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961.
Irena Grabec Švegl Mitja Kolar Božidar Ogorevc Boris Pihlar 《Analytical and bioanalytical chemistry》1998,361(4):358-362
A vermiculite modified carbon paste electrode (VMCPE) was employed for the in situ preconcentration of traces of Hg(II) and Ag(I) via an ion-exchange route. Heavy metal ions were accumulated in Britton-Robinson (BR) buffer pH 7 for Hg(II) and pH 6 for Ag(I), and afterwards reduced at –0.7 V vs. Ag/AgCl in the separate measurement solution (BR buffer pH 5 + 0.05 mol/L NaNO3) prior to the anodic stripping square-wave voltammetric (ASSWV) detection. For Hg(II) ions, at 15 min accumulation, a linear range from 1.0 × 10–7 to 8.0 × 10–6 mol/L was obtained, with a 5.7 × 10–8 mol/L limit of detection. The VMCPE response was linear for Ag(I) ions in the concentration range from 2.0 × 10–7 to 8.0 × 10–6 mol/L, at 10 min accumulation with a corresponding limit of detection of 6.3 × 10–8 mol/L. The relative standard deviation of the analytical procedure including accumulation from a 5 × 10–7 mol/L solution of Hg (15 min) or Ag(I) (10 min), electrolysis, ASSWV detection, regeneration and activation of the VMCPE, was 4% (n = 6). The optimisation of the parameters for the application of the VMCPE in combination with ASSWV detection is presented and discussed. 相似文献
962.
Gaeta C Vysotsky MO Bogdan A Böhmer V 《Journal of the American Chemical Society》2005,127(38):13136-13137
Tetraurea calix[4]arenes with four loops form exclusively heterodimers with open-chain urea calix[4]arenes when they are dissolved in aprotic solvents. These assemblies can be considered as pseudorotaxanes. If open-chain tetraureas ending with maleic imide functions are used, their Diels-Alder reaction with 1,4,5,8-tetrapentoxyanthracene leads to tetra[2]rotaxanes which cannot be split into the single calixarene parts by hydrogen bond breaking solvents. 相似文献
963.
J. V. Brenčič L. Golič I. Leban P. Šegedin 《Monatshefte für Chemie / Chemical Monthly》1979,110(5):1221-1228
Mo2Cl4
Pic
4·CHCl3 (A) (Pic=4-methylpyridine) and Mo2Br4
Pic
4 (B) crystallize in the monoclinic space group.A inC2/c (No. 15) witha=15.175 (4),b=10.847 (2),c=19.946 (6) and =104.52 (2)°;D
o=1.71 (2),D
c
=1.72 gcm–3 forZ=4.B inP2l/n
(No. 14) witha=9.270 (3),b=16.614 (5),c=9.305 (3) and =91.96 (5)°;D
o=2.03 (3),D
c
=2.05 gcm–3 forZ=2.Two halogens and 4-methylpyridines of the MoX
2
Pic
2 group are in the trans position. Mo–Mo bond lengths are 2.153 96) forA and 2.150 92) forB. Both molecules are situated on the inversion center resulting in the eclipsed configuration of the ligands around the molybdenum pair. The structure ofB has been refined to the conventionalR factors of 0.08 and 0.098. Disorder on the part of 4-methylpyridines and chloroform molecules stopped the refinement ofA at the endR value of 0.175.Mean Mo–X and Mo–N bonding distances are 2.40 (2), 2.25 (5) forA and 2.53 (3), 2.25 (1) forB. 相似文献
964.
Infrared spectra and theoretical study of the conformations of substituted benzoylketene-S,S-acetals
A. Perjéssy W. -D. Rudorf D. Loos Z. Šusteková 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1389-1396
Summary The C=O stretching frequencies of substituted benzoylketene-S,S-dimethylacetals (1a–1o) and benzoylketene-S,S-ethyleneacetals (2a–2m) were measured in CHCl3 and CCl4 and correlated with theHammett substituent constants. The correlations were split into two different and well separated lines for compounds containing electron donor and electron acceptor substituents, which were assigned tos-trans ands-cis quasiplanar conformations. The correlations of carbonyl stretching frequencies with C=O bond orders and oxygen atom charge densities calculated using the semiempirical AM1 method reveal similar results consistent with assignments of structures1 and2 to two quasiplanar conformations. The preparation of some new benzoylketene-S,S-acetals is reported as well.
Infrarotspektroskopische und theoretische Untersuchung der Konformationen substituierter Benzoylketen-S,S-acetale
Zusammenfassung Die C=O-Streckfrequenzen substituierter Benzoylketen-S,S-dimethylacetale (1a–1o) und Benzoylketen-S,S-ethylenacetale (2a–2m) wurden in CHCl3 und CCl4 gemessen und mit denHammet-Konstanten in Beziehung gesetzt. Es ergaben sich zwei deutlich unterschiedliche Gerade für Verbindungen mit Elektronenakzeptoren und mit Elektronendonatoren als Substituenten, die dens-trans- unds-cis-quasiplanaren Konformationen zugeordnet wurden. Die mittels der semiempirischen AM1 — Methode berechneten Korrelationen zwischen C=O-Streckfrequenzen und C=O-Bindungsordnungen bzw. Ladungsdichten am Sauerstoffatom ergeben ebenfalls eine Zuordnung der Verbindungen1 und2 zu zwei quasiplanaren Konformationen. Die Herstellung einiger neuer Benzoylketen-S,S-acetale wird ebenfalls beschrieben.相似文献
965.
