Sample records for halogens

Sample records 1 - 3 shown.


Metil coenzima M redutase (MCR) e o fator 430 (F430)/ Methyl coenzyme M reductase and the factor 430

Nakagaki, Shirley; Friedermann, Geraldo Roberto; Caiut, José Maurício Almeida

Resumo em inglês This review presents studies on methyl coenzyme M reductase, the biological system Factor 430 (F430) and the use of nickel(II) complexes as structural and functional models. The ability of F430 and nickel(II) macrocycle complexes to mediate the reductive dehalogenation of cyclohexyl halogens and the CH3-S bond cleavage of methyl CoM (by sodium borohydride and some intermediate species) proposed for the catalytic cycle of the biological system F430 was reviewed. The import (mais) ance of the structure of the nickel complexes and the condition of the catalytic reduction reaction are also discussed.

Scientific Electronic Library Online (Portuguese)


Fenóis halogenados e/ou sulfatados de macroalgas marinhas/ Halogenated and/or sulfated phenols from marine macroalgae

Carvalho, Luciana Retz de; Roque, Nidia F.

Resumo em inglês During the biological evolution, marine macroalgae have developed biochemicals tools in order to utilize components of seawater such as sulfates and halogens, to produce a variety of chemicals (secondary metabolites).This review shows and discuss the occurrence of sulfated and/or halogenated phenolic compounds in seaweeds.

Scientific Electronic Library Online (Portuguese)


A tabela periódica dos elementos químicos prevista por redes neurais artificiais de Kohonen/ Periodic table of the elements in the perspective of artificial neural networks

Lemes, Maurício Ruv; Pino Júnior, Arnaldo Dal

Resumo em inglês Although several chemical elements were not known by end of the 18th century, Mendeleyev came up with an astonishing achievement: the periodic table of elements. He was not only able to predict the existence of (then) new elements but also to provide accurate estimates of their chemical and physical properties. This is certainly a relevant example of the human intelligence. Here, we intend to shed some light on the following question: Can an artificial intelligence system (mais) yield a classification of the elements that resembles, in some sense, the periodic table? To achieve our goal, we have fed a self-organized map (SOM) with information available at Mendeleyev's time. Our results show that similar elements tend to form individual clusters. Thus, SOM generates clusters of halogens, alkaline metals and transition metals that show a similarity with the periodic table of elements.

Scientific Electronic Library Online (Portuguese)