Strategy of Cr detoxification by Callitriche cophocarpa

The present work focused on the qualitative and quantitative analysis of Cr detoxification strategy of aquatic cosmopolitan plant Callitriche cophocarpa. This plant species has just been described in the context of its unusual accumulation potential of Cr. The emphasis of the work was placed on the redox reaction Cr(VI)→Cr(III) which is considered to be remediation mechanism of highly reactive and mobile Cr(VI) ions. Plants were immersed for 5 days in 1 mM of Cr(VI) (potassium dichromate) or 1 mM of Cr(III) (chromium sulphate) solutions in semi-natural conditions. Cr was effectively removed from the solution up to the extent of ca.58% or 35% of the starting amount, in the case of Cr(III) and Cr(VI), respectively. No plant-induced Cr(VI) reduction accompanying Cr accumulation was observed in Cr(VI) solutions except from the apparent one, noticed at the fourth day of incubation. On the contrary to these results, according to the method of electron paramagnetic resonance spectroscopy (L-band EPR), biphasic signal of Cr(V) attending Cr(VI) to Cr(III) reduction was detected inside the plant tissue every day of investigations. Our results show that phytoextraction but not phytostabilization is the main strategy of Cr detoxification by C. cophocarpa in aquatic systems.      

Study of Photochemical Reactions of Coniferyl Alcohol. II. Comparative Structural Study of a Photochemical and Enzymatic Polymer of Coniferyl Alcohol

The structure of the polymer synthesized by UV irradiation of coniferyl alcohol was studied, using UV-visible, Raman, IR, H-NMR and ¹³C-NMR spectroscopy. The photochemical polymer was compared with the structure of the polymer obtained by peroxidase-catalyzed polymerization of coniferyl alcohol. General similarity of the spectra of the two polymers was shown. However, differences in the fine structure of particular regions of the NMR spectra, as well as in certain bands in the Raman and IR spectra, could be explained through the various bond types and organization within the polymers. These results are consistent with molecular mass distribution of the polymers. Two fractions of enzymatic polymer correspond to the main two fractions of photochemical polymer. The later polymer has additional fractions that are probably the main reason for the observed spectral differences.     

The effect of electron detachment on the structure and properties of the chlorine-acetonitrile anionic complex

The results of the theoretical study of ground state potential energy surfaces for the chlorine-acetonitrile anion and its photodetachment product are presented. The shallow potential surfaces allow for the nondefinitive position of the chlorine within the complex. The dissociation energy of the neutral complex, estimated through the thermodynamic cycle, indicates significant structural changes due to the photodetachment process. The excess negative charge is localized mostly on the chlorine atom, and the electron detachment proceeds as an electron is removed from chlorine. The process leads to drastic changes in the electrostatic interactions within the complex. The first electronic excited state corresponds to the excess electron transfer from chlorine to acetonitrile fragment. This state is a precursor of the observed charge-transfer-to-solvent state.     

Tripodal Thiols as Ligands for Molecular Magnets: Very Strong Antiferromagnetic Exchange Interactions in Vanadium(III) Clusters

The synthesis, structural and magnetic characterisation of [V^III₃O(tmme)₂(diimine)₂Cl] [diimine=2,2′‐bipyridine ( 1 ) or 1,10‐phenanthroline ( 2 )] and (HNEt₃)₂[V^III₄O(tmme)₄] ( 3 ) is reported, in which H₃tmme is tris(mercaptomethyl)ethane, MeC(CH₂SH)₃, the thiol analogue of the famous tripodal alcohol ligands typified by H₃thme [tris(hydroxymethyl)ethane, MeC(CH₂OH)₃]. Complexes 1 and 3 have “T‐shaped” and square topologies, respectively, and the latter is centred on a rare example of a square‐planar oxide. The tri‐thiolate ligands bind the periphery of the clusters and provide such strong antiferromagnetic exchange pathways that in both cases only a single total spin state is occupied up to room temperature, in the absence of metal–metal bonding. Magnetic data, electronic structure calculations and electrochemical data are reported.     

