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971.
A method is described for the precise determination of carbon and hydrogen in milligram, amounts of sample. The method is based on the manometric measurement of the amounts of carbon dioxide and water formed on combustion. A precision mercury manometer is used in which pressures are converted to mercury volumes. The latter are measured with the aid of a commercial piston-type buret using a photo-electric level indication.  相似文献   
972.
The migration of 99Tc in a weak loess aquifer was investigated in-situ with undisturbed aquifer medium columns. The columns were obtained horizontally at a depth of 3236 m in an Underground Research Facility (URF). Quartz containing 3H (HTO) and 99Tc (in the form of 99TcO4 -) was introduced into one end of the columns and the columns were covered tightly. Aquifer water was introduced into the columns directly from an experimental shaft in the UFR. Effluents from the columns were collected and the activity of 3H and 99Tc were determined with a liquid scintillation analyzer. The breakthrough curves of 3H and 99Tc indicate that 99Tc migrates a little faster than that 3H does in the aquifer.  相似文献   
973.
The solution chemistry of uranyl ion with iminodiacetate (IDA) and oxydiacetate (ODA) was investigated using NMR and EXAFS spectroscopies, potentiometry, and calorimetry. From the NMR and EXAFS data and depending on stoichiometry and pH, three types of metal:ligand complex were identified in solution in the pH range 3-7: 1:1 and 1:2 monomers; a 2:2 dimer. From NMR and EXAFS data for the IDA system and previous studies, we propose the three complex types are [UO(2)(IDA)(H(2)O)(2)], [UO(2)(IDA)(2)](2)(-), and [(UO(2))(2)(IDA)(2)(mu-OH)(2)](2)(-). From EXAFS spectroscopy, similar 1:1, 2:2, and 1:2 complexes are found for the ODA system, although (13)C NMR spectroscopy was not a useful probe in this system. For the 1:1 and 1:2 complexes in solution, EXAFS spectroscopy is ambiguous because the data can be fitted with either a long U-N/O(ether) value (ca. 2.9 A) suggesting 1,7-coordination of the ligand or a U-C interaction at a similar distance, consistent with terminal bidentate coordination. However, the NMR data of the IDA system suggest that 1,7-coordination is the more likely. The stability constants of the three complexes were determined by potentiometric titrations; the log beta values are 9.90 +/-, 16.42 +/-, and 10.80 +/- for the 1:1, 1:2, and 2:2 uranyl-IDA complexes, respectively, and 5.77 +/-, 7.84 +/-, and 4.29 +/- for the 1:1, 1:2, and 2:2 uranyl-ODA complexes, respectively. The thermodynamic constants for the complexes were calculated from calorimetric titrations; the enthalpy changes (kJ mol(-)(1)) and entropy changes (J K(-)(1) mol(-)(1)) of complexation for the 1:1, 1:2, and 2:2 complexes respectively are the following. IDA: 12 +/- 2, 230 +/- 8; 8 +/- 2, 151 +/- 9; -33 +/- 3, -283 +/- 11. ODA: 26 +/- 2, 198 +/- 12; 20 +/- 2, 106 +/- 8; -24 +/- 2; -219 +/- 8.  相似文献   
974.
The non local weighted-density approximation (WDA) to the exchange-correlation potentialV xc (r) is used to compute electron densities, ionization potentials and electron affinities of several atoms and ions. Especial care is taken in calculating and discussing 〈r 2〉 in noble gas atoms. Good results are obtained for all those quantities, but it is critical that the WDA is applied in such a way that it preserves the correct larger behaviour ofV xc (r). A comparison of the calculated electron density with that of the Hartree-Fock method shows the effects of coulomb correlation. The density rearrangements upon the introduction of correlation agree qualitatively with the results of Configuration-Interaction calculations  相似文献   
975.
Reactions of various η6-arene-η5-cyclopentadienyliron or substituted cyclopentadienyliron cations with trimethyl, triethyl or triphenyl phosphite under either thermal or photochemical conditions all resulted in the replacement of the arene ligand with three phosphite ligands to give η5-tris(trimethyl, triethyl or triphenyl phosphite)-η5-cyclopentadienyliron or substituted cyclopentadienyliron cations. The yields of the phosphite complexes were higher from photolysis than from the analogous thermolysis. Photolysis of the η6-chlorobenzene-η5-cyclopentadienyliron cation (IX) carried out in the presence of a more basic or more electron-rich aromatic ligand resulted in the exchange of the chlorobenzene of IX with the more basic arene, thus providing synthetic routes to cyclopentadienyliron complexes that may be difficult to prepare by other means. New complexes synthesized in this way are the η6-2-phenylethyl tosylate-η5-cyclopentadienyliron cation and the CpFe+ complexes of thiophene, 2-methylthiophene, 3-methylthiophene and 2,5-dimethylthiophene.  相似文献   
976.
Theoretical and experimental voltammetric studies of copper reduction in chloride media show that electrodeposition on the hanging mercury drop electrode (HMDE) is controlled by competitive reduction between Cu(II) organic species and the Cu(I)Cl2? intermediate. For reversible Cu(II) species reduction, the change from organic ligand to chloride control of the final reduction step can be predicted by thermodynamic calculation. On the other hand in irreversible systems (e.g. estuarine waters) involvement of the CuCl2? intermedite in the electrodeposition is more complex and can occur both before and after amalgamation.  相似文献   
977.
A three-step synthesis of bispidine ( 1 ) is described. Mannich condensation of N-benzyl-4-piperidone, formaldehyde, and benzylamine afforded N,N′-dibenzylbispidinone ( 5 ), which was reduced under modified Wolff-Kishner conditions to yield N,N′ -dibenzylbispidine ( 6 ). Catalytic debenzylation of this compound gave 1 .  相似文献   
978.
979.
An original concept of an enzyme multibiosensor for determination of toxic substances based on enzyme inhibition analysis has been proposed and its main performances have been analysed. For the development of this multibiosensor, two types of transducers such as potentiometric pH-sensitive field-effect transistors and conductometric thin-films interdigitated electrodes, and three enzymes, namely urease, acetylcholinesterase and butyrylcholinesterase have been used. The experimental data have been treated by multivariate correspondence analysis. A complete procedure for a simultaneous determination of some heavy metal ions and pesticides has been proposed and its advantages have been discussed.  相似文献   
980.
Yamada H  Kato C 《Talanta》1993,40(7):1049-1057
The solvent extraction of copper(II) with trimethylacetic acid using benzene and 1-octanol as solvents was performed at 25 degrees C and 0.1 mole. dm(-3) ionic strength in the aqueous phase. In contrast to the extraction of copper(II) with a saturated straight-chain carboxylic acid in benzene, the dimeric copper(II) trimethylacetate was observed to dissociate into the monomer, even at a moderately high concentration of copper(II) in the benzene phase. In the system using 1-octanol as a solvent, both the monomeric and dimeric copper(II) species are suggested to be solvated by some 1-octanol molecules. It has been found that the dimerization and adduct formation of copper(II) species in benzene may more effectively enhance the extractability of copper(II) than the solvation by 1-octanol molecules.  相似文献   
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