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Estudios de RMN MAS rápidos de 1 hora de las interacciones de enlace de hidrógeno en monocapas autoensambladas
Shane Pawsey1, Mark McCormick, Susan De Paul
1Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6.
Journal of the American Chemical Society
|April 3, 2003
Resumen
Los ácidos carboxyalquilfosfónicos se unen selectivamente a los óxidos metálicos a través de sus grupos fosfonatos, formando monocapas. La fuerza de unión difiere entre el dióxido de titanio y el dióxido de zirconio, influyendo en la estructura de las moléculas adsorbidas.
Área de la Ciencia:
- Química de las superficies.
- Ciencia de los materiales Ciencia de los materiales.
- Espectroscopia de resonancia magnética nuclear de estado sólido (RMN) Espectroscopia de resonancia magnética nuclear de estado sólido (RMN) Espectroscopia de estado sólido
Sus antecedentes:
- Comprender el comportamiento de adsorción de moléculas orgánicas funcionalizadas en superficies de óxido metálico es crucial para el diseño de materiales avanzados.
- Los ácidos carboxyalquilfosfónicos son moléculas bifuncionales con aplicaciones potenciales en la modificación de superficies y la nanotecnología.
- Estudios previos han explorado monocapas autoensambladas (SAM), pero los conocimientos estructurales detallados a nivel molecular a menudo son limitados.
Objetivo del estudio:
- Para investigar las estructuras de adsorción de ácidos carboxyalkylphosphonic en dióxido de titanio (TiO2) y dióxido de zirconio (ZrO2) superficies de óxido de metal.
- Para dilucidar los modos de unión y las interacciones interfaciales utilizando técnicas avanzadas de RMN de estado sólido.
- Para comparar las características estructurales de estas monocapas con sistemas relacionados y materiales a granel.
Principales métodos:
- Experimentos de Resonancia Magnética Nuclear (RMN) de estado sólido, incluido el giro de ángulo mágico rápido de 1H (MAS), la correlación heteronuclear (HETCOR) y el MAS de doble cuántico (DQ) de 1H.
- Adsorción de ácidos carboxyalquilfosfónicos (con diferentes longitudes de la cadena de alquilo) en nanopowders de TiO2 y ZrO2 con diferentes tamaños de partículas.
- Análisis comparativo con una monocapa autoensamblada de un ácido carboxílico terminado en tiol en nanopartículas de oro.
Principales resultados:
- Los ácidos carboxyalquilfosfónicos se adsorben selectivamente a través del grupo fosfonato, dejando colgantes los grupos ácidos carboxílicos.
- La unión más fuerte de los ácidos fosfónicos al TiO2 da como resultado protones P-OH detectables, mientras que ZrO2 muestra solo grupos P-OH residuales aislados.
- La red de enlaces de hidrógeno en la interfaz monocapa está desordenada, particularmente en sustratos no planos, a diferencia de los dímeros ordenados en los diacidos a granel.
Conclusiones:
- El grupo fosfonato es el sitio de anclaje primario de los ácidos carboxyalquilfosfónicos en TiO2 y ZrO2.
- La fuerza de unión superficial varía significativamente entre TiO2 y ZrO2, lo que afecta a la estructura de la interfaz.
- La unión desordenada de hidrógeno en la interfaz monocapa contrasta con las estructuras ordenadas en los materiales a granel, especialmente en los nanopowders.
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