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排序方式: 共有142条查询结果,搜索用时 15 毫秒
71.
Lalli PM Iglesias BA Toma HE de Sa GF Daroda RJ Silva Filho JC Szulejko JE Araki K Eberlin MN 《Journal of mass spectrometry : JMS》2012,47(6):712-719
Travelling wave ion mobility mass spectrometry (TWIM-MS) with post-TWIM and pre-TWIM collision-induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM-MS. CID performed after TWIM separation (post-TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N-protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH(3) , whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co-existing protomers of two isomeric porphyrins were also separated and characterized via post-TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO(2) loss, but a CID-resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups. 相似文献
72.
Pedro Henrique Benites Aoki Priscila Alessio Jose Antonio De Saja Carlos Jos Leopoldo Constantino 《Journal of Raman spectroscopy : JRS》2010,41(1):40-48
The synergistic effect produced by nanoparticles when incorporated into different systems used as analytical tools represents a growing research field nowadays. On the other hand, the study of interactions involving pharmacological drugs and biological membranes using phospholipids as mimetic systems is a research field already well established. Here, we combine both the anionic phospholipid dipalmitoyl phosphatidyl glycerol (DPPG) and negative Ag nanoparticles (AgNP) to form layer‐by‐layer (LbL) multilayered films using the cationic polymer poly(allylamine hydrochloride) (PAH) as the supporting polyelectrolyte, which were further investigated in the presence of a phenothiazine compound (methylene blue—MB). The molecular architecture of the LbL films in terms of controlled growth, morphology with micro and nanometer spatial resolutions, and dispersion of both AgNP and MB within the DPPG matrix was determined combining spectroscopy [ultraviolet–visible (UV–Vis) absorption and micro‐Raman spectroscopy] and microscopy [scanning electron microscopy (SEM) and atomic force microscopy (AFM)]. The results showed that the LbL films can be grown in a controlled way at nanometer thickness scale with the surface morphology susceptible to the presence of both AgNP and MB. The surface‐enhanced phenomenon was applied to investigate the LbL films taking the advantage of the strong surface‐enhanced resonance Raman scattering (SERRS) signal presented by the MB molecules. Besides, as MB is a pharmacological drug of interest, its molecular arrangements when dispersed in LbL films containing DPPG, which is the biological membrane mimetic system here, were investigated. In this case, the AgNP played a key role in achieving the MB SERRS signal. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
73.
Ana Paula Neves Ana Cristina Simões Rosa Ariane Leites Larentis Priscila Jeronimo da Silva Rodrigues Vidal Eline Simões Gonçalves Barbara Rodrigues Geraldino Gabriel Rodrigues da Silveira Leandro Vargas Barreto de Carvalho Sergio Rabello Alves 《Biomedical chromatography : BMC》2024,38(3):e5746
The general population and workers are exposed to organophosphate insecticides, one of the leading chemical classes of pesticides used in rural and urban areas. This paper aims to conduct an integrative review of the most used analytical methods for identifying and quantifying dialkylphosphate—which are metabolites of organophosphate insecticides—in the urine of exposed workers, discussing their advantages, limitations and applicability. Searches utilized the PubMed, the Scientific Electronic Library Online and the Brazilian Digital Library of Theses and Dissertations databases between 2000 and 2021. Twenty-five studies were selected. The extraction methods most used were liquid–liquid extraction (LLE) (36%) and solid-phase extraction (SPE) (36%), with the SPE being more economical in terms of time and amount of solvents needed, and presenting the best percentage of recovery of analytes, when compared with LLE. Nineteen studies (76%) used the gas chromatography method of separation, and among these, 12 records (63%) indicated mass spectrometry used as a detection technology (analyzer). Studies demonstrate that dialkylphosphates are sensitive and representative exposure biomarkers for environmental and occupational organophosphate exposure. 相似文献
74.
Carlos R. Carpintero Orlando García Ennis R. Rosas Jose E. Sanabria 《Rendiconti del Circolo Matematico di Palermo》2008,57(2):239-254
In this paper we study the relationships between the B-Browder spectra and some other spectra originating from Fredholm theory
and B-Fredholm theory. This study is done by using the localized single valued extension property. In particular, we shall
see that many spectra coincide in the case that a bounded operator T, or its dual T*, or both, admits the single valued extension property.
相似文献
75.
In this work, a new way of achieving the recovery from the EL2 metastable state is reported and analyzed theoretically. Despite being an old problem, no definitive picture of the EL2 center has been established to date. For this reason, long past the days of effervescent research on the EL2, new models and investigations keep appearing in the literature as, for example, the recently proposed autocatalytic model to describe the inter-defect correlation during the thermal recovery process [A. Fukuyama, T. Ikari, Y. Akashi, M. Suemitsu, Phys. Rev. B 67 (2003) 113202]. In the course of a re-evaluation of the EL2 for nanosecond volume holographic storage, we found that a strong laser pulse is capable of destroying the metastable state and decided to investigate further this effect. The experiment reported here consists of monitoring the transmission of a λ = 1.05 μm continuous-wave (CW) laser, used to populate the metastable state, while subjecting the sample to the incidence of a strong λ = 1.06 μm laser pulse. A full simulation of the problem has been carried out and the results could be fit very well by assuming a recovery induced by electron-hole recombination and a nonlinear free-carrier production mechanism. It is perhaps worth noting that such a fast recovery induced by the nanosecond laser may prove to be an interesting tool to initiate a recovery process (even at low temperature) in a controlled way to check the predictions of the recently proposed autocatalytic recovery process. 相似文献
76.
