Study of the complexation of Cu(II) by fulvic acids extracted from a sewage sludge and its compost

 The complexation of Cu(II) by two samples of fulvic acids (FA) extracted from the raw sewage sludge (RsFA) of a waste water processing plant and from the composted sludge (CsFA) obtained upon aerobical digestion was studied at pH 6.0. Synchronous molecular fluorescence spectroscopy was used to monitor the association of FA with Cu(II) and a self-modelling mixture analysis method (SIMPLISMA) was used to preprocess the spectral data to calculate the number of components with different quenching profiles as function of the Cu(II) concentration and their spectra. The stability constants and a rough estimation of the binding site concentrations were obtained by a Stern-Volmer analysis, by a non-linear least-square method and by a linear procedure. The analysis of the SyF spectra allowed the identification of two binding sites for both samples. The logarithm of the conditional stability constant corresponding to the 1:1 complex formed between the stronger binding site and Cu(II) is about 4 for both samples. Received: 22 April 1996 / Revised: 5 August 1996 / Accepted: 7 August 1996     

Radioactivity levels in peloids used in main Cuban spas

In this work, an approach for determining both the outer dead layer thickness of the p-type coaxial HPGe detector and the inner dead layer thickness of the n-type coaxial HPGe detector was proposed by using two full energy peak area count ratios of a X-ray and a gamma ray emitted from the same radioisotope of ¹³⁷Cs. Monte Carlo calculations and experimental measurements were conducted to determine these dead layer thicknesses. The results showed that the outer dead layer thickness reached 0.57 ± 0.03 mm on 06 Jan 2017 after nearly 3 years of use for the p-type detector. The inner dead layer thickness reached 1.21 ± 0.24 mm on 01 Aug 2016 after more than 3 years of operation for the n-type detector. Simulation model with the modified dead layer thicknesses was used to estimate full energy peak efficiencies and gamma spectra from seven radioactive sources. The results were in good agreement with the corresponding experimental values in the gamma energy region of interest.     

Catalytic alkylation of phenol with methanol over zinc aluminate

Two samples (A and B) of zinc aluminate spinel were prepared and used as catalysts of phenol methylation. Both catalysts were synthesised at hydrothermal conditions from zinc acetate and from various aluminium precursors: aluminium isopropoxide (catalyst A) or basic aluminium nitrate (catalyst B). Catalyst A was pure ZnAl₂O₄ and B - besides ZnAl₂O4 contained traces of -Al₂O₃. Reactions of phenol alkylation with methanol were carried out in the gas phase under atmospheric pressure in a standard flow reactor with fixed bed. Catalysts indicated different properties in dependence on the aluminium precursor used during preparation. In the presence of catalyst A higher selectivity of ortho-methylation of phenol was obtained. Catalyst B was active both in O-alkylation and C-alkylation.     

Solubility of Propene in Water and in a Mineral Medium for the Cultivation of a XanthobacterStrain

Solubility measurements of propene in water at atmospheric pressure and at thirteen temperatures in the range 293.15–323.15 K were carried out with a precision of 0.3%, using an apparatus based on the saturation method. The mole fractions, at a gas partial pressure of 101.325 kPa, were fitted to a Clarke–Glew–Weiss equation, which was used to calculate the standard molar Gibbs energy, enthalpy, and entropy changes for the process of transferring the propene molecules from the gaseous to the water phase. Solubility measurements of propene in the growth medium ofXanthobacter Py2 at 298.15, 303.15, and 308.15 K were also carried out at atmospheric pressure. These experimental data, expressed in Ostwald coefficients at the total pressure of 101.325 kPa, were about 2% lower than their water counterparts.     

Spectrophotometric studies on complex formation in dilute benzene solutions of [{Rh(diene)(μ–Cl)}2]–PR3–SnCl2 systems

There is no correlation between the stability of complexes formed in dilute solutions of [{Rh(diene)(–Cl)}2]–PR3–SnCl2 systems [with ligand combinations cod+PPh3, nbd+PPh3, cod+PPhMe2 and cod+ PCy3 (Cy=cyclohexyl)] and the possibility of isolating them as solids. In general, high dilution favours the formation of pentacoordinate complexes that decompose upon attempted crystallization. [RhCl(cod)(PPhMe2)2], [Rh(SnCl3)(cod)(PPh3)2], [Rh(SnCl3)(cod)(PCy3)2], [Rh(SnCl3)(cod)(PPhMe2)2] and [Rh(SnCl3)(nbd)(PPh3)2] have been identified in solution, but only the last two, previously known, have been isolated in the solid state. The steric properties of the coordinated phosphine seem to be the most important factor in determining the stabilities of [RhCl(diene)(PR3)2] complexes, whilst in the case of [Rh(SnCl3)(diene)(PR3)2] complexes the steric properties of the phosphine and the diene appear to have similar importance.     

Mass spectrometic study of speciation in aluminium-fluoroquinolone solutions

Fluoroquinolones (FQLs) are synthetic antibacterial agents containing a 4-oxo-1,4-dihydroquinoline skeleton. When concomintantly administered with other drugs which may contain metal ions, particularly Al(3+) (antacids, phosphate binders, vaccines etc) they may form metal-drug complexes. Pharmacokinetic studies showed that aluminium-quinolone interactions lead to reduced bio- availability and altered activity of the drug with possible development of the toxic effects of aluminum ion. Reliable speciation in Al(3+) - quinolone systems at micromolar concentration level is needed to better understand pharmaco- and toxicokinetics of the FQLs in the presence of Al. In this work, the speciation in solutions containing Al(3+) and FQL family members (fleroxacin, moxifloxacin and ciprofloxacin) was studied by electrospray mass spectrometry (ESI-MS), ESI-MS/MS, and laser desorption ionization (LDI) MS. The dominating species identified in all the three Al(3+)-FQL solutions, at ca 30-50 μmol L(-1) total Al concentration and 2:1 to 1:3 metal-to-ligand ratio in the pH range 3.0- 6.0, were the ions related to the complexes AlL(2+), AlL(2)(+) and AlL(3)(0) (L = ligand in the monodeprotonated form). Mixed protonated and hydroxo complexes were also formed at lower and higher pH values respectively and, as expected, dimeric and polymeric species were not observed in ESI spectra. LDI measurements confirmed the existence of the mononuclear complexes found by ESI, and indicated the formation of polymeric species. The ion [2Al(3+) +5(-)](+) was identified with all three FQLs. This ionic species most probably arises from Al(2)L(2) by clustering with free ligand anions. Comparison of literature potentiometric data with mass spectral data indicated good agreement between speciation schemes. The obtained results suggest the presence of strong interaction between FQLs and Al(3+) which may be important in affecting absorption of these drugs in the gastrointestinal tract.     

On Extreme Regression Quantiles

Smith (1994) introduced the idea of extreme regression quantiles and he developed some asymptotic results for algebraically tailed error distributions. The results provided a close analogy to standard extreme value theory for one-sample extremes. Here we obtain the following generalizations. First, an extreme value distribution theory is developed in the exponentially tailed case, where the extreme slope estimates need not diverge to infinity and may actually be consistent. The design conditions of Smith (1994) are also generalized. Second, the tail behavior measure of Jureckova´ (1981) and He et al. (1990) is considered for extreme quantiles. For algebraically tailed error distributions, the average right extreme regression fit acts like a one-sample right extreme; while in the exponentially tailed case, the tail behavior is more like that of a slightly more central order statistic.