2)3}] (9) could not be generated, quantum chemical calculations have been used to elucidate the coordination geometry expected for 5, 8 and 9. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods and -in spite of the extremely soft coordination sphere of 8 and 9 - are in accord with spectroscopic results for the cage structures.

Li6+2x[B10Se18]Sex (x ≈ 2), ein ionenleitendes Doppelsalz†

Abstract: Li6+2x[B10Se18]Sex (x ≈ 2), an Ion-conducting Double Salt Li6+2x[B10Se18]Sex (x ≈ 2) was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 °C. Subsequent cooling from 600 °C to 300 °C gave amber colored crystals with the following lattice parameters: space group I2/a (at 173 K); a = 17.411(1) A, b = 21.900(1) A, c = 17.820(1) A, β = 101.6(1)°. The crystal structure contains a well-defined polymeric selenoborate network of composition ([B10Se16Se4/2]6−)n consisting of a system of edge-sharing [B10Se16Se4/2] adamantanoid macro-tetrahedra forming large channels in which a strongly disorderd system of partial occupied Li+ cations and additional disordered Se2− anions is observed. The crystal structure of the novel selenoborate is isotypic to Li6+2x[B10S18]Sx (x ≈ 2) [1]. X-ray and 7Li magic-angle spinning NMR data suggest that the site occupancies of the three crystallographically distinct lithium ions exhibit a significant temperature dependence. The lithium ion mobility has been characterized by detailed temperature dependent NMR lineshape and spin-lattice relaxation measurements.

Lanthanoidhaltige Komplexe monovakanter Keggin- und Dawson-Polyoxoanionen / Novel Lanthanide Complexes of Monovacant Keggin- and Dawson-Type Polyoxoanions

Abstract: The new polyoxotungstates Cs₆ₙK₂ₙ[{(Pr(H₂O)₇)(Pr(H₂O)₂)(α-SiW₁₁O₃₉)}₄]ₙ ・ 33nH₂O (1), (NH₄)₁₄[{Tb(H₂O)₃(α₂-P₂W₁₇O₆₁)}₂] ・ 39H₂O (2) and (NH₄)₇.₃₃K₂.₆₇Ho₁.₃₃[{Ho(H₂O)₃(α₂- P₂W₁₇O₆₁)}₂] ・45H₂O (3) were synthesized in aqueous solution and characterized by IR and Raman spectroscopy, ³¹P NMR spectroscopy (for 2 and 3), energy dispersive X-ray fluorescence analysis and single-crystal X-ray analysis. 1 exhibits a novel one-dimensional chain-like structure which is built up from of monovacant (α-SiW₁₁O₃₉)⁸− Keggin-type anions linked by Pr(III) atoms. Half of the Pr(III) atoms are eight-coordinate (square antiprism), with four sites occupied by one anion, three by water molecules, and the eighth site by a terminal oxygen atom of a second anion. The other Pr(III) atoms are coordinated by seven water molecules and two terminal oxygen atoms of two Keggin moieties. The dimeric [{Ln(H₂O)₃(α₂-P₂W₁₇O₆₁)}₂]¹⁴⁻ anions in 2 (Ln = Tb) and 3 (Ln = Ho) consist of two (α₂-P₂W₁₇O₆₁)¹⁰⁻ Dawson-type anions linked by two trivalent lanthanides. The lanthanides exhibit a square-antiprismatic coordination sphere which is built up by three water molecules, four terminal oxygen atoms of one Dawson-anion and one oxygen atom of the second Dawson-anion. The crystal structures of the new compounds are compared with known species and the influence of the Ln(III) ionic radii is discussed

New imidazole-coordinated chemotherapeutics with low epithelial toxicity.

Abstract: The new imidazole-coordinated chemotherapeutics with low epithelial toxicity (NICE) presented in this article feature innovative drugs that combine epithelial toxicity comparable with that of carboplatin with novel carrier ligands optimized for DNA interaction. Recent identification of the pivotal role of basolateral organic cation transporters (OCTs) in cisplatin nephrotoxicity by a new model system (electrical resistance breakdown assay) facilitated the search for substances with a favorable organotoxic profile. The assay uses the high transepithelial electrical resistance (TEER) of the C7-clone of Madin-Darby canine kidney (MDCK) cells and the exclusive basolateral expression of OCT2 in these cells. TEER and caspase-3 activity of MDCK-C7-cells grown on microfilter membranes were monitored in response to exposure of either the apical or basolateral plasma membrane to platinum complexes. The impact of complexes on cancer cell lines was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide tests. Effects of substituents on pharmacological properties of NICE were systematically investigated by introducing sterically demanding groups as well as electron-donating and electron-withdrawing groups. Derivatives of NICE showed different renal epithelial toxic profiles and effects on cancer cells. NICE were significantly less toxic than cis- or oxaliplatin. The chlorine substituted NICE had no effect on epithelial integrity but markedly cytotoxic activity against amelanotic melanoma cells. Together, side effect targeted screening for new anticancer drugs with the electrical resistance breakdown assay offers an interesting approach for identifying and investigating new compounds. NICE feature the first group of platinum-based cytostatics discovered by using this system for systematic screening of new chemotherapeutics with low renal epithelial toxicity.