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121.
A series of new chiral diselenides with a N-atom in the side chain was prepared by a short synthetic sequence (Scheme 1). Only 1 mol-% of these diselenides catalyzed very effectively the diethylzinc addition to various aromatic and α,β-unsaturated aldehydes yielding the secondary alcohols in up to 98% ee (Scheme 2 and Tables 1 and 2). An asymmetric amplification was observed with these catalysts. Detailed NMR studies were performed to characterize the catalytically active species. 相似文献
122.
Ercolani G 《Journal of the American Chemical Society》2003,125(51):16097-16103
A method has been proposed to assess cooperativity in self-assembly processes. The method is based on a clear distinction between intermolecular and intramolecular processes which are compared with the corresponding reference reactions. It has been applied to two classical cases, namely the self-assembly of helicates and of porphyrin ladders, by using data previously published by the groups of Lehn and Anderson, respectively. Contrarily to the conclusions of the authors, pointing out self-assembly processes driven by positive cooperativity, the method here presented indicates in both cases the absence of cooperative effects. The methods previously used to assess cooperativity, in particular Scatchard plot and/or Hill plot, are criticized as being inappropriate for self-assembly, because they are pertinent to a specific case only, namely the intermolecular binding of a monovalent ligand L to a multivalent receptor M, a case very different from self-assembly which involves both inter- and intramolecular interactions. The present method underscores the fact that positive cooperativity in artificial self-assembling systems is probably much more rare than it was previously thought. 相似文献
123.
Giacomo Saielli Gianfranco Scorrano Alessandro Bagno Akihiro Wakisaka 《Chemphyschem》2005,6(7):1307-1315
The solvation of tetramethylammonium chloride (Me4NCl) and tetra-n-butylammonium chloride (Bu4NCl) in water-acetonitrile mixtures was investigated by mass spectrometry of clusters isolated from the solution. As far as the positive ions are concerned, clusters composed of alkylammonium ions and acetonitrile molecules only were observed, even for mixtures with high water content. In contrast, for the negative ions, clusters composed of chloride with both water and/or acetonitrile molecules were observed. For the smaller system (Me4NCl) we performed quantum chemical calculations and molecular dynamics simulations. It was found that even though water is present in the solvation shell of Me4N+, only acetonitrile has a strong electrostatic interaction with the cation. Water molecules around Me4N+ form hydrogen bonds with other water molecules, and they interact with Me4N+ mainly via dispersive interactions. These results indicate that Me4N+ behaves like a hydrophobic solute. On the other hand, the interaction of Cl- with water and acetonitrile is of comparable strength and, in both cases, the electrostatic interaction dominates. Herein we demonstrate experimentally and theoretically that positive and negative ions give rise to characteristic solvation structures in mixed solvents: even a relatively small organic cation, such as Me4N+, exhibits a hydrophobic-like solvation shell. 相似文献
124.
Gianfranco CainelliDaria Giacomini Massimo GazzanoPaola Galletti Arianna Quintavalla 《Tetrahedron letters》2003,44(33):6269-6272
This paper describes the different reactivity of E- and Z-4-alkylidene-β-lactams in acylation reactions under basic conditions. The E isomer is readily acylated, whereas the Z reacted sluggishly rearranging to the corresponding oxazin-6-one. The N-acylation of Z isomers was successfully obtained with oxalyl- or malonyl chlorides in benzene at reflux. 相似文献
125.
Raffaele Borrelli Mariangela Di Donato Andrea Peluso 《Theoretical chemistry accounts》2007,117(5-6):957-967
Mechanistic aspects of some of the early electron transfer steps occurring in photosynthetic reaction centers are discussed.
Starting from the normal modes of the redox cofactors involved in the electron transfer processes, we show how a series of
quantities which regulate electron transfer rates, such as (i) the electron transfer active modes, (ii) the intramolecular
reorganization energy, and (iii) the mutual couplings between the vibronic states of the donor and the acceptor, can be obtained
and used to draw qualitative conclusions on ET rates. 相似文献
126.
