Synthesis,characterization and X-ray crystal structures of the bis–ligand zinc(II) and cadmium(II) complexes of the methylpyruvate Schiff base of <Emphasis Type="Italic">S</Emphasis>-methyldithiocarbazate

New bis-chelated Zn^II and Cd^II complexes of empirical formula, [M(mpsme)₂] (mpsme=the anionic form of the tridentate ONS donor ligand formed from methylpyruvate and S-methyldithiocarbazate) have been prepared and characterized by conductance, i.r., electronic and n.m.r. spectroscopic techniques. Spectral evidence supports a six-coordinate distorted octahedral structure for these complexes. X-ray crystallographic structural analysis also confirms that, in both the [Zn(mpsme)₂] and [Cd(mpsme)₂] complexes, the methylpyruvate Schiff base of S-methyldithiocarbazate is coordinated to the metal ions as a uninegatively charged tridentate ONS chelating agent via the carbonyl oxygen atom, the azomethine nitrogen atom and the thiolate sulfur atom. Both complexes are assigned a distorted octahedral geometry in which the ligands are arranged meridionally around the metal ions. The distortion from regular octahedral geometry is attributable to the restricted bite angles of the ligand.     

A study of the Regge recurrence of the Δ(1236) produced in 10 GeV/c K+p interactions

Data are presented on a high mass $\text{I}\text{3}\text{2}\text{Δ}$ resonance produced in 10 GeV/c K⁺p interactions. The mass and width of the resonance, determined by a maximum likelihood fit to the pπ⁺ spectrum in the final state K⁺pπ⁺π^?, are 1895±15 MeV/c²230±50 MeV/c² respectively. The differential cross sections, dσ/dt, for the quasi two-body final states K¹(890)Δ(1236) and K¹(890)Δ(1900) are well described by the one pion exchange model. In addition the moments of the Gottfried-Jackson angular distribution of the pπ⁺ system agree with those computed from on-shell π⁺p elastic scattering data. We conclude that the two final states are produced mainly by π exchange and associate the structure observed in the moments up to NH(6,0) in the 1900 MeV region with the $\text{7}\text{2}{}^{\mathrm{+}}$ Regge recurrence of the Δ(1236). The dominant decay mode of the resonance is Δ⁺⁺(1900)→pπ⁺ but decays to pπ⁺π⁰ and nπ⁺π⁺ are also observed. Cross sections are determined for the production of the quasi two-body final states K¹(890)Δ(1236), K¹(890) Δ(1900), K¹(1420)Δ(1236) and K¹(1420)Δ(1900).     

Refinement of the crystal structure of acetylacetonatodicarbonylrhodium(I)

The structure of acetylacetonatodicarbonylrhodium(I), Rh(acac)(CO)₂, has been refined from three-dimensional X-ray diffractometer data. The complex crystallises in the triclinic space groupP¯1 with two molecules in a unit cell of dimensionsa = 6.5189(5),b = 7.7614(8),c = 9.2049(12)Å, = 106.04(1), = 91.15(1), = 100.21(1) °. Full-matrix least-squares refinement, using 1456 independent reflections, has reachedR = 0.038.The rhodium atom has a square-planar coordination with two Rh-O(acac) distances of 2.040 and 2.044Å, and two Rh-C(carbonyl) distances both equal to 1.831Å, the O-Rh-O angle is 90.8 ° and the C-Rh-C angle is 88.9 °. All twelve non-hydrogen atoms are closely planar, with an average deviation of 0.003Å, and a maximum deviation of 0.006Å, from the least-squares plane through the molecule. A second non-crystallographic plane of symmetry bisects the molecule, which therefore has essentiallymm2 (C _2v ) point symmetry. The molecules stack in such a way that the rhodium atoms of neighbouring molecules occupy the two remaining pseudo-octahedral positions, with Rh...Rh distances of 3.253 and 3.271Å.     

Mechanism responsible for initiating carbon nanotube vacuum breakdown

We report a physical mechanism responsible for initiating a vacuum breakdown process of a single carbon nanotube (CNT) during field emission. A quasidynamic method has been developed to simulate the breakdown process and calculate the critical field, critical emission current density and critical temperature beyond which thermal runaway occurs before the CNT temperature reaches its melting point. This model is in good agreement with experiments carried out with a single CNT on a silicon microtip.     

Magnetic,spectroscopic and biological properties of copper(II) complexes of the tridentate ligand, α-N-methyl-S-methyl-β-N-(2-pyridyl)methylenedithiocarbazate(NNS) and the X-ray crystal structure of the [Cu(NNS)I2] complex

