Cathodic adsorptive stripping voltammetry of nickel complexed with hydroxynaphthol blue at a static mercury drop electrode

A new method is described for the determination of Ni based on the cathodic adsorptive stripping of Ni(II) complexed with hydroxynaphthol blue (HNB) at a static mercury drop electrode. Optimal conditions were found to be: accumulation potential -0.50 V (vs. Ag/AgCl); final potential -1.10 V; accumulation time 50 sec; scan rate 200 mV/sec; linear scan mode; filter 0.1 sec; supporting electrolyte acetic acid/acetate (0.25M, pH = 6.0) and concentration of HNB 3.3 x 10(-5)M. The response of the system was found to be linear in a range of Ni concentrations from 25 ppb to the detection limit. The detection limit was found to be 1.7 nM (0.10 ppb) with 2 mins of accumulation time. The effect of various potential interferences (including a variety of cations, anions and organic surfactants) were also studied. With the exception of Co, at less than equimolar concentrations no significant interferences were observed. Al was found to interfere at high concentrations with respect to Ni, but Al concentrations up to 1000 ppb may be masked by sodium citrate or sodium fluoride. The utility of the method is demonstrated by the recovery of Ni in a doped sample of commercial mineral water.     

Stereospecific functionalization of the heterocyclic ring systems of flavan-3-OL and [4,8]-biflavan-3-OL derivatives with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)

Efficient stereospecific 4-methoxylation of both 2,3-trans- and 2,3-cis-flavan-3-ol methyl ethers with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in CHCl₃-MeOH solution is of both synthetic and degradative significance in oligomeric flavanoid chemistry.     

Triamidotriazacyclononane complexes of group 3 metals. Synthesis and crystal structures

Reaction of yttrium and lanthanide trichlorides (Ln = La, Eu, Yb) with 1 equiv of the trisodium salt of 1,4,7-tris(dimethylsilylaniline)-1,4,7-triazacyclononane (Na(3)[(SiMe(2)NPh)(3)-tacn](THF)(2)) gives good yields of the compounds [M[(SiMe(2)NPh)(3)-tacn]] (M = Y (1), Eu (3), Yb (4)) and [La[(SiMe(2)NPh)(3)-tacn](THF)] (2). Reduction of 3 with Na/Hg followed by recrystallization in the presence of diglyme yielded crystals of [Eu[(SiMe(2)NPh)(3)-tacn]][Na(diglyme)(2)] (5). Synthesis of the uranium(III) complex [U[(SiMe(2)NPh)(3)-tacn]] (6) is achieved by reaction of 1 equiv of Na(3)[(SiMe(2)NPh)(3)-tacn](THF)(2) with uranium triiodide. The U(IV) complexes, [U[(SiMe(2)NPh)(3)-tacn]X] (X = Cl (7); I (8)), were prepared via oxidation of 6 with benzyl chloride or I(2), but salt metathesis from UCl(4) provided a higher yield route for 7. The solid-state structures of 1-7 were determined by single-crystal X-ray diffraction. The ligand [(SiMe(2)NPh)(3)-tacn] generates a trigonal prismatic coordination environment for the metal center in the neutral complexes 1, 3, 4, and 6 and the ionic 5. In 2 the six nitrogen atoms of the ligand are in a trigonal prismatic configuration with the oxygen atom of the THF capping one of the triangular faces of the trigonal prism. In 7 the coordination geometry around the uranium atom is best described as bicapped trigonal bipyramidal.     

Existence and symmetry for elliptic equations in ℝn with arbitrary growth in the gradient

We define the Polish space R of non-degenerate rank-1 systems. Each non-degenerate rank-1 system can be viewed as a measure-preserving transformation of an atomless, σ-finite measure space and as a homeomorphism of a Cantor space. We completely characterize when two non-degenerate rank-1 systems are topologically isomorphic. We also analyze the complexity of the topological isomorphism relation on R, showing that it is \({F_\sigma }\) as a subset of R× R and bi-reducible to E₀. We also explicitly describe when a non-degenerate rank-1 system is topologically isomorphic to its inverse.     

