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41.
L. M. Q. C. Julião A. M. G. F. Azeredo M. S. Santos D. R. Melo B. M. Dantas J. L. Lipsztein 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(1):121-126
This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between232Th and228Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between232Th and228Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because228Ra is more efficiently taken up from the soil by plants, in comparison to228Th or232Th, and subsequently,228Th grows in from its immediate parent,228Ra. 相似文献
42.
Fernández de la Pradilla R Manzano P Montero C Priego J Martínez-Ripoll M Martínez-Cruz LA 《The Journal of organic chemistry》2003,68(20):7755-7767
A novel route to enantiopure densely functionalized epoxy sulfinyl tetrahydrofurans, based on the unexpected and highly stereoselective remote nucleophilic epoxidation of hydroxy 1-sulfinyl butadienes with t-BuOOK, followed by ring closure and subsequent epoxidation of the resulting sulfinyl dihydrofurans, is described. Alternatively, the treatment of these dienes with m-CPBA followed by acid-catalyzed cyclization gives rise to related sulfonyl dihydrofurans in high yields but with low selectivity. The stereochemical outcome of the nucleophilic epoxidation of these substrates has also been studied. 相似文献
43.
We report the synthesis, electron paramagnetic resonance and electrochemical properties of a novel stable radical of the TTM series. Its strong electron acceptor ability has been tested with (-)-epicatechin, a natural polyphenolic antioxidant. 相似文献
44.
A. M. G. F. Azeredo L. M. Q. C. Julião M. S. Santos D. R. Melo J. L. Lipsztein 《Journal of Radioanalytical and Nuclear Chemistry》1994,182(1):127-132
Internal contamination with radioactive materials of mining workers is a common problem in Brazil. This is caused by the presence of uranium, thorium, and their natural decay series associated with the mined ore. The clear examples are the workers at the niobium mine located in the state of Goiás. The niobium is associated with considerable quantities of uranium and thorium, but the mine is not legally subject to radiation protection requirements.Twenty mine workers were evaluated using in vitro bioassay techniques (urine and feces). The fecal samples were analyzed by alpha spectrometry using the method developed in the Bioassay Laboratory of the Instituto de Radioproteção e Dosimetria/CNEN which evaluates thorium and uranium isotopes simultaneously. Minor modifications were introduced to measure a higher level of activity, around 1 Bq of uranium per sample. The urine samples were analyzed by alpha spectrometry for thorium and by fluorimetry for uranium. The results obtained show that a control of the occupationally-exposed workers is necessary. 相似文献
45.
Esmeralda Rosa Angel Guerrero Mª Pilar Bosch Luis Julià 《Magnetic resonance in chemistry : MRC》2010,48(3):198-204
Photolysis of trifluoromethyl ketones (TFMKs) 1a–1e versus the non‐fluorinated ketones 2a–2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2‐methyl‐2‐nitrosopropane (MNP) and 2,4,6‐tri‐tert‐butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t‐butylperoxide, short‐chain TFMKs, such as 1,1,1‐trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long‐chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one α‐methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a γ‐hydrogen to the carbonyl group. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
46.
Alex Julià‐López Dr. Jordi Hernando Dr. Daniel Ruiz‐Molina Pablo González‐Monje Dr. Josep Sedó Dr. Claudio Roscini 《Angewandte Chemie (International ed. in English)》2016,55(48):15044-15048
A novel strategy to achieve thermally switchable photochromism in solid materials is reported, which relies on the preparation of polymeric core–shell capsules containing solutions of photochromic dyes in acidic phase‐change materials. Upon changing the phase (solid or liquid) of the encapsulated medium, one of the two photochromic states of the system is selectively stabilized on demand, allowing for reversible interconversion between direct and reverse photochromism when thermally scanning through the melting temperature of the phase‐change material. This strategy, which does not require the addition of external agents or chemical modification of the dyes, proved to be general for different spiropyran photochromes and to be applicable to the fabrication of a variety of functional materials by simply embedding the capsules obtained into a solid matrix of choice. 相似文献
47.
Mireia Baeza José Luis Montesinos Julián Alonso Jordi Bartrolí 《Analytical and bioanalytical chemistry》2009,393(4):1233-1243
The present paper reports the modeling and characterization of the physical sample dispersion process observed in rectangular
microchannels when pressure-driven pumping is used. To explain experimental results provided by the silicon fluidic device
constructed, two different mathematical models were tested. The first one is based on the diffusion–convection model, and
the second one is based on the combination of ideal reactors. The silicon designed and constructed chip includes a microfluidic
manifold with four inlet–outlet ports and a monolithically integrated optical flow cell. The microchannels, the optical flow
cell, and the input–output ports were micromachined on a silicon wafer and then sealed with Pyrex glass anodically bonded.
Optical windows were integrated in the chip, allowing simple absorbance–transmission measurements. Pressure-driven flows through
fluidic channels were controlled via three-way solenoid valves and provided by an automatic microburette operating in aspiration
mode. Experimentally obtained results demonstrate that the physical sample dispersion process can be easily modeled as a combination
of a continuous stirred tank reactor and a plug-flow reactor. 相似文献
48.
Pérez L García-Martínez JC Díez-Barra E Atienzar P García H Rodríguez-López J Langa F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(19):5149-5157
Two new fullerodendrimers, with two and four ferrocene units on their periphery, have been synthesized by 1,3-dipolar cycloaddition reactions between the corresponding azomethine ylides and C(60). These new compounds have been studied by using cyclic voltammetry and UV/Vis spectroscopy. Weak intramolecular interactions between the fullerene cage and the ferrocene groups have been found. The photochemical events of both fullerene-ferrocene dendrimers have been probed by means of steady-state and time-resolved techniques. The steady-state emission intensities of the fulleropyrrolidine-ferrocene dendrimers 1 and 2 were found to be quenched relative to the N-methylfulleropyrrolidine without substituents that was used as a model. The nanosecond transient absorption spectral studies revealed efficient charge separation in both systems, even in toluene. The lifetimes of the (C(60))(*-)-(dendron)(*+) are higher for the second-generation fullerodendrimer (with four ferrocene units) and they are of the order of tens of nanoseconds in toluene and hundreds of nanoseconds in polar solvents. 相似文献
49.
Fernández de la Pradilla R Castellanos A Fernández J Lorenzo M Manzano P Méndez P Priego J Viso A 《The Journal of organic chemistry》2006,71(4):1569-1575
Treatment of acyclic alpha-hydroxyalkyl alpha,beta-unsaturated sulfoxides with t-BuOOH/VO(acac)2 results in rapid oxidation to the unsaturated sulfones followed by an unusual regio- and stereoselective epoxidation at the unsaturated sulfones; this methodology has been applied to the preparation of carbohydrate-like fragments. 相似文献
50.