1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina. 相似文献
Epitaxial Prussian blue (PB) films are deposited electrochemically onto a Au(110) substrate. High-resolution X-ray diffraction shows that the PB films have a [111] out-of-plane orientation. The very large lattice mismatch of 148% is reduced to about 1% by the formation of (1 x 2)PB(111)[onemacr;10]//(6 x 5)Au(110)[onemacr;10] and (1 x 2)PB(111)[01onemacr;]//(6 x 5)Au(110)[onemacr;10] epitaxial relationships. Peaks in the cyclic voltammogram of PB on Au(110) are sharper than those on polycrystalline Au, consistent with higher structural order and a single out-of-plane orientation. The development of epitaxial films of PB and PB analogues will allow the measurement of the orientation-dependent properties of these molecular magnets. It will also open the door to the development of novel molecular spintronic devices, such as those which exhibit spin-dependent electron transfer. 相似文献
A photosensitive precursor (1) to phenylsulfanylcarbene 2 has been synthesized. Laser flash photolysis (308 nm) of 1 and chemical trapping studies of 2 are reported. [structure: see text] 相似文献
Since the commissioning of the first industrial Gamma Irradiator design, designers and operators of irradiation systems have been attempting to meet the specific production requirements and challenges presented to them. This objective has resulted in many different versions of irradiators currently in service today, all of which had original charters and many of which still perform very well within even the new requirements of this industry.
Continuing changes in the marketplace have, however, placed pressures on existing designs due to a combination of changing dose requirements for sterlization, increased economic pressures from the specific industry served for both time and location and the increasing variety of product types requiring processing. Additionally, certain market areas which could never economically support a typical gamma processing facility have either not been serviced, or have forced potential gamma users to transport product long distances to one of these existing facilities.
The MiniCellTM removes many of the traditional barriers previously accepted in the radiation processing industry for building a processing facility in a location. Its reduced size and cost have allowed many potential users to consider in-house processing and its ability to be quickly assembled allow it to meet market needs in a much more timely fashion than the previous designs.
The MiniCell system can cost effectively meet many of the current market needs of reducing total cost of processing and also be flexible enough to process product in a wide range of industries effectively. 相似文献
We report on the application of a new class of oligonucleotide reporter probes, QUAL probes, that "light up" when a nucleophilic phosphorothioate probe binds adjacent to a dabsyl-quenched probe. These self-ligating DNA probes were used for sequence-specific detection of 16S rRNA in Escherichia coli cells. Strong fluorescence was observed only when the phosphorothioate and quenched dabsyl probes bind side-by-side on a 16S rRNA target. The results demonstrate the use of QUAL probes to detect specific RNA sequences in bacterial cells without enzymes and without washing steps. 相似文献
We have generated a novel silver(I)-mediated unnatural DNA base pair consisting of two 2,6-bis(ethylthiomethyl)pyridine nucleobases SPy. This metallo-base pair has a remarkably high pairing stability and selectivity which rivals that of the natural base pairs dA:dT and dC:dG. UV-melting experiments revealed that the dSPy:dSPy self-pair can replace natural base pairs at multiple sites and still form stable DNA duplexes. 相似文献
The n ionization energies I and the gas-phase basicities GB of CH3-, Cl-, or CN-substituted quinuclidines have been measured by PE and ICR spectroscopy. The dependence of the shifts ΔI and ΔGB (relative to the values of the parent molecule) allow conclusions about the charge dispersal accompanying the n ionization or the protonation of quinuclidine in the gas phase. The agreement with the results of a minimal basis set abinitio calculation is excellent. Comparison of the solution pKa values with either I or GB reveals that 2-substituted quinuclidines exhibit sizeable solvent-induced proximity effects, i.e. that the corresponding quinuclidinium ions are more acidic in solution than expected on the basis of the gas-phase basicities. This agrees with earlier results concerning 2-substituted pyridines. 相似文献
Although biological imaging is mostly performed in aqueous media, it is hardly ever considered that water acts as a classic fluorescence quencher for organic fluorophores. By investigating the fluorescence properties of 42 common organic fluorophores recommended for biological labelling, we demonstrate that H2O reduces their fluorescence quantum yield and lifetime by up to threefold and uncover the underlying fluorescence quenching mechanism. We show that the quenching efficiency is significantly larger for red-emitting probes and follows an energy gap law. The fluorescence quenching finds its origin in high-energy vibrations of the solvent (OH groups), as methanol and other linear alcohols are also found to quench the emission, whereas it is restored in deuterated solvents. Our observations are consistent with a mechanism by which the electronic excitation of the fluorophore is resonantly transferred to overtones and combination transitions of high-frequency vibrational stretching modes of the solvent through space and not through hydrogen bonds. Insight into this solvent-assisted quenching mechanism opens the door to the rational design of brighter fluorescent probes by offering a justification for protecting organic fluorophores from the solvent via encapsulation.Overtones and combinations of O–H vibrations in the solvent efficiently quench red-emitting fluorophores by resonant energy transfer.相似文献