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971.
Walsh Z Levkin PA Abele S Scarmagnani S Heger D Klán P Diamond D Paull B Svec F Macka M 《Journal of chromatography. A》2011,1218(20):2954-2962
An investigation into the preparation of monolithic separation media utilising a cyanine dye sensitiser/triphenylbutylborate/N-methoxy-4-phenylpyridinium tetrafluoroborate initiating system activated by 660 nm light emitting diodes is reported. The work demonstrates multiple uses of red-light initiated polymerisation in the preparation of monolithic stationary phases within polyimide and polyimide coated channels and the modification of monolithic materials with molecules which absorb strongly in the UV region. This initiator complex was used to synthesise poly(butyl methacrylate-co-ethylene dimethacrylate) and poly(methyl methacrylate-co-ethylene dimethacrylate) monolithic stationary phases in polyimide coated fused silica capillaries of varying internal diameters, as well as within polyimide micro-fluidic chips. The repeatability of the preparation procedure and resultant monolithic structure was demonstrated with a batch of poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths in 100 μm i.d. polyimide coated fused silica capillary, which were applied to the separation of a model protein mixture (ribonuclease A, cytochrome C, myoglobin and ovalbumin). Taking an average from 12 chromatograms originating from each batch, the maximum relative standard deviation of the retention factor (k) for the protein separations was recorded as 0.53%, the maximum variance for the selectivity factor (α) was 0.40% while the maximum relative standard deviation in peak resolution was 8.72%. All maxima were recorded for the Ribonuclease A/Cytochrome C peaks. Scanning electron microscopy confirmed the success of experiments in which poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths were prepared using the same initiation approach in capillary and micro-fluidic chips, respectively. The initiating system was also applied to the photo-initiated grafting of a chromophoric monomer onto poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths within poly(tetrafluoroethylene) coated fused silica capillaries. 相似文献
972.
Mixed oxide TiO(2)-Fe(2)O(3) bi-composites have been recognised as efficient and economical sorbents with great promise for arsenic removal from groundwater. In this study, we use a fast, simple and inexpensive synthesis method for this type of bi-composite and assess its adsorption performance. The kinetics of arsenate and phosphate adsorption onto the bi-composite are determined, demonstrating rapid and stable uptake of both oxy-anions over several days and with improved performance compared to the widely used TiO(2) sorbent. A modified pseudo-second order rate equation is introduced, which allows the adsorption kinetics to be modelled as two simultaneous, parallel reaction pathways with separate kinetic parameters. This equation reproduces the experimental observations accurately across a wide range of timescales from minutes to days. Our experimental data agrees with previous interpretations of the adsorption mechanism including the formation of mono-dentate and bi-dentate inner-sphere surface complexes. The arsenate and phosphate uptake capacities of the bi-composite are reported. Equilibrium studies were conducted between pH 5 and 9 and interpreted within the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. 相似文献
973.
Alla Dolgopolova Dominik J. Weiss Reimar Seltmann Chris Stanley Barry Coles Andriy K. Cheburkin 《International journal of environmental analytical chemistry》2013,93(12):889-899
A reliable and robust procedure using closed-vessel microwave digestion of lichens and leaves for precise and accurate determination of trace elements (Pb, Zn and Cu) and stable Pb isotope ratios is presented. The method was developed using certified reference material CRM 482 Pseudovernia furfurea (Lichens), NIST 1515 (Apple Leaves) and NIST 1547 (Peach Leaves) and tested on lichens from a mining site in Russia. A mixture of 3?mL of HNO3, 3?mL of H2O2, 2?mL of H2O and 0.8?mL of HF ensured complete sample dissolution with 100?±?5% recovery for Pb, Zn and Cu at a maximum temperature of 210°C and pressure of 350?psi. The amount of HF and microwave pressure significantly influenced Pb, Zn and Cu recovery. Comparison between EMMA-XRF and ICP-AES showed a good correlation between Pb, Zn and Cu concentrations. Using the newly developed digestion method, Pb isotopes in lichens from the mining site were determined with an internal precision better than 0.02%. 相似文献
974.
