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911.
Haleden Chiririwa Freeman Ntuli Edison Muzenda Alfred Muller 《Transition Metal Chemistry》2013,38(4):393-399
The reactions of N-(2(diphenylphosphino) benzylidene) (phenyl) methanamine, Ph2PPhNHCH2-C5H4N, 1 and N-(2-(diphenylphosphino) (benzylidene) (thiophen-2-yl) methanamine, Ph2PPhNHCH2-C4H3S, 2 with MCl2(cod) and MCl(cod)Me (M = Pd, Pt; cod = 1,5-cyclooctadiene) yield the new complexes [M(Ph2PPhNHCH2-C5H4N)Cl2], M = Pd1a, Pt1b, [M(Ph2PPhNHCH2-C5H4N)ClMe], M = Pd1c, Pt 1d, [M(Ph2PPhNHCH2-C4H3S)Cl2], M = Pd2a, Pt 2b, and [M(Ph2PPhNHCH2-C4H3S)ClMe], M = Pd2c, Pt 2d, respectively. The new compounds were isolated as analytically pure crystalline solids and characterized by 31P-, 1H-NMR, IR spectroscopy, electro spray ionization-mass spectrometry (ESI-MS) and elemental analysis. The representative solid-state molecular structures of the platinum complexes 1b and 2b were determined using single crystal X-ray diffraction analysis and revealed that the complexes exhibit a slightly distorted square-planar geometry. Furthermore, the palladium complexes were tested as potential catalysts in the Heck and Suzuki cross-coupling reactions. 相似文献
912.
The rates of free radical copolymerizations at given rates of initiation can be analyzed ideally in terms of monomer feed concentrations and reactivity ratios, propagation rate constants for homopolymerizations of the particular monomers, and an overall rate constant for termination during copolymerization. This model, which is due to Atherton and North, can account for the effects of initiator concentration and viscosity of the polymerization medium on copolymerization rates. This article reports an empirical formulation for the overall termination rate constant in terms of monomer concentrations and reactivity ratios and a cross-termination factor. The new model accounts for experimental data in the styrene-methyl methacrylate system in which polarity differences between unlike radicals may result in enhanced termination rates. It also predicts observed copolymerization rates of methyl methacrylate-vinyl acetate and styrene-α-methylstyrene mixtures in which polarity effects are absent. The cross-termination factor may be approximated from reactivity ratio data for predictive purposes. 相似文献
913.
Abstract Numerous theories of polymer solution behavior have been advanced. Some make use of the techniques of statistical mechanics [1] and are unfortunately burdened with tedious mathematical manipulations, Recent years have seen the emergence of the socalled scaling laws of de Gennes [2]. These are mainly of theoretical interest and are strictly applicable to polymers with very high molecular weight in good solvents, While these theories are important as steps toward a fundamental understanding of polymer solutions, they are not easy to understand or apply to practical calculations of polymer solution properties. 相似文献
914.
André A. Adams Paul T. Charles Scott P. Veitch Alfred Hanson Jeffrey R. Deschamps Anne W. Kusterbeck 《Analytical and bioanalytical chemistry》2013,405(15):5171-5178
Quantitating explosive materials at trace concentrations in real-time on-site within the marine environment may prove critical to protecting civilians, waterways, and military personnel during this era of increased threat of widespread terroristic activity. Presented herein are results from recent field trials that demonstrate detection and quantitation of small nitroaromatic molecules using novel high-throughput microfluidic immunosensors (HTMI) to perform displacement-based immunoassays onboard a HYDROID REMUS100 autonomous underwater vehicle. Missions were conducted 2–3 m above the sea floor, and no HTMI failures were observed due to clogging from biomass infiltration. Additionally, no device leaks were observed during the trials. HTMIs maintained immunoassay functionality during 2 h deployments, while continuously sampling seawater absent without any pretreatment at a flow rate of 2 mL/min. This 20-fold increase in the nominal flow rate of the assay resulted in an order of magnitude reduction in both lag and assay times. Contaminated seawater that contained 20–175 ppb trinitrotoluene was analyzed. Figure
Displacement-based immunoassay targeting trinitrotoluene is shown 相似文献
915.
Arkadiy S. Baltenkov Steven T. Manson Alfred Z. Msezane 《Central European Journal of Physics》2011,9(5):1209-1220
A comprehensive study is undertaken of angular distributions of electron knock-out from atomic targets by fast electrons with
a small transfer of momentum. The general expressions for the parameters of the triple differential cross-section of impact
ionization in the optical limit are derived. The calculated parameters are compared with those of the angular distribution
of electrons ejected from an atom in the process of photoionization. In these processes, when the multipole transitions are
involved, the one-to-one correspondence between the photoionization and impact ionization parameters disappears. The nondipole
transitions lead to the backward/forward asymmetry of the angular distribution of ejected electrons that is absent in the
dipole approximation for ionization by both fast electrons and photons. Using the He atom as an example, the character of
the asymmetry for these two processes is qualitatively different and the backward/forward asymmetry results in macroscopic
directed motion of secondary electrons accompanying the passing of a fast electron beam through gas or plasma. The general
formulas for this drag current are derived and applied to gaseous He. 相似文献
916.
