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Efectos de los iones en las redes de agua de enlace de hidrógeno en grandes nanogotas acuosas
Jeremy T O'Brien1, Evan R Williams
1Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Journal of the American Chemical Society
|May 24, 2012
Resumen
La investigación de nanogotas acuosas con varios iones revela que la carga iónica influye en el enlace de hidrógeno de la molécula de agua. Los iones multivalentes alteran significativamente la estructura del agua, incluso en la superficie de las nanopartículas.
Área de la Ciencia:
- Química Física es la química física.
- La espectroscopia es una técnica de espectroscopia.
- Ciencia de los materiales Ciencia de los materiales.
Sus antecedentes:
- La comprensión de las interacciones entre iones y agua es crucial para varios procesos químicos y biológicos.
- El comportamiento de las gotas de agua a nanoescala difiere significativamente del agua a granel.
- Los métodos espectroscópicos proporcionan información sobre la estructura molecular y el enlace.
Objetivo del estudio:
- Para investigar el efecto de los diferentes iones (SO(4)(2-), I(-), Na(+), Ca(2+), La(3+)) en la red de enlaces de hidrógeno de las moléculas de agua en las nanopartículas.
- Para analizar la influencia de la carga y el tipo de iones en la estructura del agua en la superficie del nanodromo.
- Para determinar en qué medida los cambios estructurales inducidos por iones se propagan a la superficie.
Principales métodos:
- La espectroscopia de fotodisociación infrarroja conjunta (IRPD) se utilizó para sondear el enlace de hidrógeno en nanogotas acuosas (~ 250 moléculas de agua).
- Los espectros se registraron en la región de estiramiento de hidrógeno (~2800-3800 cm) a 133 K.
- El análisis se centró en las características correspondientes a los grupos hidroxilo (OH) unidos y libres de las moléculas de agua de superficie.
Principales resultados:
- Spectra mostró características tanto para grupos OH enlazados como libres, con este último atribuido a las moléculas de agua AAD (acepta dos, dona un enlace de hidrógeno).
- La frecuencia del tramo de AAD libre-OH se desplazó al rojo con el aumento de la carga de iones positivos, lo que indica un efecto Stark.
- Los iones monovalentes tuvieron un impacto mínimo en la red de enlaces de hidrógeno del agua a granel, mientras que los iones multivalentes la alteraron significativamente, con efectos que se extendieron a la superficie de la nanoparta.
Conclusiones:
- La carga y el tipo de iones influyen de manera demostrable en la red de enlaces de hidrógeno del agua en nanotopas.
- El efecto Stark debido a los campos eléctricos inducidos por iones afecta a las frecuencias de las moléculas de agua de superficie.
- Las modificaciones estructurales inducidas por iones en las nanogotas se propagan a la superficie, a más de 1 nm de distancia del ion.
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