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951.
《Electroanalysis》2006,18(11):1097-1104
Copolymerization of an osmium(II) functionalized pyrrole moiety, osmium‐bis‐N,N'‐(2,2′‐bipyridyl)‐N‐(pyridine‐4‐ylmethyl‐(8‐pyrrole‐1yl–octyl)‐amine)chloride ( I ) with 3‐methylthiophene was carried out. The resulting conducting polymer film exhibited a clear redox couple associated with the Os3+/2+ response and the familiar conducting polymer backbone signature. The effect of film thickness upon the redox properties of the copolymer was investigated in organic electrolyte solutions. Scanning electron micrographs (SEM) along with energy dispersive X‐ray (EDX) spectra of the copolymerized films were undertaken, both after formation and redox cycling in neutral buffer solution. These clearly show that electrolyte is incorporated into the polymer film upon redox cycling through the Os3+/2+ redox system. The Os3+/2+ response associated with the copolymer was seen to be significantly altered in the presence of ascorbic acid both in acidic and neutral pH buffer solutions. This pointed to an electrocatalytic reaction between the ascorbic acid and the Os3+ form of the copolymer. Under acidic conditions the copolymer film exhibited a sensitivity of 1.76 (±0.05) μA/mM with a limit of detection (LOD) of 1.45 μM for ascorbic acid. Under neutral pH conditions the copolymer exhibited a sensitivity of 19.26 (±1.05) μA/mM with a limit of detection (LOD) of 1.28 μM for ascorbic acid. 相似文献
952.
《Surface and interface analysis : SIA》2006,38(10):1336-1342
XPS was used to characterize the chemical changes occurring after drying or applying a heat‐treatment to beech wood samples. Our results indicate that the surface of this air‐exposed material could be strongly affected either by the ambient atmosphere during storage or by the complex atmosphere in the oven during drying or heat‐treatment. However, the O/C ratio measured after removal of a thin slice of a few millimetres of an untreated sample is in reasonable agreement with that calculated from the well‐established chemical composition of beech. Through this methodology (equivalent to scraping for hard materials) it is expected to get a realistic characterization of the wood. The reliability and repeatability of the XPS measurements have been checked and the method applied to the study of the chemical changes of the beech samples subjected to heat‐treatment. Heating at 240 °C induces a significant decrease of the O/C ratio from 0.55 before to 0.44 after the treatment. Heat‐treatment induces also a decrease of the C2 carbon contribution (carbon atom bound to a single non‐carbonyl oxygen) associated with an increase of the C1 carbon contribution (carbon atoms bound only to carbon or hydrogen atoms), in agreement with chemical modifications reported previously in the literature. Thanks to the small analysed area of the equipment used in this study, different spots were analysed to demonstrate the presence or absence of a gradient of chemical composition due to thermal degradation or migration of extractives from within the wood structure to its surface. At the scale of our observations, the different wood samples investigated (dried or heat treated) appear to be homogeneous. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
953.
《Surface and interface analysis : SIA》2005,37(9):713-720
The surface structure of polytetrafluoroethylene (PTFE) upon α‐particle irradiation has been investigated at doses in the range of 1 × 107 to 1 × 1011 Rad and compared with the surface structure of the unirradiated polymer. Both neat and 25% fiberglass content PTFE were studied. The samples, maintained at nominal room temperature, were irradiated in vacuum by 5.5 MeV 4He2+ ions generated in a tandem accelerator beam line. Static time‐of‐flight SIMS (ToF‐SIMS) was employed to probe chemical changes at the surface as a function of the irradiation level. In general, the data are indicative of increased cross‐linking at α‐doses less than 1 × 109 Rad, followed by increased fragmentation and unsaturation at α‐doses greater than 1 × 109 Rad. Throughout the irradiation regime, scission is a constant factor promoting cross‐linking, branching, and unsaturation. However, at α‐doses greater than 1 × 1010 Rad, extreme structural degradation of the polymer becomes evident and is accompanied by conversion to oxygen‐functionalized and aliphatic compounds. Thus, for PTFE in an α‐particle field, an upper exposure limit of ~1010 Rad is essential for nominal retention of molecular structure. Finally, a quantitative relationship between α‐dose and characteristic fragment ion intensity is developed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
954.
