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排序方式: 共有435条查询结果,搜索用时 31 毫秒
421.
María D. Acosta Pablo Galindo Luiza A. Moraes 《Journal of Mathematical Analysis and Applications》2014
In this paper we introduce and study the notion of homogeneous Tauberian polynomial, aiming at extending the concept of Tauberian operator. Such notion is characterized in terms of the polynomial topology for which we prove a Banach–Alaoglu type theorem. A number of examples show that the behavior of Tauberian polynomials differs from that of Tauberian operators. 相似文献
422.
Dr. Fernando Henrique Cincotto Dr. Fernando Cruz Moraes Prof. Dr. Sergio Antonio Spinola Machado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4746-4753
A novel material for the electrochemical determination of endocrine disruptors using a composite based on graphene oxide modified with cadmium telluride quantum dots has been evaluated. The morphology, structure and electrochemical performance of the composite electrodes were characterised by transmission electron microscopy, dynamic light scattering, UV‐visible absorption spectra, fluorescence spectra, Raman spectra and cyclic voltammetry. The dynamic light scattering, transmission electronic microscopy and spectrophotometric measurements all showed good distribution of the quantum dots with a small particle size. The electrochemical measurements demonstrated the high performance of the composite response in the presence of a light source. Differential pulse voltammetry allowed the development of a method to determine 17β‐estradiol levels in the range from 0.2 to 4.0 μmol L ?1 with a detection limit of 2.8 nmol L ?1 (0.76 μg L ?1). 相似文献
423.
Trapped in Imidazole: How to Accumulate Multiple Photoelectrons on a Black‐Absorbing Ruthenium Complex
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Linda Zedler Dr. Stephan Kupfer Dr. Inês Rabelo de Moraes Dr. Maria Wächtler Prof. Dr. Rainer Beckert Prof. Dr. Michael Schmitt Prof. Dr. Jürgen Popp Prof. Dr. Sven Rau Prof. Dr. Benjamin Dietzek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3793-3799
Ruthenium dyes incorporating a 4H‐imidazole chromophore as a ligand exhibit a spectrally broad absorption in the UV/Vis region. Furthermore, they show the ability to store two electrons within the 4H‐imidazole ligand. These features render them promising molecular systems, for example, as inter‐ or intramolecular electron relays. To optimize the structures with respect to their electron‐storage capability, it is crucial to understand the impact of structural changes accompanying photoinduced charge transfer in the electronic intermediates of multistep electron‐transfer processes. The photophysical properties of these (reactive) intermediates might impact the function of the molecular systems quite substantially. However, the spectroscopic study of short‐lived intermediates in stepwise multielectron‐transfer processes is experimentally challenging. To this end, this contribution reports on the electrochemical generation of anions identical to intermediate structures and their spectroscopic characterization by in situ resonance Raman and UV/Vis spectroelectrochemistry and computational methods. Thereby, an efficient two‐electron pathway to the 4H‐imidazole electron‐accepting ligand is identified. 相似文献
424.
Ademar Wong Anderson M. Santos Tiago A. Silva Fernando C. Moraes Orlando Fatibello-Filho Maria D. P. T. Sotomayor 《Electroanalysis》2023,35(1):e202200165
This work reports the construction of screen-printed electrode (SPE) modified with carbon black (CB) and magnetic Fe3O4 nanoparticles coated with molecularly imprinted polymer (mag@MIP) based on an alternative low-cost approach. The proposed device was used for the sensitive and selective voltammetric determination of the antibiotic ciprofloxacin. The results obtained from cyclic voltammetry pointed to the improvement of the SPE response toward the irreversible oxidation of ciprofloxacin after the modification of the electrode surface with CB-based film and the magnetic preconcentration of mag@MIP containing adsorbed ciprofloxacin molecules. Compared to the non-molecularly imprinted sensor (mag@NIP), the presence of cavities selective for ciprofloxacin recognition in the mag@MIP nanoparticles accounted for the improvement in analytical signal of the molecularly imprinted sensor. The application of differential pulse voltammetry for ciprofloxacin determination yielded a linear response in the concentration range of 0.5 to 7.0 μmol L−1. The repeatability and interference tests results showed that the proposed electrochemical sensor has good measurement accuracy and selectivity. The proposed device was applied for the voltammetric determination of ciprofloxacin in river water and synthetic urine samples, where recovery rates close to 100 % were recorded for all the samples. The quantification data obtained from the application of the proposed voltammetric method were quite consistent with those of the HPLC reference method. 相似文献
425.
Talita C. T. Medeiros Laurentiu G. Dabija Leonardo Parasecolo Itamar S. Melo Luiz Alberto B. Moraes Demian R. Ifa 《Journal of mass spectrometry : JMS》2023,58(7):e4956
Paper spray mass spectrometry (PS-MS) is an ambient ionization technique that allows for rapid and direct mass spectrometry analysis for a wide range of chemical compounds due to its portability, little to no sample preparation, and cost-effective materials. As applications with this technique continue to expand, the identification and discrimination of bacteria at the strain level remain a promising avenue for researchers. Although studies in the past demonstrated the applicability of PS-MS to discriminate bacteria at the strain level, no one has reported the strain-level differentiation of actinobacteria without using solvent for PS-MS. Hence, this study demonstrates that optimization of PS-MS permits the investigation and differentiation of the metabolic profiles of actinobacteria without the need for solvents, diminishing the potential for sample contamination and consequently increasing the versatility of this technique. In doing so, strains of actinobacteria (CAAT P5–21, CAAT P5–16, CAAT 8–25, CAAT P8–92, and CAAT P11–13) were grown and transferred to produce a crude growth medium. The supernatant was used for the PS-MS analyses using a Thermo Scientific LTQ mass spectrometer. Multivariate statistical analysis, including principal component analysis (PCA) and hierarchal cluster analysis (HCA), was employed to chemically distinguish the strains of bacteria. As a result, each strain of actinobacteria could be visually differentiated based on their metabolic profile. These findings demonstrate the practicability of using a liquid medium as an alternative to many other organic solvents when analyzing bacteria, making PS-MS a crucial addition to a microbiologist's research toolkit. 相似文献
426.
