The genus Machaerium (Fabaceae): taxonomy,phytochemistry, traditional uses and biological activities

Machaerium, in the family Fabaceae, predominantly is a genus of a Neotropical distribution of trees, shrubs, and lianas occurring from southern Mexico to Brazil and northern Argentina and as far as South America. Several Machaerium species are widely used in traditional medicine and are considered to have multiple medicinal properties. This review aims to provide up-to-date and comprehensive information on the taxonomy, phytochemistry, traditional uses and biological activities of plants in the genus Machaerium.     

Electrochemical synthesis and characterization of thiophene conducting polymer in aqueous micellar medium

In opposite with the usually applied synthesis in organic media, the polymerization of bithiophene in aqueous media has been studied. The use of a non-ionic surfactant (polyoxyethylene octyl phenyl ether (Triton X-100)) is useful not only to solubilize the hydrophobic monomer but it is also important to incorporate various—biologically and catalytically active—additives. In this paper, the optimization of the polymerization conditions as well as the characterization of the electrochemical, spectral and mass exchange behavior of these composite films is summarized. The layers have shown imperceptible electroactivity in monomer-free aqueous LiClO₄ solutions, and electrochemical quartz crystal microbalance (EQCM) studies exhibited scarce ion movements, caused assumingly by the fact that the dopant species—moving together with their hydrate shell in the aqueous media—could not penetrate into the hydrophobic film. In contrast, nice reversible redox transformation could be obtained in organic medium such as acetonitrile, where—according to the EQCM results—the charge carrier formation/depletion is accompanied by the incorporation/removal of ClO₄ ^? anions. In this solution, the spectral changes have proved the transformation into the conducting state, connected to both mono- and di-cation forms. The incorporation of the surfactant has been demonstrated by the extraordinary surface morphology of the polybithiophene (pBT) films, characterized by scanning electron microscopy. The elementary composition of the curious shell-shaped objects, monitored by energy dispersive X-ray spectroscopy (EDX), evidenced the presence of Triton X-100 by the increased C/S ratio compared to neat polybithiophene, while the Cl/S data reflected the changes connected to the doping level as a consequence of ClO₄ ^? anion movements. Moreover, ex situ attenuated total reflectance (ATR) FT–IR measurements clearly showed the existence of C―O bonds, also proving the successful functionalization by the surfactant, built permanently into the redox active films.     

Resonant frequencies in an elevated spherical container partially filled with water: FEM and measurement

In this paper, a numerical-experimental study of the overall dynamical response of elevated spherical tanks subjected to horizontal base motion is presented. The main objective is to gain insight in the physical response of this particular structural typology widely used in the petrochemical industry as liquefied petroleum gas (LPG) containers. In order to identify the natural frequencies of the modes that mainly contribute to the response, experimental free vibration tests on an elevated spherical tank model for different liquid levels were carried out. Next, a numerical model that takes into account the coupling between fluid and structure was developed and validated against the experimental results. A very good agreement between experimental and numerical results was obtained. The results obtained show the influence of liquid levels on natural frequencies and indicate that the sloshing has a significant effect on the dynamical characteristics of the analyzed system. In order to obtain a good representation of the overall dynamical behaviour of the system by means of a simplified lumped mass model, a minimum of three masses is suggested. Finally, appropriate names of these three masses are proposed in the present paper.     

Competitive Potentiometric Study of a Series of 18-crown-6 with Some Alkali and Alkaline Earth Metal Ions in Methanol Using an Ag+/Ag Electrode

The complexation of some alkali and alkaline earth cations with18-crown-6(18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexyl-18-crown-6 (DCY18C6), and dibenzopyridino-18-crown-6 (DBPY18C6) in a methanol solution has been studied by a competitive potentiometric titration using Ag⁺/Ag electrode as a probe. The stoichiometry and stability constants of the resulting complexes have been evaluated by the MINIQUAD program. The stoichiometry for all resulting complexes was 1:1. The order of stability of Ag⁺ complexes with desired crown ethers varied as DBPY18C6 > DCY18C6 > 18C6 > DB18C6.The stability of the resulting complexes for each of these crown ethers varies in the order ofK⁺ > Na⁺ and Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺.For each of the used metal ions the major sequence of the stability constants of the resulting complexes varies as DCY18C6 > 18C6 > DB18C6 > DBPY18C6 with minor exceptions.     

