RESUMEN
The alkali ions present in the supercages of zeolites X and Y interact with included guest molecules through quadrupolar (cation-pi), and dipolar (cation-carbonyl) interactions. The presence of such interactions can be inferred through solid-state NMR spectra of the guest molecules. Alkali ions, as illustrated in this article, can be exploited to control the photochemical and photophysical behaviors of the guest molecules. For example, molecules that rarely phosphoresce can be induced to do so within heavy cation-exchanged zeolites. The nature (electronic configuration) of the lowest triplet state of carbonyl compounds can be altered with the help of light alkali metal ions. This state switch (n pi*-pi pi*) helps to bring out reactivity that normally remains dormant. Selectivity obtained during the singlet oxygen oxidation of olefins within zeolites illustrates the remarkable control that can be exerted on photoreactions with the help of a confined medium that also has active sites. The reaction cavities of zeolites, like enzymes, are not only well-defined and confined, but also have active sites that closely guide the reactant molecule from start to finish. The examples provided here illustrate that zeolites are far more useful than simple shape-selective catalysts.
Asunto(s)
Zeolitas/química , Sitios de Unión , Cationes/química , Fenómenos Químicos , Química Física , Cristalografía/métodos , Transporte de Electrón , Electrones , Espectroscopía de Resonancia Magnética , Ensayo de Materiales/métodos , Modelos Químicos , Modelos Moleculares , Conformación Molecular , Estructura Molecular , Fotoquímica , Espectrometría de Fluorescencia , Relación Estructura-Actividad , Zeolitas/antagonistas & inhibidoresRESUMEN
It has been established that chrysotile-asbestos fibers and zeolite particles induce chromosome aberrations in human lymphocytes from whole blood cultures, peritoneal fluid cells and bone marrow cells of mice. It is shown that the level of cytogenetic response from the intraperitoneal administration of chrysotile-asbestos fibers and zeolite particles depends on the time of their exposure. Further, it is shown that SOD eliminates the cytogenetic effect of chrysotile-asbestos fibers, while catalase inhibits that of zeolite particles. Recommendations concerning testing for the mutagenic properties of mineral fibers and particles are given, and possible mechanisms of their damaging effects are discussed.
