Showing papers by "Bernt Krebs published in 2002"

The crystal structure of catechol oxidase : new insight into the function of type-3 copper proteins

Abstract: The crystal structure of catechol oxidase reveals new insight into the functional properties of the type-3 copper proteins. This class of proteins includes the closely related and better-known tyrosinase as well as hemocyanin, an oxygen transport protein. All these proteins have a dinuclear copper center, have similar spectroscopic behaviors, and show close evolutionary and functional relationships. Comparison between the 3D structures of catechol oxidase and hemocyanins reveals the structural reasons for the divergence in function.

Preparation of highly efficient manganese catalase mimics.

Abstract: The series of compounds [Mn(bpia)(mu-OAc)](2)(ClO(4))(2) (1), [Mn(2)(bpia)(2)(muO)(mu-OAc)](ClO(4))(3).CH(3)CN (2), [Mn(bpia)(mu-O)](2)(ClO(4))(2)(PF(6)).2CH(3)CN (3), [Mn(bpia)(Cl)(2)](ClO)(4) (4), and [(Mn(bpia)(Cl))(2)(mu-O)](ClO(4))(2).2CH(3)CN (5) (bpia = bis(picolyl)(N-methylimidazol-2-yl)amine) represents a structural, spectroscopic, and functional model system for manganese catalases. Compounds 3 and 5 have been synthesized from 2 via bulk electrolysis and ligand exchange, respectively. All complexes have been structurally characterized by X-ray crystallography and by UV-vis and EPR spectroscopies. The different bridging ligands including the rare mono-mu-oxo and mono-mu-oxo-mono-mu-carboxylato motifs lead to a variation of the Mn-Mn separation across the four binuclear compounds of 1.50 A (Mn(2)(II,II) = 4.128 A, Mn(2)(III,III) = 3.5326 and 3.2533 A, Mn(2)(III,IV) = 2.624 A). Complexes 1, 2, and 3 are mimics for the Mn(2)(II,II), the Mn(2)(III,III), and the Mn(2)(III,IV) oxidation states of the native enzyme. UV-vis spectra of these compounds show similarities to those of the corresponding oxidation states of manganese catalase from Thermus thermophilus and Lactobacillus plantarum. Compound 2 exhibits a rare example of a Jahn-Teller compression. While complexes 1 and 3 are efficient catalysts for the disproportionation of hydrogen peroxide and contain an N(4)O(2) donor set, 4 and 5 show no catalase activity. These complexes have an N(4)Cl(2) and N(4)OCl donor set, respectively, and serve as mimics for halide inhibited manganese catalases. Cyclovoltammetric data show that the substitution of oxygen donor atoms with chloride causes a shift of redox potentials to more positive values. To our knowledge, complex 1 is the most efficient binuclear functional manganese catalase mimic exhibiting saturation kinetics to date.

Heterodinuclear zinc(II)-iron(III) complexes and dinuclear zinc complexes as models for zinc-containing phosphatases

Abstract: Five new dinuclear model complexes for zinc-containing phosphatases with dinucleating ligands have been prepared and characterized by single-crystal X-ray crystallography. The heterodinuclear, μ-alkoxo-bridged zinc(II)−iron(III) complexes 1−3 contain the symmetric ligands N,N,N′,N′-tetrakis[2-(5,6-dimethyl)benzimidazolylmethyl]-1,3-diamino-2propanol (Htdmbpo) and N,N,N′,N′-tetrakis{2-[N′′-(2hydroxyethyl)]benzimidazolylmethyl}-1,3-diamino-2-propanol (Hthebpo), and the asymmetric ligand N,N-bis[2-(4,5-dimethyl)benzimidazolylmethyl]-N′,N′-bis(2-pyridylmethyl)-1,3-diamino-2-propanol (Hbdmbbppo), respectively. X-ray crystallography revealed that the zinc center exhibits a trigonal-bipyramidal coordination, while the octahedral coordination sphere of the iron center is completed by a solvent molecule. In contrast, the zinc complexes 4 and 5, which also have (alkoxo)(cacodylato)dimetal cores with the dinucleating ligands used in 1 and 3, exhibit both metal centers in a trigonal-bipyramidal environment. Additionally, the solution speciation of the zinc(II) complexes formed with Htdmbpo and Hbdmbbppo were determined and the activity of the in situ prepared zinc complexes towards the transesterification of the RNA model substrate 2-(hydroxypropyl)-4-nitrophenyl phosphate (hpnp) was investigated. The dinuclear [Zn2LH−1(OH)]2+ complex of both ligands efficiently promotes the transesterification. The kinetic data indicated a higher activity for the complex of the asymmetric ligand Hbdmbbppo, as a result of its stronger substrate binding ability. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Syntheses and X-ray Characterization of Novel [M4(H2O)2(XW9O34)2]n- (M=CuII, X=CuII; and M=FeIII, X=FeIII) Polyoxotungstates