Addition of Hydrogen Peroxide to Groundwater with Natural Iron Induces Water Disinfection by Photo‐Fenton at Circumneutral pH and other Photochemical Events 下载免费PDF全文
Héctor Mario Gutiérrez‐Zapata John Jairo Alvear‐Daza Julián Andrés Rengifo‐Herrera Janeth Sanabria 《Photochemistry and photobiology》2017,93(5):1224-1231
Samples of natural groundwater (with low turbidity, neutral pH and 0.3 mg L?1 iron concentration) inoculated with Escherichia coli K‐12 were exposed to simulated solar light both in the presence and in the absence 10 mg L?1 of H2O2. Results demonstrated that the viability of E. coli (by DVC–FISH) was grounded to zero after 360 min of irradiation. This abatement could be caused by the oxidative stress induced by radicals or another photo‐induced reactive oxygen species. Two 23 factorial experimental designs enabled the evaluation of the effects of chemical factors on the inactivation of E. coli. The first experimental design considered the pH, iron and H2O2, while the second evaluated the ions fluoride, carbonate and phosphate found in groundwater. pH was found to play a key role in the inactivation of E. coli. The best reduction in viability was obtained at the lower pH (6.75), while a nonsignificant effect was observed when iron or H2O2 concentrations were raised. At higher concentrations, anions, such as carbonate and phosphate, negatively affected the E. coli abatement. However, a higher concentration of fluoride accelerated it. In all experiments, the pH was observed to rise to values higher than 8.0 units after 360 min of treatment. 相似文献
77.
Silvio Cunha Rodrigo M. Bastos Priscila de O. Silva Giselle A. Nobre Costa Ivo Vencato Carlito Lariucci Hamilton B. Napolitano Cecília M. A. de Oliveira Lucília Kato Cleuza C. da Silva Diego Menezes Marcos A. Vannier-Santos 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):111-119
Summary. This work describes a two-step, one-pot synthetic method for the formal aza-[3 + 3] cycloaddition between N-alkyl substituted enaminones and benzoyl isothiocyanate, which afforded 4-thioxopyrimidines in reasonable yields. Reaction
of acyclic enaminone with a sterically hindered group attached to the nitrogen atom afforded pyridine-2-thione, yet in low
yield. The antibacterial, antifungal, and trypanocidal activities of the thioxopyrimidines were evaluated and five compounds
exhibited moderate activity against Candida albicans, Micrococcus luteus, and Trypanosoma cruzi. The solid state structures of a thioxopyrimidine, an organic disulfide, and a 1,2,4-triazole were determined by X-ray diffraction
analysis. 相似文献
78.
Ricard E Pécheyran C Sanabria Ortega G Prinzhofer A Donard OF 《Analytical and bioanalytical chemistry》2011,399(6):2153-2165
IR-femtosecond pulses were used at high repetition rates (up to 10 kHz) to ablate viscous crude oils for the determination
of trace elements by ICPMS. A special internal glass cap was fitted into the ablation cell to minimise oil splashes and remove
big particles that would be otherwise spread into the cell. Laser ablation in static and dynamic conditions (i.e. the laser
beam being moved rapidly at the surface of the sample) was studied together with some fundamental parameters like repetition
rate and fluence. Signal sensitivity and stability were found to be strongly affected by repetition rate and fluence, though
not in linear manner, and in some circumstances by the laser beam velocity. Sample transport efficiency was found to decrease
with increasing repetition rate, probably due to stronger particle agglomeration when increasing the density of primary particles.
ICPMS plasma atomisation/ionisation efficiency was also found to be affected to some extent at the highest repetition rates.
Moderate repetition rate (1 kHz), high fluence (24 J cm−2) and fast scanning velocity (100 mm s−1) were preferred taking into account signal intensity and stability. Sample transport elemental fractionation was also evidenced,
particularly as regards to carbon due to volatilisation of volatile organic species. Matrix effect occurring when comparing
the ablation of transparent (base oil) and opaque (crude oil) samples could not be completely suppressed by the use of IR
femtosecond pulses, requiring a matrix matching or a standard addition calibration approach. This approach provided good accuracy
and very low detection limits in the crude oil, in the range of ng g−1. 相似文献
79.
Oliveira FF dos Santos MR Lalli PM Schmidt EM Bakuzis P Lapis AA Monteiro AL Eberlin MN Neto BA 《The Journal of organic chemistry》2011,76(24):10140-10147
An acetate anion bearing an imidazolium cation as its charge tag was reacted with M(OAc)(2) complexes (where M = Ni, Cu, and Pd; in situ reaction) to form members of a new class of charge-tagged metal complexes. The formation of these unprecedented precatalysts with potential for cross-coupling reactions was confirmed by electrospray ionization (and tandem) mass spectrometry. The catalytic performance of the palladium complex was tested in Heck and Suzuki cross-coupling reactions, often with superior activity and yields as compared with Pd(OAc)(2). 相似文献
80.
Adilson R. Gonçalves Priscila Benar Sirlene M. Costa Denise S. Ruzene Regina Y. Moriya Sandra M. Luz Lais P. Ferretti 《Applied biochemistry and biotechnology》2005,123(1-3):821-826
Sugarcane bagasse and straw can be converted into pulps, oils, controlled-release formulations, chelating agents, and composites.
This article reviews bagasse and straw conversion efforts in Brazil. Laboratory-scale processes were developed aiming at the
integral use of these biomass byproducts. Organosolv pulping and oxidation of lignin are the most promising processes for
the rational use of sugarcane residues. Fungal pretreatment and spectroscopic characterization are also discussed. 相似文献