Synthesis of Laurylchitosan and Its Use in the Separation of Flavonoids from Aleurites moluccana by Matrix Solid-Phase Dispersion

Chitosan was modified with lauroyl chloride to prepare a solid support for the application of matrix solid-phase dispersion (MSPD) for the extraction of flavonoids from the medicinal plant Aleurites moluccana. The laurylchitosan prepared by the homogenous and heterogeneous method, was characterized using analytical methods such as potentiometric titration and infrared spectroscopy. The hydrophobic properties were studied by naphthalene incorporation. The MSPD performance was evaluated by extraction of swertisin and 2″-O-rhamnosylswertisin from the leaves of A. moluccana.     

Poly(caprolactone triol) as plasticizer agent for cellulose acetate films: influence of the preparation procedure and plasticizer content on the physico‐chemical properties

The influence of the plasticizer content and film preparation procedure on the morphology, density, thermal and mechanical properties of cellulose acetate (CA) films plasticized with poly‐(caprolactone triol) (PCL‐T), were studied. Differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), scanning electron microscopy (SEM), wide‐angle X‐ray diffraction (WAXD) and infrared spectroscopy (FT‐IR) techniques were used. The films were prepared by dry‐casting CA and CA/PCL‐T in acetone or acetone/water solutions, which produced transparent and opaque films, respectively. In contrast to the transparent films, which were dense, the opaque films presented a porous morphology. However, the presence of PCL‐T reduced the opaque film porosity, increasing, in consequence, its bulk density. The TMA results revealed that PCL‐T reduced the glass transition temperature more significantly in the transparent than in opaque films. Only the transparent CA/PCL‐T films presented a melting temperature, that reduced with higher concentrations of PCL‐T, suggesting a higher ordering (crystallinity) when the films were prepared in the absence of water, as observed from WAXD curves. The mechanical properties also showed that the transparent films were more soft and tough than the opaque films. In summary, PCL‐T was a good plasticizer agent for CA films due to the presence of hydrogen bonds between the components (FT‐IR spectra). The presence of water in the dry casting process has a significant effect mainly on film morphology and mechanical properties. Copyright © 2004 John Wiley & Sons, Ltd.     

A new enantioselective synthesis of the four stereoisomers of pallantione,the male-produced sex pheromone of Pallantia macunaima (Heteroptera: Pentatomidae)

In a previous study we reported the identification of the first ketone found in the Pentatomidae family, the sex attractant pheromone of the male stink bug Pallantia macunaima, (6R,10S)-6,10,13-trimethyltetradecan-2-one. Here we describe an efficient enantioselective route for the synthesis of the four stereoisomers of this pheromone. The synthesis was conceived as the connection of two chiral building blocks, employing (R)- or (S)-citronellol and methyl (S)-3-hydroxy-2-methylpropionate as the source of chirality.     

Titration calorimetric determination of the pairwise interaction parameters of glycerol,D-threitol,mannitol, and D-glucitol in dilute aqueous solutions

Enthalpic pairwise interaction parameters, h_jj, were determined by titration calorimetry at 25°C for dilute solutions of glycerol, D-threitol, manitol, and D-glucitol in water. The parameters for these and other polyols conform to the expression h_jj (J-kg^–1)=145+135n_OH–21.5n _OH ² –41.7 _dl ² -160.5n_dlld, where n_OH=n_C is the number of hydroxyl groups (carbon atoms), n_dl is the number of dl configuration of a vicinal pair of OH-groups, and n_dlld is the number of such configurations in the polyol molecules. A rationalization of this expression is given.     

Spectrophotometric investigation of the reaction of CU(II) and Cu(I) with 1-isonitroso-(1,2,3,4)-tetrahydrophenazine

The reactions of Cu(II) and Cu(I) with 1-isonitroso-(1,2,3,4)-tetrahydrophenazine (HITF) have been studied spectrophotometrically. Both ions form complexes with metal/ligand ratio 1:2. The complex of Cu(I) and ITF can be used for copper determination in the range 2-50 x 10(-6)M, and has been separated as the perchlorate in crystalline form. The spectrophotometric characteristics and the equilibrium constants for the ligand and for the complexes are reported.     

Determination of Nickel in Fuel Ethanol Using a Carbon Paste Modified Electrode Containing Dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 × 10⁻⁹ mol L⁻¹ and 5.2 × 10⁸ μA mol⁻¹ L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 × 10⁻⁸ to 6.9 × 10⁻⁸ mol L⁻¹. A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.     

Methomyl Detection by Inhibition of Laccase Using a Carbon Ceramic Biosensor

A sol–gel derived carbon ceramic biosensor was used for methomyl determination in vegetable extract samples based on the immobilization of laccase from Aspergillus oryzae. Esculetin was chosen as the substrate for laccase in order to measure inhibition by this pesticide. The analytical curve was linear for methomyl concentrations of 0.5 to 12.2 µM with a detection limit of 0.2 µM. The lifetime of the proposed biosensor was 60 days and the recovery from vegetable extract samples ranged from 98.0 to 104.2 %. The results using the proposed method are in agreement with those using HPLC at the 95 % confidence level.     

A Simple Hysteretic Constitutive Model for Unsaturated Flow

The present study covers the problem of rotation of a porous disk under a viscous incompressible fluid that fills the half-space above the disk, which is the generalization of the von Karman’s problem. It is found that, instead of solving the exact problem, which is rather complicated by coupling the motions of the free fluid and that contained inside the permeable disk, it is sufficient to solve a much simpler problem of the motion of the free fluid placed onto a permeable plane. Assuming the flow in the permeable disk is described by the Brinkman equations, we obtain a self-similar formulation of the problem. Employing this formulation, we also show that the boundary condition associated with continuity of the tangential strains and tangential velocity components is satisfied at the fluid–porous body interface. The coefficient for the vertical velocity component is furthermore obtained. Various extreme cases are identified.     

On the nuclearity of integral operators

Let X be a nonempty measurable subset of and consider the restriction of the usual Lebesgue measure σ of to X. Under the assumption that the intersection of X with every open ball of has positive measure, we find necessary and sufficient conditions on a L²(X)-positive definite kernel in order that the associated integral operator be nuclear. Taken nuclearity for granted, formulas for the trace of the operator are derived. Some of the results are re-analyzed when K is just an element of .      

The role of the carboxylate head group in the interaction of sodium dodecanoate with poly(ethylene oxide) investigated by electrical conductivity, viscosity, and aggregation number measurements

The binding of sodium dodecanoate (SDoD) to poly(ethylene oxide) (PEO) in aqueous solution was investigated and compared with the well-known polymer-surfactant complexes formed between PEO and sodium dodecyl sulfate (SDS). Electrical conductivity measurements indicated that the concentration ratio of bound SDoD to PEO (on monomer basis) was greater than that for the system PEO-SDS. However, the aggregation numbers of the micelles supported on the polymer chain are practically constant and similar for both surfactants at concentrations lower than the polymer saturation point. The difference in binding capability is explained in terms of a larger PEO coil expansion upon complexation of SDoD than in the case of SDS. An increase in the polymer surface favors the binding of SDoD to PEO in aqueous solution. This conclusion is supported by the results of the viscometric studies of PEO-surfactant solution.