Abstract: Two novel examples of “sandwich” type heteropolyanions were synthesized and characterized by X-ray crystal structure and elemental analysis as well as infrared spectroscopy. Na13[H3Cu4(H2O)2(CuW9O34)2]⋅39H2O (1) and Na9K[Fe4(H2O)2(FeW9O34)2]⋅32H2O (2) were prepared in aqueous solution by reaction of sodium tungstate with FeIII and CuII cations, respectively. 1 crystallizes in the monoclinic space group P21/n (a=13.054(3) A, b=17.729(4) A, c=20.998(4) A, β=93.50(3)°), while 2 is triclinic, space group P¯1 (a=12.316(2) A, b=13.716(3) A, c=14.925(3) A, α=99.36(3)°, β=104.21(3)°, γ=101.55(3)°). Each anion consists of two [XW9O34] n− moieties (X=FeIII, n=11 (1) and CuII, n=12 (2)) which can be described as α-B-isomers of the defect Keggin anion. These units are linked via a belt of four FeIIIO6 or CuIIO6 groups. Two transition metal atoms fill their octahedral coordination sphere with one additional water ligand.

Reactions of Polyfluoroarenes with MenE-MMe3 Reagents (MenE = Me2As, Me2P, Me2N, and MeS; M = Si, Sn): Synthesis of Polyfluoroaryl MenE CompoundsDedicated to Professor Dieter Naumann on the Occasion of his 60th Birthday

