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101.
Pyridine chemisorbed on acid sites of active carbon was displaced by n-butylamine and the displaced amount was measured spectrophotometrically. This amount, supposed to be proportional to the surface concentration of carboxy groups, depends on the chemical pretreatment of active carbon.
, , . , , .相似文献
102.
The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.
, , , , (Hg, Ag, Cu), , (), . , , , , , , -.相似文献
103.
Serdar Öğüt Juan C. Idrobo Julius Jellinek Jinlan Wang 《Journal of Cluster Science》2006,17(4):609-626
We examine low-energy isomeric forms, static polarizabilities, and optical absorption spectra of Ag
n
, n = 2–8, and Au
n
, n = 2–3, clusters using first principles computations within the static and time-dependent versions of the density functional theory. The noticeable decrease in the static polarizabilities of Ag7 and Ag8 compared to the values characteristic of Ag
n
, n = 2–6, is correlated with the transition from two-dimensional to three-dimensional structures at n = 7. The optical spectra computed within the time-dependent local density approximation for the most stable structures are in good agreement with the available experimental data and the results of earlier theoretical studies. Optical spectra of higher-energy isomers typically present features that are not observed in the experimental spectra. The d electrons affect the spectra of noble metal clusters by quenching the oscillator strengths through screening of the s electrons and by getting directly involved in the excitations. Due to the larger s–d hybridization in Au compared to Ag, these effects are more pronounced in Au
n
clusters. 相似文献
104.
Vítězslav Zima Jan Svoboda Klára Melánová Ji?í Dybal 《Journal of solid state chemistry》2007,180(3):929-939
Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC6H4PO3H)2, SrH(OOCC6H4PO3)·H2O, Sr3(OOCC6H4PO3)2·4H2O and Sr3(OOCC6H4PO3)2·5.7H2O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC6H4PO3)·H2O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC6H4PO3H)2 was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P21/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO8 distorted tetragonal antiprisms. 相似文献
105.
Lemaître F Lucas D Groison K Richard P Mugnier Y Harvey PD 《Journal of the American Chemical Society》2003,125(18):5511-5522
The stoichiometric and catalytic activations of alkyl halides and acid chlorides by the unsatured Pd(3)(dppm)(3)(CO)(2+) cluster (Pd(3)(2+)) are investigated in detail. A series of alkyl halides (R-X; R = t-Bu, Et, Pr, Bu, allyl; X = Cl, Br, I) react slowly with Pd(3)(2+) to form the corresponding Pd(3)(X)(+) adduct and "R(+)". This activation can proceed much faster if it is electrochemically induced via the formation of the paramagnetic species Pd(3)(+). The latter is the first confidently identified paramagnetic Pd cluster. The kinetic constants extracted from the evolution of the UV-vis spectra for the thermal activation, as well as the amount of electricity to bring the activation to completion for the electrochemically induced reactions, correlate the relative C-X bond strength and the steric factors. The highly reactive "R(+)" species has been trapped using phenol to afford the corresponding ether. On the other hand, the acid chlorides react rapidly with Pd(3)(2+) where no induction is necessary. The analysis of the cyclic voltammograms (CV) establishes that a dissociative mechanism operates (RCOCl --> RCO(+) + Cl(-); R = t-Bu, Ph) prior to Cl(-) scavenging by the Pd(3)(2+) species. For the other acid chlorides (R = n-C(6)H(13), Me(2)CH, Et, Me, Pr), a second associative process (Pd(3)(2+) + RCOCl --> Pd(3)(2+.....)Cl(CO)(R)) is seen. Addition of Cu(NCMe)(4)(+) or Ag(+) leads to the abstraction of Cl(-) from Pd(3)(Cl)(+) to form Pd(3)(2+) and the insoluble MCl materials (M = Cu, Ag) allowing to regenerate the starting unsaturated cluster, where the precipitation of MX drives the reaction. By using a copper anode, the quasi-quantitative catalytic generation of the acylium ion ("RCO(+)") operates cleanly and rapidly. The trapping of "RCO(+)" with PF(6)(-) or BF(4)(-) leads to the corresponding acid fluorides and, with an alcohol (R'OH), to the corresponding ester catalytically, under mild conditions. Attempts were made to trap the key intermediates "Pd(3)(Cl)(+)...M(+)" (M(+) = Cu(+), Ag(+)), which was successfully performed for Pd(3)(ClAg)(2+), as characterized by (31)P NMR, IR, and FAB mass spectrometry. During the course of this investigation, the rare case of PF(6)(-) hydrolysis has been observed, where the product PF(2)O(2)(-) anion is observed in the complex Pd(3)(PF(2)O(2))(+), where the substrate is well-located inside the cavity formed by the dppm-Ph groups above the unsatured face of the Pd(3)(2+) center. This work shows that Pd(3)(2+) is a stronger Lewis acid in CH(2)Cl(2) and THF than AlCl(3), Ag(+), Cu(+), and Tl(+). 相似文献
106.
Kubát P Lang K Janda P Anzenbacher P 《Langmuir : the ACS journal of surfaces and colloids》2005,21(21):9714-9720
The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules. 相似文献
107.
Miroslav Malát 《Fresenius' Journal of Analytical Chemistry》1962,186(4):418-423
Zusammenfassung Es wurden die Bedingungen der photometrischen Wismutbestimmung mit Brenzcatechinviolett bei der WellenlÄnge
max=580 nm ausgearbeitet und der Einflu\ der Fremdionen untersucht. Das Lambert-Beersche Gesetz gilt in den Konzentrationsgrenzen 0,0–6,2 g Bi/ml bei 1,6 cm Schichtdicke.
Als erste Mitteilung dieser Reihe soll die Arbeit: Malát, M.: Naturwissenschaften 48, 569 (1961) betrachtet werden. 相似文献
Summary A method is given for the photometric determination of bismuth using pyrocatechol violet, at the wave-length of max=580 nm. Interferences by foreign ions have been examined. Beer's law is obeyed from 0.0 to 6.2 g Bi/ml (1,6 cm cuvettes).
Als erste Mitteilung dieser Reihe soll die Arbeit: Malát, M.: Naturwissenschaften 48, 569 (1961) betrachtet werden. 相似文献
108.
Junfang GongEric Bonfand Eric BrownGilles Dujardin Véronique Michelet Jean-Pierre Genêt 《Tetrahedron letters》2003,44(10):2141-2144
The synthesis of chiral 1,2,3,5-substituted tetrahydropyrans has been realized via an asymmetric hetero Diels-Alder (HDA) reaction. The key step that involved a trisubstituted chiral enol ether derived from (R)-mandelic acid as the dienophile promoted the creation of three stereogenic centers with a remarkable and unprecedented endo and facial stereocontrol. The hydrogenation of the heteroadduct 2 was optimized by using Pd on charcoal and diisopropylethylamine, leading to a unique isomer. The chiral inductor was cleanly and stereoselectively removed via an acetal reduction, which demonstrated the potential of this methodology for the efficient construction of key intermediate of biologically active molecules. 相似文献
109.
110.