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Zürich, Switzerland

17 original crystals of [Λ-dinitrobis(ethylenediamine)cobalt]X complexes from the Alfred Werner collection of original samples of the University of Zurich were studied by single crystal X-ray diffraction revealing that the complexes with X=Cl, Br can undergo spontaneous chiral resolution upon crystallization. The main focus of this article was the chiral [Λ- and δ-dinitrobis(ethylenediamine)cobalt]Cl complexes, which crystallize from racemic solution in the space group P 21 mainly as synthetical twins enriched in one enantiomer, but to a small extent also as pure enantiomorphs. The twinning effect was recognized and correctly described by PhD student Richard Hessen of the Alfred Werner group (PhD thesis 1914). Richard Hessen eventually resolved the [δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complex by the conglomerate salt resolution method. Based on the availability of the pure [δ- or Λ-dinitrobis(ethylenediamine)cobalt]Cl complex, he carried out seeding experiments, which proved that the [δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complexes can be enriched to a great extent in one enantiomer by spontaneous chiral resolution. Already in the period of time from 1900 to 1904, various PhD students of Alfred Werner's group (Adolf Grün, Edith Humphrey, Ernst Zinggeler, Heinrich Schwarz, and Paul Larisch) prepared the [δ- or Λ-dinitrobis(ethylenediamine)cobalt]Cl complex. Adolf Grün and Edith Humphrey have prepared enantiomerically enriched and rarely also enantiomorphic crystals of the [Λ- or δ-dinitrobis(ethylenediamine)cobalt]Cl complex and could have separated crystals by manual crystal picking. Admittedly due to the crystal habits this would have been a difficult endeavour, but this 'Louis Pasteur method' was apparently not taken into consideration. Still in a cautiously sounding note one could state that Alfred Werner and his group had missed by this omission the opportunity for spontaneous chiral resolution of the [δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complexes in the period of time from 1900 to 1904. In addition, making this early chiral resolution story even more incredible, we found that Heinrich Schwarz and Paul Larisch applied in these early days of coordination chemistry the S-(D-,d-)camphorsulfonate anion to achieve the separation of the cis- and trans-isomers of the [dinitrobis(ethylenediamine)cobalt] complexes. They did not approach the potentially possible chiral resolution of the [cis-dinitrobis(ethylenediamine)cobalt]+ cation. But based on their synthetic procedure they did indeed accomplish chiral resolution of the cis-isomer and prepared eventually a series of the chiral [cis-,Λ-dinitrobis(ethylenediamine)cobalt]X salts; however all this was in an unintentional manner. © 2015 Universidad Nacional Autónoma de México, Facultad de Química.

Anstaett P.,Winterthurerstrasse | Leonidova A.,Winterthurerstrasse | Gasser G.,Winterthurerstrasse
ChemPhysChem | Year: 2015

The quantum yields for photouncaging reactions are mostly determined relative to other uncaging reactions, often using 1-(2-nitrophenyl)ethyl-phosphate ("caged phosphate"). Herein, we demonstrate that the quantum yields acquired by using this method can be off by an order of magnitude at the typical irradiation wavelengths around 350 nm and describe an easy-to-use alternative procedure using inexpensive azobenzene. How fast is it really going? Caged phosphate has often been used to determine the photolysis rate of caged compounds. However, at certain wavelengths this leads to wrong results. A novel protocol, based on azobenzene isomerization, can circumvent this problem. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jochmann R.,Winterthurerstrasse | Blanckenhorn W.U.,Winterthurerstrasse
Basic and Applied Ecology | Year: 2016

Environmental stressors can have unintended negative effects on beneficial organisms. Testing environmental effects of pharmaceutical residues is therefore often mandated in form of single-species ecotoxicological laboratory tests, yet differential sensitivity of species can ultimately disturb the entire community. A more realistic approach is to directly assess toxicity in the field to account for spatio-temporal variation in climate and habitat. We conducted the first field study at the landscape scale, replicated at 24 Swiss farms north of the Alps, to test the impact of a realistically low concentration (6.6. μg/kg fresh dung) of the popular parasiticide ivermectin on the beneficial cow dung insect community over the season. We found a graded negative impact of ivermectin on many but not all species, with significant reductions in ca. one third of 32 evaluated fly (Diptera) and wasp (Hymenoptera) taxa. No taxon benefited from ivermectin presence. Small hymenopteran parasitoids particularly decreased in numbers (62%), with large dipteran predators (38%) being reduced more than primary coprophagous dung consumers (23%). This supports theoretical expectations that the top trophic levels of a community are particularly vulnerable to environmental disturbance because their numbers tend to be low and their body size large, but also because pollutants can biomagnify in the food chain. Sensitivity to pollutants may further exhibit a phylogenetic signal. Ivermectin residues thus generally reduced the biodiversity of the dung insect community, but impact varied among farms, years and over the season, being lowest in autumn. We conclude that spatio-temporal replication of such higher-tier field studies is advised to capture the full extent of effects in realistic natural settings, as even low concentrations of a pharmaceutical can have varying impact on the different organisms comprising an ecosystem. Umweltgifte können sich auch auf Nützlinge negativ auswirken. Deshalb müssen neue Pharmazeutika generell auf ihre Unbedenklichkeit getestet werden falls sie, gewollt oder ungewollt, in die Umwelt gelangen. Dies geschieht häufig mittels standardisierter ökotoxikologischer Labortests gewisser Schlüsselarten, doch die Empfindlichkeit einzelner Spezies kann bekanntlich stark variieren. Ein informativerer Ansatz wäre daher, die Toxizität von Substanzen direkt im Freiland an gesamten Lebensgemeinschaften zu testen. In einer solchen Studie wurde der Einfluss einer realistisch niedrigen Konzentration (6.6. μg/kg Frischdung) des gängigen Parasitikums Ivermectin auf die Kuhdung abbauenden Insekten auf Weiden von 24 landwirtschaftlichen Betrieben in der Schweiz nördlich der Alpen über das Jahr hinweg untersucht. Ivermectin führte zu abgestuften Reduktionen der Populationen von insgesamt 32 Fliegen- (Diptera) und Wespentaxa (Hymenoptera). Bei etwa einem Drittel erhöhte sich die Mortalität signifikant, im Frühling und Sommer stärker als im Herbst. Keine Art profitierte von der Präsenz der Substanz. Kleine Parasitoide von Dungorganismen (sämtlich Hymenoptera) wurden am stärksten reduziert (62%), grosse räuberische Fliegen zu 38%, die Dungkonsumenten jedoch nur zu 23%. Dies bestätigt die theoretische Erwartung, dass Organismen der höheren trophischen Stufen empfindlicher auf Umweltstörungen reagieren: etwa weil sie selten und eher grösser sind, oder weil sich toxische Substanzen in der Nahrungskette ansammeln (Biomagnifikation). Die Unterschiede könnten jedoch auch durch phylogenetische Verwandtschaft bedingt sein. Insgesamt erhöhte Ivermectin die Sterblichkeit eines beträchtlichen Anteils der coprophagen Dunginsekten, sodass ihre Ökosystemdienstleistung empfindlich gestört werden kann. Die Durchführung solcher umfangreicheren toxikologischen Freilanduntersuchungen kann somit empfohlen werden, um ein realistischeres Bild des Umwelteinflusses einzelner schädlicher Substanzen zu erhalten. © 2016 Gesellschaft für Ökologie.

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