Ilona Šperlingová Ludmila Dabrowská Vladimír Stránský Jan Kučera Miloň Tichý 《Accreditation and quality assurance》2006,11(5):231-235
The candidate reference material (RM) was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to toluene. Homogeneity testing yielded no significant differences of urinary concentrations of o-cresol and phenol in 15 randomly selected units of RM. Stability testing showed no significant changes of concentrations of the above analytes over a period of 6 months. Property (pre-certified) values of phenol and o-cresol concentrations and their uncertainties (9.06±0.47 mg l−1 and 1.03±0.06 mg l−1, respectively) were estimated from results of a small-scale interlaboratory comparison in which two laboratories participated using four different analytical methods. 相似文献
966.
Aging of aqueous solutions of poly (vinyl alcohol) obtained by melting of gels, formed in the aging process from solutions prepared by the dissolution of the polymer in hot water, was investigated using non-Newtonian viscometry and normal stress measurement. It was shown that, if the gels undergo melting at the same temperature at which the original solutions were prepared, aging of such solutions proceeds in the same way as in the case of the original solutions. If melting occurred due to heating at lower temperature, the resulting solutions aged more quickly. 相似文献
967.
M. V. Lomonosov Moscow State University, Chemical Department. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 971–976, September–October, 1996. 相似文献
968.
Edward W. Abel Suresh K. Bhargava Maqbool M. Bhatti Muhammed A. Mazid Keith G. Orrell Vladimir Šik Michael B. Hursthouse K.M. Abdul Malik 《Journal of organometallic chemistry》1983,250(1):373-382
The dinuclear complexes [Re2X2(CO)6(RCH2EECH2R)] (X = Cl or Br, R = Ph or Me3Si, E = S or Se) have been prepared and characterized. A variable temperature 1H NMR study on these complexes demonstrated the pyramidal atomic inversion process at the coordinated sulphur and selenium atoms. Total band-shape fittings were used to yield activation parameters for the rate process, in which the two sulphur or selenium atoms undergo synchronous or correlated inversion. 相似文献
969.
Tetracyanonickelate compounds as sorptive materials and the substitution of their H2O content by D2O
Anna Sopková Katarína Györyová Michal Šingliar 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(4):369-377
The compounds NiNi(CN)4·3,5H2O and Ni(NH3)2Ni(CN)4·H2O have been studied to examine the possibility of substituting their H2O or NH3 content by D2O. Contact with D2O was performed after heating the compounds to several temperatures. Depending on the degree of decomposition of the original compounds different ranges of substitution were possible. In such manner the compounds NiNi(CN)4·3,5D2O, NiNi(CN)4·5D2O, Ni(NH3)2Ni(CN)4·D2O, and Ni(D2O)2Ni(CN)4·D2O were prepared and thermally they were less stable than the original ones. The substitution by D2O is in agreement with the sorptive properties of the original tetracyanonickelate against different organic compounds using GC, since these could substitute the guest component and sometimes also the ligands during their decomposition. 相似文献
970.
U. Lavrenčič Štangar B. Orel A. Régis Ph. Colomban 《Journal of Sol-Gel Science and Technology》1997,8(1-3):965-971
A novel low-temperature electrochromic and photochromic material in the form of gels and thin solid films composed of H3PW12O40·nH2O (WPA) incorporated in titanium oxide gel issued of Ti(OPr
i
)4 with addition of acetic acid were made via the sol-gel route by the dip-coating technique. Gels in bulk and thin film forms
have been studied with the help of FT-IR transmission, reflection absorption and Raman spectroscopy. Similarity of the characteristic
band frequencies with pure WPA confirmed that entrapped Keggin salt is well preserved inside the gel. Photochromism of WPA/TiO2 gels which appears after short exposure to UV (λ=366 nm) radiation is related to the excitation effect of branched alcohol
leading to formation of carbonyl modes due to the alcohol transformation to aldehyde. Electrochromic properties of WPA/TiO2 gel films were tested in aqueous 0.001M HClO4 and 0.1M LiClO4 electrolytes as well as in the sol-gel electrochromic device (ECD) composed of LiClO4 doped ormolyte and Sb:Mo:SnO2 counter electrode film with optically passive response. Slight improvement of the WPA/TiO2 intercalation/deintercalation kinetics was obtained with the films exhibiting one order of magnitude higher electronic conductivity
which were made with addition of in situ polymerized pyrrole with Fe(NO3)3. 相似文献