Kinetics of formation and dissociation of lanthanide(III) complexes with the 13-membered macrocyclic ligand TRITA4-

The tetraazamacrocyclic ligand TRITA(4-) is intermediate in size between the widely studied and medically used 12-membered DOTA(4-) and the 14-membered TETA(4-). The kinetic inertness of GdTRITA(-) was characterized by the rates of exchange reactions with Zn(2+) and Eu(3+). In the Zn(2+) exchange, a second order [H(+)] dependence was found for the pseudo-first-order rate constant (k(0)=(4.2 +/- 0.5) x 10(-7) s(-1); k'=(3.5 +/- 0.3) x 10(-1) M(-1)s(-1), k" =(1.4 +/- 0.4) x 10(3) M(-2)s(-1)). In the Eu(3+) exchange, at pH <5 the rate decreases with increasing concentration of the exchanging ion, which can be accounted for by the transitional formation of dinuclear GdTRITAEu(2+) species. At physiological pH, the kinetic inertness of GdTRITA(-) is considerably lower than that of GdDOTA(-)(t(1/2)= 444 h (25 degrees C) vs. 3.8 x 10(5) h (37 degrees C), respectively). However, GdTRITA(-) is still kinetically more inert than GdDTPA(2-), the most commonly used MRI contrast agent (t(1/2)= 127 h). The formation reactions of LnTRITA(-) complexes (Ln = Ce, Gd and Yb) proceed via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH(-) catalyzed process. The stability of the LnH(2)TRITA* intermediates (log K(LnH2L*)= 3.1-3.9) is lower than that of the DOTA-analogues. The rate constants of the OH(-) catalyzed step increase with decreasing lanthanide ion size, and are about twice as high as for DOTA-complexes.     

Structure and antiferroelectric properties of cesium niobate, Cs2Nb4O11

The compound cesium niobate, Cs₂Nb₄O₁₁, is an antiferroelectric, as demonstrated by double hysteresis loops in the electric field versus polarization plot. The crystal structure refinement by X-ray diffraction at both 100 and 297 K shows it to have a centrosymmetric structure in point group mmm and orthorhombic space group Pnna, which is consistent with its antiferroelectric behavior. The 100-K structure data is reported herein. The lattice is comprised of niobium-centered tetrahedra and octahedra connected through shared vertices and edges; cesium atoms occupy channels afforded by the three-dimensional polyhedral network. Antiferroelectricity is produced by antiparallel displacements of niobium atoms along the c-axis at the phase transition temperature of 165 °C. The critical field for onset of ferroelectric behavior in a single-crystal sample is 9.5 kV/cm at room temperature.     

Determining consanguinity by oligonucleotide fingerprinting with (GTG)5/(CAC)5

Simple tandemly organized (GTG)n/(CAC)n sequences are spread throughout the human chromosomes. The most informative DNA fingerprints for the testing of pedigrees and/or paternity were obtained with the simple triplet repeat probe (GTG)5 or its complement (CAC)5. These hypervariable simple-repeat fragments are stably inherited in a Mendelian fashion. Using these highly discriminating probes, all human individuals could, theoretically, be differentiated, except for genetically identical monozygotic twins. Examples from actual case work are reported and pertinent advantages of this methodology are discussed.     

Determination of uranium by XRF analysis following its preconcentration with some organic precipitants

The determination of uranium in natural waters by XRF analysis after its preconcentration with some organic precipitants is described.¹⁰⁹Cd source is used for the excitation of L-series X-rays of uranium. Separation yield, kinetics of coprecipitation and the possibility of preparing thin-layer samples for XRF analysis were studied in detail for uranium concentration with α-nitroso-β-naphtol, methylene blue with ammonium thiocyanate, tannin with urotropine and other precipitants. A procedure using coprecipitation of uranium with α-nitroso-β-naphtol from 500 ml samples of surface or waste, waters is proposed.     

Etude de la reactivite d'ylures de sulfonium et de pyridinium stabilises par un groupement cyanoformyle

The sulfonium and pyridinium ylides stabilized by a cyanoformyl group, in an acidic medium, lead to sulfonium and pyridinium salts which are equivalents of pyridinium or sulfonium ketene salts. This originality has been used to prepare new stabilized ylides, or derivatives of substituted arylacetic acids or 4-hydroxy thiazoles.     

