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71.
The reactions of K(2)PtCl(4) with N,N'-diphenylformamidine (HDPhF) and N,N'-di-p-tolylformamidine (HDTolF) produce the trans square-planar compounds PtCl(2)(HDPhF)(2), 1a, and PtCl(2)(HDTolF)(2), 1b. Compound 1a crystallizes as yellow parallelepipeds in the space group P2(1)/c with two independent molecules in the asymmetric unit and unit cell dimensions a = 23.427(7) ?, b = 16.677(6) ?, c = 12.980(4) ?, and beta = 96.10(2) degrees. These compounds are soluble in common organic solvents and have been used as starting materials for the preparation of diplatinum compounds. Treatment of 1a and 1b with NaOMe and the halide abstraction reagent TlPF(6) produces the compounds Pt(2)(&mgr;-DArF)(2)(eta(2)-DArF)(2), Ar = Ph (2a) and Tol (2b), respectively. Compound 2a crystallizes as yellow rods in the space group P&onemacr; with unit cell dimensions a = 12.296(3) ?, b = 12.310(4) ?, c = 15.374(4) ?, alpha = 90.75(2) degrees, beta = 91.02(2) degrees, and gamma = 110.20(2) degrees. Compound 2b crystallizes with a molecule of THF, as yellow rods in the space group P2(1)/c with a = 17.883(3) ?, b = 14.517(3) ?, c = 22.581(3) ?, and beta = 98.17(1) degrees. These compounds contain two cis bridging formamidinato ligands and two formamidinato ligands that are chelated to separate Pt centers. Upon heating, they further react to give the tetrabridged compounds Pt(2)(&mgr;-DArF)(4), Ar = Ph (3a), Tol (3b). Compound 3a crystallizes as orange cubes in the cubic space group I432 with a = 19.671(1) ?. On going from the bis-bridged, bis-chelate structure in 2a to the tetrabridged structure in 3a, the metal-metal separation decreases from 2.910(1) to 2.649(1) ?. Both 2band 3b have been oxidized to give the Pt(II)-Pt(III) compound Pt(2)(&mgr;-DTolF)(4)(PF(6)), 4. Compound 4 crystallizes as cubes in the tetragonal space group P4/ncc with a = 14.392(1) ? and c = 14.436(1) ?. The Pt-Pt distance in 4 is 2.5304(6) ?. 相似文献
72.
Large single crystals of NbP have been prepared. A single-crystal X-ray diffraction study shows that it crystallizes in tetragonal symmetry with space group I4(1)md (No. 109) and lattice parameters a = 3.3324(2) ?, c = 11.3705(7) ?, and Z = 4. A full matrix least-squares refinement based on a unique data set of 285 reflections (I> 2sigma(I)) yielded R(F) = 0.017 and R(w)(F(2)) = 0.046 for nine variables. The unit cell consists of one unique Nb and one P, each in trigonal prismatic coordination with the other element. There are two short and four long bond distances of Nb-P. The Nb-Nb bond distances are significantly shorter than R(c) = 4.09 ?, the critical distance required for good Nb-Nb 4d orbital overlap for niobium metal-metal bonds. NbP shows metallic behavior with rho = 4.5 x 10(-)(5) Omega cm at room temperature. Magnetic susceptibility measurements on a collection of randomly oriented single crystals indicate very weak Pauli paramagnetism ( approximately 10(-)(5) emu/mol). A discussion of the structure as well as the physical properties of NbP compared with those of previous results are presented. The band structure of NbP based on the extended Hückel (tight-binding) calculations is presented along with an analysis that reveals that the valence band is built up from three center bonds localized within Nb(3) triangles. 相似文献
73.
Summary LetC be the symmetric cusp {(x, y)2:–x
yx
,x0} where >1. In this paper we decide whether or not reflecting Brownian motion inC has a semimartingale representation. Here the reflecting Brownian motion has directions of reflection that make constant angles with the unit inward normals to the boundary. Our results carry through for a wide class of asymmetric cusps too. 相似文献
74.
Tailen Hsing 《Probability Theory and Related Fields》1993,95(3):331-356
Summary Let {
j
} be a stationary sequence of weakly dependent random variables and letM
n
(k)
be thek-th largest value of
j
, 1jn. The estimation of the parameters of the asymptotic distribution ofM
n
(k)
is considered using a procedure motivated by a limit theorem pertaining to the point process
. A number of statistical issues concerning the procedure, including how to select the tuning parameters, are addressed. The second problem that we consider is the estimation of the filter of a moving average process with heavy tails. In particular, the investigation covers the moving average stable process. Motivated by ideas in Rootzén (1978), our estimator uses information contained in the sample behavior of the process near the largest excursion.Research supported by AFOSR Contract No. 91-0030, NAVY-ONR Grant No. N00014-92-J-1007, and NSF Grant No. 9107507 相似文献
75.
