On
the basis of in situ selection utilizing a reaction
kinetics parameter, a new and straightforward method for screening
the formation of catalytically active silver-PVP nanoparticles is
reported. The method utilizes a multivariate analysis for the optimization
of the reactant concentrations in the synthesis of nanoparticles with
an analytical response based on the ability of the nanoparticles formed
to catalyze the reduction of p-nitrofenol in situ. The best synthetic conditions were selected, the
nanoparticles fully characterized, and their catalytic properties
with regard to the reduction of five nitroaromatic compounds, possessing
different substituents at the para position, were
determined. The kinetics analysis was based on the Langmuir–Hinshelwood
semi-heterogeneous model. The results showed the greater ability of
substrates to adsorb onto the nanoparticle surface compared with that
of borohydride ions and that the substrates possessing an electron-withdrawing
substituent are more catalytically favored. These differences are
discussed in terms of substrate adsorption and of a linear free-energy
relationship based on the Hammett plot.
Este trabalho apresenta um método simples, rápido e eficiente para a desacetilação de ribonucleosídeos acetilados, a partir de metanólise catalisada por trietilamina em meio aquoso. As transformações assistidas por micro-ondas favoreceram sensivelmente a velocidade de reação e forneceram os nucleosídeos desprotegidos em altos rendimentos e sob condições brandas. Além de tolerar a presença de diversos grupos funcionais e de fornecer produtos com alto grau de pureza, esta nova metodologia utiliza reagentes de baixo custo e toxicidade.A straightforward methodology for deacetylation of protected ribonucleosides was developed based on triethylamine-catalyzed solvolysis in aqueous methanol. Reactions are completed in a few minutes under microwave irradiation and the free nucleosides are obtained in high yield after simple evaporation of volatiles. Other important features include the involvement of readily available reagents and the compatibility with diverse functional groups, which make this process very attractive for broad application.
A practical method for the acetylation of purine and pyrimidine nucleosides employing a combination of acetic anhydride and potassium-exchanged molecular sieves is described. Besides the high yields obtained for the acylated nucleosides, the procedure is simple, inexpensive and environmentally benign, avoiding the use of pyridine or co-solvents as additives.
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