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441.
The phase behavior of suspensions of colloidal hard tetragonal parallelepipeds ("TPs") (also known as rectangular nanorods or nanobars) was studied by using Monte Carlo simulations to gain a detailed understanding of the effect of flat-faceted particles on inducing regular local packing and long range structural order. A TP particle has orthogonal sides with lengths a, b, and c, such that a=b and its aspect ratio is r=c/a. The phase diagram for such perfect TPs was mapped out for particle aspect ratios ranging from 0.125 to 5.0. Equation of state curves, order parameters, particle distribution functions, and snapshots were used to analyze the resulting phases. Given the athermal nature of the systems studied, it is the interplay of purely entropic forces that drives phase transitions amongst the structures observed that include crystal, columnar, smectic, parquet, and isotropic phases. In the parquet phase that occurs for 0.54相似文献
442.
Ibraheem Hamdan Bettina Wiegand Mathias Toll Martin Sauter 《Isotopes in environmental and health studies》2016,52(6):682-693
The Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ18O values in rainwater vary from ?3.26 to ?17.34?‰ (average: ?7.84?±?3.23?‰), while δ2H values range between ?4.4 and ?110.4?‰ (average: ?35.7?±?25.0?‰). Deuterium excess ranges from 17.8 to 34.1?‰ (average: 27.1?±?4.0?‰). The Local Meteoric Water Line for the study area was calculated to be δ2H?=?7.66*δ18O?+?24.43 (R2?=?0.98). Pre-event spring discharge showed variation in δ18O (range ?6.29 to ?7.17?‰; average ?6.58?±?0.19?‰) and δ2H values (range ?28.8 to ?32.7?‰; average: ?30.5?±?1.0?‰). In contrast, δ18O and δ2H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days. 相似文献
443.
444.
Ferrocene-based derivatization has raised considerable interest in many fields of analytical chemistry. This is due to the
well-established chemistry of ferrocenes, which allows rapid and easy access to a large number of reagents and derivatives.
Furthermore, the electrochemical properties of ferrocenes are attractive with respect to their detection. This paper summarizes
the available reagents, the reaction conditions and the different approaches for detection. While electrochemical detection
is still most widely used to detect ferrocene derivatives, e.g., in the field of DNA analysis, the emerging combination of
analytical separation methods with electrochemistry, mass spectrometry and atomic spectroscopy allows ferrocenes to be applied
more universally and in novel applications where strongly improved selectivity and limits of detection are required. 相似文献
445.
Bernhard Richter MD Erwin Lhle Bettina Knapp Matthias Weikert Josef Schlmicher-Thier Katherine Verdolini 《Journal of voice》2002,16(1):72-80
Objective, quantitative information is lacking in the medical community about actual working conditions for professional singers onstage, and moreover, about which conditions are safe. Physicians, speech-language pathologists, and speech scientists focusing on laryngology should have relevant information about the opera as workplace and the medical sequelae of unhealthy environments. We describe five toxic substances to which singers presenting to our clinics were exposed while working professionally on the opera stage: (1) aromatic diisocyanates, (2) penicillium frequentans in cork granulate, (3) formaldehyde in cork granulate, (4) cobalt and aluminum (pigment components), and (5) quartz sand capable of entering the alveolae. Biological considerations and clinical data for some subjects suggest a direct causal link between the exposures and the patients' complaints and findings. Our observations suggest that whenever singers complain about deleterious conditions such as dry and hot onstage climate or suspicion of the presence of harmful substances, the specific conditions existing in the theater in question should be investigated. Harmful substances are not only poorly tolerated by singers, but also they should be preventable. 相似文献
446.
Janczyk M Appel B Springstubbe D Fritz HJ Müller S 《Organic & biomolecular chemistry》2012,10(8):1510-1513
Herein we report a convenient approach for the preparation of fully protected trinucleotide synthons to be used for the synthesis of gene libraries. The trinucleotide synthons bear β-cyanoethyl groups at the phosphate residues, and thus can be used in standard oligonucleotide synthesis without additional steps for deprotection and work-up. 相似文献
447.
