Contribution à la phytochimie du genre Gentiana,VI. Etude des xanthones dans les feuilles de Gentiana bavarica L.

Ten tetraoxygenated xanthones (1-hydroxy-3, 7, 8-trimethoxyxanthone I; 1, 7-dihydroxy-3, 8-dimethoxyxanthone II; 1, 7, 8-trihydroxy-3-methoxyxanthone III; 1, 3, 7, 8-tetrahydroxyxanthone IV; 3, 7, 8-trimethoxyxanthone-1-O-primeveroside V; 7-hydroxy-3, 8-dimethoxyxanthone-1-O-primeveroside VI; 1, 8-dihydroxy-3-methoxyxanthone-7-O-acetylrutinoside VII; 7, 8-dihydroxy-3-methoxyxanthone-1-O-primeveroside VIII; 3, 7, 8-trihydroxyxanthone-1-O-primeveroside IX; 3, 7, 8-trihydroxyxanthone-1-O-glucoside X) have been isolated from leaves of Gentiana bavarica L . by means of column chromatography on polyamid. Among these xanthones, VI, VII, VIII and IX were not encountered before in nature.     

Phosphaniminato-Komplexe des Antimons. Die Kristallstrukturen von [Sb2Cl5(NPMe3)2][SbCl6] · CH3CN und [SbCl(NPPh3)]2[SbCl6]2 · 6 CH3CN

Phosphorane Iminato Complexes of Antimony. The Crystal Structures of [Sb₂Cl₅(NPMe₃)₂][SbCl₆] · CH₃CN and [SbCl(NPPh₃)]₂[SbCl₆]₂ · 6 CH₃CN The title compounds are formed by reaction of antimony pentachloride in acetonitrile solution with the phosphorane iminato complexes SbCl₂(NPMe₃) and SbCl₂(NPPh₃), respectively, which themselves are synthesized by reaction of antimony trichloride with Me₃SiNPR₃ (R = Me, Ph). The complexionic compounds are characterized by ¹²¹Sb Mössbauer spectroscopy and by crystal structure determinations. [Sb₂Cl₅(NPMe₃)₂][SbCl₆] · CH₃CN: Space group P4₁, Z = 4, 3 698 observed unique reflections, R = 0.022. Lattice dimensions at ?60°C: a = b = 1 056.0(1), c = 2 709.6(2) pm. The structure consists of SbCl₆^? ions and cations [Sb₂Cl₅(NPMe₃)₂(CH₃CN)]⁺, in which one Sb^III atom and one Sb^V atom are bridged by the N atoms of the phosphorane iminato ligands. [SbCl(NPPh₃)]₂[SbCl₆]₂ · 6 CH₃CN: Space group P1 , Z = 2, 5 958 observed unique reflections, R = 0.033. Lattice dimensions at ?60°C: a = 989.4(11), b = 1 273(1), c = 1 396(1) pm, α = 78.33(7), β = 77.27(8)°, γ = 86.62(8)°. The structure consists of SbCl₆^? ions and centrosymmetric cations [SbCl(NPPh₃)(CH₃CN)₂]₂²⁺, in which the antimony atoms are bridged by the N atoms of the phosphorane iminato ligands.     

FLUORESCENCE QUANTUM YIELDS OF 124-kDa PHYTOCHROME FROM OAT UPON EXCITATION WITHIN DIFFERENT ABSORPTION BANDS

Abstract— A fluorescence quantum yield (emission at650–850 nm) of π= (2.3 ± 0.3)10⁻³ was measured for the red-absorbing form (Pr) of 124-kDa phytochrome from etiolated oat seedlings ( Avena sativa ) upon excitation in the Soret band at Λ^exc= 380 nm. The small difference between this value and the previously determined quantum yield with Λ^exc= 640 nm, π= (3.5 ± 0.4)10⁻³is attributed to a blue-absorbing emitter responsible for the "anomalous" or "blue" emission of the chromoprotein in the region from ca. 400 to 550 nm. The absorption of Pr at 380 nm is consequently somewhat lower than that measured directly from the spectrum. Processes from upper excited states of the Pr phytochromobilin-derived chromophore other than rapid relaxation to the emitting state are not important. A quantum yield of Φ ' 1.2 times 10⁻³ is estimated for the blue fluorescence. The proportion of the blue emitters relative to Pr appears to be relatively high.     