Abstract: Trimethylsilyldimethylarsane Me3SiAsMe2 was used as a reagent for the substitution of fluorine in polyfluoroarenes C6F5X (X = F, H, Cl) and C5NF5 by the Me2As group. The reactions occur between 50 — 180 °C, either in benzene or without solvent, to give as a rule 4-X-1-(dimethylarsano)tetrafluorobenzenes XC6F4AsMe2, (1—3) and 4-dimethylarsano-tetrafluoropyridine C5NF4AsMe2 (4), respectively, in yields between 43 and 94 %. In the case of C6F6, also double substitution is observed affording 1, 4-bis(dimethylarsano)tetrafluorobenzene 5 in addition to the monosubstituted derivative. The time and temperature dependencies of the reactions increase in the sequence: C6F6< C6F5H < C6F5Cl < C5NF5. The arsanes 1 and 4 were transformed to the potentially valuable bidentate ligands 1-(dimethylarsano)-4-(dimethylphosphano)tetrafluorobenzene 6 and 4-(dimethylarsano)-2-(dimethylphosphano)trifluoropyridine 8 by reaction with trimethylsilyl-dimethylphosphane Me3SiPMe2. 6reacts with oxygen to yield the corresponding phosphane oxide 7. Trimethylsilyl-dimethylamine Me3SiNMe2 also was successfully tested as a reagent for the dimethylamination of polyfluoroarenes C6F5X [X = F, H, Cl, CF3, P(S)Me2], 1-P(S)Me2-4-H-C6F4 and 4-X-C5NF4 [X = F, PMe2, P(S)Me2]. Sulfuration of the new Me2P derivatives 8 and 20 leads to the corresponding thiophosphanes 9 and 21 (Schemes 2 and 3). Furthermore, the recently reported very efficient one-pot synthesis of Me2P substituted polyfluoroarenes (e.g. XC6F4PMe2 with X = F, Me2PC6F4) was extended to the preparation of Me2As and MeS derivatives of pentafluoropyridine using a mixture of Me3SnH, As2Me4 (or S2Me2) and C5NF5 as precursors for the one-pot reaction. The expected products 4-(dimethylarsano)tetrafluoropyridine 4 and 4-(methylthio)tetrafluoropyridine 22, respectively, were obtained in 84 and 82 % isolated yields. The novel compounds were characterized by spectroscopic (NMR, MS) and analytical data. Compounds 5, 7, 9 and 21 could be isolated in form of single crystals and their structures have been studied by X-ray diffraction. Reaktionen von Polyfluorarenen mit MenE—MMe3-Reagenzien (MenE = Me2As, Me2P, Me2N, MeS; M = Si, Sn): Synthese von MenE-substituierten Polyfluorarenen Trimethylsilyl-dimethylarsan Me3SiAsMe2 wurde bei Polyfluorarenen C6F5X (X = F, H, Cl) und Perfluorpyridin C5NF5 als Reagenz fur die Substitution von Fluor durch die Me2As-Gruppe eingesetzt. Die Reaktionen wurden in Benzol oder ohne Losungsmittel bei Temperaturen zwischen 50 und 180 °C durchgefuhrt und liefern in der Regel die 4-X-1-(Dimethylarsano)tetrafluorbenzole XC6F4AsMe2 (1 — 3) bzw. 4-Dimethylarsanotetrafluorpyridin C5NF4AsMe2 (4) in Ausbeuten von 43 — 94 %. Im Fall von C6F6 wird auch Zweifachsubstitution zum 1, 4-Bis(dimethylarsano)tetrafluorbenzol 5 beobachtet. Die Reaktivitat, gemessen am Zeitbedarf und an der Temperaturabhangigkeit der Reaktionen, wird von der Art des Polyfluorarens bestimmt und nimmt in der Reihe C6F6 < C6F5H < C6F5Cl < C5NF5 zu. Die Arsane 1 und 4 wurden mit Trimethylsilyl-dimethylphosphan Me3SiPMe2 zu den heterosubstituierten Derivaten 1-(Dimethylarsano)-4-(dimethylphosphano)tetrafluorbenzol 6 bzw. 4-(Dimethylarsano)-2-(dimethylphosphano)-trifluorpyridine 8 umgesetzt, die als potenzielle zweizahnige Liganden von Interesse sind. 6 reagiert mit Sauerstoff zum entsprechenden Phosphanoxid 7. Trimethylsilyl-dimethylamin Me3SiNMe2 wurde als Reagenz fur die Dimethylaminierung der Polyfluorarene C6F5X [X = F, H, Cl, CF3, P(S)Me2], 1-P(S)Me2-4-HC6F4 and 4-X-C5NF4 [X = F, PMe2, P(S)Me2] ebenfalls untersucht. Durch Sulfurierung der Me2P-Derivate 8 und 20 werden die Thiophosphane 9 und 21 erhalten (Schemata 2 und 3). Auserdem wurde die vor kurzem entwickelte Eintopf-Synthese fur Me2P substituierte Polyfluorarene (z. B. XC6F4PMe2 mit X = F, Me2PC6F4) auf die Darstellung von Me2As- und MeS-Derivaten des Pentafluorpyridins ausgedehnt: Als Edukte fur die Eintopf-Reaktionen wurden Me3SnH, As2Me4 (oder S2Me2) und C5NF5 verwendet. Die erwarteten Produkte 4-(Dimethylarsano)tetrafluorpyridin 4 bzw. 4-(Methylthio)tetrafluorpyridin 22 wurden in 84- bzw. 82- %iger Ausbeute isoliert. Die neuen Verbindungen wurden durch spektroskopische (NMR, MS) und analytische Daten charakterisiert. Die Vertreter 5, 7, 9 und 21 konnten in Form von Einkristallen isoliert werden; ihre Strukturen wurden durch Rontgenbeugung aufgeklart.

