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991.
Kent A. Nielsen Dr. Eric Levillain Dr. Vincent M. Lynch Dr. Jonathan L. Sessler Prof. Jan O. Jeppesen Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(2):506-516
Four tetrathiafulvalene (TTF)‐annulated porphyrins 1 – 4 were synthesized and characterized. All contain a tetraphenylporphyrin (TPP) core onto which four, two, or one TTF subunits were annulated. Absorption and fluorescence spectroscopic studies together with electrochemical investigations reveal that interactions between the porphyrin system and the annulated TTF units take place in solution. The annulation of one or more TTF units to the porphyrin core has a profound effect on the reduction potentials associated with this latter framework, with positive shifts in the range of 0.105 to 0.355 V and 0.200 to 0.370 V for the first and second reduction potential, respectively, compared to the corresponding processes in the model compound TPP, 18 . The redox potentials for the first oxidation of the TTF units are considerably shifted in 4 (ΔEox1=+0.285 V) and 2 (ΔEox1=?0.140 V), whereas for 1 and 3 these potentials remain within the region expected for a normal TTF unit. Considerable changes in the second oxidation potential associated with the TTF subunits were seen for 2 (ΔEox1=?0.085) and 3 (ΔEox1=?0.175). The emission spectra of 1 – 4 revealed that the porphyrin fluorescence is almost quenched in the neutral state of the TTF‐annulated porphyrins, a finding that is consistent with substantial electron transfer taking place from the TTF subunits to the porphyrin core. Oxidation of the TTF unit(s) (TTF→TTF.+) present in 1 – 4 leads to the emission intensity being restored. 相似文献
992.
Magnus Rueping Prof. Dr. Alexander Kuenkel Dipl.‐Chem. Francisco Tato Dr. Jan W. Bats Dr. 《Angewandte Chemie (International ed. in English)》2009,48(20):3699-3702
C′mon 1,2‐dione : A new diastereo‐ and enantioselective Lewis base catalyzed domino Michael/aldol reaction converts α,β‐unsaturated aldehydes and 1,2‐diones into chiral bicyclo[3.2.1]octane‐6‐carbaldehydes. The products are produced in good to excellent enantioselectivities (90–98 % ee) and can be transformed into bicyclic diols and triols. Additionally, a retro‐aldol cyclization provides access to valuable tetrahydrochromenones (see scheme).
993.
Marco Felici Pablo Contreras‐Carballada Dr. Yolanda Vida Dr. Jan M. M. Smits Roeland J. M. Nolte Prof. Dr. Luisa De Cola Prof. Dr. René M. Williams Dr. Martin C. Feiters Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13124-13134
Novel 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine (pytl) ligands have been prepared by “click chemistry” and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)2(pytl‐R)]Cl2 and [Ir(ppy)2(pytl‐R)]Cl (R=methyl, adamantane (ada), β‐cyclodextrin (βCD)). The two diastereoisomers of the Ir complex with the appended β‐cyclodextrin, [Ir(ppy)2(pytl‐βCD)]Cl, were separated. The [Ru(bpy)2(pytl‐R)]Cl2 (R=Me, ada or βCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Φ=0.23, τ=1000 ns) of [Ir(ppy)2(pytl‐ada)]Cl are surprisingly enhanced in [Ir(ppy)2(pytl‐βCD)]Cl (Φ=0.54, τ=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the βCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron‐withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)2(pytl‐βCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Δ and Λ isomers of the metal complex. 相似文献
994.
Abdul Niaz Jan Fischer Jiří Barek Bogdan Yosypchuk Sirajuddin Muhammad Iqbal Bhanger 《Electroanalysis》2009,21(15):1719-1722
An efficient voltammetric method was developed for the determination of maleic acid at a silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 2.0. The experimental parameters, such as pH of Britton–Robinson buffer, type of the supporting electrolyte and activation of the electrode surface were optimized. Under the optimal conditions, a linear response was observed over the 2×10?6–1×10?4 mol L?1 maleic acid concentration range, determination limit being 5×10?7 mol L?1. A highly stable response, with a relative standard deviation (RSD) of 1.6% for 45 repetitive measurements of 1×10?4 mol L?1 maleic acid showed that there was no apparent surface passivation indicating the suitability of the method. The method was successfully applied for direct determination of maleic acid in drinking and river water. 相似文献
995.
