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Catálisis ácida general intramolecular eficiente del ataque nucleófilo a un fosfodiéster por catálisis ácida general
Anthony J Kirby1, Marcelo F Lima, Davi da Silva
1University Chemical Laboratory, University of Cambridge, Cambridge CB2 1EW, U.K.
Journal of the American Chemical Society
|December 21, 2006
Resumen
La catálisis con dimetilamonio acelera la hidrólisis de los ésteres de fosfato en más de un millón de veces. Esta eficiente catálisis ácida general se mantiene hasta pH 7 debido a un enlace de hidrógeno intramolecular, crucial para las reacciones con nucleófilos.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La bioquímica es la bioquímica.
- La cinética química es la cinética química.
Sus antecedentes:
- La hidrólisis de ésteres de fosfato es fundamental en los sistemas biológicos y químicos.
- La catálisis ácida general puede mejorar significativamente las tasas de reacción.
- Comprender la reactividad de los nucleófilos es clave para predecir los resultados de las reacciones.
Objetivo del estudio:
- Para investigar el mecanismo catalítico de la hidrólisis del fosfato de metilo 8-dimetilamino-1-naftilo.
- Para determinar la influencia del grupo dimetilamonio y la unión de hidrógeno intramolecular en las velocidades de reacción.
- Para explorar la reactividad de varios nucleófilos en esta reacción de hidrólisis.
Principales métodos:
- Estudios cinéticos de la hidrólisis de ésteres fosfatados a través de un rango de valores de pH.
- Investigación de reacciones con diversos nucleófilos, incluidos los derivados de la hidroxilamina.
- Análisis computacional utilizando cálculos ab initio para apoyar propuestas mecanicistas.
Principales resultados:
- La catálisis con dimetilamonio logró aceleraciones de velocidad de aproximadamente 10^6 a pH ácido.
- El enlace de hidrógeno intramolecular mantuvo la catálisis hasta pH 7.
- La basicidad nucleófila mostró un Brønsted beta ((nuc) de 0,29, intermedio para los ésteres fosfatados.
- La hidroxilamina exhibió un aparente efecto alfa, lo que sugiere una vía de reacción específica.
Conclusiones:
- La protonación de los nucleófilos aumenta la velocidad de la hidrólisis general de los ésteres de fosfato catalizados por ácido.
- El enlace de hidrógeno intramolecular es crítico para la actividad catalítica sostenida.
- El mecanismo de reacción que involucra a la hidroxilamina probablemente se produce a través de un tautómero de pre-equilibrio.
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