Critical Behavior of the Spin-1/2 Baxter-Wu Model: Entropic Sampling Simulations

In this work, we use a refined entropic sampling technique based on the Wang-Landau method to study the spin- 1/2 Baxter-Wu model. We adopt the total magnetization as the order parameter and, as a result, do not divide the system into three sub-lattices. The static critical exponents were determined as α = 0.6697(54), β = 0.0813(67), γ = 1.1772(33), and ν = 0.6574(61). The estimate for the critical temperature was T_c = 2.26924(2). We compare the present results with those obtained from other well-established approaches, and we find a very good closeness with the exact values, besides the high precision reached for the critical temperature.     

Schizocalyx cuspidatus (A. St.-Hil.) Kainul. & B. Bremer extract improves antioxidant defenses and accelerates the regression of hepatic fibrosis after exposure to carbon tetrachloride in rats

The aim of this study was to investigate the effect of leaves extract of Schizocalyx cuspidatus (A. St.-Hil.) Kainul. & B. Bremer on hepatic morphofunctional dysfunction induced by carbon tetrachloride (CCl₄). Liver lesions were induced via intraperitoneal administration of CCl₄ every 48 h for 12 days. Forty-nine rats were randomised into seven groups: G1: CCl₄; G2: CCl₄ (animals euthanised 24 h after last CCl₄ application); G3: CCl₄ + DMSO; G4: SCE 400 mg/kg; G5: DMSO (700 μl); G6: CCl₄ + SCE 200 mg/kg and G7: CCl₄ + SCE 400 mg/kg. SCE administration resulted in reduction in hydroperoxide levels, lipidic droplets and necrosis compared to G1, G2 and G3. There was an increase in the amount of collagen fibres in G1, G2 and G3 compared to the groups. These results show that the extract of SCE leaves has great potential for the recovery of liver damage after the application of CCl₄.     

Eigenfunctions and Fundamental Solutions of the Fractional Laplace and Dirac Operators: The Riemann-Liouville Case

In this paper we study eigenfunctions and fundamental solutions for the three parameter fractional Laplace operator \(\Delta _+^{(\alpha , \beta , \gamma )}:= D_{x_0^+}^{1+\alpha } +D_{y_0^+}^{1+\beta } +D_{z_0^+}^{1+\gamma },\) where \((\alpha , \beta , \gamma ) \in \,]0,1]^3\), and the fractional derivatives \(D_{x_0^+}^{1+\alpha }, D_{y_0^+}^{1+\beta }, D_{z_0^+}^{1+\gamma }\) are in the Riemann–Liouville sense. Applying operational techniques via two-dimensional Laplace transform we describe a complete family of eigenfunctions and fundamental solutions of the operator \(\Delta _+^{(\alpha ,\beta ,\gamma )}\) in classes of functions admitting a summable fractional derivative. Making use of the Mittag–Leffler function, a symbolic operational form of the solutions is presented. From the obtained family of fundamental solutions we deduce a family of fundamental solutions of the fractional Dirac operator, which factorizes the fractional Laplace operator. We apply also the method of separation of variables to obtain eigenfunctions and fundamental solutions.     

Theoretical study of radical and neutral intermediates of artemisinin decomposition

Four artemisinin reductive decomposition routes A, B1, B2, and B3 with 13 species (QHS, 1/2, 3, 4, 5, 5a, 6, 7, 18, 18a, 19, 20, and 21) were studied at the B3LYP/6-31G** level. Structures of the species were analyzed in terms of geometrical parameters, L?wdin bond orders, partial atomic charges and spin densities, electronic and free energies, and entropy. Searches in the Cambridge Structural Database for high-level quality artemisinin-related structures were also performed. Principal Component and Hierarchical Cluster analyses were performed on selected electronic and structural variables to rationalize relationships between the routes. The A and B1 routes are possibly interconnected. Structural and electronic features of all species show that there are two clusters: A-B1 and B2-B3. The latter cluster is thermodynamically more favorable (DeltaDeltaG is -64 to -88 kcal mol(-1)) than the former (DeltaDeltaG is -58 to -59 kcal mol(-1)), but kinetical preference may be the opposite. Along the artemisinin decomposition routes, especially B2 and B3, larger structural changes including formation of branched structures and CO2 release are related to increased exothermicity of the conversions, weakened attractive oxygen-oxygen interactions, and increased entropy of the formed species. The intermediate 4 definitely belongs to some minor artemisinin decomposition route.