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121.
Danielle Goveia Fabiana Aparecida Lobo Peter Burba Leonardo Fernandes Fraceto Newton Luiz Dias Filho André Henrique Rosa 《Analytical and bioanalytical chemistry》2010,397(2):851-860
This paper deals with the development and optimization of an analytical procedure using ultrafiltration and a flow-injection system, and its application in in-situ experiments to characterize the lability and availability of metal species in humic-rich hydrocolloids. The on-line system consists of a tangential flow ultrafiltration device equipped with a 3-kDa filtration membrane. The concentration of free ions in the filtrate was determined by atomic-absorption spectrometry, assuming that metals not complexed by aquatic humic substances (AHS) were separated from the complexed species (M–AHS) retained by the membrane. For optimization, exchange experiments using Cu(II) solutions and AHS solutions doped with the metal ions Ni(II), Mn(II), Fe(III), Cd(II), and Zn(II) were carried out to characterize the stability of the metal–AHS complexes. The new procedure was then applied in-situ at a tributary of the Ribeira do Iguape river (Iguape, São Paulo State, Brazil) and evaluated using the ions Fe(III) and Mn(II), which are considered to be essential constituents of aquatic systems. From the exchange between metal–natural organic matter (M–NOM) and the Cu(II) ions it was concluded that Cu(II) concentrations >485 μg L?1 were necessary to obtain maximum exchange of the complexes Mn–NOM and Fe–NOM, corresponding to 100% Mn and 8% Fe. Moreover, the new analytical procedure is simple and opens up new perspectives for understanding the complexation, transport, stability, and lability of metal species in humic-rich aquatic environments. 相似文献
122.
D. Brynn Hibbert Danielle Blackmore Jianfeng Li Diako Ebrahimi Michael Collins Sasha Vujic Paul Gavoyannis 《Analytical and bioanalytical chemistry》2010,396(2):765-773
The probability density functions of amount ratios of compounds (total codeine/total morphine, 6-monoacetylemorphine/total
morphine, papaverine/total morphine, and noscapine/total morphine) from the analysis of seized heroin, originating from known
world regions (South East Asia, South West Asia, South America, Mexico) allows calculation of likelihood ratios for ‘unknown’
samples. Application of Bayes Theorem with a suitable prior probability, for example the frequency of a particular region
in the database, leads to the probability that a particular profile comes from a given target region. Data from 2549 seizures
of heroin at Australia’s border illustrates the method, and results are compared with simple HS1 ratio approaches for assigning
geographical origin. The method can be implemented in a spreadsheet and gives more refined intelligence of the origins of
seized drugs than simple ranges.
相似文献
123.
Charles W. Jefford Hamish G. Grant Danielle Jaggi John Boukouvalas Shigeo Kohmoto 《Helvetica chimica acta》1984,67(8):2210-2217
The photo-oxygenation of 2-(methoxymethylidene)adamantane ( 3 ) creates a zwitterionic peroxide which may be captured by acetaldehyde to give the corresponding pair of diastereoisomeric tricyclo[3.3.1.13,7]decane-2-spiro-6′ -(3′ -methyl-5′ -methoxyl′, 2′, 4′ -trioxanes) ( 4 ). Ease of capture depends strongly on solvent polarity and temperature. When these are low, yields of trioxine are high (~ 80%). Conversely, 1,2-dioxetane formation is favoured at high temperature and solvent polarity. 2-(Phenoxymethylidene)adamantane ( 5 ), on photo-oxygenation, only gives the corresponding 1,2-dioxetene, even in the presence of acetaldehyde. From a Hammett, study of the-oxygenation of the enol ether 5 and p-methoxy, p-methyl, p-chloro and m-chloro derivatives, 9, 11, 13 , and ( 15 ), a good linear relation was found between substituent constants and oxygenation rates which yielded reaction constants (ρ) of 2.59, ?2.40, ?1.09, and ?0.90 in benzene, AcOET, CH2Cl2, and MeOH respectively. This data to the formation of a zwitterionic peroxide which enjoys stabilization from its won substituents and by competing solvation and further explains the predominance of dioxetane to the detriment of trioxane formation. 相似文献
124.
The X-ray crystal structures of 4,4-dihydroxybenzophenone-2,4-dinitrophenylhydrazone (I) and 2,2-dihydroxybenzophenone-2,4-dinitrophenylhydrazone (II) have been determined in order to study the structural characteristics of these molecules that may contribute to their antiestrogenic and cytotoxic properties. These structures have been compared to other hydrazone derivatives as well as tamoxifen, an antiestrogen drug presently used clinically for the treatment of breast cancer.Crystal data: (I) C19H14N4O6 · C4H10O; MW=468.0; monoclinic,P21;a=8.601(2), b=15.502(8), c=16.851(4) Å,=98.58(2)°;Z=8; finalR=0.036 for 1904 observed reflections. (II C19H14N4O6 · H2O; MW=410.0; monoclinic,P21/c;a=7.603(2),b=19.552(4),c=12.493(3) Å,=92.11(1)°;Z=4; finalR=0.045 for 1171 observed reflections. 相似文献
125.