Synthese und Kristallstruktur des Nitridokomplexes [Na-15-Krone-5]2[MoNF4]2 · 2 CH3CN

Synthesis and Crystal Structure of the Nitrido Complex [Na-15-crown-5]₂[MoNF₄]₂ · 2 CH₃CN The title compound is synthesized by the reaction of [MoCl₄(NSCl)]₂ with excess NaF in boiling acetonitrile in the presence of the crown ether 15-crown-5. [Na-15-crown-5]₂[MoNF₄]₂ · 2 CH₃CN forms yellow crystals, which were characterized by an X-ray structure determination. Space group P1 , Z = 1. Lattice dimensions at ?90°C: a = 855.5, b = 1 069.9, C = 1 143.5 pm, α = 105.71°, β = 95.29°, γ = 102.25° (4 096 independent observed reflexions, R = 0.039). Short Na…?F contacts of 234 pm with the four axial fluoro ligands of the dimeric anion [MoNF₄]₂^2? allow formulation of a triple ion. The centrosymmetric anion is dimerized by bent fluoro bridges with Mo? F distances of 198 and 245 pm. The long Mo? F distances of the MoF₂Mo ring are in transposition to the nitrido ligands, the bond lengths of which (165 pm) correspond to triple bonds.     

[(Ph3Sn)3VO4]·CH3CN und [(Ph3Sn)3VO4]·2 DMF,Triphenylzinnvanadate mit neuartigen Kettenstrukturen

[(Ph₃Sn)₃VO₄]·CH₃CN and [(Ph₃Sn)₃VO₄]·2 DMF, Triphenyltin Vanadates with Novel Chain Structures The reaction of Na₃VO₄ with Ph₃SnCl in a water/CH₂Cl₂ mixture leads to the formation of [(Ph₃Sn)₃VO₄] ( 1 ). Recrystallization of 1 from toluene/CH₃CN gives pale yellow crystals of [(Ph₃Sn)₃VO₄]·CH₃CN ( 2 ). 2 crystallizes as coordination polymer which consists of infinite chains composed of corner‐sharing VO₄ tetrahedra and Ph₃SnO₂ trigonal bipyramides. Additionally the VO₄ groups are connected to two terminal SnPh₃‐Groups containing tin atoms in a tetrahedral environment. [(Ph₃Sn)₃VO₄]·2 DMF ( 3 ) which is obtained from Na₃VO₄ and Ph₃SnCl in a water/DMF mixture contains a polymeric chain structure similar to 2 and additionally one of the terminal SnPh₃ groups is coordinated to a DMF solvent molecule.     

Untersuchungen an Hydriden im Bereich der Phase Ti2CO1—x Fe x (x=0–0,5)

The hydrogen absorption of the phase Ti₆₄Co_32–x Fe _x (x=0...16) and its influence on the magnetic properties have been investigated. Measurements of the vapour-pressure, wide-line NMR and magnetic susceptibility have been performed. Substitution of Co by Fe does not change the amount of absorbed hydrogen. However the reaction rate of hydriding process, the activation energy of diffusion and the magnetic quantities change upon this substitution.

     

The quantitative electrochemical generation of bromine in acetic acid

The quantitative electrochemical generation of bromine at a platinum electrode in acetic acid is described. Coulometric methods for the determination of hydroquinone and 2-methylhydroquinone are reported. The best results are obtained with 0.7–1.1 M potassium acetate solutions as supporting electrolyte, and biamperometric end-point detection. The effects of water and acetic anhydride on the accuracy of titrations are discussed. Determination of the formal redox potential of the Br₂/Br^- system in a 0.9 M potassium acetate solution in acetic acid showed that bromide is oxidized directly to bromine at a platinum electrode with 100% current efficiency.     