Prof. Dr. Sjoerd Harder Dominik Naglav Dr. Christian Ruspic Prof. Dr. Claudia Wickleder Dr. Matthias Adlung Dr. Wilfried Hermes Dr. Matthias Eul Prof. Dr. Rainer Pöttgen Dr. Daniel B. Rego Prof. Dr. Frederic Poineau Prof. Dr. Kenneth R. Czerwinski Prof. Dr. Rolfe H. Herber Prof. Dr. Israel Nowik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12272-12280
The superbulky deca‐aryleuropocene [Eu(CpBIG)2], CpBIG=(4‐nBu‐C6H4)5‐cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT=2‐Me2N‐α‐Me3Si‐benzyl, with two equivalents of CpBIGH. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45 % quantum yield). The crystal structure is isomorphic to those of [M(CpBIG)2] (M=Sm, Yb, Ca, Ba) and shows the typical distortions that arise from CpBIG???CpBIG attraction as well as excessively large displacement parameter for the heavy Eu atom (Ueq=0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(CpBIG)2] (M=Sm, Eu, Yb), several physical analyses have been applied. Temperature‐dependent magnetic susceptibility data of [Yb(CpBIG)2] show diamagnetism, indicating stable divalent ytterbium. Temperature‐dependent 151Eu Mössbauer effect spectroscopic examination of [Eu(CpBIG)2] was examined over the temperature range 93–215 K and the hyperfine and dynamical properties of the EuII species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single‐crystal X‐ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low‐frequency torsional and librational modes in [Eu(CpBIG)2]. X‐ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(CpBIG)2] (Ln=Sm, Eu, Yb) compounds are divalent. The XANES white‐line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(CpBIG)2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(CpBIG)2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24270 cm?1) gives a symmetrical single band in the emission spectrum at 606 nm (νmax=16495 cm?1, FWHM: 2090 cm?1, Stokes‐shift: 2140 cm?1), which is assigned to a 4f65d1→4f7 transition of EuII. These remarkable values compare well to those for EuII‐doped ionic host lattices and are likely caused by the rigidity of the [Eu(CpBIG)2] complex. Sharp emission signals, typical for EuIII, are not visible. 相似文献
975.
Katharina Tauber Michael Fuchs Johann H. Sattler Julia Pitzer Desiree Pressnitz Dr. Dominik Koszelewski Prof. Kurt Faber Jan Pfeffer Thomas Haas Prof. Wolfgang Kroutil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):4030-4035
Various artificial network designs that involve biocatalysts were tested for the asymmetric amination of sec‐alcohols to the corresponding α‐chiral primary amines. The artificial systems tested involved three to five redox enzymes and were exemplary of a range of different sec‐alcohol substrates. Alcohols were oxidised to the corresponding ketone by an alcohol dehydrogenase. The ketones were subsequently aminated by employing a ω‐transaminase. Of special interest were redox‐neutral designs in which the hydride abstracted in the oxidation step was reused in the amination step of the cascade. Under optimised conditions up to 91 % conversion of an alcohol to the amine was achieved. 相似文献
976.
Kinematic analysis, in contrast to sophisticated molecular dynamics simulations, can provide high-level insights into conformational diversity of proteins and other biomolecules, with broad implications for human health. Here, we model a protein as a kinematic linkage and present a new geometric method to characterize molecular rigidity. While existing combinatorial constraint counting is limited to generic structures, our geometric approach is also valid for non-generic linkages. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
977.
In this work a coupled two-scale sandwich shell model is proposed, where 4-node quadrilaterals are employed both on the global and the local scale. The coupled global-local boundary value problem is derived by means of a variational formulation and ensuing linearization. A numerical simulation is carried out for linear elastic and elasto-plastic material behavior with small strains. The resulting coupled nonlinear boundary value problem is solved simultaneously in a Newton iteration with incremental load steps. Various types of sandwich models are investigated in the form of uni- and bidirectionally stiffened structures. For the unidirectionally stiffened beam, an analytical reference solution is present by means of classical beam theory. In addition, the numerical results of all coupled calculations are compared to full scale shell models, showing very good agreement while significantly reducing the size of occurring system matrices. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
978.
We consider non-autonomous wave equations $$\left\{\begin{array}{ll}\ddot{u}(t) + \mathcal{B}(t) \dot{u}(t) + \mathcal{A}(t)u(t) = f(t) \quad t{\text -}{\rm a.e.}\\ u(0) = u_{0},\, \dot{u}(0) = u_{1}.\\\end{array}\right.$$ where the operators ${\mathcal{A}(t)}$ and ${\mathcal{B}(t)}$ are associated with time-dependent sesquilinear forms ${\mathfrak{a}(t, ., .)}$ and ${\mathfrak{b}}$ defined on a Hilbert space H with the same domain V. The initial values satisfy ${u_0 \in V}$ and ${u_1 \in H}$ . We prove well-posedness and maximal regularity for the solution both in the spaces V′ and H. We apply the results to non-autonomous Robin-boundary conditions and also use maximal regularity to solve a quasilinear problem. 相似文献
979.
A method for the construction of three-dimensional statistically similar representative volume elements (SSRVEs) is presented. Since the beneficial material properties of microheterogeneous materials originate in the microstructure, its incorporation in material modeling is desired. The FE2 method is a suitable tool to accomplish this step. Applying this method, a microscopic boundary value problem, given by a representative volume element (RVE) is attached to every integration point of the macroscale. Such RVEs taken from real microstructures exhibit a high level of complexity, thus raise computational costs. The use of a SSRVE with lower complexity is able to decrease these costs. Here, different statistical measures are compared in view of the performance in the SSRVE construction procedure. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
980.
We consider quasilinear parabolic systems posed on the real line with a spatially homogeneous ground state which becomes unstable via a Hopf-, Turing-, or Turing-Hopf instability. Then close to the first instability via multiple scaling analysis a Ginzburg-Landau equation can be derived in order to describe bifurcating solutions which are slow modulations in time and space of the most unstable modes. We give an overview about the mathematical justification and explain recent error estimates. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献