BaB2S4: Das erste nicht‐oxidische Chalkogenoborat mit trigonal‐planar und tetraedrisch koordiniertem Bor

Abstract: Bislang kennt man das Auftreten von sowohl trigonal-planar als auch tetraedrisch koordiniertem Bor in einer Kristallstruktur nur aus der Bor-Sauerstoff-Chemie. Mit dem neuen Bariummetathioborat BaB2S4 stellen wir nun zum erstenmal eine Verbindung vor, deren Anionenstruktur aus zu Ketten kondensierten BS3- und BS4-Einheiten im Verhaltnis 1 : 1 besteht, die entlang der c-Achse verlaufen. BaB2S4 wurde aus Bariumsulfid, amorphem Bor und Schwefel in einer Hochtemperatur-Feststoffreaktion bei 800 °C dargestellt und kristallisiert im monoklinen Kristallsystem in der Raumgruppe Cc (Nr. 9) mit den Gitterparametern a = 6, 6465(5) A, b = 15, 699(1) A, c = 6, 0306(5) A, β = 110, 96(1)°, Z = 4. BaB2S4: The first non-oxidic Chalcogenoborate with Boron in a trigonal-planar and tetrahedral Coordination Hitherto we know boron in a trigonal-planar and a tetrahedral coordination within one crystal structure from boron oxides in various compounds. With the novel bariummetathioborate BaB2S4 we now report a crystal structure containing BS3 and BS4 units in the ratio 1 : 1 forming infinite chains along [001]. BaB2S4 was synthesized in a solid state reaction at a temperature of 800 °C from barium sulfide, amorphous boron and sulfur and crystallizes in the monoclinic space group Cc (no. 9) with the following lattice parameters: a = 6.6465(5) A, b = 15.699(1) A, c = 6.0306(5) A, β = 110.96(1)°, Z = 4.

A Tetranuclear Manganese Cluster with a Star-Shaped Mn4O6 Core Motif: Directed Synthesis using a Mononuclear Precursor Complex†

Abstract: The tetranuclear manganese(II) complex [Mn4(ppi)6](BPh4)2 (2) (Hppi = 2-pyridylmethyl-2-hydroxy phenylimine) is prepared by using the precursor complex [Mn(ppi)2]·H2O (1). Based on UV/Vis- and IR-spectroscopy data in combination with mass spectrometry it has been concluded that 1 is a mononuclear neutral MnII complex, in which two ppi ligands chelate the manganese atom. Compound 2 crystallizes in the triclinic space group P1¯ (no. 2), with a = 17.500(3), b = 17.955(4), c = 19.101(4) A, α = 113.79(3)°, β = 111.33(3)°, γ = 93.91(3)°, V = 4950(2) A3 and Z = 2. In the tetranuclear [Mn4(ppi)6]2+ complex cation Mn(1), Mn(2), and Mn(3) are equivalently coordinated by two deprotonated Hppi ligands leading to a N4O2 donor set. The environment of the central Mn(4) is formed by coordination of three [Mn(ppi)2] fragments resulting in a phenoxo bridged star-shaped Mn4O6 core motif. The average distance of directly adjacent manganese ions is 3.310 A, whereas the average distance of Mn(1), Mn(2), and Mn(3) among each other is 5.732 A.