Ottonelli M Musso G Comoretto D Dellepiane G 《The journal of physical chemistry. B》2005,109(12):5485-5490
We discuss the effect of the interchain interactions on the electronic properties of a "dimer", named (CHD(4))(2), built from two molecules of a fully carbazolyl-substituted oligodiacetylene containing four repeating units. Each carbazolyl moiety is connected to its respective backbone through a methylene spacer, and the excitations of the neutral and doubly positively charged dimer are obtained using the CIS (configuration interaction including singles) and CEO (collective electronic oscillator) models. The separation distance between the backbones is fixed to a value that could possibly imply a very weak, if any, interchain interaction between the oligomers. In the charged dimer, where we have not been able to perform CEO calculations, it can be expected from previous results that the CIS method will behave satisfactorily. Contrary to the neutral case and surprisingly enough, the simulated photoinduced absorption (PA) spectra indicate a substituent-induced strong interaction between the oligomers, due to the very large amount of excess charge on the distorted oligomer which is spread over its carbazolyl moieties. Broadening of the lowest energy band due to the latter interaction improves the agreement between the theoretical and the experimental PA spectrum for the corresponding polymer. The through-space charge transfer directly connecting the charged with the neutral molecule could supply an efficient channel for charge transport in substituted polydiacetylenes. 相似文献
127.
Vittorio Lucchini Maurizio Prato Gianfranco Scorrano Paolo Tecilla 《Journal of heterocyclic chemistry》1986,23(4):1135-1139
Substituted 4-benzoyl-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolines 3 and 6-benzoyl-5,6,6a,7,8,10a-hexahydrophenanthridines 10 are obtained through Lewis acid catalyzed addition of 1-phenyl-2-arylamino-2-methoxyethanones 2 to cyclopentadienes and 1,3-cyclohexadiene respectively. Compounds 3 can be converted to the aromatized analogues by reaction with 2,3-dichloro-5,6-dicyanobenzoquinone in refluxing benzene. Compounds 10 are oxidized by sulfur either in decalin or in quinoline to substituted 6-benzoylphenanthridines. 相似文献
128.
129.
A proteomic approach to study protein variation in GM durum wheat in relation to technological properties of semolina 总被引:1,自引:0,他引:1
Di Luccia A Lamacchia C Fares C Padalino L Mamone G La Gatta B Gambacorta G Faccia M Di Fonzo N La Notte E 《Annali di chimica》2005,95(6):405-414
Genetic manipulation of durum wheats by tobacco rab-1 genes influence the trafficking of gluten proteins through the secretory system by up- or down-regulating the transport step from the ER to the Golgi apparatus which may in turn modify functional performance of the grain. Gluten proteins were extracted from two genetically manipulated lines - Svevo B730 1-1 and Ofanto B688 1-2 - and their control lines and were analyzed by two dimensional gel electrophoresis. When the two-dimensional maps were compared by image analysis no significant differences between the GM line with an up-regulated trafficking containing the wild type tobacco rab1 (Svevo B730 1-1) and its control (Svevo control). By contrast, significant differences were found between the GM line with a down-regulated trafficking due to the tobacco rab1 mutant form (Ofanto B688 1-2) and its control (Ofanto control). Of the new protein spots detected in the down-regulated Ofanto B688 1-2 map, only a beta-amylase was identified. The remaining spots were susceptible to chymotripsin action but not to trypsin one, as in the case of the gluten protein. Rheological measurements showed that gluten quality was enhanced in the down-regulated Ofanto B688 1-2 without an increase in the amount of gluten. Proteomics is a useful and powerful tool for investigating protein changes in GMOs and in understanding events in food science and technology. 相似文献
130.
Tiziana Beringhelli Gianfranco Ciani Giuseppe DAlfonso Angelo Sironi Maria Freni 《Journal of organometallic chemistry》1982,233(3):C46-C50
The novel anions [Re3H3(CO)10(μ-O2CR)]? (R = H, CH3, CF3), obtained by reaction of [Re3H4(CO)10]? with the corresponding car?ylic acids, have been characterized by IR and NMR spectra and by X-ray analysis of the formate and trifluoroacetate derivatives. They contain a triangle of rhenium atoms, with the car?ylate group diaxially bridging on the shorter ReRe edge. 相似文献