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La cinética y la termodinámica de la formación de la cápsula hexamérica
Masamichi Yamanaka1, Alexander Shivanyuk, Julius Rebek
1The Skaggs Institute for Chemical Biology and Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Journal of the American Chemical Society
|March 5, 2004
Resumen
El resorcinareno 1b forma conjuntos hexámicos que encapsulan las sales de tetraalquilamonio en solución. La encapsulación es entrópicamente favorecida, pero la estabilidad y los tipos de cambio disminuyen con los cationes más grandes.
Área de la Ciencia:
- Química supramolecular de las moléculas.
- Química entre anfitrión y huésped.
- Química orgánica es la química orgánica.
Sus antecedentes:
- Las resorcinarenas son compuestos macrocíclicos conocidos por su capacidad para formar estructuras autoensambladas.
- Estas estructuras pueden encapsular varias moléculas huéspedes, influyendo en su entorno químico.
- Comprender los factores que rigen la estabilidad de la encapsulación y el intercambio de invitados es crucial para el diseño de nuevos sistemas moleculares.
Objetivo del estudio:
- Para investigar el autoensamblaje del resorcinareno 1b en presencia de sales de tetraalquilamonio.
- Para determinar la estequiometría y la termodinámica del proceso de encapsulación.
- Explorar la influencia del tamaño catiónico en la estabilidad y dinámica de los complejos resorcinareno-invitado.
Principales métodos:
- Formación de conjuntos de resorcinareno 1b hexamérico en CDCl saturado de agua ((3).
- Encapsulación de sales de tetraalquilamonio (2(+) Br(-)) dentro de la cavidad del resorcinareno.
- Análisis de las moléculas de disolvente coencapsuladas (CHCl(3) utilizando métodos espectroscópicos.
- Estudios termodinámicos y cinéticos de encapsulación y intercambio de huéspedes.
Principales resultados:
- El resorcinareno 1b forma cápsulas hexámicas que encapsulan una molécula de sal de tetraalquilamonio y solvente.
- La encapsulación es un proceso endotérmico, entrópicamente favorecido por la liberación de disolventes.
- La estabilidad compleja y las tasas de intercambio de invitados disminuyen con el aumento de la longitud de la cadena de alquilo del catión de amonio.
- Las mayores barreras de activación para el intercambio de invitados sugieren restricciones conformacionales en el estado de transición.
Conclusiones:
- El autoensamblaje del resorcinareno 1b proporciona un sistema huésped para las sales de tetraalquiloamonio.
- La liberación de moléculas de disolvente es una fuerza impulsora clave para la encapsulación.
- El reconocimiento molecular es dependiente del tamaño, con cationes más grandes que exhiben dinámicas de intercambio reducidas.
- Es probable que se requiera la disociación completa de una subunidad de resorcinareno para un intercambio eficiente de invitados.
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