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961.
The synthesis of [Mn12O12(O2CMe)6(p-CO2-phenyl nitronyl nitroxide)10(H2O)4]· 4H2O, (1), by direct replacement of some of the acetate groups in [Mn12O12(O2CMe)16(H2O)4] · 4H2O · 2MeCO2H, (2), with the organic radical p-HO2C-phenyl nitronyl nitroxide, (3), is reported. E.p.r. spectra show exchange narrowing in (1) due to coupling between the manganese ions and radicals. The isotropic hyperfine splitting constant from the manganese ions is a = 96 Oe at 5.5K. The magnetic susceptibility indicates antiferromagnetic exchange interactions between the manganese ions and the radicals with the Weiss constant = -25 K. The spin was determined to be S = 6 from magnetization data in the 2--30 K temperature range at 50 kOe, suggesting a mixture of ground state with excited states. 相似文献
962.
Addition–elimination reactions involving a nucleophile and a remote leaving group [SH
N(AE)tele] are well-known under basic conditions, especially amongst electron-poor six-membered heterocycles, but are less commonly
encountered for five-membered heterocycles and are rare under acidic conditions. Concentrated HCl converts 1-hydroxy-1H-pyrazolo[3,4-c] isoquinoline and 1-hydroxy-1H-pyrazolo[3,4-c]quinoline into 3-chloro-1H-pyrazolo[3,4-c]isoquinoline and 3-chloro-1H-pyrazolo[3,4-c]quinoline, respectively. However, apparently neither the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)-quinolines nor the parent 1-hydroxypyrazole undergo this reaction. Additionally, all these systems are refractory under
basic conditions. We present a plausible mechanism for the reaction, involving the 3-addition of Cl- to the diprotonated heterocycle, followed by the elimination of water. Calculations of the initial transition states and
intermediates, using optimisation at B3LYP/6-311+G(d,p), including thermochemistry [HF/6-31+G(d)], and single-point Poisson–Boltzmann
self-consistent reaction field determination of the free energy of solvation (Jaguar Poisson–Boltzmann self-consistent reaction
field), support this mechanism and reproduce the observed order of reactivity, the addition step being 2–4 kcal less favourable
for the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)quinolines and provide a rationalisation for the role of strong acid.
Received: 27 June 2002 / Accepted: 6 September 2002 /
Published online: 14 February 2003 相似文献
963.
Smith CJ Huang W Walcott CJ Turner W Grainger J Patterson DG 《Analytical and bioanalytical chemistry》2002,372(1):216-220
For measurement of biomarkers from polycyclic aromatic hydrocarbon (PAH) exposure, an analytical method is described quantifying hydroxylated PAH (OH-PAH) in urine samples. This method determined monohydroxy metabolites of naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo[c]phenanthrene, and benz[a]anthracene. The sample preparation consisted of enzymatic hydrolysis, solid-phase extraction and derivatization with a silylating reagent. Five carbon-13 labeled standards were used for isotope dilution. Analytes were separated by gas chromatography (GC) and quantified with high-resolution mass spectrometry (HRMS). This method produced good recoveries (41-70%), linearity, and specificity. Data were corrected for blank levels from the naphthalene, fluorene, and phenanthrene metabolites. Method detection limits ranged from 2 ng L(-1) for 1-hydroxypyrene to 43.5 ng L(-1) for 1-hydroxynaphthalene. Using quality control charts from two urine pools, the method can be readily applied to biomonitoring PAH exposure. 相似文献
964.
Érika Pinto Marinho A. G. Souza Danniely S. de Melo Iêda M. G. Santos Dulce M. A. Melo Walquíria J. da Silva 《Journal of Thermal Analysis and Calorimetry》2007,87(3):801-804
Because
of their electrical, magnetic and catalytic properties rare earth and transition
metal mixed oxides are important compounds. Lanthanum chromites have been
extensively used as solid oxide fuel cell (SOFC) interconnect materials. In
this work, lanthanum chromites partially substituted by alkaline earth metals
were synthesized by the urea combustion process. TG and DSC techniques were
used to evaluate the presence of the organic material in the powder after
reaction on the hot plate. The powders were calcinated at 900°C and characterized
by XRD and SEM. The results show that the particles have nanometric dimensions
and the perovskite structure was formed. 相似文献
965.
A major issue with the electrolytic conductivity measurement for pure water is the lack of standard or reference methods.
A primary method traceable to SI and suitable for pure-water conductivity measurement was developed at the Physikalisch-Technische
Bundesanstalt (PTB), Germany, as the base for the calibration method for the conductivity measuring devices at the low conductivity
level. This paper provides a novel method to calculate the bulk resistance of pure water using impedance measured at a single
frequency, which is one of the key procedures for the primary methods. 相似文献
966.
