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991.
Dr. D. Vollbardt 《Colloid and polymer science》1976,254(1):64-81
Zusammenfassung Bei der Elektrosorptionsanalyse verschiedener Aniontenside in Gegenwart von Grundelektrolytkonzentrationen ( 0,1 m NaCl) wurde festgestellt, daß auf der Grundlage von Wechselstrom-Potential (IE-E)-Kurven die kritischen Micellkonzentrationen bestimmt werden können. Die CMC-Werte ergaben sich aus Diskontinuitäten in der Konzentrationsabhängigkeit von Höhe und Scheitelpotential der wechselstrompolarogräphischen Desorptionsmaxima. Der unterschiedliche Einfluß von Alkylkettenlänge, polaren Gruppen und Stellungsisomerie auf die wechselstrompolarographischen Desorptionscharakteristika wurde untersucht. Aus den Meßergebnissen resultierten für den Zustand der Adsorptionsschichten oberhalb der CMC an der Grenzfläche Quecksilber/Elektrolyt in Abhängigkeit von der Alkylkettenlänge prinzipiell zwei Möglichkeiten. Wenn oberhalb der CMC mit zunehmender Aniontensidkonzentration höchstens geringe Änderungen. des Desorptionspeaks auftreten, bleibt der Zustand der Adsorptionsschicht unverändert. Die Entstehung neuer Desorptionspeaks und starke Diskontinuitäten in Lage und Höhe bereits vorhandener Desorptionspeaks wird dagegen durch zusätzliche Grenzflächenassoziation erklärt. Ein überzeugender Hinweis auf niedere Assoziationen (Dimerisation) im prämicellaren Bereich folgte aus einer zusätzlichen Diskontinuität, die bei geradkettigen Alkylverbindungen (R 12) auftritt.
Mit 7 Abbildungen und 2 Tabellen 相似文献
Summary Using the electrosorption analysis of different anionic surfactants in the presence of supporting electrolyte concentrations ( 0,1 m NaCl) we found that the critical micelle concentrations can by determined on the basis of alternating current-potential (IE-E)-curves. The CMC values resulted from discontinuities in the concentration dependence of height and summit potential of alternating current polarographic desorption maxima. We investigated the different influences of the alkyl chain length, of the polar groups, and of the positions of SO4Na in isomeric alkyl sulfates upon the alternating current polarographic desorption characteristics.Experimental dates show that, dependent on the alkyl chain length two possibilities exist for the state of the adsorption layers above the CMC at the interface mercury/electrolyte. 1) The state of adsorption layer remains unchanged if above the CMC no or only small changes of desorption peaks are observed. 2) The formation of new desorption peaks and strong discontinuities of position and height of the desorption peaks already existing is rationalized by additional association at the interface. We assume that an additional discontinuity which occurs with straight chain alkyl compounds (R 12) results from association (dimerisation) in the premicellar range.
Mit 7 Abbildungen und 2 Tabellen 相似文献
992.
Determination of 1-aminocyclopropane-1-carboxylic acid in apple extracts by capillary electrophoresis with laser-induced fluorescence detection 总被引:1,自引:0,他引:1
A rapid and sensitive method for the determination of 1-aminocyclopropane-1-carboxylic acid (ACC) in apple tissues has been described. This method is based on the derivatization of ACC with 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ), and separation and quantification of the resulting FQ-ACC derivative by capillary electrophoresis coupled to laser-induced fluorescence detection (CE-LIF). Our results indicated that ACC derivatized with FQ could be well separated from other interfering amino acids using 20 mM borate buffer (pH 9.35) containing 40 mM sodium dodecyl sulfate and 10 mM Brij 35. The linearity of ACC was determined in the range from 0.05 to 5 microM with a correlation of 0.9967. The concentration detection limit for ACC was 10 nM (signal-to-noise = 3). The sensitivity and selectivity of this described method allows the analysis of ACC in crude apple extracts without extra purification and enrichment procedure. 相似文献
993.
A new isocoumarin, 3-acetyl-3,4-dihydro-5,6-dimethoxy-1H-2-benzopyran-1-one, was isolated from the cortex of Phellodendron chinense schneid. The structure was determined on the basis of spectroscopic evidences. 相似文献
994.
995.
The G3(MP2) method has been employed to study the 1,4-addition reactions between singlet oxygen and five acenes, including benzene, naphthalene, anthrecene, tetracene, and pentacene. In all, nine pathways between O(2) and the five acenes have been investigated. Our calculated results indicate that all nine pathways are concerted and exothermic and that the most reactive sites on the acenes are the center ring's meso-carbons. In addition, reactivity increases along the series benzene < naphthalene < anthrecene < tetracene < pentacene. This trend is identical to that of aromaticity for the five acenes. A correlation between reactivity and aromaticity is briefly rationalized with natural bond orbital (NBO) analysis and frontier molecular orbital (FMO) analysis. Furthermore, some experimental kinetics data from the literature supporting the calculated results are cited. 相似文献
996.
纳米CoHCF修饰电极的制备及其对血红蛋白的电化学测定研究 总被引:1,自引:0,他引:1
A cobalt hexacyanoferrate (CoHCF) nanoparticle (size ca. 60 nm) chemically modified electrode (CME) was fabricated and the electrochemical behavior of hemoglobin (Hb) at this nanosized CoHCF CME was studied. In comparison with a bare glassy carbon electrode (GCE) and a general CoHCF CME electrodeposited in a traditional manner, the present nanosized CoHCF CME performed efficiently electrocatalytic reduction for Hb with relatively high sensitivity, stability, and longlife, Combined with liquid chromatography (LC), the nanosized CoHCF CME was used as the electrochemical detector of Hb in the established flow injection analysis-electrochemical determination (FIA-ECD) system. The peak current was a linear function of concentrations in the range from 2.5×10^-8 to 5.0×10^-6mol/L for Hb, with detection limit of 1.4×10^-8 mol/L. The FIA-ECD system has been successfully applied to assess the Hb content of clinic blood samples with advantages of sensitiveness, speediness, easy control and small sample-consumption. 相似文献
997.
