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排序方式: 共有482条查询结果,搜索用时 171 毫秒
11.
J. M. Navarrete T. Martínez L. Cabrera 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(2):277-279
After the Chernobyl accident in 1986, Mexico imported from an European country 28,000 tons of contaminated powder milk with
the fission product 137Cs. When the contamination was detected, the alarm among the authorities and population spread out very quickly and of course
the product was retired at once from the foodstuff market. Nevertheless, the public panic grew up in such a manner, that even
the way to manage and to dispose safely this material, considered highly dangerous, was largely discussed. Now, about two
decades ago from this event, a study has been performed to compare the level of radioactivity due to both radioisotopes present
in one saved sample: the artificial contaminant 137Cs, beside the natural, all around present 40K, in order to evaluate in a more realistic way how risky was the management, possible consumption, and final disposition
of this nourishment. This paper considers results obtained within an uncertainty degree equal to ±5%, and set up conclusions
by comparing artificial and natural radioactivity present in that contaminated powder milk. 相似文献
12.
Highly enantioselective copper(I)-fesulphos-catalyzed 1,3-dipolar cycloaddition of azomethine ylides
Cabrera S Gómez Arrayás R Carretero JC 《Journal of the American Chemical Society》2005,127(47):16394-16395
The catalyst system formed by Cu(CH3CN)4ClO4 and the planar chiral P,S-ligand Fesulphos behaves as a very efficient chiral Lewis acid in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. This catalyst shows a remarkable reactivity at low catalyst loading (0.5-3 mol %), affording in good yields the endo adducts with exceptional levels of enantioselectivity (up to >99% ee). This catalytic asymmetric procedure has a broad structural scope with regard to both azomethine and dipolarophile substitution. The first examples of catalytic asymmetric 1,3-dipolar cycloaddition with ketimine-derived azomethines are reported. 相似文献
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Arelí Durón-Castellanos Vanesa Zazueta-Novoa Hortencia Silva-Jiménez Yolanda Alvarado-Caudillo Eduardo Peña Cabrera Roberto Zazueta-Sandoval 《Applied biochemistry and biotechnology》2005,121(1-3):279-288
Different soluble NAD+-dependent alcohol dehydrogenase (ADH) isozymes were detected in cell-free homogenates from aerobically grown mycelia of YR-1
strain of Mucor circinelloides isolated from petroleumcontaminated soil samples. Depending on the carbon source present in the growth media, multiple NAD+-dependent ADHs were detected when hexadecane or decane was used as the sole carbon source in the culture media. ADH activities
from aerobically or anaerobically grown mycelium or yeast cells, respectively, were detected when growth medium with glucose
added was the sole carbon source; the enzyme activity exhibited optimum pH for the oxidation of different alcohols (methanol,
ethanol, and hexadecanol) similar to that of the corresponding aldehyde (≈7.0). Zymogram analysis conducted with partially
purified fractions of extracts from aerobic mycelium or anaerobic yeast cells of the YR-1 strain grown in glucose as the sole
carbon source indicated the presence of a single NAD+-dependent ADH enzyme in each case, and the activity level was higher in the yeast cells. ADH enzyme from mycelium grown in
different carbon sources showed high activity using ethanol as substrate, although higher activity was displayed when the
cells were grown in hexadecane as the sole carbon source. Zymogram analysis with these extracts showed that this particular
strain of M. circinelloides has four different isozymes with ADH activity and, interestingly, one of them, ADH4, was identified also as phenanthrene-diol-dehydrogenase,
an enzyme that possibly participates in the aromatic hydrocarbon biodegradation pathway. 相似文献
15.
Pérez González M Gonzalez Díaz H Molina Ruiz R Cabrera MA Ramos de Armas R 《Journal of chemical information and computer sciences》2003,43(4):1192-1199
A new application of TOPological Sub-structural MOlecular DEsign (TOPS-MODE) was carried out in herbicides using computer-aided molecular design. Two series of compounds, one containing herbicide and the other containing nonherbicide compounds, were processed by a k-Means Cluster Analysis in order to design the training and prediction sets. A linear classification function to discriminate the herbicides from the nonherbicide compounds was developed. The model correctly and clearly classified 88% of active and 94% of inactive compounds in the training set. More specifically, the model showed a good global classification of 91%, i.e., (168 cases out of 185). While in the prediction set, they showed an overall predictability of 91% and 92% for active and inactive compounds, being the global percentage of good classification of 92%. To assess the range of model applicability, a virtual screening of structurally heterogeneous series of herbicidal compounds was carried out. Two hundred eighty-four out of 332 were correctly classified (86%). Furthermore this paper describes a fragment analysis in order to determine the contribution of several fragments toward herbicidal property; also the present of halogens in the selected fragments were analyzed. It seems that the present TOPS-MODE based QSAR is the first alternate general "in silico" technique to experimentation in herbicides discovery. 相似文献
16.
Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo‐heterocycles 下载免费PDF全文
María Inés Flores‐Conde Fabiola N. de la Cruz Julio López J. Óscar C. Jiménez‐Halla Eduardo Peña‐Cabrera Marcos Flores‐Álamo Francisco Delgado Miguel A. Vázquez 《应用有机金属化学》2018,32(3)
The unprecedented reaction of ketone‐containing aromatic pyridinium salts 3a ‐ e and alkynyl Fischer complexes 1a ‐ f proceeds via a mild domino process to provide 4,6‐disubstituted pyran‐2‐ones 5a ‐ k and 2,3,5‐trisubstituted furans 6a ‐ h (45‐97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products. 相似文献
17.
The extent to which the occurrence of falls, the dominant feature of human attempts to balance a stick at their fingertip,
can be predicted is examined in the context of the “Dragon-King” hypothesis. For skilled stick balancers, fluctuations in
the controlled variable, namely the vertical displacement angle θ, exhibit power law behaviors. When stick balancing is made
less stable by either decreasing the length of the stick or by requiring the subject to balance the stick on the surface of
a table tennis racket, systematic departures from the power law behaviors are observed in the range of large θ. This observation
raises the possibility that the presence of departures from the power law in the large length scale region, possibly Dragon-Kings,
may identify situations in which the occurrence of a fall is more imminent. However, whether or not Dragon-Kings are observed,
there is a Weibull-type survival function for stick falling. The possibility that increased risk of falling can, at least
to some extent, be predicted from fluctuations in the controlled variable before the event occurs has important implications
for the development of preventative strategies for the management of phenomena ranging from earthquakes to epileptic seizures
to falls in the elderly. 相似文献
18.
The synthesis of 6-ami no-5-nitro-4-thioxo-pyrimidines starting from the C-adducts of nitro-keteneaminals and acyl isothiocyanates is described. 相似文献
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