Simultaneous spectrophotometric determination of cadmium, copper and zinc

A method for the simultaneous spectrophotometric determination of cadmium, copper and zinc based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide is proposed. The absorption curves of these complexes overlap severely in the scanning range 380–480 nm. The analyte concentrations are calculated by a least squares fit of the pure spectra to the mixture spectra. A linear determination range of 0.1–1.7 μg/ml for cadmium, 0.1–1.3 μg/ml for copper and 0.2–1.2 μg/ml for zinc were obtained. The effect of interference was studied. The method has been applied to the determination of these metal ions in various type of materials.     

Biocatalytic removal of nickel and vanadium from petroporphyrins and asphaltenes

Asphaltenes from a crude oil rich in heavy metals (Castilla crude oil) were fractionated and partially characterized. Biocatalytic modifications of these fractionated asphaltenes by three different hemoproteins: chloro-peroxidase (CPO), cytochrome C peroxidase (Cit-C), and lignin peroxi-dase (LPO) were evaluated in both aqueous buffer and organic solvents. The reactions were carried out in aqueous buffers, ternary systems of toluene: isopropanol: water, and aqueous-miscible organic solvent solutions with petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary systems and aqueous miscible-organic solvent systems than in the aqueous buffer systems. However, only the CPO-mediated reactions were effective in eliminating the Soret peak in both aqueous and organic solvent systems. The effects of CPO-mediated reactions on the release of the metals complexed with the porphyrins and asphaltenes were also determined. Chloroperoxidase was able to alter components in the heavy fractions of petroleum and remove 53 and 27% of total heavy metals (Ni and V, respectively) from petroporphyrin-rich fractions and asphaltenes     

C-H activations at iridium(I) square-planar complexes promoted by a fifth ligand

In the presence of ligands such as acetonitrile, ethylene, or propylene, the Ir(I) complex [Ir(1,2,5,6-eta-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1-kappa-4,5,6-eta-C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; eta2-C2H4, 3; eta2-C3H6, 4), respectively, through a sequence of C-H oxidative addition and insertion elementary steps. The rate of this transformation depends on the nature of L and, in the case of NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggesting the formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affords the Ir(III) complex [Ir(1-kappa-4,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinate Ir(I) compound [Ir(1,2,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in model complexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-H oxidative addition transition states of lower energy than that found in the absence of these ligands. Key species in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediates preceding the intramolecular C-H oxidative addition step, which are generated after release of one cyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is also investigated for complexes [IrCl(L)(PiPr3)2] (L = eta2-C2H4, 27; eta2-C3H6, 28). In the presence of NCMe, these complexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) via the common cyclometalated intermediate [IrClH{kappa-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The most effective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generated by photochemical release of the alkene ligand. However, in the absence of light, the reaction rates display dependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrile adducts.     

Infrared spectrum of benzene in bromine and carbon tetrachloride solutions

The benzene—bromine complex at room temperature has been re-studied by infrared with bromine in excess of benzene. Solutions of 0.225 M benzene in bromine—carbon tetrachloride mixtures were studied. Under this condition, the spectral changes of measurable benzene absorption bands were observed more clearly than previously. The out-of-plane vibrations of benzene were observed to shift to higher frequencies. The equilibrium constant was found to be 0.11 ? mole^?1. The accord with the equilibrium constant derived from benzene rich systems supports the concept of a specific interaction. A C_6V symmetry is favoured for the geometry of the complex.     

Periodic solutions for second order singular damped differential equations

We study the existence of positive periodic solutions for second order singular damped differential equations by combining the analysis of the sign of Green?s functions for the linear damped equation, together with a nonlinear alternative principle of Leray–Schauder. Recent results in the literature are generalized and significantly improved.     

Optimized Synthesis of Silver Nanoparticles by Factorial Design with Application for the Determination of Melamine in Milk

A colorimetric method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without any stabilizer, using sodium borohydride as the reducing agent. Optimization of the variables for the formation of the nanoparticles was performed by factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0?±?2.7?nm. Spectrophotometric measurements performed at 475?nm showed a linear range from 0.033 to 1.50?mg?L^?1 of melamine with limits of detection and quantification of 0.009 and 0.031?mg?L^?1, respectively. The method provided highly sensitive determination of melamine in milk.     

WATER MOVEMENT CAUSED BY SPREADING SURFACTANTS IN UNSATURATED SYSTEMS OF PARTICLES OF NONUNIFORM SIZE

The movement of water originated by the spreading of two surfactants was analyzed in glass beads as well as on soil systems, both of particles of nonuniform size

The higher difference of surface tension produced in the system by 1 -hexadecanol compared to that of 1-tetradecanol led therefore to a higher amount of water moved. Decreased proportion of the smaller sized particles in glass beads system produced a decrease in the total water moved by both surfactants.

Organic matter acted in soil as a second surfactant in glass beads. This effect was compared in glass beads systems once 1-hexadecanol was evenly distributed among the particles as continuous film, which played a role alike that of organic matter in soil and then a second surfactant 1-tetradecanol was added. These additional surfactant effect diminished the difference between initial and final surface tension (surface tension depression) of the system and so the total water moved.

The soil organic matter (1.7%) modified the water movement curve in the presence of low (0.2g) content of 1-hexadecanol, whereas for high content of either alcohol (0.4g) or low content of 1-tetradecanol content (0.2g) the water movement curves were the same     

On the Number of Type Change Loci of a Generalized Complex Structure

In this note, we describe a procedure to construct generalized complex structures whose type change locus has arbitrarily many path components on products of the circle with a connected sum of closed 3-manifolds. As an application, we use the procedure to exhibit such geometric structures on a myriad of simply connected 4-manifolds among many others.