Dichloracetylen als stabiler Komplexligand Die Kristallstruktur von PPh4[WCl5(C2Cl2)] · 0,5 CCl4

Dichloro Acetylene as Complex Ligand. Crystal Structure of PPh₄[WCl₅(C₂Cl₂)] · 0.5 CCl₄ Tungsten hexachloride and dichloro acetylenediethyletherate react in boiling CCl₄ in presence of C₂Cl₄ as reducing agent forming [Et₂O · WCl₄(C₂Cl₂)]. In vacuo the complex looses ether giving the dichloro acetylene complex [WCl₄(C₂Cl₂)]₂ which is dimeric with chloro bridges. Both complexes react with tetraphenylphosphonium chloride to form PPh₄[WCl₅(C₂Cl₂)] which is equally prepared by ligand exchange of PPh₄[WCl₅(C₂I₂)] with silver chloride. All dichloro acetylene complexes are red to brown crystalline solids sensitive to moisture, and are thermally and mechanically very stable compared with the highly explosive dichloro acetylene. The compounds are characterized by their i.r. spectra; [Et₂O · WCl₄(C₂Cl₂)] was additionally investigated by ¹³C-nmr spectroscopy. PPh₄[WCl₅(C₂Cl₂)] · 0.5 CCl₄ formes dark brown crystals; according to the structural investigation by X-ray diffraction methods the compound crystallizes orthorhombic in the space group Pbca with 8 formula units per unit cell (1317 observed, independent reflexions, R = 0.049). The cell dimensions are a = 1702 pm, b = 1675 pm and c = 2228 pm. The compound consists of [WCl₅(C₂Cl₂)]? anions and PPh₄⊕ cations including CCl₄ molecules without bonding interactions. The tungsten atoms are seven-coordinated by five chlorine atoms and two carbon atoms. The dichloro acetylene ligand is bonded symmetrically side-on and has a C? C bond length of 128 pm. The W? C distances are 201 pm, the four equatorial Cl atoms have W? Cl bond lengths of 234 pm whereas the chlorine atom in trans-position to the W? C₂ group is situated in a distance of 244 pm.     

Stereocontrolled synthesis of the DE ring system of the marine alkaloid upenamide

[reaction: see text] A stereocontrolled synthesis of the DE fragment (2) of the marine alkaloid upenamide (1) is described. The synthesis proceeds in 12 steps from caprolactone (10) and 20-25% overall yield.     

Studies on bis(3,5-di-t-butyl-1,2-benzoquinone 1-oximato)manganese(II) and its mixed-ligand complexes

The synthesis, spectroscopy, and redox-reactivity towards PPh(3) of bis(3,5-di-t-butyl-1,2-benzoquinone 1-oximato)manganese(II), Mn(ox)(2), and its mixed-ligand complexes, Mn(ox)L(x) [L(x)=8-hydroxyquinolinato (L(1)), 2,2'-bipyridine (bpy) (L(2)), 1,10-Phenanthroline (phen) (L(3)) and N-(2-hydroxyphenyl)-3,5-di-t-butylsalicylaldiminato (L(4))] complexes, are presented. While some complexes exhibit solid-state ESR spectra they were ESR-silent in toluene or CHCl(3) at 300 K. The reduction of all ESR-silent complexes with an excess of PPh(3), independently from the nature of secondary L(x) ligands, results in the appearance of a six-line hyperfine coupling of 55Mn (I=5/2) (A(Mn)=95-100 G) and a seven-line radical signal, which was assigned to phosphiniminophenoxyl type radicals (g=2.0056-2.0075, A(P)=8. 5 G and A(N)=1.875 G).