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31.
Guldi DM Hirsch A Scheloske M Dietel E Troisi A Zerbetto F Prato M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):4968-4979
Control over the interchromophore separation, their angular relationship, and the spatial overlap of their electronic clouds in several ZnP-C(60) dyads (ZnP=zinc porphyrin) is used to modulate the rates of intramolecular electron transfer. For the first time, a detailed analysis of the charge transfer absorption and emission spectra, time-dependent spectroscopic measurements, and molecular dynamics simulations prove quantitatively that the same two moieties can produce widely different electron-transfer regimes. This investigation also shows that the combination of ZnP and C(60) consistently produces charge recombination in the inverted Marcus region, with reorganization energies that are remarkably low, regardless of the solvent polarity. The time constants of electron transfer range from the mus to the ps regime, the electronic couplings from a few tens to several hundreds of cm(-1), and the reorganization energies remain below 0.54 eV and can be as low as 0.16 eV. 相似文献
32.
Dirk Schwäbisch 《Journal of fluorine chemistry》2004,125(1):119-124
Starting with 1,2,4,6-tetra-O-acetyl-3-O-dodecyl-β-d-glucose (1), mixed alkyl-perfluoroalkyl substituted sugar derivatives with an anomeric perfluoroalkylthio group and an O-alkyl group in the 3 position were synthesized via 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucose (4). The latter was S-perfluorohexylated with 1-iodoperfluorohexane in a dithionite initiated reaction yielding perfluorohexyl 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (5). Experiments with the aim compound 5 completely to deacetylate ended in surprising results. Thus, methanolic methanolate solution produced the orthoester 7 as the result of α-fluoride replacement by methoxy groups as well as the methyl glucoside 8 as the result of a transglycosylation reaction. Alumina supported cesium fluoride cleaved regioselectively the two acetyl groups in the 4- and 6-position yielding perfluorohexyl 2-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (10). A complete deacetylation of 5 to amphiphile 11 succeeded only with methanolic tert-butanolate. However, the products 8 and 10 were likewise formed. 相似文献
33.
Binuclear Nickel(0) Complexes with “Snake Ligands” of 1-Azadiene Type: Model Systems of the Oxidative Coupling of 1-Azadienes and 1.3-Dienes at Nickel(0) Synthesis, properties, and reactions of dimeric nickel(0) complexes with special 1-azadiene typ ligands (“snake ligands”) are described. The X-ray analysis of a typical compound (Bis-(bis-cinnamaldehyde-N,N'-propylendiimine)-dinickel(0)) shows that both central atoms have the coordination number 3. The four 1-azadiene groups are coordinated in a different way: unidendate coordination by N-Ni(1) bond and bidendate coordination by N-Ni(1) and olefine-Ni(2) bond. The compound is a good model system for the oxidative coupling reaction of 1-azadienes with 1.3-dienes at 2 nickel(0) centres. IR and electronic spectra show other complexes with this type of ligands to have an analogous coordination sphere. 相似文献
34.
Cheng L Yang J Yao Y Price DW Dirk SM Tour JM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1335-1341
The assembly of thioacetyl-terminated oligo(phenylene ethynylene)s (OPEs) on Au and Pt surfaces under an electric potential (electrochemical assembly, EA) was compared to assembly at an open circuit (conventional self-assembly, CSA). Cyclic voltammetry and ellipsometry were used to characterize the adsorption kinetics of self-assembled monolayers formed by these two techniques. The adsorption rate of the EA was remarkably faster at positive potentials but slower at negative potentials than that of the CSA, The EA at 400 mV proceeded about 800 times faster than the CSA when exposed to the same solution concentrations. The adsorption rates of both EA and CSA were found to be dependent on the molecular structures of OPEs. OPEs containing electron-donating groups assemble faster than those with electron-withdrawing groups. The amount of time that the thioacetyl-terminated OPE is in the presence of the base, for removal of the acetyl group to generate the thiolate, is called the deprotection time. Deprotection times play a critical role in achieving the maximum difference in adsorption rates between the EA and the CSA. The assembly must be initiated no later than 5 min after the basic deprotection is commenced so that the thiolate concentration remains low. The difference in the adsorption rates between EA and CSA might enable selective deposition of certain OPEs onto specific electrodes. 相似文献
35.
von Wangelin AJ Neumann H Gördes D Klaus S Strübing D Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(18):4286-4294
The acid-catalyzed condensation chemistry of simple amides and aldehydes provides a highly prolific source of diverse reactants for irreversible follow-up reactions. Amide-aldehyde mixtures have been successfully employed in multicomponent syntheses of N-acyl alpha-amino acids (via palladium-catalyzed amidocarbonylation) and various cyclohexene, cyclohexadiene, and benzene derivatives (via the amide-aldehyde-dienophile (AAD) reaction). 相似文献
36.
Volkmer D Bredenkötter B Tellenbröker J Kögerler P Kurth DG Lehmann P Schnablegger H Schwahn D Piepenbrink M Krebs B 《Journal of the American Chemical Society》2002,124(35):10489-10496
Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins. 相似文献
37.
Bier FF Kleinjung F Schmidt PM Scheller FW 《Analytical and bioanalytical chemistry》2002,372(2):308-313
Binding and catalytic activity of the type II restriction endonuclease EcoRI on immobilized DNA has been observed in real time using three different evanescent wave biosensors and two different immobilization techniques. The method gives direct access to the turnover number (kcat) without the necessity for the determination of any concentration or activity. The combination of different evanescent wave techniques gives access to the catalytic mechanism and allows the determination of the rate limiting step. 相似文献
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