Palladium complexes bearing the dipyridyl ligand: synthesis,structural studies,and use in the Heck reaction

Two new palladium complexes derived from the di(2-pyridinyl)methanone N-(2-pyridinyl)hydrazone (DPMNPH) ligand are reported. The compounds were characterized by elemental analysis, spectroscopic studies, and, for the DPMNPH ligand, single-crystal X-ray diffraction analysis. The DPMNPH ligand crystallized as orthorhombic with the space group P2₁2₁2₁. The H1 atom is intramolecularly bonded to the pyridinic N4 with N1–H1 = 0.92(3) Å, H1···N4 = 1.87(2) Å, N1···N4 = 2.615(2) Å, and N1–H1···N4 = 137(2)°. Both complexes were excellent catalysts in the Heck reaction in the presence of base.     

Construction of Quaternary Stereocenters by Nickel‐Catalyzed Heck Cyclization Reactions

A nickel‐catalyzed Heck cyclization for the construction of quaternary stereocenters is reported. This transformation is demonstrated in the synthesis of 3,3‐disubstituted oxindoles, which are prevalent motifs seen in numerous biologically active molecules. The method shows broad scope, proceeds in synthetically useful yields, and provides a rare means to construct stereochemically complex frameworks by nonprecious‐metal catalysis.     

Thermally affected characterization region by Barkhausen noise

The controlling of some industrial components require the development of new and particular nondestructive testing techniques. The testing method using Barkhausen noise (BN) is a particular one which can be applied to ferromagnetic materials. It is a magnetic nondestructive evaluation method and can provide very important information about the material structure. The aim of our work is to study the material structure using this technique to characterize the region submitted to thermal processing. Samples of steel have been heated at temperatures between 650 degrees C and 1,200 degrees C with variable parameters (time processing, maintenance time, etc.). Acoustic BN processing allows an easy interpretation of results. Micrographs of samples have been obtained to confirm the results obtained by BN.     

Karyotypic similarity among Barycholos ternetzi and five species of the genus Eleutherodactylus from southeastern Brazil (Anura, Brachycephalidae)

Comparative cytogenetic analyses were carried out in six species of Brachycephalidae from southeastern Brazil. Barycholos ternetzi, Eleutherodactylus binotatus, Eleutherodactylus guentheri, Eleutherodactylus juipoca, Eleutherodactylus parvus and Eleutherodactylus sp. have 2n=22 karyotypes with a marked variation in the morphology of chromosome pairs 8, 10 and 11, which are of telocentric or metacentric types, resulting in FN=38, 40 and 44. Eleutherodactylus have a single chromosome pair bearing Ag-NOR, i.e. pair 1 in E. binotatus, pair 6 in E. guentheri and E. parvus, and pair 11 in E. juipoca and Eleutherodactylus sp. In contrast, B. ternetzi showed Ag-positive sites in the chromosome pairs 1, 4, 5, 9 and 11, and only one to three labelings per metaphase in each individual. Nevertheless, the main chromosome pair with Ag-NOR in the species seems to be the 11th, like in E. juipoca and Eleutherodactylus sp. The NOR site was confirmed by fluorescence in situ hybridization (FISH) technique in E. binotatus and in B. ternetzi, bearing 1p1p and 9p11p11p Ag-NOR pattern, respectively. All the species exhibited predominantly centromeric C-banding pattern, but interstitial bands have also been observed in some cases. In E. binotatus, there is an indication of geographical difference in the distribution of the interstitial C-bands. The fluorochromes GC-specific chromomycin A(3) (CMA(3)) and AT-specific 4',6-diamidino-2-phenylindole (DAPI), with distamycin A (DA) counterstaining, provided the molecular content of some repetitive regions in the karyotypes of the species. One male of E. binotatus presented an extensive heteromorphism, involving at least five different pairs, probably as a consequence of multiple reciprocal translocations. Such rearrangements might be responsible for the multivalent chain seen in the meiosis of this specimen, as well as in another male, although not exhibiting chromosome heteromorphism. The remaining males and those belonging to the other species have always shown 11 bivalents in diplotene and metaphase I cells. In all male specimens, metaphases II presented 11 chromosomes. Despite the observed discrepancies, the five species of Eleutherodactylus have a great uniformity in the 2n=22 karyotypes, suggesting an assemblage of species from southeastern and southern Brazil, in contrast to northern and northeastern assemblage which is characterized by higher diploid numbers. Undoubtedly, B. ternetzi could be included in that proposed assemblage, due to its karyotypic similarity with the Eleutherodactylus species, as evidenced in the present study. This fact strongly supports the close relationships of both genera, previously inferred on the basis of several characters shared by their species.     

