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991.
Alan Shaver Paul J. Fitzpatrick Kosta Steliou Ian S. Butler 《Journal of organometallic chemistry》1979,172(4):C59-C62
μ,μ′-(1,3-Dithiolatocyclohepta-4,6-diene)hexacarbonyldiiron(I) was prepared by the reaction of 2,3,4-trithiabicyclo[4,3,1]deca-6,8-diene with Fe2(CO)9. The carbonyls undergo rapid site exchange within each Fe(CO)3 group but there is no exchange of carbonyls between the two different Fe(CO)3 moieties. The novel bicyclic nature of the bridging ligand results in a short iron—iron bond distance and a long sulfur—sulfur distance as compared to other members of this class. 相似文献
992.
B. Schoofs T. Mouganie B. A. Glowacki V. Cloet S. Hoste I. Van Driessche 《Journal of Sol-Gel Science and Technology》2007,41(2):113-122
Today, the deposition of coated conductors on a variety of substrates is often performed using a vacuum or low pressure technique.
However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and attaining independence
of geometric constraints of the substrates are areas in which vacuum techniques will need sustained development in order to
answer industrial demands. The development of the next generation of deposition methods, based on deposition under atmospheric
environment and from aqueous precursor solutions is a real challenge. This work describes the deposition of thin NdBa2Cu3O7-y layers on SrTiO3 single crystals based on a new sol-gel dip coating process using aqueous precursor solutions. Two inorganic aqueous sol-gel
routes were investigated, a metal nitrate–citric acid based and a metal acetate–triethanol amine based solution. Using detailed
thermal analysis, it is shown that adjusting the different parameters during thermal treatment can be used to control the
morphology of the films. Also special attention is given to the microstructure of the thin film because of its relevance to
the superconducting transport properties of the coated conductor system. 相似文献
993.
994.
Griffiths PC Hirst N Paul A King SM Heenan RK Farley R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(16):6904-6913
The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface. 相似文献
995.
Abstract— The UV photolysis of the aromatic amino acid, tryptophan (Trp), in the Ca2+ -binding protein, cod paralbumin, type III, was studied using electron paramagnetic resonance (EPR) spectroscopy in the temperature range 4–80 K. For the Ca2+ -bound protein, irradiation with UV light (250–400 nm) resulted in the generation of atomic hydrogen with a hyperfine splitting of 50.9 mT, whereas in the Ca2+ -free form, where the Trp is exposed to solvent, the trapped atomic hydrogen was not in evidence. In the same spectra, the radical signal in the g = 2.00 region could be detected. The line shape of the Ca2+ -bound form is similar to the EPR line shape obtained for Trp in micellar systems. In contrast, the EPR line shape for the Ca2+ -free form is essentially featureless up to 80 K. The EPR spectra of the photoproducts of Trp and the nature of the photoreactions are therefore sensitive to the environment of Trp within the protein. 相似文献
996.
The coordinatively unsaturated uranium(IV) complex U[N(C6H5)2]4 has been prepared via the stoichiometric reaction of diphenylamine with [(Me3Si)2N]2
H2. U[N(C6H5)2]4 coordinates Lewis bases such as Et2O, THF, pyridine or (EtO)3PO, based on electronic absorption spectroscopy and 1H NMR studies. Exchange between U[N(C6H5)2]4 and U[N(C6H5)2]4(L), where L is THF or pyridine, is rapid on the NMR time-scale between 307 and 323 K. Measurement of equilibrium constants for L = THF provides ΔH and ΔS values of −60 kJ mol−1 and −1.8 × 102 J K−1 mol−1, respectively. U[N(C6H5)2]4 coordinates and binds (EtO)3PO much more tightly (Keq = & > 104 M−1) than THF or pyridine with the exchange rate between U[N(C6H5)2]4 and U[N(C6H5)2]4[OP(OEt)3] being close to the NMR time-scale. 相似文献
997.
Mustafa R. Ibrahim Zacharia A. Fataftah Paul von Ragu Schleyer Peter D. Stout 《Journal of computational chemistry》1987,8(8):1131-1138
Sets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon-carbon bonds from ab initio total energies (3-21G and 6-31G* basis sets, and, to a more limited extent, for MP2/6-31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6-31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3-21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon-carbon bonds in nitrogen- and oxygen-containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experiment in most cases. 相似文献
998.