Alkylidynephosphanes and -arsanes. I [P ≡ C? S]?[Li(dme)3]+ – Synthesis and Structure O,O′-Diethyl thiocarbonate and bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide dissolved in 1,2-dimethoxyethane, react below 0°C to give ethoxy trimethylsilane and tris(1,2-dimethoxyethane-O,O′)lithium 2λ3-phosphaethynylsulfanide – [P≡C? S]? [Li(dme)3]+ – ( 1a ). Apart from bis(trimethylsilyl)sulfane or carbon oxide sulfide, dark red concentrated solutions of λ3-phosphaalkyne 1 are also obtained from reactions of carbon disulfide with bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide or with the homologous lithoxy-methylidynephosphane ( 2 ) [1]. The ir spectrum shows two absorptions at 1762 and 747 cm?1 characteristic for the P≡C and C? S stretching vibrations. The nmr parameters {δ(31P) ? 121.3; δ(13C) 190.8 ppm; 1JCP 18.2 Hz} resemble much more values of diorganylamino-2λ3-phosphaalkynes than those of bis(1,2-dimethoxyethane-O,O′)lithoxy-methylidyne-phosphane ( 2a ). As found by an X-ray structure analysis (P21/c; a = 1192.6(16); b = 1239.1(19); c = 1414.8(26) pm; β = 105.91(13)° at ?100 ± 3°C; Z = 4 formula units; wR = 0.064) of pale yellow crystals (mp. + 16°C) isolated from the reaction with O,O′-diethyl thiocarbonate, the solid is built up of separate [P≡C? S]? and [Li(dme)3]+ ions. Typical bond lengths and angles are: P≡C 155.5(11); C? S 162.0(11); Li? O 206.4(17) to 220.3(20) pm; P≡C? S 178.9(7)°. 相似文献
955.
Positive and negative ions of Ar/SF6 and Ar/SF6/O2 plasmas (etching plasmas) and of Ar/O2 plasmas (cleaning plasmas) in Pyrex tubes have been investigated using a mass spectrometer-wall probe diagnostic technique. The measurement of negative ions proved to be a very sensitive method for the detection of wall material. In etching plasmas with small admixtures of SF6, oxygen was found as the only representative of wall material. At larger amounts of SF6, silicon could be detected. In cleaning plasmas with small admixtures of O2 applied to a previously etched Pyrex surface, fluorine was found, indicating the reversal of fluoridation by oxygenation. 相似文献
956.
A theorem of Deza asserts that ifH
1, ...,H
m
ares-sets any pair of which intersects in exactlyd elements and ifm ≧s
2 −s+2, then theH
i
form aΔ-system, i.e.
. In other words, every large equidistant (0, 1)-code of constant weight is trivial. We give a (0, +1, −1) analogue of this
theorem. 相似文献
957.
A New Tricyclic Sulfur-rich Phosphane From the products of the reaction of P4S3 with tert-Butyliodide the compound (t-Bu(S)P)2P4S3 was isolated in low yield. The compound is stable and has a structure related to the hydrocarbon brexane. By reaction with triphenylphosphin the compounds (t-BuP)(t-Bu(S)P)P4S3 and (t-BuP)2P4S3 were obtained. The 31P-nmr spectra of all compounds were solved and used to determine the structure of the molecules. A complete set of 31P-nmr data is given. 相似文献
958.
Summary The SCF method is applied to determine the (gas phase) structure of [(CF3)2PN]2NVCl2, which agrees with the solid-state X-ray structure within typical errors of 2 pm and 2° in bond distances and angles. The electronic structure of atoms forming the ring is best described in terms of divalent N– and tetravlent P+ with appreciable declocalization of nitrogen lone pairs into low-lying empty orbitals of neighbouring atoms P and V. No evidence for aromaticity of the ring system is found. 相似文献
959.
综述了近年来利用一些新型的含氟砌块,通过它们的环加成反应来高效地合成 含氟杂环化合物的研究,其中包括以下两个部分:(1)用1,3—偶极环加成反应合 成五元含氟杂环化合物;(2)用杂原于Diels-Alder反应合成六元含氟杂环化合物. 相似文献
960.
A. Neumaier 《Geometriae Dedicata》1979,8(2):189-205
Zusammenfassung Es werden zwei neue Koordinatisierungsmethoden für affine Ebenen gegeben, und zwar durch homogene bzw. stark balancierte Tupelsysteme. Ihre Brauchbarkeit wird u.a. demonstriert an einer Charakterisierung der Kollineationsgruppen einer affinen Ebene mit der Eigenschaft (R) Für alle i l
enthält der Stabilisator von i nur Perspektivitäten mit Zentrum i. Außerdem wird der Satz bewiesen: Für eine Elation der geraden Ordnung d in einer projektiven Ebene der Ordnung v gilt 2d|v. Dieses Resultat impliziert schon bekannte Ergebnisse von Hughes (d=2) und Hall.
We give two new coordinatization methods for affine planes by means of homogeneous (resp. strong balanced) tuple systems. Their usefulness is demonstrated by proving a characterization of collineation groups of an affine plane with the property (R): The stabilizer of every i l contains only perspectivities with centre i. Besides, we prove: If a projective plane of order v contains an elation of even order d then 2d|v. This implies known results of Hughes (d=2) and Hall.相似文献