Junggeburth SC Schwinghammer K Virdi KS Scheu C Lotsch BV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(7):2143-2152
The transfer of supramolecular templating to the realm of metal–organic frameworks opens up new avenues to the design of novel hierarchically structured materials. We demonstrate the first synthesis of mesostructured zinc imidazolates in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), which acts as a template giving rise to ordered lamellar hybrid materials. A high degree of order spanning the atomic and mesoscale was ascertained by powder X‐ray diffraction, electron diffraction, as well as solid‐state NMR and IR spectroscopy. The metrics of the unit cells obtained for the zinc methylimidazolate and imidazolate species are a=(11.43±0.45), b=(9.55±0.35), c=(27.19±0.34) Å, and a=(10.98±0.90), b=(8.95±0.95), c=(26.33±0.34) Å, respectively, assuming orthorhombic symmetry. The derived structure model is consistent with a mesolamellar structure composed of bromine‐terminated zinc (methyl)imidazolate chains interleaved with motionally rigid cationic surfactant molecules in an all‐trans conformation. The hybrid materials exhibit unusually high thermal stability up to 300 °C, at which point CTAB is lost and evidence for a thermally induced transformation into poorly crystalline mesostructures with larger feature sizes is obtained. Treatment with ethanol effects the extraction of CTAB from the material, followed by facile transformation into pure microporous ZIF‐8 nanoparticles within minutes, thus demonstrating a unique transition from a mesostructure into a microporous zinc imidazolate. 相似文献
448.
B Horn C Limberg C Herwig M Feist S Mebs 《Chemical communications (Cambridge, England)》2012,48(66):8243-8245
Reaction of a nickel(0) carbonyl complex, K(2)[L(tBu)NiCO](2), with N(2)O generates a cyclic carbonate compound composed of six [Ni(II)(CO(3))K](+) units. The same product can also be obtained using O(2) as the oxidant in a solid-state/gas reaction. These conversions represent unique examples of a nickel-bound CO oxidation by N(2)O and O(2), respectively. 相似文献
449.
Yarman A Gröbe G Neumann B Kinne M Gajovic-Eichelmann N Wollenberger U Hofrichter M Ullrich R Scheibner K Scheller FW 《Analytical and bioanalytical chemistry》2012,402(1):405-412
The aromatic peroxygenase (APO; EC 1.11.2.1) from the agraric basidomycete Marasmius rotula (MroAPO) immobilized at the chitosan-capped gold-nanoparticle-modified glassy carbon electrode displayed a pair of redox peaks
with a midpoint potential of −278.5 mV vs. AgCl/AgCl (1 M KCl) for the Fe2+/Fe3+ redox couple of the heme-thiolate-containing protein. MroAPO oxidizes aromatic substrates such as aniline, p-aminophenol, hydroquinone, resorcinol, catechol, and paracetamol by means of hydrogen peroxide. The substrate spectrum overlaps
with those of cytochrome P450s and plant peroxidases which are relevant in environmental analysis and drug monitoring. In
M. rotula peroxygenase-based enzyme electrodes, the signal is generated by the reduction of electrode-active reaction products (e.g.,
p-benzoquinone and p-quinoneimine) with electro-enzymatic recycling of the analyte. In these enzyme electrodes, the signal reflects the conversion
of all substrates thus representing an overall parameter in complex media. The performance of these sensors and their further
development are discussed. 相似文献
450.
An analytical methodology for quality control analyses of IgG and their impurities is presented using a new UV‐LIF (266 nm) detector inside the cassette of a CE instrument and its performance was evaluated. The observed sensitivity was very close to that obtained by silver staining of slab gels (LOD of 25 ng/mL), while the sensitivity of the analysis is 80 times better than with CE/UV absorption (214 nm). Examples of the analysis of pharmaceutical and other commercial IgGs are provided and the kinetics of the reduction of IgG by β‐mercaptoethanol is reported, demonstrating the ease of performing the analysis. 相似文献