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21.
Rosenberg Edward Freeman William Carlos Zinnia Hardcastle Kenneth Yong Jin Yoo Milone Luciano Gobetto Roberto 《Journal of Cluster Science》1992,3(4):439-457
The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to 3-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in 3-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth. 相似文献
22.
Eric Steiner Carl Djerassi Ernesto Fattorusso Silvana Magno Luciano Mayol Circo Santacroce Donato Sica 《Helvetica chimica acta》1977,60(2):475-481
Two acetylenic steroids, cholest-5-en-23-yn-3β-ol ( 5 ) and 26,27-dinorcholest-5-en-23-yn-3β-ol ( 3 ), and another unsaturated steroidalcohol, stigmasta-5,23-dien-3β-ol ( 7 ), were isolated from the sponge Calyx nicaaensis. The structures of these two acetylenic steroids were established by synthesis. Several attempts to synthesize the marine steroids alcohol calysterol ( 1 ), with a cyclopropene-containing side chain, starting from cholest-5-en-23-yn-3β-ol are also recorded. Addition of ethyl-diazo-acetate to the triple bond was performed, but the reduction to the methyl derivative yielded decomposition products. 相似文献
23.
Mario Sechi Luciano Sannia Maria Orecchioni Fabrizio Carta Giuseppe Paglietti Nouri Neamati 《Journal of heterocyclic chemistry》2003,40(6):1097-1102
HIV‐1 integrase (IN) is a very promising and validated target for the development of therapeutic agents against AIDS. In an effort to design and synthesize biological isosteric analogs of β‐diketoacid‐containing inhibitors of IN, we prepared a series of substituted isoxazole carboxylic acids. Several of these compounds inhibited catalytic activities of purified IN at micromolar concentration range. With an aim to prepare a large number of analogues based on the isoxazole pharmacophore we focused our study on a series of 3,5‐disubstituted isoxazole isomers. For a rapid structural analysis we discovered a convenient 1H‐nmr method for distinguishing between isomeric structures based on their H‐4 assignments. This “finger print” approach to isomer identification will be useful in combinatorial chemistry settings where a mixture can be further derivatized. 相似文献
24.
Sergio Cabani Paolo Gianni Vincenzo Mollica Luciano Lepori 《Journal of solution chemistry》1981,10(8):563-595
The thermodynamic properties G
h
o,H
h
o, and C
p,h
oassociated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties C
p
o
,2 and V2
2 of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted. 相似文献
25.
Giampaolo Giacomelli Anna Maria Caporusso Luciano Lardicci 《Tetrahedron letters》1981,22(37):3663-3666
The reduction of a series of α,β-unsaturated ketones has been studied under various experimental conditions, by using β-branched trialkylalanes. Asymmetric induction phenomena are observed when optically active trialkylalanes are used. 相似文献
26.
Roberta Seraglia Pietro Traldi Roberta Bertani Giacomo Facchin Luciano Pandolfo 《Journal of mass spectrometry : JMS》1994,29(11):619-624
A fast atom bombardment (FAB) mass spectrometric study on the open-chain compound 1,3-bis(cyanomethylenetriphenylphosphorane)propane-1,3-dione and on the cyclic zwitterionic compounds 4-oxy-5-triphenylphosphonium-6-methyl-2-pyrone and 4-oxy-5-triphenylphosphonium-6-phenyl-2-pyrone, obtained by reaction of carbon suboxide, C3O2, with stabilized phosphorus ylides, Ph3PCHX (X?CN, COMe, COPh), is described. The FAB mass spectrometric behaviour of these compounds is compared with that shown by tri-phenylphosphoranilideneketene, Ph3P ? C ? C ? O, and by 4-hydroxy-6-methyl-2-pyrone, with the aid of metastable ion data and collision spectroscopy. 相似文献
27.
