Verbesserte Mikroborbestimmung im Picogramm-Bereich bei Gegenwart der Eisenmetalle

Ohne Zusammenfassung

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Improved microdetermination of boron in the picogram range in presence of the iron metals

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Wit danken der Deutschen Forschungsgemeinschaft sowie dem Landesamt für Forschung des Landes Nordrhein-Westfalen für Sachbeihilfen und den Herren stud. chem. U. Schinke und stud. chem. R. Langenberg für ihre sorgfältige Mitarbeit.     

Etude d'impulsions lumineuses breves par interferometrie a deux ondes

We have studied the evolution of the light transmitted through matter in which an optical breakdown is taking place. With a two-waves interferometer made a birefringent plate between polarizers we get informations about the time correlation function of the fields. With an interferometer made of two identical harmonic generating plates separated by a dispersion medium, we learn about the correlation function of the square of the fields. Both systems act as spectral filters with a notch cosine-shaped centered at the incident frequency. We have also observed a transient angular spreading of the beam not previously emphasized which brings a further complication in the picture.     

Discovery of powerful uranyl ligands from efficient synthesis and screening

New tripodal gem-(bis-phosphonates) uranophiles were discovered by a screening method that allowed for the selection of ligands with strong uranyl-binding properties in a convenient microtiter-plate format. The method is based on competitive uranium binding by using Sulfochlorophenol S as chromogenic chelate. This dye compound was found to present high uranyl complexation properties and allowed to highlight ligands presenting association constants for UO(2+)(2) up to 10(18) at pH 7.4 and 10(20) at pH 9. A collection of 40 known ligands including polycarboxylate, hydroxamate, catecholate, hydroxypyridonate and hydroxyquinoline derivatives was tested. Also screened was a combinatorial library prepared from seven amine scaffolds and eight acrylates bearing diverse chelating moieties. Among these 96 tested candidates, a tripod derivative bearing gem-bis-phosphonates moieties was found to present the highest complexation properties over a wide range of pH and was further studied.     

1,25-Dihydroxyvitamin D3 and analogues protect primary human keratinocytes against UVB-induced DNA damage

Exposure to UVB irradiation is a major risk factor for the development of skin cancer. Therefore, it is important to identify agents that can offer protection against UVB-caused damage. Photocarcinogenesis is caused largely by mutations at sites of incorrectly repaired DNA photoproducts, of which the most common are the cyclobutane pyrimidine dimers (CPDs). In this study, we demonstrated that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] protects primary human keratinocytes against the induction of CPDs by UVB. This protection required pharmacologic doses 1,25(OH)2D3 and an incubation period of at least 8 h before irradiation. Furthermore, we provided arguments indicating that the anti-proliferative capacity of 1,25(OH)2D3 underlies its protective effect against UVB-induced DNA damage. Finally, we showed that 19-nor-14-epi-23-yne-1,25(OH)2D3 (TX 522) and 19-nor-14,20-bisepi-23-yne-1,25(OH)2D3 (TX 527), two low-calcemic analogues of 1,25(OH)2D3, were even 100 times more potent than the parent molecule in inhibiting UVB-caused DNA damage. These molecules are therefore promising candidates for the chemoprevention of UVB-induced skin cancer.     

Efficient dynamic kinetic resolution of secondary amines with Pd on alkaline earth salts and a lipase

Combination of Pd, supported on alkaline earth type supports with a lipase results in a selective catalytic system for dynamic kinetic resolution of benzylic amines.