RESUMO
Supported nanocrystals of original shapes are highly desirable for the development of optimized catalysts; however, conventional methods for the preparation of supported catalysts do not allow shape control. In this work, we have synthesized concave platinum nanocubes exposing {110} crystallographic facets at 20 °C. In the presence of a crystallographically oriented Pt(111) support in the reaction medium, the concave nanocubes grow epitaxially on the support, producing macroscopic nanostructured surfaces. Higher reaction temperature produces a mixture of different nanostructures in solution; however, only the nanostructures growing along the 111 direction are obtained on the Pt(111) support. Therefore, the oriented surface acts as a template for a selective immobilization of specific nanostructures out of a mixture, which can be regarded as an "epitaxial resolution" of an inhomogeneous mixture of nanocrystals. Thus, a judicious choice of the support crystallographic orientation may allow the isolation of original nanostructures that cannot be obtained in a pure form.
RESUMO
Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid-ß (Aß) is found in AD brains, and Cu-Aß could contribute to this oxidative stress, as it is able to produce in vitro H2O2 and HOË in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu-Aß-catalyzed H2O2 production is however not known, although it was proposed that H2O2 is directly formed from O2 via a 2-electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase-1 (SOD1) to show, for the first time, that H2O2 production by Cu-Aß in the presence of ascorbate occurs mainly via a free O2Ë(-) intermediate. This finding radically changes the view on the catalytic mechanism of H2O2 production by Cu-Aß, and opens the possibility that Cu-Aß-catalyzed O2Ë(-) contributes to oxidative stress in AD, and hence may be of interest.
Assuntos
Peptídeos beta-Amiloides/química , Cobre/química , Peróxido de Hidrogênio/química , Oxigênio/química , Peptídeos/química , Superóxidos/química , Superóxido Dismutase/químicaRESUMO
Evaluation of Zn affinity for the amyloid-ß peptide involved in Alzheimer's disease and its modified counterparts is reported. This was made possible by the use of a new water-soluble chelator, the properties of which have also been described. Changes in the peptide sequence that impact Zn affinity are briefly discussed.