A nucleophilic substitution reaction between 4-tert-butylbenzyl bromide and a series of iodide salts has been performed in oil-in-water microemulsions based on either a fatty alcohol ethoxylate or a sugar surfactant. The reaction kinetics was compared with the kinetics of the same reaction performed in a microhomogeneous reaction medium, d-MeOH. Previous results showing a particularly high reactivity in the microemulsion based on the fatty alcohol ethoxylate was confirmed. It was shown that in both microemulsions the reaction rate was almost independent of the choice of counterion to iodide. This indicates that complexation of the cation with the surfactant headgroup, which, in particular, could have taken place with surfactants containing oligooxyethylene chains (a “crown ether effect”), seems not to be of importance.
127I NMR studies, as well as quadrupole splitting experiments performed by 2H NMR, indicate that there is a certain accumulation of iodide at the oil–water interface of the microemulsions. It is difficult to draw any quantitative conclusions in this respect, however.
The results obtained in this study, combined with results from previous investigations of the same reaction, indicate that the unexpectedly high reactivity obtained in the microemulsion based on a surfactant containing an oligooxyethylene headgroup is most probably due to the nucleophile being poorly solvated when present in the headgroup layer of such a microemulsion. Poorly solvated anions are known to be highly reactive nucleophiles. 相似文献
The influence of added colloidal particles on the phase separation of mixed aqueous polymer solutions is investigated. Two types of particles (polystyrene latex or silica) and different combinations of segregating polymers (dextran of varying molar mass combined with poly(ethylene oxide) (PEO) of varying molar mass, or Ucon, a copolymer of ethylene oxide and propylene oxide) were used. All systems displayed particle-induced instability effects, but the extent of the effect varied strongly between the various combinations and with the amount of added salt. Very large instability effects were seen in certain mixtures. Two mechanisms, both relying on the adsorption of at least one of the polymers to the particle surface, seem to operate. Close to the cloud-point curve of the particle-free polymer1/polymer2/water mixture, adsorption of PEO or Ucon to the particles gives rise to a capillary-induced phase separation. Close to the dextran/water axis of the phase diagram, the adsorbing polymer gives rise to a surface modification of the particles, which then interacts repulsively with the surrounding dextran solution. 相似文献
A new method for the solid-phase synthesis of enantiomerically enriched highly substituted ring-fused 2-pyridinones 13 has been developed. The synthesis mediates introduction of substituents at two positions in the 2-pyridinone ring in a diverse manner and is suitable for parallel synthesis. (19)F NMR spectroscopy was used as a tool to monitor each of the five steps in the reaction sequence. The optimized conditions thus obtained were then used to prepare a library of 20 2-pyridinones with high yields. The library members were chosen from a statistical multivariate design to ensure diversity and reliable data for structure-activity relationships. Screening of the library against the bacterial periplasmic chaperone PapD was performed using surface plasmon resonance. Three new 2-pyridinones with a higher affinity for the chaperone PapD than the previous best 13[10,1] were found, and important structural features could be deduced. 相似文献
Dissociative recombination (DR) of the dimer ion (NO)(2) (+) has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2 eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69+/-0.02. The second most important channel yields NO+NO fragments with a probability of 0.23+/-0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(upsilon=0)+N((4)S)+O((3)P), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer. 相似文献
Rapid addition of Grignard reagents to pyridine N-oxides under mild conditions gave stereodefined dienal oximes in good to excellent yields. This reaction provides an efficient access to substituted olefins with defined stereochemistry that are potentially of interest as bioactives themselves or as versatile synthetic intermediates. 相似文献
Advances in Computational Mathematics - It is well known in the literature that standard hierarchical matrix ( ${\mathscr{H}}$ -matrix)-based methods, although very efficient for asymptotically... 相似文献
The use of non-polar, small polymers as matrices for the analysis of low molecular weight compounds in polymer-assisted laser desorption/ionization mass spectrometry (PALDI-MS) is demonstrated. The matrices evaluated were either based on an oligothiophene or a benzodioxin backbone. Metallocenes, polycyclic hydrocarbons, a fluorosurfactant, and a subset of small organic compounds with various functionalities, served as model analytes. The mechanism of ionization charge transfer is discussed and ionization potentials for the matrices in the study have been estimated using density functional theory (DFT) calculations. Some of the results are possibly contradictory to the generally accepted limiting conditions for gas-phase charge-transfer reactions. These results are interpreted in the light of energy pooling. Also a new mass calibration procedure for the low-mass region in positive ion mode is presented, and some aspects of the ionization/desorption process leading to radical cations are studied. 相似文献
We present a novel concept for the creation of lipid vesicle microarrays based on a patterning approach termed Molecular Assembly Patterning by Lift-off (MAPL). A homogeneous MAPL-based single-stranded DNA microarray was converted into a vesicle array by the use of vesicles tagged with complementary DNAs, permitting sequence-specific coupling of vesicles to predefined surface regions through complementary DNA hybridization. In the multistep process utilized to fulfill this achievement, active spots consisting of PLL-g-PEGbiotin with a resistant PLL-g-PEG background, as provided by the MAPL process, was converted into a DNA array by addition of complexes of biotin-terminated DNA and NeutrAvidin. This was then followed by addition of POPC vesicles tagged with complementary cholesterol-terminated DNA, thus providing specific coupling of vesicles to the surface through complementary DNA hybridization. Quartz crystal microbalance with dissipation (QCM-D) and optical waveguide lightmode spectroscopy monitoring were used to optimize the multistep surface modification process. It was found that the amount of adsorbed biotinDNA-NeutrAvidin complexes decreases with increasing molar ratio of biotinDNA to NeutrAvidin and decreasing ionic strength of the buffer solution. Modeling of the QCM-D data showed that the shape of the immobilized vesicles depends on the amount of available anchoring groups between the vesicles and the surface. Fluorescent microscopy images confirmed the possibility to create well-defined patterns of DNA-tagged, fluorescently labeled vesicles in the micrometer range. 相似文献
We here report a remarkably slow rearrangement of binding modes for a binuclear ruthenium(II) complex upon interaction with DNA. It has been previously shown that Delta,Delta-[mu-(11,11'-bidppz)(phen)4Ru2]4+ binds to DNA in one of the grooves. However, we find that this is only an initial, metastable, binding mode, which is extremely slowly reorganized into an intercalative binding geometry. The slow rearrangement and dissociation, revealed by flow linear dichroism and fluorescence spectroscopy, are concluded to be a result from the complex being threaded through the DNA, with one of the bridging aromatic dppz ligands intercalated between the base pairs of the DNA, placing one metal center in the minor groove and one in the major groove. A negative LD, a high luminescence quantum yield, and long luminescence lifetimes, similar to the intercalating complex Delta-[Ru(phen)2dppz]2+, indicate intercalation of the bidppz moiety. The unique slow dissociation of the complex in its final DNA-binding mode suggests that this class of threading, partially intercalated binuclear complexes may be interesting in the context of cancer therapy. Also, their unique optical and photophysical properties could make such complexes, either alone or scaffolded by DNA structures, of interest for the development of nanometer-sized molecular optoelectronic devices. 相似文献