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671.
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673.
Andreas F. Glas Sabine Schneider Dr. Melanie J. Maul Ulrich Hennecke Dr. Thomas Carell Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(40):10387-10396
UV‐light irradiation induces the formation of highly mutagenic lesions in DNA, such as cis‐syn cyclobutane pyrimidine dimers (CPD photoproducts), pyrimidine(6‐4)pyrimidone photoproducts ((6‐4) photoproducts) and their Dewar valence isomers ((Dew) photoproducts). Here we describe the synthesis of defined DNA strands containing these lesions by direct irradiation. We show that all lesions are efficiently repaired except for the T(Dew)T lesion, which cannot be cleaved by the repair enzyme under our conditions. A crystal structure of a T(6‐4)C lesion containing DNA duplex in complex with the (6‐4) photolyase from Drosophila melanogaster provides insight into the molecular recognition event of a cytosine derived photolesion for the first time. In light of the previously postulated repair mechanism, which involves rearrangement of the (6‐4) lesions into strained four‐membered ring repair intermediates, it is surprising that the not rearranged T(6‐4)C lesion is observed in the active site. The structure, therefore, provides additional support for the newly postulated repair mechanism that avoids this rearrangement step and argues for a direct electron injection into the lesion as the first step of the repair reaction performed by (6‐4) DNA photolyases. 相似文献
674.
Melanie J. Bugler Stephen T. Grimes Melanie J. Leng Simon D. Rundle Gregory D. Price Jerry J. Hooker Margaret E. Collinson 《Rapid communications in mass spectrometry : RCM》2009,23(18):2939-2951
Experimental measurements of the 18O/16O isotope fractionation between the biogenic aragonite of Viviparus contectus (Gastropoda) and its host freshwater were undertaken to generate a species‐specific thermometry equation. The temperature dependence of the fractionation factor and the relationship between Δδ18O (δ18Ocarb. – δ18Owater) and temperature were calculated from specimens maintained under laboratory and field (collection and cage) conditions. The field specimens were grown (Somerset, UK) between August 2007 and August 2008, with water samples and temperature measurements taken monthly. Specimens grown in the laboratory experiment were maintained under constant temperatures (15°C, 20°C and 25°C) with water samples collected weekly. Application of a linear regression to the datasets indicated that the gradients of all three experiments were within experimental error of each other (±2 times the standard error); therefore, a combined (laboratory and field data) correlation could be applied. The relationship between Δδ18O (δ18Ocarb. – δ18Owater) and temperature (T) for this combined dataset is given by: (T is in °C, δ18Ocarb. is with respect to Vienna Pee Dee Belemnite (VPDB) and δ18Owater is with respect to Vienna Standard Mean Ocean Water (VSMOW). Quoted errors are 2 times standard error). Comparisons made with existing aragonitic thermometry equations reveal that the linear regression for the combined Viviparus contectus equation is within 2 times the standard error of previously reported aragonitic thermometry equations. This suggests there are no species‐specific vital effects for Viviparus contectus. Seasonal δ18Ocarb. profiles from specimens retrieved from the field cage experiment indicate that during shell secretion the δ18Ocarb. of the shell carbonate is not influenced by size, sex or whether females contained eggs or juveniles. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
675.
Polyampholyte microgel particles, containing both methacrylic acid and 2-(dimethylamino) ethyl methacrylate (a weak base),
in a mainly N-isopropyl acrylamide network, have been prepared by free-radical dispersion polymerisation. The swelling properties of the
particles have been shown to be pH and temperature dependent and to exhibit a minimum in size at the iso-electric point. The
uptake and release of cetylpyridinium chloride and Triton X-100, into and from, the polyampholyte microgel particles have
been investigated as a function of pH. The absorbed amounts at different pH values have been related to various specific interactions
between the surfactant and the microgel network. 相似文献
676.
