Flow injection on-line acid digestion and pre-reduction of arsenic for hydride generation atomic absorption spectrometry-a feasibility study

A flow injection (FI) manifold is described which makes possible on-line microwave-assisted acid digestion, followed by pre-reduction of As(V) to As(III) and its determination by hydride generation atomic absorption spectrometry. The merging zone technique is used in order to reduce acid consumption for digestion. The efficiency of acid digestion is increased by pressure which is built up in-line by a flow restrictor. Flows for sample pretreatment and hydride generation can be optimized independently. L-cysteine was found superior to potassium iodide as the pre-reductant because much lower reagent and acid concentrations are required, much harsher conditions can be tolerated for acid digestion, and the integrated absorbance signals for arsenic in blood and standards are essentially identical, making possible the use of the standard calibration procedure.

The sampling frequency is 7–10/hr, depending on the conditions chosen, and the limit of detection, i.e. the concentration giving a signal equal to three times the standard deviation of the signal of the blank solution, is 0.25 μg/l for a 500 μl sample volume. The recovery of 10 μg/l As(V) added to a blood sample was 94 ± 2 and 98 ± 2% (n = 3) in absorbance and integrated absorbance, respectively.     

Effets de la nature de substituants sur les constantes d'acidité et les constantes de stabilité des complexes de quelques acides nitroso-5-barbituriques

The effects of substituents on the acidity constants and stability constants of complexes of some 5-nitrosobarbituric acids). The acidity constants of some 5-nitrosobarbituric acids (violuric acids) vary according to the degree of substitution and the nature of the substituent at the 1- and 3-positions of the pyrimidine ring. The value obtained at ionic strength 0.5 mol l^?1 made it possible to calculate the stability constants of simple complexes of divalent cations (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Fe²⁺). Potentiometric titrations were applied.     

Direct intramolecular arylation of unactivated arenes: application to the synthesis of aporphine alkaloids

The direct intramolecular C-H arylation of unactivated arenes is a viable strategy for the synthesis of aporphine alkaloids. These reactions occur with 3 to 5 mol% catalyst and generate the aporphine skeleton in up to 99% yield.     

Unique example of flexible phenol coordination in mononuclear manganese compounds

The synthesis and characterization of six novel mononuclear Mn(II) and Mn(III) complexes are presented. The tripodal ligands 2-((bis(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (HL1), 2-[[((6-methylpyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino]methyl]-4-nitrophenol (HL2), (2-pyridylmethyl)(6-methyl-2-pyridylmethyl)(2-hydroxybenzyl)amine (HL3) and 2-((bis(pyridin-2-ylmethyl)amino)methyl)-4-bromophenol were used. All ligands provide an N3O donor set. The compounds [Mn(II)(HL1)Cl2].CH3OH (1), [Mn(III)(L1)Cl2] (2), [Mn(II)(HL2)(EtOH)Cl2] (3), [Mn(II)(HL3)Cl2].CH3OH (4), [Mn(III)(HL4)Br2] (5) and [Mn(III)(L1)(tcc)] (6), with tcc = tetrachlorocatecholate dianion, were synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, IR and UV-vis spectroscopy, cyclic voltammetry, and elemental analysis. Compound 1 crystallizes in the triclinic space group P1, compounds 2, 3 and 4 were solved in the monoclinic space group P2(1)/c, whereas the structure determination of and succeeded in the orthorhombic space groups Pbca and P2(1)2(1)2(1), respectively. Notably, the crystal structures of 1 and 3 are the first Mn(II) complexes featuring a non-coordinating phenol moiety. Compound 2 oxidizes 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations with a turnover number of kcat = 173 h(-1). The electronic influence of different substituents in para position of the phenol group is lined out.