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811.
Areeg Abdelrahman Johannes M. Hermann Prof. Dr. Timo Jacob Dr. Ludwig A. Kibler 《Chemphyschem》2019,20(22):2989-2996
The adsorption of acetate on an Au(111) electrode surface in contact with acetic acid at pH 2.7 was imaged in-situ using scanning tunnelling microscopy (STM). Two different ordered structures were imaged for acetate adsorbed in the bidentate configuration on the unreconstructed surface at 0.95 V (vs. the saturated calomel electrode, SCE). The first structure, , is metastable and transforms at constant potential within 20 minutes to a structure, which is thermodynamically more favourable. The acetate adlayer starts to form at step edges and propagates via nucleation and growth onto terraces. The findings from in-situ STM are in agreement with the electrochemical behaviour of acetate on Au(111) characterized by voltammetry. A comparison is made with formate adsorption on Au(111). While acetate is not reactive, in contrast to formate, it can act as a spectator species in formic acid electrooxidation. 相似文献
812.
Mohamed Gaber Marei Morcos Michael Mishrikey Ibrahim El-Sayed El-Kholy 《Journal of heterocyclic chemistry》1986,23(6):1849-1852
3-Iodo-4H-pyran-4-ones have been synthesised in excellent yield by the reaction of acetylenic β-diketones with iodine monochloride and were converted into the corresponding 4H-pyran-4-thiones. The iodopyrones and thiopyrones gave with methylamine the respective N-methylpyridones and thiopyridones. The structure of the above compounds was confirmed from their spectral characteristics. 相似文献
813.
Juha-Pekka Himanen Timo Korpela 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(2):177-183
The thermodynamics of the complexation of cyclodextrins (CDs) to naphthyl, phenyl and thienyl subtituted 1,3-diketones, used as sensitizers in time-resolved fluorescence analysis of lanthanides, was studied by gel chromatography. The complexation occurs predominantly at the aromatic end of the diketones with a strength comparable to related aromatic compounds. The effects of CDs on the fluorescence of an europium (III) ion with diketones in an aqueous solution were tested for their applicability in time-resolved fluorescence analysis. 相似文献
814.
Gaber M. Abu El-Reash Magdy M. Bekheit Kamal M. Ibrahim 《Transition Metal Chemistry》1990,15(5):357-360
Summary The synthesis and characterization of CrII, MnII, FeII, CoII, NiII, PdII, CuII, ZnII, CdII and UO
2
2+
complexes of 1-meotinoyl-4-phenyl-3-thiosemicarbazide (H2NTS) are reported. I.r. spectral data show that the ligand behaves in a bidentate and/or tetradentate manner. An octahedral structure is proposed for the CrII, FeII and NiII complexes; a tetrahedral structure for the MnII, CoII and Cu(NTS)·2H2O complexes; and a square planar structure for the PdII and Cu(HNTS)Cl·H2O complexes. The i.r. data suggest that the FeII complex contains a hydroxo bridge. 相似文献
815.
The kinetics of oxidation of N,N-dimethyl- and N,N,N,N-tetramethyl-p-phenylenediamines, to the corresponding semiquinonediimine radical and the quinonediimine, with a macrocyclic copper(II)-complex were studied at pH7. Under pseudo-first order conditions, the reaction rate for the N,N,N,N-tetramethyl derivative was much faster than for N,N-dimethyl-p-phenylenediamine, due to the increased probability of electron transfer. The reaction rate decreases with increasing acidity of the medium as a result of protonation of the amine nitrogen atoms. The rate constants and activation parameters were evaluated and the reaction was found to be enthalpy controlled. Furthermore, kinetic measurements revealed a remarkable superadditive effect when CuCl2 solution was added, even at concentrations lower than that of the copper complex. This observation was used for the kinetic determination of copper ions at concentrations <10–5M. 相似文献
816.
The cathodic deposition of silver whiskers as microwires in the electrochemical cell Ag/AgBr/Ag has been investigated. From growth experiments observed with an optical microscope, we conclude that the growth process occurs exclusively at the interface of the silver wires with the solid electrolyte. The basal contacts of the microwires show different morphologies without clear correlation to the substrate. The silver crystals often show a hexagonal morphology, but XRD gives no definite information on the structure of the wires. The measured exchange current density is in the order of 100 mA/cm2. The growth rate and the diameter of the microwires can be controlled by variation of the current. 相似文献
817.
Recent quantum mechanical (QM) calculations for a monolayer of H(2)O on Ru(0001) suggested a novel stable structure with half the waters dissociated. However, different studies on Pt(111) suggested an undissociated bilayer structure in which the outer half of the water has the OH bonds toward the surface rather than the O lone pair. Since water layers on Pt are important in many catalytic processes (e.g., the fuel cell cathode), we calculated the energetics and structure of the first monolayer of water on the Pt(111) surface using QM [periodic slab using density functional calculations (DFT) with the PBE-flavor of exchange-correlation functional]. We find that the fully saturated surface ((2)/(3) ML) has half the water almost parallel to the surface (forming a Pt-O Lewis acid-base bond), whereas the other half are perpendicular to the surface, but with the H down toward the surface (forming a Pt-HO agostic bond). This leads to a net bond energy of 0.60 eV/water = 13.8 kcal/mol (the standard ice model with the H up configuration of the water molecules perpendicular to the surface is less stable by 0.092 eV/water = 2.1 kcal/mol). We examined whether the partial dissociation of water proposed for Ru(0001) could occur on Pt(111). For the saturated water layer ((2)/(3) ML) we find a stable structure with half the H(2)O dissociated (forming Pt-OH and Pt-H covalent bonds), which is less favorable by only 0.066 eV/water = 1.51 kcal/mol. These results confirm the interpretation of combined experimental (XAS, XES, XPS) and theoretical (DFT cluster and periodic including spectrum calculations) studies, which find only the H down undissociated case. We find that the undissociated structure leads to a vertical displacement between the two layers of oxygens of approximately 0.42 A (for both H down and H up). In contrast, the partially dissociated system leads to a flat structure with a separation of the oxygen layers of 0.08 A. Among the partially dissociated systems, we find that all subsurface positions for the dissociated hydrogen are less favorable than adsorbing on top of the free Pt surface atom. Our results suggest that for less than (1)/(3) ML, clustering would be observed rather than ordered monolayer structures. 相似文献
818.
Timo Weidl 《Communications in Mathematical Physics》1996,178(1):135-146
LetE i(H) denote the negative eigenvalues of the one-dimensional Schrödinger operatorHu??u″?Vu,V≧0, onL 2(∝). We prove the inequality (1) $$\mathop \sum \limits_i |E_i (H)|^{ \gamma } \leqq L_{\gamma ,1} \mathop \smallint \limits_\mathbb{R} V^{\gamma + 1/2} (x)dx,$$ for the “limit” case γ=1/2. This will imply improved estimates for the best constantsL γ,1 in (1) as 1/2<γ<3/2. 相似文献
819.
820.
Timo A. Nieminen Theodor Asavei Vincent L.Y. Loke Norman R. Heckenberg Halina Rubinsztein-Dunlop 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(14-16):1472-1482
A key element in the generation of optical torque in optical traps, which occurs when electromagnetic angular momentum is transferred from the trapping beam to the trapped particle by scattering, is the symmetries of the scattering particle and the trapping beam. We discuss the effect of such symmetries on the generation and measurement of optical torque in optical tweezers, and some consequent general principles for the design of optically driven micromachines. 相似文献