Selective determination of hydrogen peroxide by adduct formation with a dinuclear iron(III) complex and flow injection analysis/tandem mass spectrometry

Abstract: A highly selective method for the determination of hydrogen peroxide is presented. In a flow injection analysis (FIA) instrument, the analyte is brought into contact with a dinuclear heptadentate iron(III) complex. The formation of the peroxide adduct is quantified using electrospray tandem mass spectrometry (ESI-MS/MS). Selected reaction monitoring (SRM) based on the transition from the triply charged peroxide adduct with m/z = 251.2 to the triply charged fragment ion of m/z = 240.5 is performed. The limit of detection for hydrogen peroxide is 10−7 mol dm−3, limit of quantification is 3 × 10−7 mol dm−3, and a linear range of 2.5 decades starting at the limit of quantification is observed.

Novel Thioborates of Cesium: Cs3BS3 and Li2CsBS3

Abstract: The new compounds Li 2 CsBS 3 and Cs 3 BS 3 were prepared from the metal sulfide(s), amorphous boron and sulfur in solid state reactions at high temperatures. The crystal structures were determined by single crystal X-ray diffraction experiments. The purity of the products was proved by powder diffraction. Li 2 CsBS 3 crystallizes in the orthorhombic space group Pnma (no. 62) with a = 10.004(2), b = 8.000(2), c = 8.082(2) A, and Z = 4, while Cs 3 BS 3 is isotypic to Rb 3 BS 3 in the monoclinic space group P2 1 /c (no. 14) with a = 10.397(1), b = 6.660(1), c = 13.618(1) A, β = 101.31(1)°, and Z = 4. Both compounds contain isolated [BS 3 ] 3 - anions with boron in a trigonal-planar coordination.

The Crystal Structure of Catechol Oxidase: New Insight into the Function of Type‐3 Copper Proteins

Abstract: The crystal structure of catechol oxidase reveals new insight into the functional properties of the type-3 copper proteins. This class of proteins includes the closely related and better-known tyrosinase as well as hemocyanin, an oxygen transport protein. All these proteins have a dinuclear copper center, have similar spectroscopic behaviors, and show close evolutionary and functional relationships. Comparison between the 3D structures of catechol oxidase and hemocyanins reveals the structural reasons for the divergence in function.

Transition metal complexes with proton sponges as ligands

Abstract: Transition metal complexes with chino[7,8-h]chinolines and cyclopentadieno[1,2-h: 4,3-h']dichinolines as proton sponge ligands and method for the production thereof. Said complexes are suitable as catalysts e.g. palladium complexes for a Heck reaction and for amination and C-H activation reactions. The platinum and palladium complexes are potentially good cytostatics.

Method for producing macrocyclic monoepoxide having at least one double bond

Abstract: PROBLEM TO BE SOLVED: To provide a method for selectively epoxidizing one cis-double bond in a macrocyclic olefin. SOLUTION: This method comprises a catalytic selective epoxidation of a cis-double bond in a macrocyclic aliphatic hydrocarbon having 8-20 cyclic carbon atoms and having at least one trans-double bond and optionally at least one side chain; wherein the catalytic system comprises a phase-transfer catalyst and a polyoxometalate which consists of a tungsten- or molybdenum-based polyoxometalate and contains at least another group 14-16 element, and optionally contains at least one group 4-12 transition metal atom.

Cover Picture: Angew. Chem. Int. Ed. 14/2002

Abstract: The cover picture shows a polyhedral representation of a polyoxovanadate core {V6O13(OMe)6}2−, which is linked to two vanadyl moieties. These are coordinated through the N2O2 donor set of organic ligands, which additionally stabilize the hexavanadate through two hydrogen bonds. This compound can be considered as “bridging the gap” between polyoxometalates and classic coordination compounds. Fittingly, in the background, is Mungsten railway bridge near Wuppertal, Germany, which links the towns of Remscheid and Solingen. The bridge, which was built in 1897, at a height of 107 m, an arch width of 170 m, and a total length of 500 m was considered an engineering masterpiece of its time in Europe. More about the successful linkage of two important classes of compounds is reported in the communication by M. Piepenbrink, M. U. Triller, N. H. J. Gorman, and B. Krebs on pp. 2523 ff.