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91.
Triangles and tetrahedra: metal directed self-assembly of metallo-supramolecular structures incorporating bis-beta-diketonato ligands 总被引:1,自引:0,他引:1
Clegg JK Lindoy LF Moubaraki B Murray KS McMurtrie JC 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2417-2423
The interaction of six aryl-linked bis-beta-diketones, including a new naphthylene linked species, with copper(II), iron(III) and, in one instance gallium(III), has been investigated with the aim of obtaining metallo-supramolecular assemblies exhibiting different geometries. New examples of two assembly types incorporating the above bis-beta-diketones (L) were generated. The first type is represented by a range of molecular triangles of formula [Cu(3)(L-H(2))(3)](solvent)(n) while the second is given by a corresponding selection of less-common neutral molecular tetrahedra of formula [Fe(4)(L-H(2))(6)](solvent)(n) as well as [Ga(4)(L-H(2))(6)].8.5THF.0.5H(2)O; an example of each type has been characterised by X-ray crystallography. A magnetochemical investigation of [Fe(4)(-H(2))(6)].6THF is reported. The susceptibility is Curie like and consistent with very weak coupling occurring between the iron(III) d(5)(high spin) centres. The X-ray structures of two trinuclear copper(II) as well as a tetranuclear iron(III) and a tetranuclear gallium(III) assembly confirm their discrete triangular and tetrahedral geometries, respectively. The structure of the gallium(III) species is closely related to that of the corresponding iron(III) species. The tetrahedral structures provide rare examples of such assemblies encapsulating guest solvent molecules--in each case tetrahydrofuran is incorporated in the central cavity. 相似文献
92.
Chemaly SM Jack LA Yellowlees LJ Harper PL Heeg B Pratt JM 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2125-2134
Studies of the emission spectra of four Co(III) cobinamides (diaquo-, aquohydroxo-, dihydroxo- and dicyano-) show (1) that the excited states corresponding to the alphabeta and epsilon absorption bands behave like the S(1) and S(2) levels in the non-alternant hydrocarbon azulene (with emission from S(2)> S(1) in violation of Kasha's rule) and (2) that the excited states include a TICT (twisted intramolecular charge transfer) mechanism, as in the simpler cyanines, but where the TICT state gives rise to dual fluorescence instead of cis-trans isomerisation. Combined with the previously reported dual fluorescence from the S(1) level in synthetic metal corrinoids and in the naturally-occurring metal-free corrin, this provides evidence that the existence of an additional (metastable) ground state with a significantly different vibronic splitting and nuclear configuration is an intrinsic property of the basic corrin ligand (irrespective of the nature of the side-chains and the metal ion or even the absence of a metal) which distinguishes it from porphyrin. The occurrence of hysteresis (and its associated oscillations) in redox reactions of the cobinamides involving both the Co(III/II) and Co(II/I) couples indicates that the corrin ligand also has an intrinsic ability to exist in different conformations or "allosteric" forms with differing redox potential, which further distinguishes it from the porphyrin ligand. Possible links between the existence of an additional metastable ground state and of allosteric changes and the likely reasons for the selection of corrin over a porphyrin for the vitamin B(12)-dependent enzymes are discussed. 相似文献
93.
Benkoski JJ Bowles SE Korth BD Jones RL Douglas JF Karim A Pyun J 《Journal of the American Chemical Society》2007,129(19):6291-6297
The assembly and direct imaging of ferromagnetic nanoparticles into one-dimensional mesostructures (1-D) are reported. Polymer-coated ferromagnetic colloids (19 nm, 24 nm) were assembled at a crosslinkable oil-water interface under both magnetic field induced and zero-field conditions and permanently fixed into 1-D mesoscopic polymer chains (1-9 mum) in a process referred to as Fossilized Liquid Assembly (FLA). In the FLA process, nanoparticle chains were fixed at the oil interface through photopolymerization, enabling direct visualization of organized mesostructures using atomic force microscopy. Using the FLA methodology, we systematically investigated different conditions and demonstrated that dispersed ferromagnetic colloids possess sufficient dipolar interactions to organize into mesoscopic assemblies. Application of an external magnetic field during assembly enabled the formation of micron-sized chains which were aligned in the direction of the applied field. This universal methodology is an attractive alternative technique to cryogenic transmission electron microscopy (cryo-TEM) for the visualization of nanoparticle assembly in dispersed organic media. 相似文献
94.
FTIR-RAIRS and ATR techniques are shown to provide a powerful means of investigating the molecular behaviour responsible for the pyroelectric properties of organic monolayer assemblies on silicon and aluminised glass. Spectral changes, associated with either proton transfer or head group rearrangement, are well correlated with the level of pyroelectric response for two different devices. The technique promises to be extremely important for the elucidation of the microscopic properties of molecular electronic devices. 相似文献
95.
96.