Three novel heteropolytungstates, [Cu(phen)2]4[α-SiW12O40] (1), [Cu4(4,4′-bpy)3(2,2′-bpy)4][α-SiW12O40] · H2O (2) and [Cu(4,4′-bpy)(4,4′-Hbpy)0.5]2[PW12O40] (3) (phen = 1,10-phenanthroline, 4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine), have been synthesized and characterized
by elemental analyses, IR, TG analyses and single-crystal X-ray diffraction. Compound (1) exhibits interesting chiral layer constructed from interperpendicular helical chains running along a crystallographic 21 axis in the c and a directions. Furthermore, the chiral layers are connected by the [α-SiW12O40]4− anions via hydrogen bonding interactions to form a 3D superamolecular structure. The [Cu4(4,4′-bpy)3(2,2′-bpy)4]4+ coordinated complexes in compound (2) are packed together via the aromatic π–π stacking interactions and exhibit an interesting 3D sandglasslike “host” network with 1D channels, in which
[α-SiW12O40]4− anions “guests” reside. Compound (3) has a unique 2D superamolecular network, which is composed of cationic CuI coordination polymer chains and discrete [PW12O40]3− polyoxoanions as linkers. It is noteworthy that the monprotonated 4,4′-bpy ligands of (3) act as arms and connect the adjacent 2D network, generating a 3D interpenetrating superamolecular structure. 相似文献
967.
Five new CuII complexes of general formula [Cu2(Rdtc)tpmc](ClO4)3, (1)–(5), where tpmc and Rdtc
– refer to N,N,N,N-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of CuII ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the (C=N) and (C=S) vibrations which decrease in the order of the complexes: Pipdtc>N-Mepipdtc>Pzdtc>Morphdtc>Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g
eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria. 相似文献
968.
Jorge Casas-Sanchez M. Asuncion Alsina Mathias K. Herrlein Concepció Mestres 《Colloid and polymer science》2007,285(12):1351-1360
Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties
is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol
(PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant
area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts
in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria.
The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers
with the lipids assayed at the air/water interface. 相似文献
969.
On Oxygen Perovskites with Pentavalent Ruthenium A BIIIRuVO6 with AII = Ba, Sr The perovskites Ba2BIIIRuVO6 with BIII = La, Nd, Sm, Eu, Gd, Dy, Y, are cubic (BIII = La: a = 8,544 Å; Y: a = 8,337 Å); with a partial order for BIII and RuV. The Sc compound, Ba2ScRuO6, has a hexagonal 6 L structure (a = 5.795 Å; c = 14.229 Å; sequence (hcc)2)2. The lattice of the Sr perovskites, Sr2BIIIRuVO6, with BIII = Eu, Gd, Dy, Y is rhombic distorted. The IR and FRI spectra are discussed. 相似文献
970.
Aydin Tavman Naz M. Agh-Atabay Sadik Guner Fahrettin Gucin Basaran Dulger 《Transition Metal Chemistry》2007,32(2):172-179
2-(5-H/Me/Cl-1H-benzimidazol-2-yl)-phenol ligands form 1:1 electrolytes, 5-coordinate monometallic complexes with iron(III) nitrate. The geometry of the [Fe(L)(OH)(H2O)2](NO3) complexes was derived from theoretical calculation in DGauss/DFT level (DZVP basis set) on CACHE. In all of the complexes
the ligands are bidentate, via one imine nitrogen atom and phenolate oxygen atom. The coordination is completed with a hydroxide ion, and two water molecules,
adopting a distorted square pyramidal geometry. The structures of the compounds were confirmed on the basis of elemental analysis,
molar conductivity, magnetic moment, FT-Raman, FT-IR (mid-IR, far-IR), EPR and u.v.–vis. The antimicrobial activities of the
free ligands, their hydrochloride salts, and the complexes were evaluated using the disk diffusion method in dimethyl sulfoxide
(DMSO) as well as the minimal inhibitory concentration (MIC) dilution method, against nine bacteria and the results are compared
with several known antibiotic agents. Antifungal activities were reported for Candida albicans, Kluyveromyces fragilis, Rhodotorula rubra, Debaryomyces hansenii, Hanseniaspora guilliermondii, and the results were referenced against nystatin, ketaconazole, and clotrimazole antifungal agents. In most cases, the compounds
tested showed broad-spectrum (Gram+ & Gram− bacteria) activities that were either more active or as potent as the references. 相似文献