Molecular Structures from Density Functional Calculations with Simulated Annealing

The geometrical structure of any aggregate of atoms is one of its basic properties and, in principle, straightforward to predict. One chooses a structure, determines the total energy E of the system of electrons and ions, and repeats the calculation for all possible geometries. The ground state structure is that with the lowest energy. A quantum mechanical calculation of the exact wave function Ψ would lead to the total energy, but this is practicable only in very small molecules. Furthermore, the number of local minima in the energy surface increases dramatically with increasing molecular size. While traditional ab initio methods have had many impressive successes, these difficulties have meant that they have focused on systems with relatively few local minima, or have used experiment or experience to limit the range of geometries studied. On the other hand, calculations for much larger molecules and extended systems are often forced to use simplifying assumptions about the interatomic forces that limit their predictive capability. The approach described here avoids both of these extremes: Total energies of predictive value are calculated without using semi-empirical force laws, and the problem of multiple minima in the energy surface is addressed. The density functional formalism, with a local density approximation for the exchange-correlation energy, allows one to calculate the total energy for a given geometry in an efficient, if approximate, manner. Calculations for heavier elements are not significantly more difficult than for those in the first row and provide an ideal way to study bonding trends. When coupled with finite-temperature molecular dynamics, this formalism can avoid many of the energetically unfavorable minima in the energy surface. We show here that the method leads to surprising and exciting results.     

Kinetic determination of tellurium based on its inhibitory effect on the palladium(II)-catalysed reaction between pyronine G and hypophosphite ion

A kinetic method for the determination of Te based on its inhibitory effect on the PdII-catalysed reaction between pyronine G and H2PO2- is described. The influence of experimental variables on the rate of the process and the potential interfering effect of a large number of ions has been studied. Under the selected experimental conditions: 6 x 10(-5) M pyronine G; 0.6 M H2PO2-; pH 2.6, adjusted with Britton-Robinson buffer; 0.80 microgram ml-1 of PdII; and a temperature of 22 +/- 0.2 degrees C, Te was determined in the concentration range 0.08-0.85 microgram ml-1. The method was applied to the determination of Te in waters and lead concentrates.     

Spectrophotometric determination of boron with an azomethine H derivative

Summary An azomethine H derivative, 1-(2,4-dihydroxybenzylidene-amino)-8-hydroxynaphthalene-3,6-disulphonic acid (azomethine HR) was examined and proposed as a spectrophotometric reagent for boron, as compared with azomethine H. Azomethine HR reacts with boron in aqueous solution (pH 7.5) to form a yellow complex having an absorption maximum at 425 nm. The sensitivity is 3.5-fold greater than with azomethine H when the same reagent concentration is applied. Basic conditions for the determination of boron have been worked out. The method is applicable to sea and hot spring waters. The standard deviation is ±2.1%.

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Spektralphotometrische Borbestimmung mit einem Azomethin H-Derivat

     

The determination of vanadium,molybdenum and tungsten by infrared spectroscopy

The infrared spectra of the 8-hydroxyquinolinates of molybdenum, vanadium and tungsten in the region 3–15 μ were investigated. It was found possible to determine the elements quantitatively, singly or in pairs, with an error of about 3%. Molybdenum was determined at 10.80 μ and 10.93 μ, vanadium at 10.50 μ, and tungsten at 10.61 μ or 10.90 μ.     

Effects of <Emphasis Type="Italic">L</Emphasis>-Carnitine on Sucrose-Induced Hyperlipidaemia

Summary. L-Carnitine, L-(−)-β-hydroxy-γ-trimethylaminobutyrate, plays an important role as a factor necessary for the transport of long-chain fatty acids into the mitochondria. In order to investigate the influence of L-carnitine on hyperlipidaemias, the experimental model of the sucrose-induced hypertriglyceridaemia of the rat was used. In these experiments L-carnitine in the dose of 11 mg per day and 100 g body weight (over the period of 1 week) was able to antagonize the sucrose-induced hypertriglyceridaemia and the increase of serum free fatty acid level in female rats of the Wistar strain. Carnitine administration did not change the activities of lipogenic enzymes and fatty acid synthesis in the liver. However, L-carnitine increases the rate of hepatic fatty acid oxidation. Our results indicate a hypotriglyceridemic and free fatty acid lowering effect of L-carnitine, and suggest the use of this compound in the therapy of hyperlipidaemias.