摘要:

Acid leaching (with 1 mol dm-3HNO3) was combined with slurry nebulization in inductively coupled plasma mass spectrometry, with mixed-gas plasmas and flow injection, in an attempt to facilitate the quantitative analysis of heterogeneous materials such as soils. Matrices analyzed ranged from marine sediment to metal-contaminated soil, and were chosen for their variety in elemental composition and matrix structure. Slurries were prepared by first grinding the material to less than 3 &mgr;m in high-purity water and then diluting to 0.1% (w/v) with 1 mol dm-3HNO3, which served as both a dispersing and a leaching agent. The resulting slurries were injected (0.25 cm3) into a deionized distilled water carrier. Under these conditions, the sensitivity was about 85% of that achieved by continuous nebulization. Multivariate optimization of the nitrogen percentage, forward torch power, and aerosol carrier gas flow rate was conducted to find conditions maintaining sensitivity constant between different slurries. Since no set of conditions was optimal for all elements, a compromise set was selected, which resulted in accurate results for La and Pb in a series of reference materials, by calibrating with aqueous standards. On the other hand, the results for V and Cr were almost systematically low, indicating that the compromise plasma conditions did not allow complete atomization/ionization of these elements.Key words: inductively coupled plasma mass spectrometry, slurry nebulization, flow injection, mixed-gas plasma.

ISSN:0008-4042    

DOI:10.1139/v99-042

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

1H,13C, and15N NMR spectra have been measured for a series of isostructural aryl (heteroaryl) vinyl sulfides and compared with analogues of vinyl ethers. It was found that "intramolecular interaction" of the &agr;-hydrogen of the vinyl group with endocyclic nitrogen takes place in 2-vinylthiopyridines. This is in common with the findings for 2-vinyloxypyridine and the intramolecular interaction is shown to have a profile characteristic of hydrogen bonding. Also, the NMR spectral data show that this type of interaction is more intense (~1.5 times) in 2-vinyloxypyridine than in 2-vinylthiopyridine. This is probably due to the greater electronegative effect of oxygen compared to that of sulfur. To discuss these findings further in detail, ab initio calculations have been made, and the conformational energy map and the NMR chemical shifts have been discussed. The ab initio calculations, which were carried out on the D95++(d,p) basis set at the B3LYP level, confirm the planar structure of 2-vinyloxy- and 2-vinylthiopyridines, while other analogues of these ethers and sulfides were essentially nonplanar. Gauge-Independent Atomic Orbital (GIAO) calculations of the shielding constants, based on the same basis set, support the extraordinary low-field shift of the &agr;-hydrogen in the vinyl group when it is situated close to endocyclic nitrogen. All these calculations support our proposal that the vinyl proton is involved in intramolecular hydrogen bonding in 2-vinyloxy- and 2-vinylthiopyridines.Key words: NMR, intramolecular hydrogen bonding, ab initio calculation, GIAO.

ISSN:0008-4042    

DOI:10.1139/v99-038

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Crystals of [Fe (2methylimidazolate)2·0.13(FeCp2)]x,1, are orthorhombic,a= 8.0654(11),b= 15.3504(5),c= 19.3388(9) Å,Z= 8, space groupPnnm. The structure was solved by direct methods and refined by full-matrix least-squares procedures toR(F,I3&sgr;(I)) = 0.057 (Rw(F2, all data) = 0.142). The structure involves tetrahedral iron(II) centers linked in chains by single imidazolate ligand bridges. The chains are cross-linked by additional imidazolates to generate a complex 3-D network of linear channels in which ferrocene molecules are trapped. [Cu(1,2,4-triazolate)2]x,2, is shown by indirect evidence to have a polymeric structure in which copper(II) ions are bridged by triazolate ligands. Magnetic susceptibilities were measured on powdered samples over the temperature range 2-300 K at applied fields of 0-55 000 G. Both materials exhibit antiferromagnetic exchange at temperatures above a magnetic phase transition: 27 K for1and 35 K for2. At temperatures below these transitions the compounds exhibit weak ferromagnetism, likely resulting from canted spin structures. Cycling the applied magnetic field between +55 000 G and -55 000 G at 4.8 K generates hysteresis loops for both materials. Remnant magnetizations of 200 and 55 cm3G mol-1and coercive fields of 5000 and 2500 G are obtained for1and2, respectively.Key words: iron, 2-methylimidazolate, copper, 1,2,4-triazolate, canted spins, ferromagnets

