Peroxide derivatives of molybdenum(VI) in neutral and alkaline media

Summary The peroxidation of molybdenum(VI) was investigated in neutral and alkaline media. The stability constants of the peroxo complexes were determined by spectrophotometric measurement as (9.12±0.67)×10^–7, (2.68±0.17) ×10⁵, (1.26±0.06)×10⁶ and (1.58±0.02) for the 11, 21 (yellow), 31 and 41 (red) species. The diperoxomolybdate disproportionates into the tetraperoxo derivative when treated with alkali. Formation of the tetraperoxo complex was found to be pH dependent according to a curve, with maximum at pH 10. Acidification of tetraperoxomolybdate solution results in the regeneration of hydrogen peroxide and the diperoxo complex is reformed.     

Composite Ferric Oxyhydroxide-Containing Phases Formed in Neutral Aqueous Solutions of Tryptophan and Indole-3-Acetic Acid

Mössbauer, FTIR and XRD analyses showed that in aqueous medium in air in the presence of L-tryptophan (Trp) or indole-3-acetic acid (IAA) the ambient-temperature ageing of the precipitates formed from ferrous sulphate at pH7 gave composite phases with varying proportions of -FeOOH (a dominating crystalline phase), -FeOOH (both fine-grained, showing superparamagnetic behaviour at 298 K, and relatively better crystallized) and amorphous ferric hydroxide. The experimental data suggested a competition for adsorption sites at the oxyhydroxide surface in the suspension during phase transformations, as well as the transformation of -FeOOH (and/or amorphous ferric hydroxide) to -FeOOH via the dissolution-reprecipitation mechanism. The formation of certain ferric oxyhydroxide phases in the presence of Trp and IAA — released e.g., in the course of bacterial and plant metabolism — can contribute to the regulation of soil mineral composition.     

Some diels—alder reactions of η1-bonded cyclopentadienylmetal compounds

Bis(cyclopentadienyl)mercury readily undergoes Diels—Alder reactions with RCCR (R = CO₂Me or CF₃), CF₃CFCFCF₃, CF₃CFCF₂, (CF₃)₂CC(CN)₂, C₂(CN)₄ and Ph$\text{NCONNC}$O to give stable adducts characterised by¹H, ¹⁹F and ¹³C NMR, spectroscopy. Similar reactions of CF₃CCCF₃ and CF₃CFCFCF₃ with the cyclopentadiene derivatives Me₃MC₅H₅ and (Me₃M)₂C₅H₄ (M = Si, Sn) are also described.     

Therapeutic monitoring of imipramine and desipramine by micellar liquid chromatography with direct injection and electrochemical detection

A micellar liquid chromatographic (MLC) procedure was developed for the clinical monitoring of imipramine and its active metabolite, desipramine. The determination of these highly hydrophobic substances was carried out after direct injection of the serum samples using a mobile phase composed of 0.15 m SDS--6% (v/v) pentanol buffered at pH 7, pumped at 1.5 mL/min into a C(18) column (250 x 4.6 mm), and electrochemical detection at 650 mV. Using this MLC method, calibration was linear (r > 0.995) and the limits of detection (ng/mL) were 0.34 and 0.24 for imipramine and desipramine, respectively. Repeatabilities and intermediate precision were tested at three different concentrations in the calibration range and a CV (%) below 2.2 was obtained. In this MLC procedure, the serum is determined without treatment, thus allowing repeated serial injections without changes in retention factors, and reducing the time and consumables required to carry out the pretreatment process. The assay method can be applied to the routine determination of serum imipramine and its metabolite in therapeutic drug monitoring.     

Flow-injection approach for the determination of the dynamic response characteristics of ion-selective electrodes. Part 1. Theoretical considerations

A single-line flow-injection system with a straight tube reactor is proposed for investigating the dynamic response behaviour of ion-selective electrodes. The principle of the method is based on the fact that the concentration—time curve at the electrode surface can be described theoretically in the flow-injection system under certain practically realizable conditions. The response of the ion-selective electrode to that input signal can be measured experimentally. Thus, knowing the input and the output signal of an ion-selective electrode, an appropriate model describing its dynamic behaviour can be selected among the relevant models existing in the literature. Theoretical expressions for predicting the transient response of ion-selective electrodes in the flow system when the rate-determining step is an ion-transport process through a diffusion layer or a kinetic process were elaborated.     

Mössbauer studies in thermally treated iron-samarium mixed oxide system

Mössbauer spectroscopy and X-ray diffractometry have been used to study Sm–Fe mixed oxides (with different SmFe atomic ratios) annealed at 550, 850, 1000 and 1250 °C. The room temperature Mössbauer spectra can be interpreted in terms of one, two or three sextets and in some cases by an additional doublet depending on the composition and the heat treatment. The sextets have been associated with SmFeO₃ perovskite, Sm₃Fe₅O₁₂ garnet and -Fe₂O₃ hematite. These results are in agreement with those of X-ray diffractometric measurements, which give a clear, evidence of the presence of these phases.     

A chemometric study of the simultaneous determination of calcium and magnesium in natural waters

A method for the simultaneous spectrophotometric determination of calcium and magnesium in mineral waters with an FIA system is tested. The method is based on the reaction between the analytes and arsenazo(III) at pH 8.5. The calculations of the amounts of both analytes in the samples are carried out with the H-point standard addition method (HPSAM) for ternary mixtures, and with a partial least squares (PLS) model after a proper variable selection. The results obtained for the determination of calcium were comparable using both methods. The employment of the HPSAM brings to our attention the influence of the calcium concentration in the sample to the development of the reaction between magnesium and arsenazo(III). HPSAM also permits to estimate the concentration of magnesium in the samples.     

Study of the crystallization kinetics in amorphous Fe83P17 alloy

The crystallization kinetics of Fe₈₃P₁₇ amorphous alloy has been studied by Mössbauer spectroscopy and X-ray diffractometry. The samples were annealed isothermally at two different temperatures (315 °C and 325 °C). During isothermal annealing of the samples three phases were observed: crystalline Fe₃P phase, crystalline -Fe phase and the amorphous phase. The value of the Avrami exponent was found to be about 2.0 at each annealing temperature. This suggests that the growth rate of the crystals is controlled by volume diffusion and the nucleation rate decreases during crystallization. The activation energy obtained for the overall crystallization process was 193±43 kJ mol^–1.     

Novel approach for asymmetric synthesis of fluorinated beta-amino sulfones and allylic amines

[reaction: see text] Enantiomerically pure gamma-fluoroalkyl beta-amino sulfones are readily synthesized in three steps starting from fluorinated imidoyl chlorides and arylmethyl sulfones. A complementary two-step sequence starting from chiral fluorinated beta-amino sulfoxides has also been developed. To illustrate the application of this procedure, a new method for the synthesis of alpha-fluoroalkyl allylic amines in optically pure form involving a Julia methylenation-desulfonylation reaction is presented.     

Enantioselective synthesis of 2-arylpiperidines from chiral lactams. A concise synthesis of (-)-anabasine

Cyclodehydration of achiral or racemic aryl-delta-oxoacids with (R)-phenylglycinol stereoselectively affords chiral non-racemic bicyclic lactams, from which the enantiodivergent synthesis of (R)- and (S)-2-phenylpiperidine, the diastereodivergent synthesis of cis- and trans-3-ethyl-2-phenylpiperidine, and the enantioselective synthesis of the piperidine alkaloid (-)-anabasine is reported.