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91.
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. 相似文献
92.
Ralf Garbe Jürgen Pebler Kurt Dehnicke Dieter Fenske Helmut Goesmann Gerhard Baum 《无机化学与普通化学杂志》1994,620(4):592-598
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 SbIII atom and one SbV 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. 相似文献
93.
FLUORESCENCE QUANTUM YIELDS OF 124-kDa PHYTOCHROME FROM OAT UPON EXCITATION WITHIN DIFFERENT ABSORPTION BANDS 总被引:1,自引:0,他引:1
Claudio G. Colombano Silvia E. Braslavsky Alfred R. Holzwarth Kurt Schaffner 《Photochemistry and photobiology》1990,52(1):19-22
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 Λexc = 380 nm. The small difference between this value and the previously determined quantum yield with Λexc = 640 nm, π= (3.5 ± 0.4)10−3 is 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. 相似文献
94.
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]22? 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. 相似文献
95.
[(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. 相似文献
96.
Kurt Hiebl Engelbert Tuscher Helmut Bittner 《Monatshefte für Chemie / Chemical Monthly》1979,110(4):869-877
The hydrogen absorption of the phase Ti64Co32–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. 相似文献
97.
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. 相似文献
98.
[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. 相似文献
99.
Riek R Fiaux J Bertelsen EB Horwich AL Wuthrich K 《Journal of the American Chemical Society》2002,124(41):12144-12153
Transverse relaxation-optimized spectroscopy (TROSY) or generation of heteronuclear multiple quantum coherences during the frequency labeling period and TROSY during the acquisition period have been combined either with cross-correlated relaxation-induced polarization transfer (CRIPT) or cross-correlated relaxation-enhanced polarization transfer (CRINEPT) to obtain two-dimensional (2D) solution NMR correlation spectra of (15)N,(2)H-labeled homo-oligomeric macromolecules with molecular weights from 110 to 800 kDa. With the experimental conditions used, the line widths of the TROSY-components of the (1)H- and (15)N-signals were of the order of 60 Hz at 400 kDa, whereas, for structures of size 800 kDa, the line widths were about 75 Hz for (15)N and 110 Hz for (1)H. This paper describes the experimental schemes used and details of their setup for individual measurements. The performance of NMR experiments with large structures depends critically on the choice of the polarization transfer times, the relaxation delays between subsequent recordings, and the water-handling routines. Optimal transfer times for 2D [(15)N,(1)H]-CRIPT-TROSY experiments in H(2)O solutions were found to be 6 ms for a molecular weight of approximately 200 kDa, 2.8 ms for 400 kDa, and 1.4 ms for 800 kDa. These data validate theoretical predictions of inverse proportionality between optimal transfer time and size of the structure. The proton longitudinal relaxation times in H(2)O solution were found to be of the order of 0.8 s for structure sizes around 200 kDa, 0.4 s at 400 kDa, and 0.3 s at 800 kDa, which enabled the use of recycle times below 1 s. Since improper water handling results in severe signal loss, the water resonance was kept along the z-axis during the entire duration of the experiments by adjusting each water flip-back pulse individually. 相似文献
100.
5-(N-Methoxy-N-methyl)amino-3-aryl-1,3,4-oxadiazol-2(3H)-ones 3 undergo a heteroretro-ene reaction in refluxing methanol in which the leaving enophile is formaldehyde. The resulting 5-(methylimino)-3-aryl-1,3,4-oxadiazolidin-2-one 4 may be viewed as a kinetic product which tautomerizes to the more stable 5-(methylamino)-3-aryl-1,3,4-oxadiazol-2(3H)-one 5 as the thermodynamic product. Comparison of calculated reaction energies reveals that the presence of the heterocyclic ring facilitates the retro-ene reaction, but the expulsion of formaldehyde is predicted to be highly exothermic even in its absence. 相似文献