Mary E. Gimon-Kinsel Gary R. Kinsel Ricky D. Edmondson David H. Russell 《Journal of the American Society for Mass Spectrometry》1995,6(7):578-587
A two-stage linear time-of-flight mass spectrometer is used to investigate the requirements for performance of laser photodissociation of peptide and protein ions. Results are presented that demonstrate that desorption and dissociation laser pulses can be synchronized to irradiate ions that travel at high velocities down the drift tube of a time-of-flight mass spectrometer. For example, 193-nm photodissociation of bovine insulin and doubly charged lysozyme is demonstrated, and laser power studies suggest that dissociation is initiated by the absorption of a single 193-nm photon. These results are encouraging because they suggest that laser photodissociation of high molecular weight proteins can lead to fragmentation on time scales compatible with time-of-flight mass spectrometry. 相似文献
76.
Assefa Z Omary MA McBurnett BG Mohamed AA Patterson HH Staples RJ Fackler JP 《Inorganic chemistry》2002,41(24):6274-6280
The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)(2)Au][Au(CN)(2)], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au.Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 A is seen for 2. The intrachain Au...Au separation is 3.457(1) and 3.396(2) A in 1 and 2, respectively. As a result of this weak Au...Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) A, b = 23.877(6) A, c = 6.914(1) A, V = 992.3(3) A(3), and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3 (No. 148), with Z = 18, a = 22.587(2) A, b = 22.587(2) A, c = 9.814(2) A, V = 4336 A(3), and R = 0.0283. 相似文献
77.
Ming Z. Gao 《Tetrahedron letters》2004,45(29):5649-5652
The novel structures of sulfur-containing chiral bis(oxazoline) compounds which have been synthesized have been determined by X-ray crystal diffraction analyses. A high enantioselectivity (ee >99%) in the asymmetric cyclopropanation of diphenylethene with diazoester using the bis(oxazoline)-Ru(II) catalyst was obtained. 相似文献
78.
S. M. Kormali D. L. Swindle E. A. Schweikert 《Journal of Radioanalytical and Nuclear Chemistry》1976,31(2):413-436
A survey has been made on the application of charged particle activation analysis for the detection of traces of medium Z
elements (40≤Z≤58, 72, 74) using protons and deuterons of 20 MeV,3He and4He ions of 40 MeV. The product nuclides considered were γ-ray emitting radioisotopes with half lives ranging from 10 min to
3 days. Based on the thick target yields obtained, proton activation was found to provide an optimum compromise between sensitivity
and selectivity. 相似文献
79.
Piyarat Thanakoses Nagat Abd Alla Mostafa Mark T. Holtzapple 《Applied biochemistry and biotechnology》2003,107(1-3):523-546
Using the MixAlco process, biomass can be converted into carboxylic acids, which can be chemically converted into mixed alcohol
fuels. This study focused on the use of countercurrent fermentation to anaerobically convert sugarcane bagasse and chicken
manure to mixed carboxylic acids using a mixed culture of mesophilic microorganisms from terrestrial and marine sources. Bagasse
was pretreated with lime to increase digestibility. The continuum particle distribution model (CPDM) simulated continuous
fermentors based on data collected from batch experiments. This model saves considerable time in determining optimum operating
conditions. For an 80% bagasse/20% chicken manure fermentation with terrestrial inoculum at a volatile solids loading rate
(VSLR) of 7.36 g/(L of liquid·d) and a liquid residence time (LRT) of 8.88 d, total carboxylic acid productivity, total acid
selectivity, and yield were 2.49 g/(L of liquid·d), 0.581 g of total acid/g of VS digested, and 0.338 g of total acid/g of
VS fed, respectively, at a concentration of 18.7 g of total acid/L. At the same VSLR and LRT, fermentation with marine inoculum
gave higher total acid productivity, total acid selectivity, and yield than fermentation with terrestrial inoculum. For an
80% bagasse/20% chicken manure fermentation with marine inoculum at a VSLR of 3.83 g/(L of liquid·d) and an LRT of 12.1 d,
total carboxylic acid productivity, total acid selectivity, and yield were 1.38 g/(L of liquid·d), 0.667 g of total acid/g
of VS digested, and 0.359 g of total acid/g of VS fed, respectively, at a concentration of 16.2 g of total acid/L. 相似文献
80.
John A. McLean Brandon T. Ruotolo Kent J. Gillig David H. Russell 《International journal of mass spectrometry》2005,240(3):301
Matrix-assisted laser desorption/ionization (MALDI) coupled with ion mobility–mass spectrometry (IM–MS) provides a rapid (μs–ms) means for the two-dimensional (2D) separation of complex biological samples (e.g., peptides, oligonucleotides, glycoconjugates, lipids, etc.), elucidation of solvent-free secondary structural elements (e.g., helices, β-hairpins, random coils, etc.), rapid identification of post-translational modifications (e.g., phosphorylation, glycosylation, etc.) or ligation of small molecules, and simultaneous and comprehensive sequencing information of biopolymers. In IM–MS, protein-identification information is complemented by structural characterization data, which is difficult to obtain using conventional proteomic techniques. New avenues for enhancing the figures of merit (e.g., sensitivity, limits of detection, dynamic range, and analyte selectivity) and optimizing IM–MS experimental parameters are described in the context of deriving new information at the forefront of proteomics research. 相似文献