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601.
Tromp M Sietsma JR van Bokhoven JA van Strijdonck GP van Haaren RJ van der Eerden AM van Leeuwen PW Koningsberger DC 《Chemical communications (Cambridge, England)》2003,(1):128-129
UV-Vis, combined with ED-XAFS shows, for the first time, the evolution of inactive Pd dimers and trimers, that are a possible first stage in the deactivation process of important palladium catalysed reactions, leading to larger palladium clusters and eventually palladium black. 相似文献
602.
van den Bos LJ Codée JD van Boom JH Overkleeft HS van der Marel GA 《Organic & biomolecular chemistry》2003,1(23):4160-4165
A tethered nucleophilic substitution strategy for the stereoselective introduction of axially oriented amino functions on suitably protected gluco- and mannopyranosides is presented. The obtained oxazine is a versatile building block, which after some manipulation, could be used in the construction of highly functionalised oligosaccharides. 相似文献
603.
Jonkheijm P Hoeben FJ Kleppinger R van Herrikhuyzen J Schenning AP Meijer EW 《Journal of the American Chemical Society》2003,125(51):15941-15949
Three hydrogen-bonded oligo(p-phenylenevinylene)s, OPV3, OPV4, and OPV5, that differ in conjugation length have been synthesized and fully characterized. All three compounds contain chiral side chains, long aliphatic chains, and a ureido-s-triazine hydrogen bonding unit. (1)H NMR and photophysical measurements show that the OPV oligomers grow hierarchically in an apolar solvent; initially, dimers are formed by hydrogen bonds that subsequently develop into stacks by pi-pi interactions of the phenylenevinylene backbone with induced helicity via the chiral side chains. SANS measurements show that rigid cylindrical objects are formed. Stacks of OPV4 have a persistence length of 150 nm and a diameter of 6 nm. OPV3 shows rigid columnar domains of 60 nm with a diameter of 5 nm. Temperature and concentration variable measurements show that the stability of the stacks increases with the conjugation length as a result of more favorable pi-pi interactions. The transfer of the single cylinders from solution to a solid support as isolated objects is only possible when specific concentrations and specific solid supports are used as investigated by AFM. At higher concentrations, an intertwined network is formed, while, at low concentration, ill-defined globular objects are observed. Only in the case of inert substrates (graphite and silicium oxide) single fibers are visible. In the case of the repulsive surfaces (mica and glass), clustering of the stacks occurs, while, at attractive surfaces (gold), the stacks are destroyed. 相似文献
604.
This paper introduces a new class of games, highway games, which arise from situations where there is a common resource that agents will jointly use. That resource is an ordered set of several indivisible sections, where each section has an associated fixed cost and each agent requires some consecutive sections. We present an easy formula to calculate the Shapley value, and we present an efficient procedure to calculate the nucleolus for this class of games. 相似文献
605.
Jeroen?van?Dongenj.vandongen@phys.uu.nl" title="jvdongen@einstein.caltech.edu j.vandongen@phys.uu.nl" itemprop="email" class="gtm-email-author">Email author 《Physics in Perspective (PIP)》2007,9(2):212-230
Two important and unpleasant events occurred in Albert Einstein’s life in 1920: That August an antirelativity rally was held
in the large auditorium of the Berlin Philharmonic, and a few weeks later Einstein was drawn into a tense and highly publicized
debate with Philipp Lenard on the merits of relativity at a meeting in Bad Nauheim, Germany. I review these events and discuss
how they affected Einstein in light of new documentary evidence that has become available through the publication of Volume
10 of the Collected Papers of Albert Einstein.
Jeroen van Dongen is Associate Editor with the Einstein Papers Project at the California Institute of Technology and Veni
Research Fellow of the Netherlands Organisation for Scientific Research (NWO) at Utrecht University. 相似文献
606.
