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951.
Krzysztof Gaw?dzki David P. Herzog Jan Wehr 《Communications in Mathematical Physics》2011,308(1):49-80
We study a simple stochastic differential equation that models the dispersion of close heavy particles moving in a turbulent
flow. In one and two dimensions, the model is closely related to the one-dimensional stationary Schr?dinger equation in a
random δ-correlated potential. The ergodic properties of the dispersion process are investigated by proving that its generator is
hypoelliptic and using control theory. 相似文献
952.
The degradation of several aliphatic and aromatic polyesters with lipases from Candida cylindracea (CcL) and Pseudomonas species (PsL) was investigated applying nanoparticles of the polymers. Nanoparticles (diameters 50 nm to 250 nm) of a particle concentration up to 6 mg/ml could be prepared by a precipitation technique without adding any stabilizing agents in the aqueous solutions. Using a titration system to monitor ester cleavage, enzymatic degradation experiments could be performed in the time scale of some minutes. A kinetic model is proposed which is based on a surface erosion process dependent on molar ester bond density and enzyme loading. Experimental evidence provided that degradation of the particles occurs uniformly at the surface after a Langmuir type adsorption of the enzyme. Rate constants and the maximal enzyme loadings of enzyme were estimated from the kinetic model for different polyesters and the rate constants correlate well with the length of the diacid component of the polyester. Comparison of degradation rates of polyester films and nanoparticles revealed that nanoparticles of aliphatic polyesters are in the amorphous state. Hence, differences of the rate constants reflect the direct influence of the polymer structure on the enzymatic hydrolysis not overlaid by effects of crystallinity. 相似文献
953.
Adam Strachota Martin Černý Zdeněk Chlup Miroslav Šlouf Jiřina Hromádková Josef Pleštil Hana Šandová Petr Glogar Zbyněk Sucharda Martina Havelcová Jana Schweigstillová Ivo Dlouhý Vladislav Kozák 《Journal of Non》2012,358(20):2771-2782
The optimization of the synthesis of silicon oxycarbide ceramics via the sol–gel/pyrolysis route is described, starting from several alkylalkoxysilanes and vinylalkoxysilanes. The main aim was to achieve low weight losses during cure and pyrolysis and also a compact ceramics morphology. The theoretical composition of the pyrolysates was changed between SiO1.5C and SiO1.2C2.3, by varying monomer types and ratios. An assessment of the real composition was performed using energy-dispersive X-ray spectroscopy. The smallest weight losses were obtained for the resins based on vinyltriethoxysilane and dimethyldiethoxysilane which were additionally modified by the addition of a small amount of boric acid. Somewhat higher weight losses combined with the best toughness were found for resins based on non-vinylated silsesquioxane with a low content on linear dimethylsiloxane units. As an alternative, a precursor (SiO0.9C2.8) was prepared via hydrosilylation, based on cyclic dimethylsiloxane oligomers interconnected to a network, but its weight losses were higher than those of sol–gel silicon oxycarbide. 相似文献
954.
Ivo Stassen Prof. Dirk De Vos Prof. Rob Ameloot 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14452-14460
Materials processing, and thin‐film deposition in particular, is decisive in the implementation of functional materials in industry and real‐world applications. Vapor processing of materials plays a central role in manufacturing, especially in electronics. Metal–organic frameworks (MOFs) are a class of nanoporous crystalline materials on the brink of breakthrough in many application areas. Vapor deposition of MOF thin films will facilitate their implementation in micro‐ and nanofabrication research and industries. In addition, vapor–solid modification can be used for postsynthetic tailoring of MOF properties. In this context, we review the recent progress in vapor processing of MOFs, summarize the underpinning chemistry and principles, and highlight promising directions for future research. 相似文献
955.
956.