Copper(II) complexes of general formula, Cu(NNS)X ₂ · nH₂O (NNS = the 2-formylpyridine Schiff base of N-methyl-S-methyldithiocarbazate; X = Cl^–, Br^–, I^–, NCS^–; n = 0, 2) have been synthesized and characterized by elemental analysis and by magnetic and spectroscopic techniques. Based on magnetic and spectroscopic data, a monomeric five-coordinate square-pyramidal structure is assigned to these complexes. The crystal and molecular structure of [Cu(NNS)I₂] has been determined by X-ray diffraction. The complex has a monomeric square-pyramidal structure with the ligand coordinated to the copper(II) ion via the pyridine nitrogen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth and fifth coordination sites are occupied by the iodide ligands. Antimicrobial tests indicate that Schiff base is inactive against the bacteria, Bacillus subtilis (mutant defective DNA repair), Pseudomonas aeruginosa, methicillin resistant Staphylococcus aureus and Bacillus subtilis (wild type) and weakly active against the fungi, Candida albicans, Candida lypolytica, Saccharomyces cereviseae and Aspergillus ochraceous but its copper(II) complexes, Cu(NNS)X ₂ are strongly active against these organisms. A cytotoxicity study of the compounds against leukemic and cervical cancer cells showed that the Schiff base is inactive, but the complexes, [Cu(NNS)I₂] and [Cu(NNS)(NCS)₂] · 2H₂O exhibit significant activity against cervical cancer cells with CD₅₀ values of 4.8 and 4.2 g, respectively.     

Three-dimensional structure determination of N-(p-Tolyl)-dodecylsulfonamide from powder diffraction data and validation of structure using solid-state NMR spectroscopy

The three-dimensional structure, conformation, and packing of molecules in the solid state are crucial components used in the optimization of many technologically useful materials properties. Single-crystal X-ray diffraction is the traditional and most effective method of determining 3-D structures in the solid state. Obtaining single crystals that are sufficiently large and free of imperfections is often laborious, time-consuming, and, occasionally, impossible. The feasibility of an integrated approach to the determination and verification of a complete three-dimensional structure for a medium-sized organic molecule without using single crystals is demonstrated for the case of an organic stabilizer compound N-(p-tolyl)-dodecylsulfonamide. The approach uses a combination of powder XRD data, several computational packages involving Monte Carlo simulations and ab initio quantum mechanical calculations, and experimental solid-state NMR chemical shifts. Structure elucidation of N-(p-tolyl)-dodecylsulfonamide revealed that the Bravais lattice is monoclinic, with cell dimensions of a = 38.773 A, b = 5.507 A, c = 9.509 A, and beta = 86.35 degrees, and a space group of P21/c.     

Microencapsulation of nisin in alginate-cellulose nanocrystal (CNC) microbeads for prolonged efficacy against Listeria monocytogenes

The present study was undertaken to develop edible nisin-microencapsulated beads in order to inhibit growth of Listeria monocytogenes in ready-to-eat (RTE) ham. Different concentrations of nisin (16, 31, and 63 μg/ml) were microencapsulated into alginate-cellulose nanocrystal beads. Microencapsulation kept the available nisin (63 μg/ml) content 20 times greater compared with free nisin (63 μg/ml) during 28 days of storage at 4 °C. Results showed that 63 μg/ml microencapsulated nisin exhibited 31.26 μg/ml available nisin content after 28 days of storage at 4 °C, whereas there was no available nisin content left for free nisin. Cooked ham slices were then coated by the microencapsulated nisin beads, inoculated with L. monocytogenes [~3 log colony-forming units (CFU)/g], and stored at 4 °C under vacuum packaging for 28 days. The beads containing 16, 31, and 63 μg/ml nisin significantly (P ≤ 0.05) reduced the L. monocytogenes counts by 2.65, 1.50, and 3.04 log CFU/g after 28 days of storage compared with free nisin. Furthermore, microencapsulated nisin beads did not change the physicochemical properties (pH and color) of RTE ham during storage.     

Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet

We present inelastic neutron scattering and thermodynamic measurements characterizing the magnetic excitations in a disordered spin-liquid antiferromagnet with non-magnetic substitution. The parent compound Ba(3)Mn(2)O(8) is a dimerized, quasi-two-dimensional geometrically frustrated quantum disordered antiferromagnet. We substitute this compound with non-magnetic V(5+) for the S=1 Mn(5+) ions, Ba(3)(Mn(1-x)V (x))(2)O(8), and find that the singlet-triplet excitations which dominate the spectrum of the parent compound persist for the full range of substitution examined, up to x=0.3. We also observe additional low-energy magnetic fluctuations which are enhanced at the greatest substitution values.     

Unveiling structure-property relationships in Sr2Fe(1.5)Mo(0.5)O(6-δ), an electrode material for symmetric solid oxide fuel cells

We characterize experimentally and theoretically the promising new solid oxide fuel cell electrode material Sr(2)Fe(1.5)Mo(0.5)O(6-δ) (SFMO). Rietveld refinement of powder neutron diffraction data has determined that the crystal structure of this material is distorted from the ideal cubic simple perovskite, instead belonging to the orthorhombic space group Pnma. The refinement revealed the presence of oxygen vacancies in the as-synthesized material, resulting in a composition of Sr(2)Fe(1.5)Mo(0.5)O(5.90(2)) (δ = 0.10(2)). DFT+U theory predicts essentially the same concentration of oxygen vacancies. Theoretical analysis of the electronic structure allows us to elucidate the origin of this nonstoichiometry and the attendant mixed ion-electron conductor character so important for intermediate temperature fuel cell operation. The ease with which SFMO forms oxygen vacancies and allows for facile bulk oxide ion diffusivity is directly related to a strong hybridization of the Fe d and O p states, which is also responsible for its impressive electronic conductivity.