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41.
Sonochemical polymerization of diphenylmethane 总被引:1,自引:0,他引:1
Sonolysis of diphenylmethane (DPhM) has been studied under the effect of 20 kHz ultrasound (absorbed acoustic power 0.45 W/ml, surface area of sonotrode 1 cm(2), volume of sonicated solution 100 ml) under argon at 60 degrees C. The solid product of the sonolysis was characterized by elemental analysis, FTIR, 13C MAS NMR, TGA/DSC, XRD and TEM techniques. It was found that the sonolysis of DPhM causes formation of the polymer with the composition similar to crosslinked polystyrene. Assumed mechanism of DPhM sonolysis consists of DPhM molecules dissociation inside the cavitating bubble. Secondary radical scavenging and radical recombination processes yields the sonopolymer in the liquid phase. The breakdown of the aromatic ring during DPhM sonolysis confirms that a very high temperature established in the cavitating bubble. 相似文献
42.
43.
Superexchange interactions between metal centers coordinated to various conjugated polymer backbones have been shown to enhance the rate of electron transport through the polymer. Results for Ru and Os bipyridine moieties complexed to polybenzimidzoles and poly(bithiophene-co-bithiazole)s are reviewed. The evidence for superexchange mediated electron transport, and the factors that influence the rate of electron hopping between metal centers, are discussed. 相似文献
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46.
Alexander M. Macmillan Dalibor Panek Colin D. McGuinness John C. Pickup Duncan Graham W. Ewen Smith David J. S. Birch Jan Karolin 《Journal of Sol-Gel Science and Technology》2009,49(3):380-384
By using the fluorescent dye 6-propionyl-2-(N,N-dimethylamino) naphthalene (PRODAN) to monitor methanol generated during tetramethyl orthosilicate polymerization we have
optimised the encapsulation of protein in silica sol–gel monoliths with respect to completion of hydrolysis and distillation
in order to remove methanol such that protein can be added without denaturation. A minimum of 24 h at +4 °C was found to be
required before hydrolysis is complete and 3–5 min of vacuum distillation at 50 °C and 300 mbar needed to remove methanol
before the gel is formed. The biocompatibility of a tetramethyl orthosilicate sol–gel monolith was demonstrated by preserving
the trimer protein allophycocyanin (APC) in its native form for up to 500 h. This obviates the previously essential requirement
of covalently binding the trimer together in order to prevent dissociation into monomers and has enabled observation of native
APC trimer in a sol–gel pore for the first time down to the single molecule level using combined fluorescence spectroscopy
and confocal microscopy. The higher stability afforded by the protocol we describe could impact on the application of sol–gel
materials to single-molecule studies of wider bearing such as protein folding and aggregation. 相似文献
47.
The reaction of 1,2-diaminoanthraquinone with Vulcan XC72 carbon in 4 M HCl produces two distinct surface bound anthraquinone species, with formal potentials of ca. ?0.03 and ?0.19 V vs. SCE. The more positive couple is very stable to electrochemical cycling and has been assigned to the expected benzimidazole linkage. The other wave, which decays over hours of cycling is thought to be due to an amine linkage. This type of linkage also appears to be formed spontaneously when 1,2-diaminoanthraquinone is adsorbed onto Vulcan XC72 from methanol. 相似文献
48.
R. J. Pickup 《Chromatographia》1997,44(1-2):101-101
49.
Massah AR Dreiocker F Jackson RF Pickup BT Oomens J Meijer AJ Schäfer M 《Physical chemistry chemical physics : PCCP》2011,13(29):13255-13267
An extensive set of organozinc iodides, useful for Negishi-type cross-coupling reactions, are investigated as respective cations after formal loss of iodide in the gas phase. Firstly, two new alkylzinc compounds derived from Tyrosine (Tyr) and Tryptophan (Trp) are closely examined. Secondly, the influence of specific protecting groups on the subtle balance between intra- and intermolecular coordination of zinc in these reagents is probed through trifluoroacetyl (TFA)-derivatized alkylzinc compounds. Finally, the influence of the strongly coordinating bidentate ligand N,N,N',N'-tetramethylethylenediamine (TMEDA) on the structure of alkylzinc cations is further explored in order to better understand the stability of the respective complexes towards water. A combination of electrospray (ESI)-MS/MS, accurate ion mass measurements, infrared multiple-photon dissociation (IRMPD) spectroscopy and computational modelling allowed the full characterisation of all dimethylformamide (DMF)-solvated and TMEDA-coordinated alkylzinc cations in the gas phase. The calculations indicate that the zinc cation in gas-phase alkylzinc-DMF or TMEDA-complex ions preferentially adopts a tetrahedral coordination sphere with four ligands. Additionally, conformers with only three binding partners bound to zinc but with effectively combined hydrogen-bond interactions are also found. Collision induced dissociation (CID) patterns demonstrate that the zinc-DMF interaction in tetrahedral four-coordinate mono-DMF-zinc complex ions as well as the interaction between TMEDA and zinc in the corresponding complex ions is even stronger than typical covalent bonds. In most cases, all major features of the IRMPD spectra are consistent with only a single major isomer, allowing secured identification and assignment. 相似文献
50.
Ross AJ Dreiocker F Schäfer M Oomens J Meijer AJ Pickup BT Jackson RF 《The Journal of organic chemistry》2011,76(6):1727-1734
The structure of the alkylzinc-tetramethylethyl-enediamine (TMEDA) cluster cation 3 has been determined in the gas phase by a combination of tandem mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and DFT calculations. Both sets of experimental results establish the existence of a strongly stabilizing interaction of TMEDA with the zinc cation. High-level DFT calculations on the alkylzinc-TMEDA cluster cation 3 allowed the identification of two low energy conformers, each featuring a four-coordinate zinc atom with a bidentate TMEDA ligand, and internal coordination from the carbonyl group of the Boc group to zinc. The experimental IRMPD spectrum is reproduced with an appropriately weighted combination of the IR spectra of the two conformers identified by theory. DFT calculations on the structure of the alkylzinc halide 2 with coordinated TMEDA using the PCM model of water solvent suggest that TMEDA can promote ionization of the zinc-iodine bond in organozinc iodides under aqueous conditions, providing a credible explanation for the role of TMEDA in stabilizing the carbon-zinc bond. Reaction of the serine-derived iodide 1 with aryl iodides "on water", promoted by nano zinc in the presence of PdCl(2)(Amphos)(2) (5 mol %) and TMEDA, leads to the formation of protected phenylalanine derivatives 4 in reasonable yields. In the case of ortho-substituted aryl iodides and aryl iodides that are solids at room temperature, conducting the reaction at 65 °C gives improved results. In all cases, the product 5 of reductive dimerization of the iodide 1 is also isolated. 相似文献