Michael Klein Gabriel P. Lansbergen Jan A. Mol Sven Rogge Prof. Raphael D. Levine Prof. Francoise Remacle Prof. 《Chemphyschem》2009,10(1):162-173
A silicon field‐effect transistor is operated as a logic circuit by electrically addressing the ground and excited electronic states of an embedded single dopant atom. Experimental results—complemented by analytical and computational calculations—are presented. First, we show how a complete set of binary logic gates can be realized on the same hardware. Then, we show that these gates can be operated in parallel on the very same dopant up to the logic level of a full adder. To use the device not as a switch but as a full logic circuit, we make essential use of the excited electronic states of the dopant and of the ability to shift their energy by gating. The experimental ability to use two channels to measure the current flowing through the device and the conductance (dI/dV) allows for a robust reading of the output of the logic operations. 相似文献
996.
Giulio Scocchi Dr. Paola Posocco Jan‐Willem Handgraaf Dr. Johannes G. E. M. Fraaije Prof. Maurizio Fermeglia Prof. Sabrina Pricl Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7586-7592
We present an innovative, multiscale computational approach to probe the behaviour of polymer–clay nanocomposites (PCNs). Our modeling recipe is based on 1) quantum/force‐field‐based atomistic simulation to derive interaction energies among all system components; 2) mapping of these values onto mesoscopic bead–field (MBF) hybrid‐method parameters; 3) mesoscopic simulations to determine system density distributions and morphologies (i.e., intercalated versus exfoliated); and 4) simulations at finite‐element levels to calculate the relative macroscopic properties. The entire computational procedure has been applied to two well‐known PCN systems, namely Nylon 6/Cloisite 20A and Nylon 6/Cloisite 30B, as test materials, and their mechanical properties were predicted in excellent agreement with the available experimental data. Importantly, our methodology is a truly bottom‐up approach, and no “learning from experiment” was needed in any step of the entire procedure. 相似文献
997.
Farhat Waqar Saida Jan Bashir Mohammad Muhammad Hakim Shah Alam Wasim Yawar 《中国化学会会志》2009,56(2):335-340
An analytical method has been developed for the preconcentration of rare earth elements (REEs) in seawater for their determination by inductively coupled plasma optical emission spectrometry (ICP‐OES). An indigenously synthesized chelating resin was used for the preconcentration of (REEs) which was based on immobilization of fluorinated β‐diketone group on solid support styrene divinyl benzene. Sample solutions (adjusted to optimized pH) were passed through a polyethylene column packed with 250 mg of the resin. Experimental conditions consisting of pH, sample flow rate, sample volume and eluent concentration were optimized. The established method has been applied for the preconcentration of light, medium and heavy REEs in coastal sea water samples for their subsequent determination by (ICP‐OES). Percentage recoveries of La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu were ≥ 95%, a preconcentration factor of 200 times, and relative standard deviations < 5% were achieved. 相似文献
998.
When employing nearest neighbor classifiers scaling of input variables is often useful. In this paper we propose a small modification in usual data preprocessing: scaling of variables should be done by use of pooled variances instead of overall ones. Thus prediction accuracy is distinctly improved in some situations. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
999.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
1000.
Junwon Han Byung Ho Jeon Chang Y. Ryu James J. Semler Young K. Jhon Jan Genzer 《Macromolecular rapid communications》2009,30(18):1543-1548
Interaction chromatography has been employed to validate that adsorption of poly[styrene‐co‐(4‐bromostyrene)] (PBrxS) random copolymers, where x denotes the mole fraction of 4‐bromostyrene (4–BrS) in PBrxS in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co‐monomer sequence distribution in PBrxS.