Earlier work by Lindenbaum and Boyd has demonstrated the important role of hydrophobic interactions involving the water solvent in determining the osmotic coefficients and properties of aqueous solutions of the tetraalkylammonium halides. Osmotic coefficients of solutions of tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium bromides in the more highly structured solvent D2O have now been determined by the gravimetric isopiestic method, using reference solutions of NaCl in D2O. The data were fitted to the Rush-Johnson and Pitzer equations. Satisfactory agreement with the results for aqueous solutions at comparable concentrations indicates that the solution chemistry of these quaternary ammonium bromides is not highly dependent on the degree of structure of the pure solvents. Supplementary data for mixtures of Me4NBr with Et4NBr, Pr4NBr, or Bu4NBr in both H2O and D2O are consistent with this conclusion.On leave 1980–82 from Banaras Hindu University, India 相似文献
Insoluble complexes are formed in acidic aqueous media when poly(acrylic acid) (PAA) and poly-(vinylbenzo-18-crown-6) (P18C6) or polyvinylbenzoglymes are mixed. Complex formation results from hydrogen bonding between carboxyl groups and crown ether- or glyme–oxygen atoms as well as from hydrophobic interactions. The precipitation is pH dependent and was determined as a function of the ratio PAA to P18C6 or to polyglyme at different HCl concentrations in 10?4M solutions of polycrown or polyglyme. Precipitation is nearly quantitative in 0.01N HCl. The compositions of PAA/P18C6 precipitates were determined as a function of the initial PAA/P18C6 ratio in solution. The complexes with P18C6 can be solubilized in acidic media when crown-complexable cations (K+, Cs+, Ba2+) are added, but the charged P18C6 reprecipitates in basic solution as a polysalt complex with the PAA–polyanion. More stable PAA–P18C6 complexes in the form of fibers can be obtained by interfacial complex formation. Poly(methacrylic acid) is less effective as a complex former. 相似文献
Summary A series of cobalt(II), nickel(II) and copper(II) complexes of 2-picolinamineN-oxide, HA, has been prepared. Solids of formula [M(HA)3](BF4)2 (M=cobalt(II) or nickel(II); [Cu(HA)2]X2 (X=BF
4–
, NO
3–
); [Co(HA)2X2] (X=Cl– or Br–); [Ni(HA)2Cl2] and [Cu(HA)X2] (X=Cl– or Br–] have been isolated and characterized by partial elemental analyses, molar conductivities, magnetic susceptibilities, DSC-TGA, and spectral methods. All complexes were found to be monomeric, and their spectral parameters are compared with those of the metal ion complexes ofN-alkyl-2-picolinamineN-oxides, 2-dialkylaminopyridineN-oxides and 2-picolinamine. The cobalt(II) and nickel(II) halide complexes spectrally show a mixture of octahedral and tetrahedral centres. 相似文献
Summary The chlorides and bromides of cobalt(II), nickel(II) and copper(II) along with the acetates of the latter two metal ions and copper(II) tetrafluoroborate were used to prepare complexes ofN-2-(5-picolyl)-N-phenylthiourea (5MTUH). 5MTUH coordinates as a bidentate ligand via the pyridyl nitrogen and the sulphur atoms in the cobalt(II) complexes and the compounds isolated with Cu(BF4)2 and CuCl2. Complexes of stoichiometry [Cu(5MTU)X] (X=Br or C2H3O2) appear to have the deprotonated ligand coordinated via the pyridyl andN thioamide nitrogens and the sulphur atom. The nickel(II) complexes involve monodentate 5MTUH with sulphur being the donor atom. A violet, octahedral [Co(5MTUH)2Cl2] complex and a blue, tetrahedral [Co(5MTUH)Cl2] complex have been isolated, but with CoBr2 only an octahedral complex could be prepared. 相似文献
(±)-α and β-Himachalene, 5 and 6 , have been synthesized in a convergent manner from 3,3-dimethylacrolein ( 9 ), the ester enolate 10 and the silyloxypentadienyllithium 7 . The key steps are the regioselective γ-addition of the dienal 13 to 7 and the intramolecular Diels-Alder addition 15 → 16 . Hydrogenolysis of the diethylphosphate group and functionalization at C (5) completed the synthesis of 5 and 6 . 相似文献
Chitosan is alternated with sulfonated polystyrene (PSS) to build layer‐by‐layer (LBL) films that are used as sensing units in an electronic tongue. Using impedance spectroscopy as the principle method of detection, an array using chitosan/PSS LBL film and a bare gold electrode as the sensing units was capable of distinguishing the basic tastes – salty, sweet, bitter, and sour – to a concentration below the human threshold. The suitability of chitosan as a sensing material was confirmed by using this sensor to distinguish red wines according to their vintage, vineyard, and brands.
PCA Plot for red wine samples obtained from impedance measurements at 1 kHz for the sensor array comprising a 3‐bilayer chitosan/PSS film and a bare gold electrode. 相似文献
The di-Co(2+) complex, [Co(2+)(mu-OH)(oxapyme)Co(2+)(H(2)O)](+), contains an unsymmetrical binucleating ligand (oxapyme) which provides five- and six-coordinate metal sites when a hydroxide bridge is introduced. This complex absorbs 1 equiv of O(2) irreversibly in solution, producing an unstable di-Co(3+) oxygenated product. The oxygenated product has been studied at low temperatures, where its electronic absorption and (1)H NMR spectra were recorded. It is probable that the oxygenation reaction involves a one-site addition two-metal oxidation reaction to produce an end-on-bonded peroxide ligand at the available coordination site, giving the complex [Co(3+)(mu-OH)(oxapyme)Co(3+)(mu(1)-O(2))](+). Addition of 1 equiv of HClO(4) to this oxygenation product gives a stable peroxide complex, [Co(3+)(mu,eta(1):eta(2)-O(2))(oxapyme)Co(3+)](2+), where one of the oxygen atoms bridges the two metals and is sideways bonded to one of the metals. The formation of this stable complex involves expulsion of the OH(-) bridge. Addition of NO(2)(-) to the sideways-bonded peroxide complex leads to the formation of another stable complex, [Co(3+)(mu,eta(1):eta(1)-O(2))(oxapyme)Co(3+)(NO(2))](+), where the peroxide forms a classic di-end-on bridge to the two metals. Both of these complexes have been fully characterized. Addition of acid to this second stable dioxygen complex leads to the release of HNO(2) and the formation of the mu,eta(1):eta(2) sideways-bonded peroxide complex. 相似文献
The assay of benzylpenicillin by iodimetric titration, spectrophotometry with a mercury(II) chloride—imidazole reagent, titration with mercury(II) nitrate in acetate buffer solution, and titration with mercury(II) perchlorate in aqueous pyridine solution, was examined in four laboratories. The first two methods were applied to two samples (the third one being the reference sample), the mercury(II) nitrate titration to three, and the mercury(II) perchlorate method to two samples. The four methods gave very similar results, but the purity obtained with the mercury(II) perchlorate method was slightly lower, and this procedure is less desirable because pyridine is used as solvent. There were no great differences in the relative standard deviations of the four methods. The titration with mercury(II) nitrate is preferred because it is an absolute method. 相似文献