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Estado muy alterado del transporte de protones en piscinas ácidas en micelas invertidas cargadas

Hongxia Hao¹, Ellen M Adams^2,3, Sarah Funke⁴

¹Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California94720, United States.

Journal of the American Chemical Society

|January 12, 2023

Resumen

El transporte de protones en micelas inversas cargadas (RMs) se ve obstaculizado significativamente. Los tensioactivos cargados como NaAOT y CTABr impiden el salto de protones, ralentizando la dinámica dentro de estas piscinas de ácido confinadas.

Área de la Ciencia:

Química Física
Química computacional
Ciencias de los materiales

Sus antecedentes:

Las micelas inversas (RMs) son nanoestructuras versátiles utilizadas para confinar soluciones acuosas.
Comprender el transporte de protones en entornos confinados es crucial para la catálisis y los procesos biológicos.
Los tensioactivos cargados en RM pueden alterar significativamente las propiedades de los fluidos confinados.

Objetivo del estudio:

Investigar los mecanismos de transporte de protones en micelas inversas (RM) con agentes tensioactivos cargados.
Para correlacionar los resultados de la simulación con los datos espectroscópicos experimentales (absorción TeraHertz y relajación dieléctrica).
Para aclarar el papel de la carga de surfactante en la dinámica de protones dentro de las piscinas ácidas confinadas.

Principales métodos:

Se emplearon simulaciones de campo de fuerza reactivo para modelar la dinámica de los protones.
El análisis se centró en los mecanismos de transporte dentro de los RM de bis ((2-etilhexil) sulfosuccinato de sodio (NaAOT) y bromuro de cetiltrimetilamonio (CTABr).
Comparación con RM no iónicos y firmas espectroscópicas experimentales.

Principales resultados:

El salto de protones fue suprimido en los RM NaAOT en comparación con los RM no iónicos.
El mecanismo de Grotthuss para el transporte de protones fue completamente inhibido en los RM de CTABr.
Los grupos de cabeza y contraiones cargados alteraron las concentraciones de iones interfaciales, aumentando el pH efectivo dentro de los RM.
La localización de protones cerca de contraiones / bases conjugadas obstaculizó las configuraciones Eigen y Zundel, favoreciendo el salto oscilatorio localizado.

Conclusiones:

Los tensioactivos cargados impiden significativamente el transporte de protones en las micelas inversas.
La dinámica lenta de protones observada se atribuye a las interacciones electrostáticas y al pH local alterado.
El salto oscilatorio localizado se vuelve dominante, especialmente en los RM de CTABr, lo que lleva a tiempos de residencia de protones extendidos.

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