Pb5I2P28 is the first compound containing a former unseen [P3I2]4+ unit, connecting two crystallographically independent adjacent [PbP14]2? polyphosphide strands. The polyanion substructure is closely related to the one realized in the HgPbP14 structure type, with a homo‐nuclear coordination of the cations to the polyanions. It has been prepared by using the mineralizator concept for polyphosphides from the elements and PbI2 as the mineralizator species. The new polyphosphide has a pronounced tendency to form easy cleavable, needle shaped crystals featuring massive stacking vaults. Nevertheless, a single crystal structure determination was possible from inter‐grown crystals. Pb5I2P28 crystallizes monoclinically in the space group P21/n (No. 14) with lattice parameters of a = 9.792(2), b = 17.717(2), c = 19.191(3) Å, β = 96.39(1)°, V = 3308.6(8) Å3. Depending on the preparation route, the aspect ratio of the needle shaped crystals can be varied. 相似文献
677.
Melanie Haugg Viktoria Kaiser Christoph Schmidtkunz Thomas Welsch 《Electrophoresis》2009,30(2):396-402
During the last 15 years, methods for the capillary electrophoretic separation of different bacteria species have been developed, which exploit their characteristic cell surface‐charge to volume ratio. A special variant, the polymer‐based CE of bacteria, includes a focusing step, which forces the bacteria cells to form aggregates at the beginning of the electrophoretic process, resulting in very high apparent efficiencies. Our experiments presented in this article reveal that the migration time of bacteria species in polymer‐based CE increases with a growing amount of injected cells. Thus, the electrophoretic mobilities are not characteristic for the single cells of one species, but for the aggregates of the bacteria species, which are formed during the focusing process. Electrophoretic mobility (EM) data are obviously inapplicable for the identification of bacteria if the concentration of the bacteria sample solution is not constant. Fractions taken during the electrophoretic separation of different bacteria species were cultivated and tested for species purity. Interestingly, the electrophoretic bands were never pure, as all of them contained different mixtures of the injected species. We attribute this to the formation of stable mixed‐species aggregates during polymer‐based focusing. The mixed clusters migrate in the electric field with consistent velocity as a whole and are not separated electrophoretically. 相似文献
678.
679.
Talebi N Sigle W Vogelgesang R Koch CT Fernández-López C Liz-Marzán LM Ögüt B Rohm M van Aken PA 《Langmuir : the ACS journal of surfaces and colloids》2012,28(24):8867-8873
In this paper, we present a systematic investigation of symmetry-breaking in the plasmonic modes of triangular gold nanoprisms. Their geometrical C(3v) symmetry is one of the simplest possible that allows degeneracy in the particle's mode spectrum. It is reduced to the nondegenerate symmetries C(v) or E by positioning additional, smaller gold nanoprisms in close proximity, either in a lateral or a vertical configuration. Corresponding to the lower symmetry of the system, its eigenmodes also feature lower symmetries (C(v)), or preserve only the identity (E) as symmetry. We discuss how breaking the symmetry of the plasmonic system not only breaks the degeneracy of some lower order modes, but also how it alters the damping and eigenenergies of the observed Fano-type resonances. 相似文献
680.
Szesni N Kaiser M Putzien S Fischer RW 《Combinatorial chemistry & high throughput screening》2012,15(2):170-179
Supported Ionic Liquid Phase (SILP) catalysts have been prepared by effective immobilization of [Cu(TMEDA)(OH)]Cl in a nano-metric film of an ionic liquid on various oxidic support materials. The catalysts were tested for the oxidative homocoupling of 1-alkynes to the corresponding diynes in in a combined high throughput and conventional batch reaction approach. Among the screened support materials silica based materials performed best. The results indicate that for the specific reaction the thickness of the ionic liquids layer and therefore the mobility of the homogeneous copper complex within the ionic liquid layer as deduced from solid state nmr measurements have major impact on the catalytic performance. The optimized catalysts could be recycled up to four times without any loss of activity. 相似文献