Jeanne Brygier Michel Gelbcke Claude Guermant Michelle Nijs Danielle Baeyens-Volant Yvan Looze 《Applied biochemistry and biotechnology》1993,42(2-3):127-135
Carbonylimidazol-l-yl-mPEG is obtained quantitatively by reacting methoxypoly(ethyleneglycol) (mPEG) with 1.1 Eq of N,N′-carbonyldiimidazole
in the presence of a stoechiometric amount of 4-dimethyl-aminopyridine used as hypernucleophilic acylation catalyst. Carbonylimidazol-l-yl-mPEG is quite stable in aqueous solutions with half-lives up to 70 h in pHs ranging from 6.0 to 7.0 at 25‡C. From reactivity
studies toward amines with various nucleophilic strengths, it is suggested that carbonylimidazol-l-yl-mPEG may be best used to modify α-amino terminal function of proteins selectively or to introduce amino function on PEG chains. 相似文献
126.
Emilio Pardo Dr. Danielle Cangussu Dr. Marie-Claire Dul Rodrigue Lescouëzec Dr. Patrick Herson Yves Journaux Dr. Emerson F. Pedroso Dr. Cynthia L. M. Pereira Dr. M. Carmen Muñoz Prof. Dr. Rafael Ruiz-García Dr. Joan Cano Dr. Pedro Amorós Prof. Dr. Miguel Julve Prof. Dr. Francesc Lloret Prof. Dr. 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2008,120(22):4279-4284
127.
The dehydroxy-fluorination of propargylic alcohols occurs with a complete regiocontrol and a good to complete stereocontrol, in contrast to the reactions performed on allylic alcohols. The gem-difluorination of propargylic ketones occurs smoothly in contrast to enones which have a very low reactivity towards DAST or Deoxo-fluor™. It is proposed that the large differences in the stabilization energies of the key carbonium ion intermediates (either propargylic or allylic) could explain these strong differences in reactivity during nucleophilic fluorination. The calculations of isodesmic reactions are in full agreement with this proposal. 相似文献
128.
Eric L. Petersen Danielle M. Kalitan Gilles Bourque John M. Simmie 《Proceedings of the Combustion Institute》2007,31(1):447-454
Shock tube experiments and chemical kinetic modeling were performed to further understand the ignition and oxidation kinetics of various methane-propane fuel blends at gas turbine pressures. Ignition delay times were obtained behind reflected shock waves for fuel mixtures consisting of CH4/C3H8 in ratios ranging from 90/10% to 60/40%. Equivalence ratios varied from lean (? = 0.5), through stoichiometric to rich (? = 3.0) at test pressures from 5.3 to 31.4 atm. These pressures and mixtures, in conjunction with test temperatures as low as 1042 K, cover a critical range of conditions relevant to practical turbines where few, if any, CH4/C3H8 prior data existed. A methane/propane oxidation mechanism was prepared to simulate the experimental results. It was found that the reactions involving CH3O˙, CH3O˙2, and ?H3 + O2/HO˙2 chemistry were very important in reproducing the correct kinetic behavior. 相似文献
129.
Kohut-Svelko N Reynaud S Dedryvère R Martinez H Gonbeau D François J 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1575-1583
A simple way to obtain a conducting nanocomposite is described, and the conducting particles are characterized. Core-shell particles [polystyrene-polyaniline (PANI)] have been obtained by the dispersion process from three types of polystyrene latexes: a no-cross-linked core stabilized by a nonylphenolethoxylate (NP40) and two cross-linked cores stabilized by NP40 and a mixture NP40/Surfamid (a surfactant bearing an amide group). The surface of these particles has been extensively characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and scanning electron microscopy. A maximum coverage of 94% was obtained for the high PANI content as revealed by XPS analysis. A better coverage was obtained for the cross-linked polystyrene latex stabilized by the Surfamid. The amide group of this surfactant allows the H-bonding formation with the PANI backbone and, thus, improves the conductivity. It was shown that a uniform coverage of the core particles was not required to ensure a good conductivity. 相似文献
130.
Bourgeois ME Wajer FT Roth M Briguet A Décorps M van Ormondt D Segebarth C Graveron-Demilly D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,163(2):277-287
This paper analyzes the effects of intra-scan motion and demonstrates the possibility of correcting them directly in k-space with a new automatic retrospective method. The method is presented for series of 2D acquisitions with Cartesian sampling. Using a reference k-space acquisition (corrected for translations) within the series, intra-scan motion parameters are accurately estimated for each trajectory in k-space of each data set in the series resulting in pseudo-random sample positions. The images are reconstructed with a Bayesian estimator that can handle sparse arbitrary sampling in k-space and reduces intra-scan rotation artefacts to the noise level. The method has been assessed by means of a Monte Carlo study on axial brain images for different signal-to-noise ratios. The accuracy of motion estimates is better than 0.1 degrees for rotation, and 0.1 and 0.05 pixel, respectively, for translation along the read and phase directions for signal-to-noise ratios higher than 6 of the signals on each trajectory. An example of reconstruction from experimental data corrupted by head motion is also given. 相似文献