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91.
A. G. Taranto J. W. de M. Carneiro F. G. de Oliveira M. T. de Araujo C. R. Correa 《Journal of Molecular Structure》2002,580(1-3):207-215
Artemisinin is a sesquiterpene lactone with an endoperoxide function that is essential for its antimalarial activity. Endoperoxides are supposed to act on heme leading to the reduction of the peroxide bond and production of radicals, which can be responsible for killing the parasite. The geometries of artemisinin, radical anions and neutral species generated by rearrangement after reduction of the peroxide bond were fully optimized with the AM1 and PM3 semi-empirical methods, in order to characterize the intermediates formed during the process. Among the radicals calculated along the pathway for reductive decomposition of artemisinin, the secondary radical centered on carbon C4 has the highest stability when compared to other radicals that can be achieved either by hydrogen migration to the original O-centered radical or by homolytic break of C–C bond. This suggests that the C4-centered radical may be the species responsible for killing the parasite, as has been indicated previously in experimental studies. 相似文献
92.
Guimarães KL Castro RH Gouvêa D 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11645-11650
The standard methods for obtaining adsorption isotherms on colloidal suspensions are usually very time consuming and involve a large number of steps and assumptions that increase the experimental errors. In this work, an alternative method is proposed to evaluate the adsorption behavior of electrosteric-stabilized systems based on electrokinetic sonic amplitude signal measurements. The new method, entitled "zeta-sorption", is noticeably less time-consuming when compared to conventional procedures but showed great precision and reliability confirmed by comparison with data obtained from conventional routes on alumina-polyacrylate and alumina-citric acid aqueous suspensions. The experimental conditions that restrict the applicability of the new method were identified and justified by discussing the possible ion exchanges. 相似文献
93.
The potentiometric determination of zinc in chloride solutions with a coated wire electrode is described. The electroactive membrane contains the chlorozincate(II) salt of Aliquat 336S in poly (vinyl chloride). The electrode shows a useful response over the range 10-5 M–10-1 M zinc(II) in 3 M total chloride solutions in the pH range 1.5–6. The electrode is more responsive to the divalent tetrachlorozincate(II) than to the monovalent trichlorozincate(II) species. Applications in compleximetric titrations, and to the analysis of zinc oxide and zinc concentrates are reported. 相似文献
94.
C. B. Zamboni L. C. Oliveira L. Dalaqua Jr J. Mesa 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):331-334
Summary Neutron activation analysis technique, using Au as flux monitor, was applied to determine element concentrations of Ca, K,
Na, Mg, Mn and Sr in certified reference material (NIST 1400 Bone Ash). The results were compared with those using comparative
INAA and they were compatible. The same results were obtained using the recommended k0 factors, in order to obtain the activation cross section as input in concentration for the same reference material. Some
applications in the health area aiming clinical evaluation in bone samples of medium and small-sized animals were performed
and the viability of using this methodology was discussed. 相似文献
95.
Hiléia K. S. Souza V. R. da Silveira F. M. M. Borges Dulce M. A. Melo H. Scatena Jr. O. A. de Oliveira A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(2):433-436
Thermal behavior of rare earth nitrate complexes
with 2-azacyclononanone (AZA) with Ln(NO3)3·3(AZA)
composition (where Ln=Gd, Er and Ho) was
analyzed in kinetic point of view. Kinetic parameters were calculated from
thermogravimetric data. All obtained results were similar. The first decomposition
step was representative to the loss of ligand and the residue was essentially
Ln2O3. Furthermore, a reaction
path was proposed for the thermal decomposition of the Ln(NO3)3·3(AZA). 相似文献
96.
The kinetics of the dehydration of CsNd(SO4)2 · 4 H2O to CsNd(SO4)2 · H2O and then to CsNd(SO4)2 are studied by isothermal weight change. The reactions are phase-boundary-controlled. Reaction mechanism and activation energy depend on sample weight. 相似文献
97.
