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31.
The acidity functions of aqueous trifluoroacetic and trifluoromethanesulphonic acid mixtures, and aqueous hexafluoropropane-2, 2-diol solutions, have been determined by differential pulse polarography. The apparent shift of the half-wave potential for the ferrocene—ferricinium couple, as the solvent composition is changed, is used to indicate the change in potential of a glass electrode; acidity is measured as the HGF acidity function. The densities of two of these solvent systems as a function of composition are also reported. Trifluoromethanesulphonic acid—water mixtures represent the strongest aqueous acid solvent system so far studied. 相似文献
32.
Sequence heterogeneity in a portion of the mitochondrial cytochrome c oxidase subunit 1 gene (pcox1) was measured for the hookworms, Ancylostoma caninum from Australia, A. duodenale from China, and Necator americanus from China and Togo using single-strand conformation polymorphism (SSCP) analysis combined with DNA sequencing. The pcox1 sequences were characterised for individual nematodes displaying genetic variation within each of the three species, and those were compared with pcox1 sequences of four other species of hookworm. While intraspecific variation in the pcox1 sequence ranged from 0.5 to 8.6% for A. caninum, 0.3 to 3.3% forA. duodenale, and 0.3 to 4.3% for N. americanus, interspecific differences varied from 4.8 to 12.9%. Sequence data also provided information on nucleotide compositions and substitution patterns. Genetically distinct groups were detected within A. caninum and A. duodenale, indicating significant population substructuring within these species. Also, N. americanus individuals from China all differed from those from Togo at four nucleotide positions, supporting a previous proposal (based on ribosomal DNA sequence data) that N. americanus may represent a species complex. The findings indicated the value of pcox1 sequence data and the mutation scanning approach for studying the genetic structures of hookworm populations, which should have important epidemiological relevance. 相似文献
33.
Robin L. Garrell John C. Smyth Frank R. Fronczek Richard D. Gandour 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(1):73-78
Single crystal X-ray analysis of the 2:1 acetonitrile complex of 18-crown-6 is reported. Crystals of the complex are monoclinic,P21/n, witha=9.123(3),b=8.524(3),c=13.676(4) Å, =104.68(3)°, andD
c
=1.118 g cm–3 forZ=2. The complex lies on a center of symmetry, with the crown in theD
3d conformation. Methyl groups of the acetonitrile molecules have weak interactions with the crown oxygen atoms, and are tilted 31.7° from the host's threefold axis. Methyl hydrogen atoms are rotationally disordered about the acetonitrile axis.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82057 (12 pages). 相似文献
34.
Bedford RB Bruce DW Frost RM Goodby JW Hird M 《Chemical communications (Cambridge, England)》2004,(24):2822-2823
Iron(III) salen and related complexes are active catalysts for the coupling, under mild and simple reaction conditions, of aryl Grignard reagents with primary and secondary alkyl halide substrates bearing beta-hydrogens. 相似文献
35.
The synthesis of the first derivatives of bis(pyrrolo[3,4-d])tetrathiafulvalene has been studied in detail. Starting from the readily available 2,5-dimethylpyrrole (11) and N-phenyl-2,5-dimethylpyrrole, bis(2,5-dimethylpyrrolo[3,4-d])tetrathiafulvalene (8) and the N,N'-disubstituted derivatives 6, 7, 9, and 10 were prepared in good yields by practical procedures. In contrast to the other types of aromatic annelated tetrathiafulvalenes (TTFs), which have appreciably higher oxidation potentials than TTF, the redox behavior of the pyrrolo tetrathiafulvalenes (TTFs) is very close to that of TTF itself. The potential of pyrrolotetrathiafulvalenes as a new series of organic metal building blocks is shown by the two-probe conductivities of the tetracyanoquinodimethane (TCNQ) complexes of the N-phenyl compound 7 and the N-methyl compound 9, which give higher values than TTF-TCNQ under similar conditions. 相似文献
36.
Robin K. Harris Judith A. K. Howard Abdolraouf Samadi-Maybodi Jing Wen Yao Warren Smith 《Journal of solid state chemistry》1995,120(2)
The first crystal structure is reported for a silicate clathrate hydrate involving a triply charged cation [C18H30N3]3+ and an octameric cubic silicate cage. The structure is essentially a host/guest system, with the silicate cages linked into a framework by hydrogen bonding to water molecules. The space group is P
with Z = 2, and the asymmetric unit includes a complete cation and half the anion, plus 21 water molecules (4 of which are in disordered positions). Solid-state (CPMAS) 29Si and 13CNMR spectra are consistent with the diffraction-determined structure and indicate substantial distortion of the anion from cubic symmetry. Solution-state spectra of precursor solutions and of melted material are also presented and discussed. 相似文献
37.
Monwar M Oh SJ Rinaldi PL McCord EF Hutchinson RA Buback MM Latz H 《Analytical and bioanalytical chemistry》2004,378(6):1414-1427
Poly(n-butylacrylate-co-carbon monoxide-co-ethylene) (polyEBC) samples prepared from 13C-labeled monomer, n-butyl acrylate, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex structure of the terpolymer, 2D-1H/13C-heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced resonances in the spectra of two polymer samples, one polymer resulting from synthesis with 1-13C-n-butylacrylate monomer and a second polymer obtained from a synthesis with 2-13C-n-butylacrylate monomer. High-resolution 2D-NMR combined with 13C-labeling of the polymer greatly simplifies the 2D-NMR spectra, selectively enhances the weak peaks from low occurrence B-centered triad structures, and aids in their resonance assignments. In all experiments, the sample temperature was 120 degrees C, to ensure a homogeneous solution and sufficient molecular mobility. Electronic Supplementary Material: Supplementary material (1D 13C NMR spectra of the 13C-labeled and unlabeled polymers) is available in the online version of this article at http://dx.doi.org/100.1007/s00216-003-2402-3. 相似文献
38.
A prenyloxycoumarin from Psiadia dentata 总被引:2,自引:0,他引:2
Fortin H Tomasi S Jaccard P Robin V Boustie J 《Chemical & pharmaceutical bulletin》2001,49(5):619-621
A new coumarin identified as 5-hydroxy-6-methoxy-7-(3-methyl-but-2-enyloxy)-2H-1-benzopyran-2-one (isoobtusitin) was isolated from Psiadia dentata. This compound showed, in vitro, a moderate inhibitory activity against poliovirus and a very weak activity against (HIV), whereas it was inactive against (HSV1), (VSV), and murine tumoral cell lines (3LL, L1210). 相似文献
39.
A three step synthesis of 2-pentafluorosulfanylnaphthalene is reported. Initial addition of SF5Cl to benzobarralene was followed by elimination to form 2-pentafluorosulfanylbenzobarralene. Heating of this compound with 3,6-bis-(2-pyridyl)-1,2,4,5-tetrazine led to elimination of the ethylene bridge via a sequence of cycloadditions and retro-cycloadditions to form the title compound. 相似文献
40.
Prestegane B -the first higher plant occured dibenzyl butanolide lignan with two -phenols- and its dimethylether were isolated from and the structure determinations were performed with the aid of high resolution NMR and Mass fragmentation for the former, and with 2-D J resolved 1H NMR studies and synthesis for the latter. 相似文献