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991.
Bin-Salamon S Brewer S Franzen S Feldheim DL Lappi S Shultz DA 《Journal of the American Chemical Society》2005,127(15):5328-5329
This communication describes the preparation and characterization of a valence tautomer complex covalently attached to gold nanoparticles. Variable-temperature IR spectroscopy is used to determine the equilibrium thermodynamic parameters for the valence tautomerization. These results are compared with a nonsurface combined valence tautomer complex. The results show that surface confinement attenuates both DeltaH degrees and DeltaS degrees . We attribute these changes to a reduced accessible molecular surface area. 相似文献
992.
Oligoribonucleotides (RNA) and modified oligonucleotides were subjected to low-energy collision-induced dissociation in a hybrid quadrupole time-of-flight mass spectrometer to investigate their fragmentation pathways. Only very restricted data are available on gas-phase dissociation of oligoribonucleotides and their analogs and the fundamental mechanistic aspects still need to be defined to develop mass spectrometry-based protocols for sequence identification. Such methods are needed, because chemically modified oligonucleotides can not be submitted to standard sequencing protocols. In contrast to the dissociation of DNA, dissociation of RNA was found to be independent of nucleobase loss and it is characterized by cleavage of the 5'-P-O bond, resulting in the formation of c- and their complementary y-type ions. To evaluate the influence of different 2'-substituents, several modified tetraribonucleotides were analyzed. Oligoribonucleotides incorporating a 2'-methoxy-ribose or a 2'-fluoro-ribose show fragmentation that does not exhibit any preferred dissociation pathway because all different types of fragment ions are generated with comparable abundance. To analyze the role of the nucleobases in the fragmentation of the phosphodiester backbone, an oligonucleotide lacking the nucleobase at one position has been studied. Experiments indicated that the dissociation mechanism of RNA is not influenced by the nucleobase, thus, supporting a mechanism where dissociation is initiated by formation of an intramolecular cyclic transition state with the 2'-hydroxyl proton bridged to the 5'-phosphate oxygen. 相似文献
993.
Baudry Y Pasini D Nishihara M Sakai N Matile S 《Chemical communications (Cambridge, England)》2005,(38):4798-4800
Voltage-sensitive blockage by ADP, ATP and phytate (IP6) demonstrates that active-site contraction toward the middle of newly synthesized rigid-rod beta-barrels provides a general strategy to rationally create and modulate the voltage sensitivity (and to increase the efficiency) of molecular recognition by synthetic multifunctional pores. 相似文献
994.
Aggregation of poly(para-phenyleneethynylene)s is efficiently suppressed by introduction of branched oligoethyleneglycol side chains rendering the polymer backbone, which is readily obtained using an A2 + BB' polycondensation protocol, soluble and highly emissive in aqueous environments. 相似文献
995.
Ruth K Dinnebier RE Tönnes SW Alig E Sänger I Lerner HW Wagner M 《Chemical communications (Cambridge, England)》2005,(27):3442-3444
Solvent-free [LiCH2SMe]infinity forms a layer structure consisting of four- (Li2C2), five- (Li2CS2), and six-membered (Li2C2S2) rings in the solid state; the compound violently explodes upon heating to T=160+/-5 degrees C under an argon atmosphere. 相似文献
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Ohne ZusammenfassungHerrnAlexander Ostrowski zum sechzigsten Geburtstag gewidmetDiese Note enthält Teilergebnisse einer Untersuchung, die mit UnterstÜtzung der Deutschen Forschungsgemeinschaft ausgefÜhrt wurde. 相似文献