1,3–Dichloro‐5,5–Dimethylhydantoin (DCH) and Trichloromelamine (TCM) as Efficient Catalysts for the Chemoselective Trimethylsilylation of Hydroxyl Group with 1,1,1,3,3,3–Hexamethyldisilazane (HMDS) Under Mild Conditions

A highly convenient method for the trimethylsilylation of alcohols and phenols via treatment by hexamethyldisilazane in the presence of 1,3–dichloro‐5,5–dimethylhydantoin (DCH) and/or trichloromelamine (TCM) as a catalyst has been developed. A wide variety of hydroxyl groups were selectively protected in CH₂Cl₂/CH₃CN under mild conditions.     

Aqueous NaHSO4 catalyzed regioselective and versatile synthesis of 2-thiazolamines

The green acidic catalyst NaHSO₄ was used for the synthesis of some novel substituted 2-thiazolamines in water under mild conditions in high regioselectivity. Correspondence: Shahnaz Rostamizadeh, Department of Chemistry, Faculty of Sciences, K.N. Toosi University of Technology, P. O. Box: 15875-4416, Tehran, Iran.     

An improved hybrid continuum‐atomistic four‐way coupled model for electrokinetics in nanofluidics

In this study, an efficient hybrid continuum‐atomistic method is proposed to study electrokinetic transport of aqueous solutions in nanofluidics. The aqueous phase is considered as a continuous phase containing immersed ion particles. The behavior of the system is then simulated through utilization of an improved hybrid continuum‐atomistic four‐way coupled approach, including the MultiPhase Particle‐In‐Cell method for the short‐ranged interaction between the ion particles, the Brownian force for the collision between the aqueous phase molecules and the ion particles, and a wall force accounting for the short‐ranged interaction of ions and walls. The validation of the proposed model with the results of Molecular Dynamics simulations suggests that this model can be a promising approach for studying the electrokinetic phenomena in more complicated geometries where the Molecular Dynamics approach is computationally prohibitive. Finally, the effects of electrokinetic parameters, such as the height of the channel, the external electric field, and bulk ionic concentration, on the electroosmotic flow in a nanochannel are investigated and discussed.     

Crystal structure and molecular stereochemistry of polymeric Cu2(DMP)4(DMSO) as a platform for phosphate diester binding

Treatment of a solution of CuCl₂ in dimethyl phosphate (DMP) in an inert solvent under nitrogen atmosphere resulted in a light blue fluorescence powder. Slow evaporation of H₂O‐DMSO solution of this powder led to the formation of blue‐sky crystals of a new polymeric Cu(II) complex, with a unit cell composed of Cu₂(DMP)₄(DMSO), (1). The crystal and molecular structure of the complex was established crystallographically. Compound (1) crystallizes in the monoclinic space group P2₁/n with a = 12.8920(11)Å, b = 13.1966(11)Å, c = 14.7926(13)Å, α = 90°, β = 98.943(2)°, γ = 90° and Z = 4. A square pyramidal environment for the metal center is established by coordination of oxygen atoms of four bridging DMP ligands in the basal positions and a tri‐centered oxygen atom of DMSO in the apical disposition. The sixth position is also affected by a weak interaction with the sulfur atom of DMSO. The phosphorous atom in the bridging DMP is arranged in a deformed tetrahedron with gg conformation for methyl esters with C_2v symmetry. Accordingly, the angles of methoxy substituents are unexpectedly smaller than the bridging oxygens, and synchronous z‐in and z‐out distortions are suggested for DMP anion. The oxygen atom of SOCuCu’ fragment derived from DMSO, functions as a tri‐centered nuclei lie almost in a trigonal triangle environment. This study helps provide further insights into the binding nature of phosphate esters to the active sites of enzymes, which catalyze phosphoryl transfer reactions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)