Jack C. Kim Sang-Duk Bae Ji-A Kim Soon-Kyu Choi 《Journal of heterocyclic chemistry》1998,35(3):531-533
A Regioselective synthesis of (R)-11-hydroxyaporphine 2 directly from (R)-10,11-dihydroxyaporphine ((R)-apomorphine, 1 ) is described for the first time. The isopropylidene ketal ring of 10,11-(isopropyl-idenyldioxy)aporphine 5 obtained by the isopropylidenation of apomorphine was regioselectively opened by ten equivalents of trimethylaluminum to give (R)-10-hydroxy-11-tert-butyloxyaporphine 6 . The free 10-hydioxyl position of 6 was triflated with N-pbenyltrifluoromethanesulfonimide and potassium carbonate under reflux to give (R)-10-[(trifluoromethyl)sulfonyloxy]-11-tert-butyloxyaporphine 7 . The reduced product, 11-tert-butyloxyaporphine 8 was prepared from 7 by a palladium-catalyzed hydrogenolysis. The ether cleavage of (R)-11-tert-butyloxyaporphine with 48% hydrobromic acid afforded the desired (R)-11-hydroxyaporphine 2 in good yield. 相似文献
97.
Calculations involving molecular orbitals have appeared in the chemical literature over the past few years, but all have used smalltrans-polyenes. We now report extended Huckel molecular orbital calculations ontrans-polyenes of up to 18 double bonds (36 carbons and 38 hydrogen atoms). Information obtained from these calculations include total energies, bond gaps, and net charges on each atom. Also found is that the band gap approaches 1.41 eV as the number of double bonds approaches infinity. This value is quite close to reported experimental values. Data are also presented for polyenes assuming equal C-C bond lengths. 相似文献
98.
Biological events occurring at the implant-host interface, including protein adsorption are mainly influenced by surface properties of the implant. Titanium alloys, one of the most widely used implants, has shown good biocompatibility primarily through its surface oxide. In this study, a surface sol-gel process based on the surface reaction of metal alkoxides with a hydroxylated surface was used to prepare ultrathin titanium oxide (TiOx) coatings on silicon wafers. The oxide deposited on the surface was then modified by self-assembled monolayers (SAMs) of silanes with different functional groups. Interesting surface morphology trends and protein adhesion properties of the modified titanium oxide surfaces were observed as studied by non-specific protein binding of serum albumin. The surface properties were investigated systematically using water contact angle, ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Results showed that the surface sol-gel process predominantly formed homogeneous, but rough and porous titanium oxide layers. The protein adsorption was dependent primarily on the silane chemistry, packing of the alkyl chains (extent of van der Waals interaction), morphology (porosity and roughness), and wettability of the sol-gel oxide. Comparison was made with a thermally evaporated TiOx-Ti/Si-wafer substrate (control). This method further extends the functionalization of surface sol-gel derived TiOx layers for possible titanium alloy bioimplant surface modification. 相似文献
99.
Khadidja Bourahla Mustapha Rahmouni Joan Fraga‐Dubreuil Jean Pierre Bazureau Jack Hamelin 《Journal of heterocyclic chemistry》2007,44(1):193-199
The synthesis of new 3‐substituted coumarins appended to imidazolium, pyridinium, 3‐dimethylamino pyridinium, 3‐chloro pyridinium and 3‐bromo pyridinium salts is reported. These salts were prepared by tandem reactions, followed by quantitative anionic metathesis. The structure of these new 3‐substituted coumarins was established by NMR (1H, 13C) and high‐resolution mass spectrometry. 相似文献
100.
This article describes a portable microfluidic technology for determining the minimum inhibitory concentration (MIC) of antibiotics against bacteria. The microfluidic platform consists of a set of chambers molded in poly(dimethylsiloxane) (PDMS) that are preloaded with antibiotic, dried, and reversibly sealed to a second layer of PDMS containing channels that connect the chambers. The assembled device is degassed via vacuum prior to its use, and the absorption of gas by PDMS provides the mechanism for actuating and metering the flow of fluid in the microfluidic channels and chambers. During the operation of the device, degas driven flow introduces a suspension of bacterial cells, dissolves the antibiotic, and isolates cells in individual chambers without cross contamination. The growth of bacteria in the chambers in the presence of a pH indicator produces a colorimetric change that can be detected visually using ambient light. Using this device we measured the MIC of vancomycin, tetracycline, and kanamycin against Enterococcus faecalis 1131, Proteus mirabilis HI4320, Klebsiella pneumoniae, and Escherichia coli MG1655 and report values that are comparable to standard liquid broth dilution measurements. The device provides a simple method for MIC determination of individual antibiotics against human pathogens that will have applications for clinical and point-of-care medicine. Importantly, this device is designed around simplicity: it requires a single pipetting step to introduce the sample, no additional components or external equipment for its operation, and provides a straightforward visual measurement of cell growth. As the device introduces a novel approach for filling and isolating dead-end microfluidic chambers that does not require valves and actuators, this technology should find applications in other portable assays and devices. 相似文献