Thermal properties,phase transitions,vibrational and reorientational dynamics of [Mn(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

[Mn(NH₃)₆](NO₃)₂ crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm \( \overline{3} \) m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at T _C1 ^h  = 207.8 K and T _C1 ^c  = 207.2 K, and the second registered as a smaller anomaly at T _C2 ^h  = 184.4 K and T _C2 ^c  = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δ_s(HNH)F_1u mode suggests that the NH₃ ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol^?1. In the phase transition at T _C2 ^c probably only a some of the NH₃ ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol^?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, ²/₆ of all NH₃ ligands were seceded. Stages II and III are connected with an abruption of the next ²/₆ and ¹/₆ of total NH₃, respectively, and [Mn(NH₃)](NO₃)₂ is formed. The last molecule of NH₃ per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO₃)₂ leading to the formation of gaseous products (O₂, H₂O, N₂ and nitrogen oxides) and solid MnO₂.     

Studies on the uptake of different arsenic forms and the influence of sample pretreatment on arsenic speciation in White mustard (Sinapis alba)

The concentration and speciation of arsenic incorporated by plants grown in the presence of different arsenic compounds was compared, and the influence of plant sample pretreatment and extraction procedures on the recovery and reliability of speciation analyses was studied. It was concluded that sample pretreatment greatly affected the extraction efficiency, but did not change arsenic speciation. The most suitable extraction procedure involved dried plant material without the use of liquid nitrogen. To assess the ability of White mustard to uptake arsenic in different forms, samples were cultivated in nutrient solutions containing either As(III), As(V), monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA). The translocation factor was the highest (0.70) when DMA was added to the nutrient solution, however the overall As concentration in plant tissues was the lowest in this case. Only inorganic As was found in plant tissues when either As(III) or As(V) was added to the nutrient solution. When organic arsenic was present in the nutrient medium, however, it was partially transformed by the plants into inorganic forms.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

Electrodeposition of gold nanoparticles at a solid|ionic liquid|aqueous electrolyte three-phase junction

Gold nanoparticles have been electrodeposited on an electrode through electrogeneration at an ITO|AuCl₄^? solution in an ionic liquid|aqueous electrolyte three-phase junction. The electrodeposition was carried out by inverted double-pulse potential chronoamperometry. The direct reduction of AuCl₄^? ions at the electrode is followed by a counterion transfer through the liquid|liquid interface. Contrary to the electrodeposition from a single ionic liquid phase, scanning electron microscopy reveals that the shape of the resulting nanoparticles is highly angular and well-developed with a diameter of 110 ± 30 nm. Catalytic oxidation of glucose on the modified electrode is demonstrated.     

A fast determination of yohimbine in pharmaceuticals by micellar electrokinetic chromatography

A method for the fast determination of yohimbine, a potent adrenoreceptor antagonist used for the treatment of sexual dysfunctions, is proposed in this article. MEKC under basic and acidic conditions (sodium borate, pH 9.5 and sodium phosphate, pH 2.5) with SDS was developed. The effect of the experimental parameters, e.g. pH, SDS concentration and injection time, on yohimbine migration was also studied. Both methods were validated in terms of linearity, limits of detection and quantification, accuracy, and precision using caffeine as an internal standard. The application for the determination of yohimbine in hand-made medicaments is also investigated in this study.      

Determination of selenomethionine, selenocysteine, and inorganic selenium in eggs by HPLC–inductively coupled plasma mass spectrometry

A method for the simultaneous determination of selenomethionine (SeMet), selenocysteine (SeCys), and selenite [Se(IV)] in chicken eggs was developed. A sample preparation protocol including defatting, protein denaturation, and carbamidomethylation was optimized in order to achieve complete protein digestion and to avoid SeCys losses. Quantification was carried out by reversed-phase HPLC–inductively coupled plasma mass spectrometry (ICP MS) after quantitative isolation of the selenium-containing fraction by size-exclusion liquid chromatography. The detection limits were 0.06, 0.003, and 0.01 μg g⁻¹ (dry weight) for SeCys, Se(IV) and SeMet, respectively, and the precision was 5–10%. The end products of carbamidomethylation of the different selenium species were identified for the first time by electrospray QTOF MS after custom-designed 2D HPLC purification. Differences in selenium speciation in egg yolk and white were highlighted, the yolk containing more SeCys and the white more SeMet. An insight into selenium bioaccessibility in eggs was obtained by digestion with simulated gastric and gastrointestinal juices and size-exclusion HPLC-ICP MS.