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排序方式: 共有602条查询结果,搜索用时 218 毫秒
31.
Tiago Augusto Donegatti Alnilan Lobato Eliana A. R. Duek Luís Moreira Gonçalves Elisabete Alves Pereira 《Electrophoresis》2020,41(18-19):1576-1583
Aminoglycosides are a relevant class of antibiotics widely used by medics and veterinaries. There are a variety of reasons that make their determination relevant, such as quality control, environment and food contamination assessment, drug-release studies, among others. The lack of a chromophore makes aminoglycoside spectrophotometric detection particularly challenging, often requiring derivatization. In this work, an indirect detection method, making use of imidazole as a probe, applying CZE was successfully tested. It did not require derivatization, which simplified the sample preparation. Suitable figures of merit were obtained; recoveries between 95 and 105%, adequate repeatability and precision, correlation coefficients (r) above 0.998, and limits of detection (LODs) of 3.2 and 11 mg/L for gentamicin and paromomycin, respectively. As a proof-of-concept, it was also applied in a simple controlled release experiment that was well fitted using the Hill equation. 相似文献
32.
Fernanda Cosme Alice Vilela Luís Moreira Carla Moura Jos A. P. Enríquez Luís Filipe-Ribeiro Fernando M. Nunes 《Molecules (Basel, Switzerland)》2020,25(24)
‘Mencía’/‘Jaen’ it’s an important red grape variety, exclusive of the Iberian Peninsula, used in wine production namely in Bierzo D.O. and Dão D.O., respectively. This work evaluates the effect of the two different “terroirs” on the phenolic composition and chromatic characteristics of ‘Mencía’/‘Jaen’ monovarietal wines produced at an industrial scale in the same vintage. Using Principal Component Analysis (PCA), Partial Least Squares-Discrimination Analysis (PLS-DA), and Orthogonal PLS-DA (OPLS-DA) it was found that peonidin-3-coumaroylglucoside, petunidin-3-glucoside, malvidin-3-coumaroylglucoside, peonidin-3-glucoside, malvidin-3-acetylglucoside, malvidin-3-glucoside, and ferulic acid were the phenolic compounds with the highest differences between the two regions. PLS regression allowed to correlate the differences in lightness (L*) and redness (a*) of wines from ‘Jaen’ and ‘Mencía’ to differences in colored anthocyanins, polymeric pigments, total pigments, total anthocyanins, cyanidin-3-acetylglucoside, delphinidin-3-acetylglucoside, delphinidin-3-glucoside, peonidin-3-coumaroylglucoside, petunidin-3-glucoside and malvidin-3-glucoside in wines, and the colorless ferulic, caffeic, and coutaric acids, and ethyl caffeate. The wines a* values were more affected by colored anthocyanins, ferulic acid, total anthocyanins, delphinidin-3-acetylglucoside, delphinidin-3-glucoside and petunidin-3-acetylglucoside, and catechin. The positive influence of ferulic acid in the a* values and ferulic, caffeic, coutaric acids, and ethyl caffeate on the L* values can be due to the co-pigmentation phenomena. The higher dryness and lower temperatures during the September nights in this vintage might explain the differences observed in the anthocyanin content and chromatic characteristics of the wines. 相似文献
33.
Christina C. Roggatz Mercedes González-Wangüemert Hugo Pereira Maria João Rodrigues Manuela Moreira da Silva Luísa Barreira 《Natural product research》2016,30(18):2034-2040
This work reports for the first time the nutritional profile and antioxidant potential of the edible sea cucumber Holothuria arguinensis from the North-eastern Atlantic. H. arguinensis has high levels of protein, with the amino acids profile dominated by alanine, glycine and proline and low lysine/arginine ratios. Its carbohydrate and energetic contents are also low as well as the total lipid levels, although its lipid profile is rich in polyunsaturated fatty acids (PUFA), especially arachidonic, eicosapentaenoic and docosahexaenoic acids. In addition, H. arguinensis has high levels of calcium. The water and ethanol extracts show ability to scavenge free radicals and to chelate copper and iron ions. Our results indicate that H. arguinensis has a balanced nutritional quality suitable for human consumption. In addition, it contains compounds with antioxidant potential; thus its intake can contribute for a healthy and well-balanced diet. 相似文献
34.
Eveline De Robertis Gabriela F. Moreira Raigna A. Silva Carlos A. Achete 《Journal of Thermal Analysis and Calorimetry》2011,106(2):347-354
Quality control of fuel-related properties of biodiesel, such as thermal stability, is needed to obtain consistent engine
performance by fuel users, since biodiesel is susceptible to auto-oxidation when exposed to air, light, and temperature during
storage. In this work two pure standard reference materials of biodiesels produced from soy oil and animal feedstocks were
studied. Differential scanning calorimetry and thermogravimetry measurements were performed and the analysis of the results
revealed small temperature variations in the thermal events among the two standards, these differences are due mainly to their
chemical composition, been highly influenced by the amounts of unsaturated esters. 相似文献
35.
36.
E. Rodrigues S. Vaz V.M.S.S. Gil M. Caldeira A.M.G. Moreira Da Silva 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):395-397
A 1H-NMR study of the interactionsbetween -cyclodextrin (-CD) and included phenolic molecules (chloragenic acid and caffeic acid ) in aqueous medium is reported. The results confirm that inclusion occurs. Data analysis by the continuous variation method shows that all the complexes have 1 : 1 stoichiometries. Values for the apparent association constants of the inclusion compounds are estimated and compared with previously reported values. 相似文献
37.
Aida Moreira Da Silva José Empis José J.c. Teixeira-Dias 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(1):81-97
In aqueous solution, the apparent association constant at room temperature for the 1 : 1 inclusion of S-(+)-carvone in - cyclodextrin is double of that for R-(-)-carvone, whereas, at 45 °C, both enantiomers have association constants two orders of magnitude smaller, with the S-(+) inclusion being then slightly weaker than the R-(-) encapsulation. Calculations carried out at the molecular mechanics, AM1 and STO-3G levels confirm the preferential inclusion of the S-enantiomer and provide important clues for understanding chiral discrimination by -cyclodextrin. 相似文献
38.
Fajardo M. Pérez Alcázar G. A. Moreira A. M. Speziali N. L. 《Hyperfine Interactions》2004,158(1-4):395-400
The local environment of implanted 111Ag (t
1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following
the 60 keV low dose (1 × 1013 cm−2) 111Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps,
at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free SZn sites (ν
Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive
lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore
measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30%
of the 111Ag atoms, 7% of which were located in regions of high defects concentration. 相似文献
39.
Oliveira JS Sousa EH Basso LA Palaci M Dietze R Santos DS Moreira IS 《Chemical communications (Cambridge, England)》2004,(3):312-313
The in vitro kinetics of inactivation of both wild-type and I21V InhA enzymes by [FeII(CN)5(INH)]3- indicate that this process requires no activation by KatG, and no need for the presence of NADH. This inorganic complex may represent a new class of lead compounds to the development of anti-tubercular agents aiming at inhibition of a validated target. 相似文献
40.
Similarly and highly charged plates in the presence of multivalent counterions attract each other and form electrostatically bound states. Using Monte-Carlo simulations, we obtain the interplate pressure in the global parameter space. The equilibrium plate separation, where the pressure changes from attractive to repulsive, exhibits a novel unbinding transition. A systematic and asymptotically exact strong-coupling field theory yields the bound state from a competition between counterion entropy and electrostatic attraction, in agreement with simple scaling arguments and simulations. 相似文献