Tugarinov V Kay LE Ibraghimov I Orekhov VY 《Journal of the American Chemical Society》2005,127(8):2767-2775
An approach for recording four-dimensional (4D) methyl (1)H-(13)C-(13)C-(1)H NOESY spectra with high resolution and sensitivity is presented and applied to Malate Synthase G (723 residues, 82 kDa). Sensitivity and resolution have been optimized using a highly deuterated, methyl-protonated sample in concert with methyl-TROSY, sparse data sampling in the three indirect dimensions, and 4D spectral reconstruction using multidimensional decomposition (MDD). A sparse data acquisition protocol is introduced that ensures that sufficiently long indirect acquisition times can be employed to exploit the decreased relaxation rates associated with methyl-TROSY, without increasing the duration of the 4D experiment beyond acceptable measurement times. In this manner, only a fraction ( approximately 30%) of the experimental data that would normally be needed to achieve a spectrum of high resolution is acquired. The reconstructed 4D spectrum is of similar resolution and sensitivity to three-dimensional (3D) (13)C-edited NOE spectra, is straightforward to analyze, and resolves ambiguities that emerge when 3D data sets only are considered. 相似文献
28.
A sensitive 3D NMR pulse scheme, (H)C(CA)NH-COSY, is presented for the assignment of (13)C(delta)(1) Ile chemical shifts in large perdeuterated, methyl-protonated proteins. The nonlinearity of branched amino acids, such as Ile, significantly degrades the quality of TOCSY schemes which transfer magnetization from methyl carbons to the backbone (13)C(alpha) positions, and in applications to high molecular weight proteins (correlation times on the order of 40-50 ns), this compromises the sensitivity of spectra used for methyl assignment. The experiment presented utilizes COSY-based transfer steps and refocuses undesirable (13)C-(13)C scalar couplings that degrade the efficiency of TOCSY transfers. The (H)C(CA)NH-COSY scheme is tested on an (15)N,(13)C,(2)H-[Leu, Val, Ile (delta 1 only)]-methyl-protonated maltose binding protein (MBP)/beta-cyclodextrin complex at 5 degrees C (molecular tumbling time 46 +/- 2 ns), facilitating the assignment of (13)C(delta 1) chemical shifts for 18 of the 19 Ile residues for which backbone assignments were previously obtained. Both sensitivity and resolution of the resulting spectra are shown to be significantly better than those for a similar TOCSY-based approach. 相似文献
29.
Castagnola M Zuppi C Rossetti DV Vincenzoni F Lupi A Vitali A Meucci E Messana I 《Electrophoresis》2002,23(12):1769-1778
The general properties of dendrimers and in particular their electrolytic characteristics that are relevant in electrokinetic separations, are described. In order to confirm theoretical considerations on commercial dendrimer charge and hydrodynamic radius, several capillary zone electrophoresis (CZE) experiments were performed. Electrophoretic mobilities measured at different pH values indicated a sensible increase of dendrimer hydrodynamic radius at pH values lower than 2.5. This was probably due to the Coulombic repulsion of charged amine groups of the inner dendrimer shells. The principal reasons that should address the use of dendrimers as pseudostationary phases in micellar electrokinetic chromatography (MEKC) are discussed. Moreover, a survey of different separations performed utilizing dendrimers in MEKC as well as of several future plausible uses of various classes of dendrimers is presented. 相似文献
30.
Luciano Toscano Ennio Seghetti Giuseppe Fioriello 《Journal of heterocyclic chemistry》1976,13(3):475-480
The behavior of 5,6-dihydro-4H-pyrido[3,2,1-jk]carbazol-4-one (10) , 1,2,7,8-tetrahydro-3H-quino[1,8-ab][1]benzazepin-3-one (11) , 1,2-dihydro-9H-[1]benzazepino[1,9-ab] [4,1]benzoxazepin-4 (3H)one (13) , and 1,2-dihydro-8H-[1]benzazepino[1,9-cd] [1,5]benzoxazepin-4(3H)one (14) towards the Schmidt reaction has been determined in polyphosphoric acid and in benzeneor chloroform-sulfuric acid. Evidence for the structure of the new heterocyclic systems obtained from these four compounds is presented. 相似文献