Fei Qi Anna Moiseev Joachim Deubener Alfred Weber 《Journal of nanoparticle research》2011,13(3):1325-1334
Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO2 and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at
elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO2/SiO2 particles were synthesized by a flame aerosol process with TiCl4 and SiCl4 as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO2/SiO2 samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO2 P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for
comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means
of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was
found that SiO2 stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content
of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO2 layer/bridge as spacer between TiO2 particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination
at 1,000 °C. Due to the stabilizing effect of SiO2 the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase
in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either
due to intensified cracking of the SiO2 layer or due to enhanced transport of SiO2 into the necks thus releasing additional titania surface. 相似文献
917.
Iglev H Fischer MK Gliserin A Laubereau A 《Journal of the American Chemical Society》2011,133(4):790-795
The photodetachment of aqueous hydroxide (OH(?)(aq) and OD(?)(aq)) is studied using femtosecond pump?probe and pump?repump?probe spectroscopy. The electron is detached after excitation of the hydroxide ion to a charge-transfer-to-solvent (CTTS) state at 202 nm. An early intermediate is observed that builds up within 160 fs and is assigned to nonequilibrated OH?electron pairs. The subsequent dynamics are governed by thermalization, partial recombination, and dissociation of the pairs, yielding the final hydrated electrons and hydroxyl radicals. An additional pulse at 810 nm is used for secondary excitation of the intermediate species so that more insight is gained into the recombination process(es). Using this technique we observe a novel geminate recombination channel of OH with adjacent hydrated electrons. This channel leads to ultrafast quenching (700 fs) of almost half the initial number of radicals. The fast mechanism displays an isotope effect of 1.4 (for OD(?)(aq) quantum yield 35%, time constant 1.0 ps). This process was not observed in similar experiments on aqueous bromide and seems to be related to the special properties of the hydroxide ion and its local H-bonding environment. Our findings underline the high reactivity of the prehydrated electron. 相似文献
918.
Yulian Pang Shuheng Fan Qunying Wang Dennis Oprych Alfred Feilen Knut Reiner Dietmar Keil Yuriy L. Slominsky Sergey Popov Yingquan Zou Bernd Strehmel 《Angewandte Chemie (International ed. in English)》2020,59(28):11440-11447
Cyanines comprising either a benzo[e]‐ or benzo[c,d]indolium core facilitate initiation of radical photopolymerization combined with high power NIR‐LED prototypes emitting at 805 nm, 860 nm, or 870 nm, while different oxime esters function as radical coinitiators. Radical photopolymerization followed an initiation mechanism based on the participation of excited states, requiring additional thermal energy to overcome an existing intrinsic activation barrier. Heat released by nonradiative deactivation of the sensitizer favored the system, even under conditions where a thermally activated photoinduced electron transfer controls the reaction protocol. The heat generated internally by the NIR sensitizer promotes generation of the initiating reactive radicals. Sensitizers with a barbiturate group at the meso‐position preferred to bleach directly, while sensitizers carrying a cyclopentene moiety unexpectedly initiated the photosensitized mechanism. 相似文献
919.
Ramona Samba Kai Fuchsberger Ilona Matiychyn Sebastian Epple Lydia Kiesel Alfred Stett Wolfgang Schuhmann Martin Stelzle 《Electroanalysis》2014,26(3):548-555
In this work, composite microelectrodes from poly(3,4‐ethylenedioxythiophene) (PEDOT) and carbon nanotubes (CNT) are characterized as electrochemical sensing material for neurotransmitters. Dopamine can be detected using square wave voltammetry at these microelectrodes. The CNTs improve the sensitivity by a factor of two. In addition, the selectivity towards dopamine in the presence of ascorbic acid and uric acid was examined. While both electrodes, PEDOT and PEDOT‐CNT are able to detect all measured concentrations of dopamine in the presence of uric acid, small concentrations of dopamine and ascorbic acid are only distinguishable at PEDOT‐CNT electrodes. Changing the pH has a strong influence on the selectivity. Moreover, it is possible to detect concentrations as low as 1 µM dopamine in complex cell culture medium. Finally, other catecholamines like serotonin, epinephrine, norepinephrine and L ‐dopa are also electrochemically detectable at PEDOT‐CNT microelectrodes. 相似文献
920.
Dr. Markus Kalmutzki Dr. Markus Ströbele Dipl.‐Chem. Frank Wackenhut Prof. Dr. Alfred J. Meixner Prof. Dr. H.‐Jürgen Meyer 《Angewandte Chemie (International ed. in English)》2014,53(51):14260-14263
Calcium cyanurate is synthesized by reacting calcium chloride with potassium cyanate following a solid‐state reaction. The formation of the new compound Ca3(O3C3N3)2 (CCY), which occurs by the cyclotrimerization of cyanate ions, was examined thermoanalytically and the crystal structure was determined by single‐crystal structure analysis. The structure of CCY is closely related to the structure of the well‐known oxoborate β‐BaB2O4 (BBO). Second harmonic generation (SHG) measurements on crystal powders show a higher SHG efficiency for CCY than for BBO by about one order of magnitude. 相似文献