ISSN:0008-4042    

DOI:10.1139/v99-063

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The room-temperature reaction of Me3Ga with benzimidazole 2-carboxylic acid in xylene solvent has yielded a novel crystalline hexameric gallium compound with "MeGa" moieties bridged by the doubly depronotated ligand precursor. Crystals of [MeGa(4,5-benzimidazolato-2-carboxylato)]6·(C6H6)·(m-Me2C6H4)2are monoclinic,a= 18.091(2),b= 17.094(2),c= 13.2215(5) Å,Z= 2, space groupC2/m. The structure was solved by direct methods and refined by full-matrix least-squares procedures toR(F,I3&sgr;(I)) = 0.064 (Rw(F2, all data) = 0.134). The hexameric Ga complex contains a six-membered ring of Ga atoms, bridged by the benzimidazolate ligands with the benzo rings projecting alternately above and below the Ga plane, thus forming a ball-shaped molecule. The complex could have idealD3dsymmetry, but it contains an encapsulated molecule of benzene, which distorts the regularity of the Ga6hexagon, and reduces the symmetry of the complex to the crystallographically observedC2h. The coordination geometry at each of the two independent GaO2N2C centres approximates a trigonal bipyramid, with a N2C trigonal plane, and the O atoms above and below; average dimensions are Ga-O = 2.176(2), Ga-N = 1.973(3), Ga-C = 1.927(5) Å, O-Ga-O = 165°. The unit cell also contains fourm-xylene solvent molecules (outside the molecular cage).Key words: gallium, crystal structure, benzene intercalate, benzimidazolecarboxylic ac

ISSN:0008-4042    

DOI:10.1139/v99-064

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Reaction of pyridinium and phosphonium 2-carboxy-1-formyl-2-oxoethylides with oxybis(diphenylborane) yields 5-(2-oxo-1-(pyridinio or phosphonio)ethylidene)-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclopentanones, which represent novel types of boron nitrogen and boron phosphorus betaines, respectively. Crystals of 5-(2-oxo-1-pyridinioethylidene)-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclopentanone,1a, are monoclinic,a= 15.589(3),b= 12.366(2),c= 20.1869(11) Å, &bgr; = 111.227(2)°,Z= 8 (two independent molecules), space groupP21/a; and those of 5-[2-oxo-1-(triphenylphosphonio)ethylidene]-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclo-pentanone,11, are monoclinic,a= 9.6922(7),b= 25.027(2),c= 11.3041(4) Å, &bgr;= 92.1418(13)°,Z= 4 (two independent molecules), space groupP21. The structures were solved by direct methods and refined by full-matrix least-squares procedures toR(F,I3&sgr;(I)) = 0.047 and 0.042 (Rw(F2, all data) = 0.096 and 0.088), respectively, for1aand11.Key words: pyridinium ylides, phosphonium ylides, bisacyl methylide diphenylboron chelates, boron nitrogen betaines, boron phosphorus betaines, organoboron compounds, crystal structu

ISSN:0008-4042    

DOI:10.1139/v99-067

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In weakly acidic, aqueous buffer (MeCO2-+ bipy), the complex ion [Mn2IV(&mgr;-O)2(&mgr;-MeCO2)(bipy)2(H2O)2]3+,1(bipy = 2,2prime-bipyridine), coexists in rapid equilibrium with its hydrolytic derivatives, [Mn2IV(&mgr;-O)2(bipy)2(H2O)4]4+,2, and [Mn2IV(&mgr;-O)2(&mgr;-MeCO2)(bipy)(H2O)4]3+,3. The solution quantitatively oxidizes hydrogen peroxide to oxygen and ascorbic acid to dehydroascorbic acid, itself being reduced to MnII. In the presence of excess reductant, the reactions follow simple first-order kinetics with no evidence for the accumulation of a significant amount of any intermediate manganese complex. The ascorbate anion shows overwhelming kinetic dominance over ascorbic acid, but no evidence is available for deprotonation of hydrogen peroxide. The preferred intimate mechanism for hydrogen peroxide is inner sphere but that for ascorbic acid is uncertain. For both reductants, increased extent of aquation leads to increased kinetic activity in the order:1<2<3.Key words: kinetics, manganese, ascorbic acid, hydrogen peroxide, 2,2prime-bipyridine.

ISSN:0008-4042    

DOI:10.1139/v99-062

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The absorption and emission spectra and the fluorescence lifetimes and quantum yields of alloxazine and several of its N- and C- methyl-substituted derivatives, including two isoalloxazines, have been measured in a nonpolar solvent (1,2-dichloroethane), a polar aprotic solvent (acetonitrile), and a polar protic solvent (ethanol). The excited state decays are all single exponential, suggesting that only one emitting species is present in all cases. The spectroscopic data show that the emitting species is the &pgr;,&pgr;* electronic excited state corresponding to the ground state of the absorbing molecule; there is no evidence of excited state proton transfer for any of these solutes in any of the three solvents. The longer lifetimes and larger fluorescence quantum yields of the isoalloxazines compared with the alloxazines can be attributed exclusively to significantly slower rates of radiationless relaxation in the excited isoalloxazines. The remission and emission spectra of these same compounds adsorbed on cellulose are similar to the corresponding absorption and emission spectra in homogeneous solution, suggesting that the emitting species are the same in the adsorbed state as they are in homogeneous solution. However, the adsorbed excited species exhibit non-exponential temporal decay, attributed to inhomogeneities in the binding of the chromophore to cellulose. The emission spectra of polycrystalline samples of alloxazine and lumichrome suggest the possible occurrence of double intermolecular excited state proton transfer, but this interpretation is not supported by the further photophysical data obtained here.Key words: photophysics, spectroscopy, alloxazine, lumiflavin, cellulose.