Fluoro‐ and Perfluoralkylsulfonylpentafluoroanilides: Synthesis and Characterization of NH Acids for Weakly Coordinating Anions and Their Gas‐Phase and Solution Acidities 下载免费PDF全文
Julius F. Kögel Thomas Linder Fabian G. Schröder Jörg Sundermeyer Sascha K. Goll Daniel Himmel Ingo Krossing Karl Kütt Jaan Saame Ivo Leito 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5769-5782
Fluoro‐ and perfluoralkylsulfonyl pentafluoroanilides [HN(C6F5)(SO2X); X=F, CF3, C4F9, C8F17] are a class of imides with two different strongly electron‐withdrawing substituents attached to a nitrogen atom. They are NH acids, the unsymmetrical hybrids of the well‐known symmetrical bissulfonylimides and bispentafluorophenylamine. The syntheses, the structures of these perfluoroanilides, their solvates, and some selected lithium salts give rise to a structural variety beyond the symmetrical parent compounds. The acidities of representative subsets of these novel NH acids have been investigated experimentally and quantum‐chemically and their gas‐phase acidities (GAs) are reported, as well as the pKa values of these compounds in acetonitrile (MeCN) and DMSO solution. In quantum chemical investigations with the vertical and relaxed COSMO cluster‐continuum models (vCCC/rCCC), the unusual situation is encountered that the DMSO‐solvated acid Me2SO–H‐N(SO2CF3)2, optimized in the gas phase (vCCC model), dissociates to Me2SO‐H+–N(SO2CF3)2? during structural relaxation and full optimization with the solvation model turned on (rCCC model). This proton transfer underlines the extremely high acidity of HN(SO2CF3)2. The importance of this effect is studied computationally in DMSO and MeCN solution. Usually this effect is less pronounced in MeCN and is of higher importance in the more basic solvent DMSO. Nevertheless, the neglect of the structural relaxation upon solvation causes typical changes in the computational pKa values of 1 to 4 orders of magnitude (4–20 kJ mol?1). The results provide evidence that the published experimental DMSO pKa value of HN(SO2CF3)2 should rather be interpreted as the pKa of a Me2SO‐H+–N(SO2CF3)2? contact ion pair. 相似文献
957.
Sensing of Double‐Stranded DNA/RNA Secondary Structures by Water Soluble Homochiral Perylene Bisimide Dyes 下载免费PDF全文
Jana Gershberg Dr. Marijana Radić Stojković Marko Škugor Dr. Sanja Tomić Dr. Thomas H. Rehm Stefanie Rehm Dr. Chantu R. Saha‐Möller Dr. Ivo Piantanida Prof. Dr. Frank Würthner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7886-7895
A broad series of homochiral perylene bisimide (PBI) dyes were synthesized that are appended with amino acids and cationic side chains at the imide positions. Self‐assembly behavior of these ionic PBIs has been studied in aqueous media by UV/Vis spectroscopy, revealing formation of excitonically coupled H‐type aggregates. The interactions of these ionic PBIs with different ds‐DNA and ds‐RNA have been explored by thermal denaturation, fluorimetric titration and circular dichroism (CD) experiments. These PBIs strongly stabilized ds‐DNA/RNA against thermal denaturation as revealed by high melting temperatures of the formed PBI/polynucleotide complexes. Fluorimetric titrations showed that these PBIs bind to ds‐DNA/RNA with high binding constants depending on the number of the positive charges in the side chains. Thus, spermine‐containing PBIs with six positive charges each showed higher binding constants (logKs=9.2–9.8) than their dioxa analogues (logKs=6.5–7.9) having two positive charges each. Induced circular dichroism (ICD) of PBI assemblies created within DNA/RNA grooves was observed. These ICD profiles are strongly dependent on the steric demand of the chiral substituents of the amino acid units and the secondary structure of the DNA or RNA. The observed ICD effects can be explained by non‐covalent binding of excitonically coupled PBI dimer aggregates into the minor groove of DNA and major groove of RNA which is further supported by molecular modeling studies. 相似文献
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