Experimental and theoretical 15 N and 13 C NMR data for the three nitrobenzaldehyde guanylhydrazones are reported. The theoretical data were obtained using sequential molecular dynamics/quantum mechanics methodology for the calculation of flexible molecules in a condensed phase, followed by the use of the GIAO/DFT method with the 6-311G** basis set. The experimental 15 N chemical shifts for the guanylhydrazones are compared with the calculated shifts.
Tobacco farmers are routinely exposed to complex mixtures of inorganic and organic chemicals present in tobacco leaves. In this study, we examined the genotoxicity of tobacco leaves in the snail Helix aspersa as a measure of the risk to human health. DNA damage was evaluated using the micronucleus test and the Comet assay and the concentration of cytochrome P450 enzymes was estimated. Two groups of snails were studied: one fed on tobacco leaves and one fed on lettuce (Lactuca sativa L) leaves (control group). All of the snails received leaves (tobacco and lettuce leaves were the only food provided) and water ad libitum. Hemolymph cells were collected after 0, 24, 48 and 72 h. The Comet assay and micronucleus test showed that exposure to tobacco leaves for different periods of time caused significant DNA damage. Inhibition of cytochrome P450 enzymes occurred only in the tobacco group. Chemical analysis indicated the presence of the alkaloid nicotine, coumarins, saponins, flavonoids and various metals. These results show that tobacco leaves are genotoxic in H. aspersa and inhibit cytochrome P450 activity, probably through the action of the complex chemical mixture present in the plant.
ABSTRACT:The influence of nonbonded interactions in the kinetics of formation of chalcogenol (thiol and selenol) esters from chalcogenoacetylenes was studied by molecular modeling. Using semiempirical and density functional theory methods it was possible to explain the differences between the reaction rates for the analogous sulfur and selenium chalcogenoacetylenes as well as evaluate the structural and electronic effects (nonbonded interactions) on the formation of the esters. The differences in the reaction rates can be explained in terms of the carbocation stabilization by the chalcogen atom. It is proposed that these differences are due to the differences in the intensity of the dominant interaction * CO /n Y between the nonbonding orbitals of sulfur and selenium with the vacant orbital of carbon in the cationic transition state.
A química computacional vem sendo desenvolvida no seio das universidades como uma alternativa para a pesquisa em química, sendo já reconhecida como área de pesquisa. Neste artigo, discutimos o uso do referencial vygotskyano para compreender como se processa o aprendizado de conceitos e representações químicas com o uso da mesma. Apresentamos as alternativas que professores possuem para utilizar softwares de química computacional, bem como um exemplo de atividade que foi desenvolvido pela pesquisadora na própria Fundação Liberato. Concluímos que, mesmo ainda sendo tema de pesquisa em ensino, é inegável sua atual contribuição ao aprendizado de química, e, portanto, recomendamos o seu uso.
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