New Diphosphopentamolybdate K<Subscript>5</Subscript>[HP<Subscript>2</Subscript>Mo<Subscript>5</Subscript>O<Subscript>23</Subscript>] · 10H<Subscript>2</Subscript>O: Synthesis,Structure, and Characterization

A new diphosphopentamolybdate(VI) K₅[HP₂Mo₅O₂₃] · 10H₂O has been prepared employing solution method and characterized by single crystal X-ray diffraction, energy dispersive analysis, infrared spectroscopy, thermal stability analysis, cyclic voltammetry analysis, and ultraviolet visible spectroscopy. The compound crystallizes in the orthorhombic sp. gr. Pcab: a = 15.9661(10) Å, b = 19.0832(10) Å, c = 20.0970(9) Å, V = 6123.27(10) Å3, Z = 8. The crystal structure contains the polyanion units [HP₂Mo₅O₂₃]^5– around the potassium cations and lattice water. The [HP₂Mo₅O₂₃]^5– subunits are connected together through K?O?Mo bridges and hydrogen bonds. The crystal shape morphology was simulated using the Bravais–Friedel–Donnay–Harker model.     

Emission of 8Begs in the interaction of 12C with nuclei at incident energies up to 33 MeV/amu

The spectra of ⁸Be_gs fragments emitted in the interaction of 100, 200, 300 and 400 MeV ¹²C with ⁵⁹Co, ⁹³Nb and ¹⁹⁷Au have been measured and analysed. Our analysis suggests that, before breaking up, ¹²C may suffer a considerable energy loss which increases with increasing incident energy. The amount of excitation energy provided to the target nucleus in this process increases with decreasing charge of the target nucleus. Received: 3 May 2001 / Accepted: 5 June 2001     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Acid-rain monitoring in East Asia with a portable-type ion-exclusion–cation-exchange chromatographic analyzer

A monitoring system consisting of a portable-type conductimetric ion-exclusion–cation-exchange chromatographic (CEC) analyzer and a meteorological satellite data analyzer has been investigated for the evaluation of the effects of acid precipitation on natural and urban environments in East Asia. The portable ion-exclusion–CEC analyzer uses a polymethacrylate-based weakly acidic cation-exchange resin column in the H⁺-form and a weak-acid eluent (tartaric acid–methanol–water) and is applied for the simultaneous determination of anions (SO₄²⁻, NO₃⁻, and Cl⁻) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) in precipitation transported from mainland China to central Japan, as mapped by the meteorological satellite data analyzer. Linear calibration graphs of peak area versus concentration for anions and cations were observed in the concentration range 0–1.0 mM for the anions and 0–0.5 mM for the cations. Detection limits at a signal-to-noise ratio of 3 were in the range 5.18–12.1 ppb for the anions and 6.58–16.5 ppb for the cations. The practical utility of this monitoring system is presented.     

Bis­[4‐(di­methyl­amino)­pyridinium] hexa­chloro­stannate(IV)

In the title compound, 4‐(di­methyl­amino)­pyridine is proton­ated on the pyridine N atom. The N(CH₃)₂ moiety is twisted 4.4 (2)° from the pyridine‐ring plane. The octahedral [SnCl₆]^2? anion is hydrogen bonded via trans‐Cl atoms to pyridinium N atoms from two cations forming (C₇H₁₁N₂)₂[SnCl₆] structural units.