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51.
52.
We use Monte Carlo simulations in two dimensions to study the depletion forces between two hard squares in a suspension of hard rods or disks. We determine the effects of size and concentration of rods and disks on the potential of mean force between the squares. Both rods and disks produce a short-range depletion attraction between the two squares. The depletion interaction can be strong enough to outweigh the (rotational) entropic repulsion between the squares at certain sizes and concentrations of the rods and disks. We also probe the relative orientation that two squares adopt as they approach each other and we observe rich behavior, in which the relative orientation depends on the size, concentration, and shape of the depletion agent. Simple models based on the ideas of Asakura and Oosawa [J. Chem. Phys. 22, 1255 (1954)] can explain trends in the potentials of mean force obtained from the simulations. 相似文献
53.
Krishnan S Ward RJ Hexemer A Sohn KE Lee KL Angert ER Fischer DA Kramer EJ Ober CK 《Langmuir : the ACS journal of surfaces and colloids》2006,22(26):11255-11266
Polystyrene-b-poly(4-vinylpyridine) copolymers were quaternized with 1-bromohexane and 6-perfluorooctyl-1-bromohexane. Surfaces prepared from these polymers were characterized by contact angle measurements, near-edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy. The fluorinated pyridinium surfaces showed enhanced antibacterial activity compared to their nonfluorinated counterparts. Even a polymer with a relatively low molecular weight pyridinium block showed high antimicrobial activity. The bactericidal effect was found to be related to the molecular composition and organization in the top 2-3 nm of the surface and increased with increasing hydrophilicity and pyridinium concentration of the surface. 相似文献
54.
John V. Baxley Kristen E. Kobylus 《Journal of Computational and Applied Mathematics》2010,234(9):2699-2708
For a given positive integer N, we provide conditions on the nonlinear function f which guarantee that the boundary value problem
55.
Kristen A. McReynolds Laura K.G. Ackerman William W. Brennessel 《Journal of fluorine chemistry》2010,131(11):1108-5467
New synthetic routes to (NHC)copper-trifluoroacetate and -chlorodifluoroacetate complexes were developed (NHC = N-heterocyclic carbenes) so baseline reactivity patterns could be established for the decarboxylative trifluoromethylation of organic halides. In the presence of aryl halides, loss of CO2 from these new precursors occurred at 160 °C concurrent with the formation of aryl-CF3. 相似文献
56.
Cagri Üzüm Nora Kristen Regine von Klitzing 《Current Opinion in Colloid & Interface Science》2010,15(5):303-314
The review addresses the influence of polyelectrolytes on the statics and dynamics of thin liquid films. Both, changes of interfacial and bulk properties, contribute to the overall behaviour of thin films formed from aqueous polyelectrolyte solutions. Therefore, the chapter is separated into two parts: polyelectrolytes at film interfaces and polymers in film bulk. 相似文献
57.
Kristen L. Randall Dayana Argoti Joseph D. Paonessa Yi Ding Zachary Oaks Yuesheng Zhang Paul Vouros 《Journal of chromatography. A》2010,1217(25):4135-4143
Exposure to 4-aminobiphenyl (4-ABP), an environmental and tobacco smoke carcinogen that targets the bladder urothelium, leads to DNA adduct formation and cancer development [1]. Two major analytical challenges in DNA adduct analysis of human samples have been limited sample availability and the need to reach detection limits approaching the part-per-billion threshold. By operating at nano-flow rates and incorporating a capillary analytical column in addition to an online sample enrichment step, we have developed a sensitive and quantitative HPLC–MS/MS method appropriate for the analysis of such samples. This assay for the deoxyguanosine adduct of 4-ABP (dG-C8-4-ABP) gave mass detection limits of 20 amol in 1.25 μg of DNA (5 adducts in 109 nucleosides) with a linear range of 70 amol to 70 fmol. 4-ABP-exposed human bladder cells and rat bladder tissue were analyzed in triplicate, and higher dose concentrations led to increased numbers of detected adducts. It was subsequently established that sample requirements could be further reduced to 1 μg digestions and the equivalent of 250 ng DNA per injection for the detection of low levels of dG-C8-4-ABP in a matrix of exfoliated human urothelial cell DNA. This method is appropriate for the characterization and quantification of DNA adducts in human samples and can lead to a greater understanding of their role in carcinogenesis and also facilitate evaluation of chemopreventive agents. 相似文献
58.
Cecilio Marquez Rosa M. Rabanal Serafiin Valverde Liliana Eguren Aurea Perales Jos Fayos 《Tetrahedron letters》1980,21(52):5039-5042
Two diterpenes, capitatin 4 and teucapitatin 5 have been isolated from Teucrium capitatum. The X-ray structure of 4, including absolute stereochemistry, is given. Diterpene 4 has been chemically related to picropolin 1 and picropolinone 2, thereby establishing the absolute stereochemistry of these two neoclerodane-type diterpenes. 相似文献
59.
Raman spectra of a series of isomorphous hexafluorometallates (TlSbF6; BaMF6, M = Si, Ge, Sn, and Ti, space group ) have been measured under high pressures up to 25 kbar with a new opposed sapphire anvil cell. Pressure calibration has been achieved by means of the R1 fluorescence band of ruby. The frequency of the only Raman active lattice mode (libration of the octahedral anion) of each compound shows a higher pressure dependence than do the internal vibrations of the anions. The Eg components of the ν5 modes of the MF6 octahedra which are coupled to the Eg lattice modes because of their same symmetries and small frequency differences exhibit higher pressure sensitivities than do the uncoupled internal modes. These findings may be used as a further means for symmetry assignment. BaGeF6 undergoes a reversible phase transition at 9.6 kbar; the split librational modes of the high-pressure phase show the highest pressure dependences of up to about 3 cm?1 · kbar?1 found in this investigation. 相似文献
60.
Woods KK Maehigashi T Howerton SB Sines CC Tannenbaum S Williams LD 《Journal of the American Chemical Society》2004,126(47):15330-15331
The crystal structure of [d(CGCAAATTTGCG)]2 has been determined to 1.5 A resolution, representing the first high-resolution structure of this DNA fragment. The ion interactions are novel. A spermine molecule replaces a Mg2+ observed in analogous structures. Unlike lower-resolution structures, the minor groove is narrow and the major groove lacks extra Watson-Crick hydrogen bonds. In addition, a monolayer of solvent sites, including a "spine of hydration", is visible in the minor groove. The crystal of [d(CGCAAATTTGCG)]2 was grown from a solution containing spermine, magnesium, and lithium. The conformation recapitulates that of "monovalent-minus" DNA. 相似文献