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51.
Conductometric measurements of tetrabutylammonium perchlorate in propylene carbonate-acetonitrile and propylene carbonate-toluene mixtures at 25°C are reported. Limiting molar conductances, association constants and distance of closest approach of ions are calculated. The experimental data were analyzed by means of the Lee-Wheaton equation. The Gilkerson's solvent-solute interaction energy term was calculated from a plot of association constant logarithmvs. reciprocal dielectric constant. 相似文献
52.
The effect of pressure on the dissociation constant of hydrofluoric acid was determined by using the indicator technique at 25°C at an ionic strength of 0.1m over a pressure range of 1 to 2000 atm. A value of 3.14 for pK
a
*
at I =0 was obtained by extrapolation to zero ionic strength at 1 atm. The pressure dependence yielded a partial molar volume change of –9.6 cm3-mol–1 and a compressibility change of — 35×10–3 cm3-mol–1 –atm–1 for the dissociation. The dependence of ionic strength on the association constant K
A
*
of NaF was studied at 25°C and 1 atm. Extrapolation to I=0 yielded a pK
A
*
of –0.78. The pressure dependence of K
A
*
gave a change of volume of 3.26 cm3-mol–1 and a change in compressibility of 6×10–3 cm3-mol–1-atm–1 for the formation of the ion pair. 相似文献
53.
A novel membrane sensor for selective monitoring of iodide, consisting of a triiodide‐ketoconazole ion pair complex dispersed in a PVC matrix, plasticized with a mixture of 2‐nitrophenyl octyl ether and dioctylphtalate with unique selectivity toward iodide ions, is described. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The optimized membrane demonstrates a near‐Nernstian response for iodide ions over a wide linear range from 1.0 × 10?2 to 1.0 × 10?5 M, at 25 ± 1 °C. The electrode could be used over a wide pH range 3–10 and has the advantages of high selectivity, fast response time and good lifetime (over 4 months). It was successfully used as indicator electrode in potentiometric titrations and direct potentiometric assay of iodide ions. 相似文献
54.
Recognition of sheared and normal DNA by a novel metal complex [Co(phen)2hpip]3+ (phen=1,10-phenanthroline, HPIP=2-(2-hydroxyphenyl)imidazole[4,5-f][1,10]phenanethroline) is studied by molecular modeling. Calculating results indicate that, this complex can specifically recognize DNA segment of sequence –MMNNMM– (M means mismatch base pairs and N means normal base pairs). Intercalating from minor groove between the middle normal duplex into the sheared DNA with the depth of 1.2 nm is of preference and enantioselectivity is observed. Comparison on the two DNA structures of optimal conformation and analysis on the interaction between DNA and the two tail ligands of the complex show that, the effect of the two neighboring mismatch duplexes on the structure of the middle normal base pairs and the steric interaction between the mismatch duplexes and the two tail ligands of the complex are the essential reason to the segment specificity. Investigation on the detailed energy terms indicate that, in effecting enantioselectivity, the electrostatic distribution of the complex is in the majority and steric interaction is at the next place. But, steric interaction is surely the only factor determining the intercalating from minor groove. 相似文献
55.
Single crystals of the first anhydrous thallium nickel phosphates were prepared by reaction of heterogeneous Tl/Ni/P alloys with oxygen. TlNi4(PO4)3 (pale‐yellow, orthorhombic, space group Cmc21, a = 6.441(2)Å, b = 16.410(4)Å, c = 9.624(2)Å, Z = 4) crystallizes with a structure closely related to that of NaNi4(PO4)3. Tl4Ni7(PO4)6 (yellow‐brown, monoclinic, space group Cm, a = 10.711(1)Å, b = 14.275(2)Å, c = 6.688(2)Å, β = 103.50(2)°, Z = 8) is isotypic with Na4Ni7(PO4)6, and Tl2Ni4(P2O7)(PO4)2 (brown, monoclinic, space group C2/c, a = 10.389(2)Å, b = 13.888(16)Å, c = 18.198(3)Å, β = 103.1(2)°, Z = 8) adopts the K2Ni4(P2O7)(PO4)2 structure. Tl2Ni4(P2O7)(PO4)2 could also be prepared in nearly single phase form by reaction of Tl2CO3, NiO, and (NH4)2HPO4. 相似文献
56.
Chesnokov S. A. Cherkasov V. K. Abakumov G. A. Kurskii Yu. A. Shurygina M. P. Mamysheva O. N. Shavyrin A. S. 《Russian Chemical Bulletin》2003,52(3):718-724
Photoreduction of o-benzoquinones in the presence of p-bromo-N,N-dimethylaniline under irradiation ( > 500 nm) affords the corresponding pyrocatechols and hydroxyphenyl ethers. The latter are unstable and, in turn, decompose in the dark reaction to pyrocatechols. The ratio between pyrocatechol and hydroxyphenyl ether formed upon the photoreaction is determined by the structure of o-quinone, namely, the presence and bulk of substituents in positions 3 and 6 of the ring. The yield of pyrocatechol is maximal (60—65%) if the substituents are the same (H and H, But and But) or insignificantly differ (Pri and But), regardless of its bulk. 相似文献
57.
58.
The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail. 相似文献
59.
60.
J. Hajšlová R. Schoula K. Holadová J. Poustka 《International journal of environmental analytical chemistry》2013,93(2-4):163-173
Abstract The suitability of three GC-ECD systems for the separation of a model mixture containing various congeners of PCBs together with persistent chlorinated aromatics (pesticides and their metabolites, industrial chemicals) was tested. Analyses were performed on two parallel capillaries, the stationary phase of one of them was always in routine practice very common 5% phenyl-methylpolysiloxane, the second one was either 50% phenylmethylpolysiloxane or 7% phenyl-7% cyanopropyl-methylpolysiloxane. The number of unresolved (coeluted) analytes was significantly reduced in these systems and thus unbiased quantitation of PCBs and other components used for regulation was possible. The utilization of this type of multidimensional chromatography for rapid and reliable analysis of real samples (fish oil, human fat) was documented. 相似文献