Paul Von Ragu Schleyer Andrzej Sawaryn Alan E. Reed Pavel Hobza 《Journal of computational chemistry》1986,7(5):666-672
Electron correlation corrections have a considerable influence on the relative stabilities of lithium isocyanide ( 1 ), lithium cyanide ( 2 ), and the bridged form, 3 . While Hartree-Fock theory finds 1 to be most stable and 3 not to be a minimum, MP2/6-31G* optimization indicates 3 to be the global minimum. At higher levels employing full fourth-order Møller-Plesset theory and a quadruply split valence and polarized basis set (MP4STDQ/6-311+G*), 2 is only about 2 kcal/mol less stable than 1 and 3 , which are indicated to have nearly the same energy. LiNC thus is similar to C(Na)N and C(K)N, both of which are known to prefer T-shaped (bridged) structures in the gas phase. However, to an even greater extent than formerly realized, rotation of the lithium cation around the cyanide anion nucleus should be practically free. ΔH (LiCN) = 32.8 kcal/mol is estimated from the calculated lithium cation affinity of 151.2 kcal/mol. In addition, we find at the MP4SDTQ/6-31+G*//MP2/6-31G* level that the bridged form of NaCN is favored by 2–3 kcal/mol over the corresponding linear forms, which have nearly the same energy. 相似文献
999.
Density-functional electronic structure calculations are performed on the molecules Cr2(hpp)4, Mo2(hpp)4, and W2(hpp)4, where the bridging ligand, hpp, is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine. The calculated electronic densities are used to determine the Fukui functions. These molecules are unique not only in their ability as electron donors but also because orbital relaxation plays a decisive role in their reactivity. Unlike other examples in the literature, the reactivity of these compounds cannot be expressed solely in terms of the highest occupied and lowest unoccupied Kohn-Sham orbitals but only using the Fukui function, which includes the effects of orbital relaxation. 相似文献
1000.
Soga O van Nostrum CF Ramzi A Visser T Soulimani F Frederik PM Bomans PH Hennink WE 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9388-9395
Amphiphilic AB block copolymers consisting of thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) and poly(ethylene glycol), pHPMAmDL-b-PEG, were synthesized via a macroinitiator route. Dynamic light scattering measurements showed that these block copolymers form polymeric micelles in water with a size of around 50 nm by heating of an aqueous polymer solution from below to above the critical micelle temperature (cmt). The critical micelle concentration as well as the cmt decreased with increasing pHPMAmDL block lengths, which can be attributed to the greater hydrophobicity of the thermosensitive block with increasing molecular weight. Cryogenic transmission electron microscopy analysis revealed that the micelles have a spherical shape with a narrow size distribution. 1H NMR measurements in D2O showed that the intensity of the peaks of the protons from the pHPMAmDL block significantly decreased above the cmt, indicating that the thermosensitive blocks indeed form the solidlike core of the micelles. Static light scattering measurements demonstrated that pHPMAmDL-b-PEG micelles with relatively large pHPMAmDL blocks possess a highly packed core that is stabilized by a dense layer of swollen PEG chains. FT-IR analysis indicated that dehydration of amide bonds in the pHPMAmDL block occurs when the polymer dissolved in water is heated from below to above its cmt. The micelles were stable when an aqueous solution of micelles was incubated at 37 degrees C and at pH 5.0, where the hydrolysis rate of lactate side groups is minimized. On the other hand, at pH 9.0, where hydrolysis of the lactic acid side groups occurs, the micelles started to swell after 1.5 h of incubation and complete dissolution of micelles was observed after 4 h as a result of hydrophilization of the thermosensitive block. Fluorescence spectroscopy measurements with pyrene loaded in the hydrophobic core of the micelles showed that when these micelles were incubated at pH 8.6 and at 37 degrees C the microenvironment of pyrene became increasingly hydrated in time during this swelling phase. The results demonstrate the potential applicability of pHPMAmDL-b-PEG block copolymer micelles for the controlled delivery of hydrophobic drugs. 相似文献