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101.
In neutral DMF, ellipticinium cations 9 R—E+H—2 CH3 undergo a reversible 1 e addition (standard potential ca. ?1.35 V) to yield a neutral radical which rapidly dimerizes (dimerization rate constant ca. 107 mol?1 1 s?1). In basic DMF or in the presence of superoxide anion, the corresponding conjugated bases undergo a reversible 1 e addition accompanied by a fast and reversible proton addition (standard potential at pHDMF 0 ca. ?0.52 V) to yield the same neutral radical. R being H, OCH3 or OH, there is no effect of the substituent at the C-9 position on the electrochemical process. 相似文献
102.
Kenneth K. Chan Donald D. Giannini Anne H. Cain John D. Roberts William Porter William F. Trager 《Tetrahedron》1977,33(8):899-906
Fourier-transform 13C NMR spectra of nine coumarinoid compounds of medicinal interest are reported. All of the carbon resonances are assigned with the aid of various spectral techniques and stable isotopic labeling. The substituent effects on the chemical shifts in several systems are also discussed. 相似文献
103.
Halland N Alstrup Lie M Kjaersgaard A Marigo M Schiøtt B Jørgensen KA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):7083-7090
The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed. 相似文献
104.
Issam SM Mohamed G Dominique LM Thierry M Farid L Nejib M 《Applied biochemistry and biotechnology》2004,112(2):63-78
The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one beta-glucosidase (beta-glu x). The enzyme was purified to apparent homogeneity by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography (HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that beta-glu x may be a homodimer. For p-nitrophenyl beta-d-glucopyranoside hydrolysis, apparent Km and Vmax values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55-60 degrees C and pH 5.0, respectively. beta-Glu x was strongly inhibited by Fe2+ and activated about 35% by Ca2+. beta-Glu x possesses strong transglucosylation activity in comparison with commercially available beta-glucosidases. The production rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50 degrees C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and 3C nuclear magnetic resonance spectroscopy. 相似文献
105.
Chevelkov V van Rossum BJ Castellani F Rehbein K Diehl A Hohwy M Steuernagel S Engelke F Oschkinat H Reif B 《Journal of the American Chemical Society》2003,125(26):7788-7789
In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state. 相似文献
106.
107.
The reaction of [Cr(NCCH(3))(6)](2+) with dioxygen in acetonitrile (MeCN) solution acidified with HBF(4) gave red crystals of the binuclear complex [(CH(3)CN)(5)Cr(OH)Cr(NCCH(3))(5)](BF(4))(5) (1). From the X-ray crystal structure of 1, the Cr-O-Cr angle was found to be 147.5(2) degrees. Magnetic susceptibility measurements of 1 showed an antiferromagnetic coupling between the two chromium(III) centers with a triplet energy J = 35.9(1) cm(-1). On redissolution of 1 in MeCN, the hydroxo bridge was deprotonated, and a green solution of the complex [(CH(3)CN)(5)CrOCr(NCCH(3))(5)](4+) formed. The electronic absorption spectrum of this solution is very similar to the spectrum of the classical complex [(H(3)N)(5)CrOCr(NH(3))(5)](4+) with intense bands in the UV and near-UV region. From the temperature dependence of the absorption spectrum near 12900 cm(-1), the triplet energy J was found to be 1067(19) cm(-1). The acidity of the hydroxo bridge in 1 is very high with an acid dissociation constant K(a) > 1 M. 相似文献
108.
Antonio Cnovas Jesús Fonrodona Juan-Julio Bonet Marie Claire Brians Jos Luis Brians 《Helvetica chimica acta》1980,63(8):2380-2389
The UV. irradiation of 17 β-hydroxy-2-aza-4-androsten-3-one (1) , N-methyl-17 β-hydroxy-2-aza-4-androsten-3-one (3) , 17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (2) and N-methyl-17 β-hydroxy-4-aza-5 β-androst-1-en-3-one (4) , gives rise to 1,10-seco (from 1 and 3 ) and 5, 10-seco (from 2 and 4 ) steroids. 相似文献
109.
Jossang A Cavé A Saez J Bartoli MH Cavé A Jossang P 《The Journal of organic chemistry》1996,61(9):3023-3030
Monterine 1 as well as granjine 3, 1R,1'S configured biphenylic bisbenzylisoquinoline alkaloids, generate two highly populated conformers. The interconversion of two forms was detected by saturation tranfer in (1)H NMR NOEs experiments. Tridimensional structure of the conformers was determined on the basis of (1)H NMR analysis of anisotropic shielding protons, by NOEs measurements and vicinal proton coupling constants of CH1-CH(2)alpha and CH1'-CH(2)alpha'. The structures established from NMR data were further refined to observe the mobility of 3D conformations by molecular dynamics simulation in vacuo. The highly populated conformers, monterine 1a and 1b, as well as granjine 3a and 3b, are interconvertible by rotation about the C1'-Calpha', Calpha'-C9', and C11'-C11 bonds and inversion of the benzyl D ring by reference to CH(2)alpha'. The slow exchange system was investigated by dynamic NMR spectroscopy: DeltaG()(c) 77.9 KJ/mol and k(c) 200 s(-)(1) for monterine 1; DeltaG()(c) 77.7 KJ/mol and k(c) 211 s(-)(1) for granjine 3. Natural and synthetic biphenylic bisbenzylisoquinolines displayed, in vitro, cytotoxic activities against human prostate and breast cancer cell lines. 相似文献
110.
Aboelella NW Lewis EA Reynolds AM Brennessel WW Cramer CJ Tolman WB 《Journal of the American Chemical Society》2002,124(36):10660-10661
The X-ray structure of a 1:1 Cu/O(2) adduct revealed side-on (eta(2)) O(2) coordination. Density functional calculations corroborated the structure, indicated a significant contribution of a Cu(III)-(O(2)(2-)) resonance form, and provided insights into the key bonding interactions. Reaction of a 1:1 adduct supported by a slightly different beta-diketiminate ligand with Cu(I) reagents resulted in the formation of novel asymmetric bis(mu-oxo) complexes that were identified by EPR, UV-vis, and Raman spectroscopy, as well as by an X-ray structure in one instance. 相似文献