Kool J Van Liempd SM Harmsen S Schenk T Irth H Commandeur JN Vermeulen NP 《Analytical and bioanalytical chemistry》2007,388(4):871-879
Reactive oxygen species (ROS) can damage proteins, cause lipid peroxidation, and react with DNA, ultimately resulting in harmful
effects. Antioxidants constitute one of the defense systems used to neutralize pro-oxidants. Since pro-oxidants and antioxidants
are found ubiquitously in nature, pro-and antioxidant effects of individual compounds and of mixtures receive much attention
in scientific research. A major bottleneck in these studies, however, is the identification of the individual pro-oxidants
and antioxidants in mixtures. Here, we describe the development and validation of an on-line post-column biochemical detection
system for ROS-producing compounds and antioxidants in mixtures. Inclusion of cytochrome P450s and cytochrome P450 reductase
also permitted the screening of compounds that need bioactivation to exert their ROS-producing properties. This pro-oxidant
and antioxidant detection system was integrated on-line with gradient HPLC. The resulting high-resolution screening technology
was able to separate mixtures of ROS-producing compounds and antioxidants, allowing each species to be characterized rapidly
and sensitively. 相似文献
607.
The synthesis and self-assembly behavior of biohybrid ABC triblock copolymers consisting of a synthetic diblock, polystyrene-b-polyethylene glycol (PSm-b-PEG113), where m is varied, and a hemeprotein, myoglobin (Mb) or horse radish peroxidase (HRP), is described. The synthetic diblock copolymer is first functionalized with the heme cofactor and subsequently reconstituted with the apoprotein or the apoenzyme to yield the protein-containing ABC triblock copolymer. The obtained amphiphilic block copolymers self-assemble in aqueous solution into a large variety of aggregate structures. Depending on the protein and the polystyrene block length, micellar rods, vesicles, toroids, figure eight structures, octopus structures, and spheres with a lamellar surface are formed. 相似文献
608.
Billen J Guillarme D Rudaz S Veuthey JL Ritchie H Grady B Desmet G 《Journal of chromatography. A》2007,1161(1-2):224-233
To study the influence of the particle size distribution (PSD), we measured the chromatographic performance of a series of sub-2 microm particle high performance liquid chromatography (HPLC) columns packed with four different particle mixtures having a purposely imposed different size distribution. Using the reduced kinetic plot representation by plotting the separation impedance (E(0)) versus the plate number ratio (N(opt)/N), the different columns could be classified according to their chromatographic performance without the need to specify a mean particle diameter or a molecular diffusion coefficient, as is needed in the classical reduced plate height and flow resistance analysis. The present analysis shows that it is not so much the width or span of the particle size distribution, but rather the presence of fines that greatly determines the chromatographic performance of particulate columns. 相似文献
609.
Bacterial volatiles: the smell of small organisms 总被引:4,自引:0,他引:4
This review describes volatiles released into the air by bacteria growing on defined media. Their occurrence, function, and biosynthesis are discussed, and a total of 308 references are cited. An effort has been made to organize the compounds according to their biosynthetic origin. 相似文献
610.
Luijten J Vorenkamp EJ Schouten AJ 《Langmuir : the ACS journal of surfaces and colloids》2007,23(21):10772-10778
The reversible manipulation of the helix screw sense in surface-grafted poly(beta-phenethyl-L-aspartate) (PPELA) films by means of external stimuli was investigated. Ringopening polymerization of beta-phenethyl-L-aspartate N-carboxyanhydride initiated from primary amino-functionalized silicon and quartz substrates results in surface-grafted PPELA films in which the end-grafted polypeptide chains have a right-handed alpha-helical conformation. Upon annealing of the film at 150 degrees C for 30 min, a helix screw sense inversion takes place and the grafted chains adopt a left-handed pi-helical conformation. In the solid state, this left-handed pi-helical form is completely stable and cannot be changed by reheating and/or cooling. Upon immersion of the annealed grafted film in chloroform or other helicogenic solvents, the grafted polypeptide chains completely revert to their original right-handed alpha-helical form. Successive annealing and solvent treatment steps show that this helix sense inversion cycle can be repeated many times. 相似文献