Immobilization of protein on ferromagnetic Dacron 总被引:1,自引:0,他引:1
A. M. A. Carneiro LeÃo E. A. Oliveira L. B. Carvalho 《Applied biochemistry and biotechnology》1991,31(1):53-58
Ferromagnetic Dacron (polyethyleneterephthalate) is proposed as a matrix to immobilize proteins covalently. Dacron in powder was magnetized by reacting ferrous (Fe+2) and ferric (Fe+3) ions with its hydrazide form at pH 8.3. Ferromagnetic hydrazide Dacron was converted to ferromagnetic azide Dacron and amyloglucosidase (E.C. 3.2.1.3) was covalently bound through the latter group. The catalytic property of the enzyme was preserved (8% of the specific activity estimated for the soluble enzyme) and all the magnetic amyloglucosidase Dacron derivative was recovered by using a magnetic field. No activity was detected in the supernatant. 相似文献
98.
Alpha emitters from uranium mining in the environment 总被引:1,自引:0,他引:1
Uranium mining and milling activities usually generate an enhancement of radionuclide concentrations in the environment that
may cause increased radiological exposure to mankind. For risk assessment and radiological protection of man and environment
in these areas, usually, it is needed to implement radiological surveillance of water, soils, agricultural products, aerosols,
and mining waste discharges as well. Radionuclides to be monitored in priority are alpha-emitting nuclides of the uranium
natural series. Radioactivity analysis of materials from uranium mining areas of Portugal shows departure from secular radioactive
equilibrium amongst uranium series radionuclides, thus rendering invalid the assumption of equilibrium and requiring the actual
determination of each radionuclide. Radionuclide measurements performed with high resolution alphaspectrometry, as reported
herein, produce accurate results on specific radionuclides that are essential in computing radiation doses to critical groups
of the population. 相似文献
99.
de Oliveira PR Rittner R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):30-37
The conformational equilibria of 3-X-cyclohexanol [X=F (1), Cl (2), Br (3), I (4), Me (5), NMe(2) (6) and MeO (7)] and of 3-X-methoxycyclohexane [X=F (8), Cl (9), Br (10), I (11), Me (12), NMe(2) (13) and MeO (14)] cis isomers were determined from low temperature NMR spectra and PCMODEL calculated coupling constants. The energy differences between aa and ee conformers were obtained from these data (DeltaG(J)(av) and DeltaG(PC)(av), respectively) and also by the additivity principle from data for the monosubstituted cyclohexanes (DeltaG(Ad)). H-1 and H-3 hydrogen vicinal coupling constants and DeltaG(J)(av) values showed that the diequatorial conformer is predominant in the conformational equilibrium of the compounds studied at low temperature. However, DeltaG(PC)(av) data show that compounds 6 and 7 constitute an exception, since they are almost equally populated by ee and aa at room temperature, due to stabilization of their aa conformer by an intramolecular hydrogen bond. DeltaG(Ad) values, obtained according to the additivity principle, show a better agreement for compounds 2 and 3, since the 1,3-diaxial steric effect is counterbalanced by the formation of an intramolecular hydrogen bond (IAHB). For the remaining compounds, DeltaG(Ad) values underestimate the energy differences, since the 1,3-diaxial steric effect, between X and OH or OCH(3), is absent in the monosubstituted compounds used as references. Moreover, the DeltaG(PC)(av), calculated from the coupling constants, obtained through the PCMODEL program, are rather smaller than the DeltaG(J)(av) values, since the program does not have parameters for the effect, observed in this report, of a substituent at gamma position on coupling constants values for the hydrogen under consideration. 相似文献
100.
Paul N Nashine VC Hoops G Zhang P Zhou J Bergstrom DE Davisson VJ 《Chemistry & biology》2003,10(9):815-825
The development of novel artificial nucleobases and detailed X-ray crystal structures for primer/template/DNA polymerase complexes provide opportunities to assess DNA-protein interactions that dictate specificity. Recent results have shown that base pair shape recognition in the context of DNA polymerase must be considered a significant component. The isosteric azole carboxamide nucleobases (compounds 1-5; ) differ only in the number and placement of nitrogen atoms within a common shape and therefore present unique electronic distributions that are shown to dictate the selectivity of template-directed nucleotide incorporation by DNA polymerases. The results demonstrate how nucleoside triphosphate substrate selection by DNA polymerase is a complex phenomenon involving electrostatic interactions in addition to hydrogen bonding and shape recognition. These azole nucleobase analogs offer unique molecular tools for probing nonbonded interactions dictating substrate selection and fidelity of DNA polymerases. 相似文献