In this work, a CE equipment, online hyphenated to an IT MS analyzer by a linear sheath liquid interface promoting ESI, was used to develop a method for quantitative determination of amino acids. Under appropriate conditions (BGE composition, 0.8% HCOOH, 20% CH3OH; sheath liquid composition, 0.8% HCOOH, 60% methanol; V ESI, +4.50 kV), analytical curves of all amino acids from 3 to 80 mg/L were recorded presenting acceptable linearity (r >0.99). LODs in the range of 16-172 micromol/L were obtained. BSA, a model protein, was submitted to different hydrolysis procedures (classical acid and basic, and catalyzed by the H+ form of a cation exchanger resin) and its amino acid profiles determined. In general, the resin-mediated hydrolysis yields were overall similar or better than those obtained by classical acid or basic hydrolysis. The resulting experimental-to-theoretical BSA concentration ratios served as correction factors for the quantitation of amino acids in Brazil nut resin generated hydrolysates. 相似文献
427.
Pinheiro RC Soares CM de Castro HF Moraes FF Zanin GM 《Applied biochemistry and biotechnology》2008,146(1-3):203-214
The conditions for maximization of the enzymatic activity of lipase entrapped in sol–gel matrix were determined for different
vegetable oils using an experimental design. The effects of pH, temperature, and biocatalyst loading on lipase activity were
verified using a central composite experimental design leading to a set of 13 assays and the surface response analysis. For
canola oil and entrapped lipase, statistical analyses showed significant effects for pH and temperature and also the interactions
between pH and temperature and temperature and biocatalyst loading. For the olive oil and entrapped lipase, it was verified
that the pH was the only variable statistically significant. This study demonstrated that response surface analysis is a methodology
appropriate for the maximization of the percentage of hydrolysis, as a function of pH, temperature, and lipase loading. 相似文献
428.
Fernando C. Moraes Ivana Cesarino Dyovani Coelho Valber A. Pedrosa Sergio A. S. Machado 《Electroanalysis》2012,24(5):1115-1120
An easy way to determine norepinephrine (NE) in biological fluid using a platinum ultramicroelectrode array (Pt‐UMEAs) is described. Issues related to UME electrode surface treatment and characterizations are also addressed. At optimized experimental conditions the dynamic concentration range was 1.0 to 10.0 µmol L?1 with a detection limit of 40.5 nmol L?1. The repeatability of current responses for injections of 5 µmol L?1 NE was evaluated to be 4.0 % (n=10). This approach obtained excellent sensitivity, a reliable calibration profile and stable electrochemical response for norepinephrine detection. The content of NE in urine samples without any preconcentration, purification, or pretreatment step, was successfully analyzed by the standard addition method using the Pt‐UMEAs. 相似文献
429.
Alex Neves Junior Romildo Dias Toledo Filho Eduardo de Moraes Rego Fairbairn Jo Dweck 《Journal of Thermal Analysis and Calorimetry》2012,108(2):725-731
Thermogravimetry (TG) and derivative thermogravimetry (DTG) were used to analyze the early stages of hydration of a high-initial
strength and sulphate resistant Portland cement (HS SR PC) within the first 24 h of setting. The water/cement (W/C) mass ratios
used to prepare the pastes were 0.35, 0.45, and 0.55. The hydration behavior of the pastes was analyzed through TG and DTG
curves obtained after different hydration times on calcined cement mass basis to have a same composition basis to compare
the data. The influence of the W/C ratio on the kinetics of the hydration process was done through the quantitative analysis
of the combined water of the main hydration products formed in each case. TG and DTG curves data calculated on calcined mass
basis of all the results were converted to initial cement mass basis to have an easier way to analyze the influence of the
W/C ratio on the free and combined water of the different main hydrated phases. The gypsum content of the pastes was totally
consumed in 8 h for all cases. A significant part of the hydration process occurs within the first 14 h of setting and at
24 h the highest hydration degree, indicated by the respective content of formed calcium hydroxide, occurs in the case of
the highest initial water content of the paste. 相似文献
430.
Costa EV Dutra LM Nogueira PC Moraes VR Salvador MJ Ribeiro LH Gadelha FR 《Natural product communications》2012,7(2):265-266
The essential oil from the leaves of Annona vepretorun was obtained by hydrodistillation using a Clevenger-type apparatus and analyzed by GC-MS and GC-FID. Eighteen compounds representing 98.1% of the crude essential oil were identified. The major compounds identified were bicyclogermacrene (43.7%), spathulenol (11.4%), alpha-felandrene (10.0%), alpha-pinene (7.1%), (E)-beta-ocimene (6.8%), germacrene D (5.8%), and p-cymene (4.2%). The trypanocidal activity against Trypanosoma cruzi epimastigote forms, as well as, the antimicrobial and antioxidant proprieties was investigated. The essential oil showed a potent trypanocidal activity with IC50 value of 31.9 +/-1.3 microg x mL(-1). For antimicrobial activity, the best result was observed against Candida tropicalis with a MIC value of 100 microg x mL(-1). For antioxidant capacity the essential oil showed weak activity. 相似文献