A Novel Method for Permeability Estimation from Micro-tomographic Images

Transport in Porous Media - A methodology has been developed to create a pore network model (PNM) from the geometrical/topological information extracted from the micro-tomographic images of a...     

Redox behavior of juglone in buffered aq.: Ethanol media

The present work reports the redox mechanism of 5-hydroxynaphthalene-1,4-dione (HND), commonly known as juglone, in buffered aqueous media having 50% of ethanol. HND followed different mechanistic routes depending upon the pH of the media and more than one pK_a were evaluated from the changes in the slope of the E_p vs. pH plot. The change of pH from acidic to neutral conditions was found to switch the mechanism from CEC to EE mechanism. Pulse techniques were utilized to determine the number of electrons involved in the oxidation and/or the reduction step and to ensure the nature of the redox process. Based upon the obtained results, an electrode reaction mechanism was proposed. Computational studies of HND supported the experimental results. UV-Visible spectroscopy was also employed for the detailed characterization of the compound in a wide range of pH and for the determination of its pK_a.     

Structural studies on cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) complexes of 1-malonyl-bis(4-phenylthiosemicarbazide)

Summary Several new complexes of the title ligand (H₂MPTS) with Co^II, Ni^II, Cu^II, and Cd^II have been prepared. Structural assignments of the complexes have been made based on elemental analysis, molar conductivity, magnetic moment and spectral (i.r.,¹H n.m.r., reflectance) studies. The compounds are non-conductors in dimethylsulphoxide. The neutral molecule is coordinated to the metal(II) sulphate as a bidentate ligandvia the two carbonyl groups. The ligand reacts with the metal(II) chlorides with the liberation of two hydrogen ions, behaving as a bianionic quadridentate (NONO) donor. Enolization is confirmed by the pH-titration of H₂ MPTS and its metal(II) complexes against NaOH. A distorted octahedral structure is proposed for the Cu^II complex, while a square planar structure is suggested for both Co^II and Ni^II complexes. The stoichiometry of the complexes formed in EtOH and buffer solutions, their apparent formation constants and the ranges for obedience to Beer's law are reported for Co^II, Ni^II and Cu^II ions. The ligand pK values are calculated. The antimicrobial activity of H₂ MPTS and its Co^II, Ni^II, Cu^II and Mn^II complexes is demonstrated.     

Sodium Bromide Catalysed Regioselective Cleavage of Oxitanes with Chlorotrimethylsilane

Sodium bromide efficiently catalyses the regioselective cleavage of oxiranes with chlorotrimethylsilane to the corresponding O-silylated chlorohydrins in excellent yields.     

Solitary waves for the perturbed nonlinear Klein–Gordon equation

In this work, we study the perturbed nonlinear Klein–Gordon equation. We shall use the sech-ansätze method to derive the solitary wave solutions of this equation.     

Determination of histidine and related compounds in rumen fluid by liquid chromatography

A liquid chromatographic procedure was developed for quantitative determination of histidine (His), histidinol (HDL), histamine (HTM), urocanic acid (URA), imidazolepyruvic acid (ImPA), imidazoleacetic acid (ImAA), and imidazolelactic acid (ImLA) in rumen fluid. The method is based on direct injection analysis by UV absorbance detection at 220 nm. The separation was performed under 2 different chromatographic conditions on a LiChrospher 100 NH2 column. In the first chromatographic system, the mobile phase used for isocratic elution was 67 mM potassium phosphate buffer (monobasic and dibasic) pH 6.45-90% acetonitrile in water (21 + 79); in the second system, an acetonitrile gradient in 63 mM potassium phosphate buffer (monobasic) pH 3.0, obtained by addition of 60 mM phosphoric acid, was used. Analyses of both systems were completed within 32 and 25 min, respectively. The limits of detection of these compounds were (microM): His, 2.8; HDL, 3.7; HTM, 4.0; URA, 0.75; ImPA, 4.7; ImAA, 1.2; and ImLA, 1.3. Recovery of these compounds added to rumen fluid was 97.4-103.0% within a 1-day study and 95.4-99.0% on different day studies. Detectable levels of His were found in the deproteinized rumen fluid of goats, with average concentrations of 16.10, 10.43, 11.14, and 13.62 microM in the rumen fluid collected before the morning feeding and 2, 4, and 6 h after feeding, respectively. HDL, HTM, URA, ImPA, ImAA, and ImLA were not detected in the rumen fluid before and after feeding. Trp, Phe, and Tyr were also identified in the rumen fluid, with average concentrations of 8.25, 29.04, and 12.6 microM, respectively, before the morning feeding.     

Normal bases via general Gauss periods

Gauss periods have been used successfully as a tool for constructing normal bases in finite fields. Starting from a primitive th root of unity, one obtains under certain conditions a normal basis for over , where is a prime and for some integer . We generalize this construction by allowing arbitrary integers with , and find in many cases smaller values of than is possible with the previously known approach.

     

Heterocyclic compounds. XI. Potential post-coital antifertility agents

A series of heterocyclic analogs of diarylethylene and triarylethylene were synthesized as potential anti-implantation agents. Tested in rats as oral, post-coital antifertilily agents, a few of our compounds showed some activity.     

New enantiomeric polylactide-block-poly(butylene succinate)-block-polylactides: syntheses, characterization and in situ self-assembly

In situ self-assemblies of new biodegradable triblock PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA have been investigated in acetonitrile solution. At first, two series of PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA, respectively denoted as the P and Q triblock copolyester series, were prepared with fixed PBS block ((overline) M(n,NMR) = 6.9 kDa) and diverse enantiomeric PLLA/PDLA blocks. Further, their chemical structures and thermal properties were characterized by means of titration, nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), polarimeter, wide-angle X-ray diffraction (WAXD) and thermal analytical instruments. When mixing the synthesized enantiomeric copolyester pairs denoted as P(1)/Q(1) - P(8)/Q(8) in acetonitrile solution at 60 degrees C, in situ self-assemblies were found to happen for the P(4)/Q(4) to P(8)/Q(8) pairs, bearing longer enantiomeric PLA block lengths. DSC and WAXD analysis of the self-assembled microparticles demonstrated that PLLA/PDLA racemic crystals were formed for the P(5)/Q(5) - P(8)/Q(8) systems, as evidenced by their melting points over 200 degrees C, and a new X-ray diffraction peak detected at 2theta = 11.8 degrees . Moreover, morphological studies by scanning electron microscopy (SEM) indicated the formation of disk- or platelet-like microparticles. It was noted that the diameters of the microparticles self-assembled in situ decreased from 1.28-1.50 mum down to 480-660 nm, through tailoring the enantiomeric PLA block length. Other factors, such as a central PBS block, the enantiomeric block length and the preparation conditions were suggested to play important roles in the in situ self-assembly of these enantiomeric triblock copolyesters. These results provide a facile way to self-assemble hydrophobic, biodegradable microparticles, through tuning the important van der Waals stereocomplexation interactions between two enantiomeric blocks in solution.