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101.
Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10?1–1 × 10?5 M sodium thiocyanate. 相似文献
102.
The reductive determination of cadmium and zinc is used to illustrate the effects of pulse repetition times in differential pulse voltammetry at solid electrodes. With 100-ms repetition times, signal-to-background ratio is shown to improve in flow-injection response studies at a copper-amalgam working electrode for both voltage scanning and amperometric operation, allowing scan rates up to 100 mV s?1, and detection limits of 0.07–0.15 ng for cadmium and zinc after deaeration of sample solutions. Peak widths at baseline in the range 12–30 s, depending on flow rate, are obtained in the flow-injection system for cadmium and zinc at working potentials of ?0.77 and ?1.27 V, respectively. Interferences occur when cadmium is in large excess over zinc, although the voltammetric peaks do not overlap. 相似文献
103.
Andrzej Czopnik Nataly Shitsevalova Alexander Krivchikov Vasyl Pluzhnikov Yuriy Paderno 《Journal of solid state chemistry》2004,177(2):507-514
We have measured heat capacity and thermal expansion of rare earth dodecaborides REB12 (RE=Y, Tb-Tm, Lu). YB12 and LuB12 are diamagnetics whereas the other dodecaborides are ordered antiferromagnetically. The amplitude of the heat capacity discontinuity at the Néel temperature and the shape of the heat capacity variation in the critical region for all these antiferromagnetics are characteristics for amplitude-modulated magnetic structures. In the ordered state TbB12 reveals two first-order phase transitions, most likely due to magnetic structure changes. The heat capacity of ErB12 just below the Néel point shows an anomaly of unclear origin. From the Schottky contribution to the heat capacity we have determined crystal field parameters. They are completely different than that is estimated from Point Charge Model. 相似文献
104.
Dmitriy M. Volochnyuk Dmitriy A. Sibgatulin Alexander N. Chernega 《Tetrahedron》2005,61(11):2839-2847
The reaction of 1,1,1,5,5,5-hexafluoroacetylacetone with push-pull enamines having a methyl group at the α-position was investigated. It was found that the reaction is sensitive both to the structure of enamines and to reaction conditions. As a result, a set of bistrifluoromethyldialkylanilines and ethyl bistrifluoromethylsalicylate was prepared. Plausible mechanisms and factors influencing the course of the reaction are discussed. 相似文献
105.
Immobilized sulfhydryl groups were prepared by partial thiolation of NH2-glass beads. The microenvironment of the immobilized SH groups was varied by different chemical modifications of neighboring
NH2 groups. Introduction of a strong charge in the surroundings of immobilized sulfhydryls results in their dramatic stabilization
against autooxidation. This effect is due to the salting of O2 from the surface microlayer of the thiolated beads. 相似文献
106.
Conditions for the determination of electrophoretic mobilities of bacteria by capillary electrophoresis (CE) were explored. Most precise values are obtained using fused silica capillaries of 1–3 m length (0.25 mm inner diameter), a background buffer with an ionic strength of 0.0015 mol/L and a pH value of 7–10 at a field strength of 120 V/cm. Capillary electrophoretic separation of three different bacteria populations on the basis of their mobility differences could be realized. Electrophoretic band widths of all bacteria populations investigated are relatively large compared to molecule bands. It finds its explanation in the different distribution of surface charge density to cross-sectional area of each single cell of a population. 相似文献
107.
Alexander R. Giaquinto Richard E. Lindstrom James Swarbrick Antonio LoSurdo 《Journal of solution chemistry》1977,6(10):687-701
Solubility and apparent molar volume data are used to demonstrate effects of amide alkylation on amide-water interactions at 25° C. Precise measurements were made of the apparent molar volumes of the amides in binary amide-water mixtures using a dilatometric technique. The results show that the apparent molar volumes of alkyl-substituted amides in water pass through a minimum at an amide concentration which varies inversely with the degree of alkylation. Further studies showed that the solubilities of methyl paraben (methyl-p-hydroxybenzoate) and naphthalene in various amide-water solvent systems increased in characteristic fashion with amide alkylation. 相似文献
108.
Yuri A. Berlin Alexander L. Burin Vitalii V. Goldanskii 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,37(4):333-339
The “paradox of optical isomers” revealed by Hund in 1927 is re-examined taking into account the interaction of a chiral molecule with phonons of optically inactive solids below the Debye temperature θD. It has been shown, that in the strong coupling limit, where the dephasing rate is much higher than the energy splitting frequency, the interaction can lead to a complete loss of coherence between mirror-antipodal states of the molecule due to the phonon-induced dephasing. This, in turn, suppresses tunnelling oscillations between them, so that transitions, which are reversible in time for an isolated chiral molecule become irreversible for the same molecule placed in a low-temperature matrix. In order to propose a particular mechanism of such stabilization, contributions of a single- and multi-phonon processes in the dephasing rate have been evaluated. It has been established that only the two-phonon scattering provides the sufficiently strong dephasing in low-temperature solids. Such a two-phonon mechanism is responsible for the stabilization of molecular chiral states as long as the temperature of the medium is lower θD, but exceeds a few Kelvin degrees. These findings are discussed in the context of the evolutionary concept known as “the cold prehistory of life”. 相似文献
109.
Liquid-liquid cloud point diagrams of solutions of nearly monodisperse samples of polystyrene (PS), and binary mixtures of nearly monodisperse PS’s, both in methylcyclohexane (MCH), were determined for several polymer molecular weights (Mw) at 0.1 MPa. The bimodal mixtures (PS[Mw(1),ρ(1)] + PS[Mw(2),ρ(2)], Mw(1)=90×103 g/mol, Mw(2)=13×103 g/mol, 5.78 × 103 g/mol, and 2.2 × 103 g/mol, ρ=1.06) were prepared constraining 〈Mw〉=38.6×103 g/mol, ρ=Mw/Mn is the polydispersity index. In each case the cloud point curves (CPC’s) for the bimodal mixtures are strongly skewed, lying well above CPC for 〈Mw〉 when φ<φCRITICAL, and below CPC for 〈Mw〉 when φ>φCRITICAL; φ is volume fraction polymer in the polymer/solvent mixture. The experimental results are discussed in the context of empirical and mean-field representations. 相似文献
110.
Alexander Kaiser Klaus K. Mayer Andreas Sellmer Wolfgang Wiegrebe 《Monatshefte für Chemie / Chemical Monthly》2003,43(11):343-354
The molecular ion 1 of N-(n-propoxy)benzaldimine I rearranges by an 1,5-H-shift to the δ-distonic ion 2 which subsequently cyclizes to the α-distonic ion 3. Homolytic cleavage of the N–O bond in 3 results in the δ-distonic ion 4 which expels CH2O leading to the β-distonic ion 5. Ion 5 is also formed from the molecular ions of tetrahydrooxazines II and III and from M+• of phenylazetidine IVa. In a subsequent step, ion 5 cyclizes to the N-protonated 3,4-dihydroisoquinolinium ion 6. The syntheses of II–IV and their derivatives are described. 相似文献