Structural Studies Using X-ray Absorption Spectroscopy of Intermediates Formed by Reaction of Ozone with Halogeno(dodecaphenylporphyrinato)manganese(III) Derivatives

Difference EXAFS and XANES studies at the Mn K-edge are reported which shed light on the mechanisms of activation of the title compounds by ozone. The reaction of ozone with either the chloro- or b..

Planktotrons: A novel indoor mesocosm facility for aquatic biodiversity and food web research

We established a new indoor mesocosm facility, 12 fully controlled “Planktotrons”, designed to conduct marine and freshwater experiments for biodiversity and food web approaches using natural or artificial, benthic or planktonic communities. The Planktotrons are a unique and custom-tailored facility allowing long-term experiments. Wall growth can be inhibited by a rotating gate paddle with silicone lips. Additionally, temperature and light intensity are individually controllable for each Planktotron and the large volume (600 L) enables high-frequency or volume-intense measurements. In a pilot freshwater experiment various trophic levels of a pelagic food web were maintained for up to 90 d. First, an artificially assembled phytoplankton community of 11 species was inoculated in all Planktotrons. After 22 d, two ciliates were added to all, and three Daphnia species were added to six Planktotrons. After 72 d, dissolved organic matter (DOM, an alkaline soil extract) was added as an external disturbance to six of the 12 Planktotrons, involving three Planktotrons stocked with Daphnia and three without, respectively. We demonstrate the suitability of the Planktotrons for food web and biodiversity research. Variation among replicated Planktotrons (n = 3 minimum) did not differ from other laboratory systems and field experiments. We investigated population dynamics and interactions among the different trophic levels, and found them affected by the sequence of ciliate and Daphnia addition and the disturbance caused by addition of DOM

STRUCTURAL CHARACTERIZATION OF BIMETALLIC PORPHYRIN COMPLEXES USING DIFFERENCE EXAFS SPECTROSCOPY

La technique d'EXAFS différentiel a été employée pour préciser la structure du composé 1 = [OEP : Ge-Fe(CO)4]. C'est tout d'abord le déplacement axial du germanium (ΔH = 0.45 ± 0.05 Å) qui a été déterminé à partir de spectres de différences impliquant 2 = [TpTP : GeCl2], 3 = [TpTP : GeF2] et 4 = [OEP : GeF2]. La distance métal-métal R(Ge*...Fe) = 2.35 ± 0.02 Å a été déduite de nouvelles analyses différentielles impliquant cette fois 5 = [OEP : V=0] et 6 = [DPEP : V=0] comme références.Difference EXAFS spectroscopy has been used for a structural characterization of 1 = [OEP : Ge-Fe(CO)4]. The axial shift of germanium ΔH = 0.45 ± 0.05 Å was first deduced from differential FT analyses involving 2 = [TpTP : GeCl2], 3 = [TpTP : GeF2] and 4 = [OEP : GeF2]. The metal-metal distance R(Ge*...Fe) = 2.35 ± 0.02 Å was obtained from further differential FT analyses involving 5 = [OEP : V=0] and 6 = [DPEP : V=0] as références

Chiral atropisomeric metalloporphyrins in the enantioselective styrene epoxidation

N-Phosphorylimines undergo Lewis acid-catalyzed Diels-Alder reactions with Danishefsky's diene. Application of the chiral catalyst zinc (II)- (S)-BINOL results in good-to-low asymmetric induction but poor chemical conversion. However, the absolute stereochemistry of novel aza-Diels-Alder cycloadducts, such as diethyl 4-oxo-2-phenyl-3,4-dihydropyridin-1(2H)-ylphosphonate, can be determined using circular dichroism (CD). Comparison between experimental and TDDFT-calculated CD spectrum shows that use of the (S)-catalyst results in predominant formation of the (6R) cycloadducts

Optical methods for the detection of heavy metal ions

International audienc

Electrooxidation of porphyrin free bases: Fate of the π-cation radical

International audienceIn contrast to metalloporphyrins with non-electroactive metal centres, the π-cation radicals of porphyrin free bases (H2OEP, H2TPP, H2CdiE) electrogenerated in strictly anhydrous solvents are not stable and give rise to a quantitative chemical reaction. Conjunction of electrochemical and spectroscopic data (UV/VIS, EPR and NMR) demonstrates unambiguously that the porphyrin skeleton is not modified during the chemical reaction. The reaction product is the protonated free base, and thus the free base can be regenerated by reduction of the protons