硝酸根离子介质中偏钛酸钡的水热合成 总被引:1,自引:0,他引:1
以硝酸和钛酸四丁酯为原料,在240℃的碱液中成功地制备了四方相BaTiO3运用XRD、DSC和IR等技术碱度、硝酸根离子、钛源活性、填充度等因素对BaTiO3形成、粒度和物相的作用,KOH最适宜浓度为1.0mol/L,碱液中BaTiO3是BaO-TiO2体系中最稳定的物相,硝酸根离子参与了BaTiO3晶体的成核和生长,钛源的高活性和高填充度有利于四方BaTiO3的形成。 相似文献
998.
Using renewable green hydrogen and carbon dioxide (CO2) to produce methanol is one of the fundamental ways to reduce CO2 emissions in the future, and research and development related to catalysts for efficient and stable methanol synthesis is one of the key factors in determining the entire synthesis process. Metal nanoparticles stabilized on a support are frequently employed to catalyze the methanol synthesis reaction. Metal-support interactions (MSIs) in these supported catalysts can play a significant role in catalysis. Tuning the MSI is an effective strategy to modulate the activity, selectivity, and stability of heterogeneous catalysts. Numerous studies have been conducted on this topic; however, a systematic understanding of the role of various strengths of MSI is lacking. Herein, three Cu/ZnO-SiO2 catalysts with different strengths of MSI, namely, normal precipitation Cu/ZnO-SiO2 (Nor-CZS), co-precipitation Cu/ZnO-SiO2 (Co-CZS), and reverse precipitation Cu/ZnO-SiO2 (Re-CZS), were successfully prepared to determine the role of such interactions in the hydrogenation of CO2 to methanol. The results of temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) characterization illustrated that the MSI of the catalysts was considerably affected by the precipitation sequence. Fourier transform infrared reflection spectroscopy (FT-IR) results indicated that the Cu species existed as CuO in all cases and that copper phyllosilicate was absent (except for strong Cu-SiO2 interaction). Transmission electron microscopy (TEM), X-ray diffraction (XRD), and N2O chemical titration results revealed that strong interactions between the Cu and Zn species would promote the dispersion of Cu species, thereby leading to a higher CO2 conversion rate and improved catalytic stability. As expected, the Re-CZS catalyst exhibited the highest activity with 12.4% CO2 conversion, followed by the Co-CZS catalyst (12.1%), and the Nor-CZS catalyst (9.8%). After the same reaction time, the normalized CO2 conversion of the three catalysts decreased in the following order: Re-CZS (75%) > Co-CZS (70%) > Nor-CZS (65%). Notably, the methanol selectivity of the Re-CZS catalyst was found to level off after a prolonged period, in contrast to that of Co-CZS and Nor-CZS. Investigation of the structural evolution of the catalyst with time on stream revealed that the high methanol selectivity of the catalyst was caused by the reconstruction of the catalyst, which was induced by the strong MSI between the Cu and Zn species, and the migration of ZnO onto Cu species, which caused an enlargement of the Cu/ZnO interface. This work offers an alternative strategy for the rational and optimized design of efficient catalysts. 相似文献
999.
Zusammenfassung Mit bekannten mikroanalytischen Arbeitsmethoden — Oberflächenreaktionen, Abstrichuntersuchungen mit dem Korundstäbchen, Schutzschichtreaktionen sowie dem Abdruckverfahren — lassen sich archaeometrische Probleme einer Lösung näherbringen. Die Art der Korrosion kupferhaltiger Oberflächen wurde diskutiert.
Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974. 相似文献
Application of microanalytical methods to the solution of artistic- and cultural historical problems
Summary Archeometrical problems are brought closer to a solution by means of known microanalytical procedures-surface reactions, surface scraping studies with the corundum rod, protective layer reactions as well as the imprint method. A discussion of the corrosion of copper-bearing surfaces is included.
Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974. 相似文献
1000.
Summary The sorption property of water vapor by poly(vinyl acetate) (PVAc) of relatively low glass transition temperature (T
g) was studied at temperatures nearT
g.Tcg of humidity-controlled samples of various moisture contents was measured and its variation with the moisture content was determined.T
g of the dry sample was estimated by dilatometry and DSC methods, and to confirm the value, the temperature dependence of mutual diffusion coefficient of the system of water vapor + PVAc was determined. A difference between the sorption mechanisms of water vapor by PVAc at 20 and 30 °C was observed: two sorption mechanisms are involved at 30 °C, while three mechanisms at 20 °C are involved which include the above two and another intermediate one. In earlier stage of sorption, at both 20 and 30 °C, water molecules sorbed by PVAc showed a tendency towards aggregation, while a mixing effect was found at higher stage of the sorption.
With 7 figures 相似文献
Zusammenfassung In der Arbeit werden Wasserdampfsorptionseigenschaften von Polyvinylacetat mit relativ niedriger Glastemperatur (T g) in der Nähe vonT g untersucht. Es wurden Plastizitätseinflüsse und Veränderungen vonT g mit dem Wassergehalt studiert. Es wurde gefunden, daß bei 30 °C ein 2-Stufen-Sorptionsmechanismus, bei 20 °C ein 3-Stufen-Mechanismus existiert.
With 7 figures 相似文献