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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.
Zhou J Kelly WL Bachmann BO Gunsior M Townsend CA Solomon EI 《Journal of the American Chemical Society》2001,123(30):7388-7398
Using a single ferrous active site, clavaminate synthase 2 (CS2) activates O(2) and catalyzes the hydroxylation of deoxyguanidinoproclavaminic acid (DGPC), the oxidative ring closure of proclavaminic acid (PC), and the desaturation of dihydroclavaminic acid (and a substrate analogue, deoxyproclavaminic acid (DPC)), each coupled to the oxidative decarboxylation of cosubstrate, alpha-ketoglutarate (alpha-KG). CS2 can also catalyze an uncoupled decarboxylation of alpha-KG both in the absence and in the presence of substrate, which results in enzyme deactivation. Resting CS2/Fe(II) has a six-coordinate Fe(II) site, and alpha-KG binds to the iron in a bidentate mode. The active site becomes five-coordinate only when both substrate and alpha-KG are bound, the latter still in a bidentate mode. Absorption, CD, MCD, and VTVH MCD studies of the interaction of CS2 with DGPC, PC, and DPC provide significant molecular level insight into the structure/function correlations of this multifunctional enzyme. There are varying amounts of six-coordinate ferrous species in the substrate complexes, which correlate to the uncoupled reaction. Five-coordinate ferrous species with similar geometric and electronic structures are present for all three substrate/alpha-KG complexes. Coordinative unsaturation of the Fe(II) in the presence of both cosubstrate and substrate appears to be critical for the coupling of the oxidative decarboxylation of alpha-KG to the different substrate oxidation reactions. In addition to the substrate orientation relative to the open coordination position on the iron site, it is hypothesized that the enzyme can affect the nature of the reactivity by further regulating the binding energy of the water to the ferrous species in the enzyme/succinate/product complex. 相似文献
28.
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
29.
The authors study an example, suggested by E. De Giorgi, of a second-order uniformly elliptic partial differential operator in divergence form with continuous coefficients on a smooth domain in the plane such that the associated harmonic measure on the boundary is not absolutely continuous with respect to the ordinary surface measure. 相似文献
30.
Gian Paolo Chiusoli Mirco Costa Luciano Pallini Giuliana Terenghi 《Transition Metal Chemistry》1982,7(6):304-306
Summary In presence of nickel or palladium catalysts, nucleophiles can attack vinylcyclopropanes with concomitant ring cleavage. With palladium catalysts in presence of appropriate substituents the terminal carbon atom of the resulting open chain is able to add to two molecules of a conjugated diene giving rise to long-chain unsaturated compounds. 相似文献