ISSN:0008-4042    

DOI:10.1139/v99-076

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The C-polysaccharide is an antigen common to all known serotypes ofStreptococcus pneumoniaebacteria and is a potential target for vaccine preparation. The final uncertainty in the structure of its repeating unit, a pentasaccharide phosphate containing two phosphorylcholine side chains, has been resolved by determining the configuration of ribitol. Assignment of configuration was performed by synthesis of the two trisaccharide phosphate fragments that have eitherD- orL-ribitol at their centers and comparison of their1H and13C NMR spectral data with that of the natural polysaccharide. The syntheses employed common synthons added in different orders to an asymmetrically substituted chiral ribitol derivative to obtain opposite chiralities in the ribitol segments. The data for the trisaccharide containingD-ribitol was almost identical to that of the natural material while that for the trisaccharide containingL-ribitol differed significantly. In particular, the chemical shift differences between the two protons of the primary carbons of ribitol units directly attached to the &bgr;-2-acetamido-2-deoxy-galactopyranosyl residue were 0.10, 0.12, and 0.33 ppm, in the natural polysaccharide, theD-ribitol-containing trisaccharide, and theL-ribitol-containing trisaccharide, respectively. The average difference between the13C NMR chemical shifts of corresponding ribitol carbons from the natural polysaccharide and theD-ribitol-containing trisaccharide phosphate was 0.034 ppm. This evidence indicates that ribitol in the C-polysaccharide has theD-configuration and that a very similar mixture of conformations in the ribitol portions is present for the natural polysaccharide and theD-ribitol-containing trisaccharide phosphate.Key words: C-polysaccharide,Streptococcus pneumoniae, ribitol, dibutylstannylene acetal, determination of configuration.

ISSN:0008-4042    

DOI:10.1139/v99-056

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The electrochemical oxidation of gallium in a cell containing a solution of 3,5-di-tert-butylcatechol (H2dbc) in a mixture of liquid ammonia and diethyl ether gives rise to the complex Ga(dbqdi)2, where dbqdi is a tridentate ligand formed by the condensation of two molecules of H2dbc and ammonia. The same paramagnetic molecule can be prepared by treating GaCl3with H2dbc in ethanol with concentrated aqueous ammonia, with subsequent aerial oxidation. The crystal parameters are triclinic, space groupP,a= 11.6140(8),b= 12.3415(9),c= 20.765(1) Å, &agr; = 89.491(1)°, &bgr; = 74.287(1)°, &ggr; = 75.748(1)°,Z= 2, andR= 0.0542 for 7578 unique reflections. The structure, which is based on a GaO4N2kernel, is discussed on the basis of crystallographic and ESR results.Key words: gallium, electrochemical synthesis, electron spin resonance, X-ray crystallogra

ISSN:0008-4042    

DOI:10.1139/v99-052

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The voltammetric electroreduction properties of 1,2,5-thiadiazole 1,1-dioxide derivatives with different 3,4 substituents have been investigated in aprotic (mainly acetonitrile) solvent solution. The 3,4 substituents, selected according to the characteristics of their &pgr;-system, were phenanthro-9,10 (connected &pgr;-system) and acenaphtho-1,2 (fused &pgr;-system). New measurements are also presented for 3,4-diphenyl (separated &pgr;-systems). The basic properties of the substrates were investigated through voltammetry in acidic acetonitrile solutions. The substrates were more easily electroreduced (between -0.6 and -1.0 V vs. Ag/Ag+, acetonitrile solvent) than the parent (non-1,1-dioxide) heterocycles (which are electroreduced at ca. -2.5 V). They were also more easily electroreduced (by ca. 0.4 V) than the corresponding diketones (benzil, 9,10-phenanthrenequinone, and acenaphthenequinone). The influence on voltammetric behavior of the electron-withdrawing properties of the 1,2,5-thiadiazole 1,1-dioxide ring and that of the structure of the molecules was analyzed in light of previous structural studies by X-ray crystallography and theoretical chemistry calculations. Bulk electrolysis experiments in acidic acetonitrile solutions of the phenanthro[9,10-c] derivative produced its previously unreported dihydrogenated derivative (thiadiazoline), which oxidizes easily. Infrared spectroscopy data suggested that the structure of this compound differs from that of 3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide.Key words: organic electrochemistry, 1,2,5- thiadiazoles, structure-reactivity relations.

ISSN:0008-4042    

DOI:10.1139/v99-051

出版商:NRC Research Press    

年代:1999

数据来源: NRC