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Cambio conformacional del radical HOCO: excitación vibratoria selectiva y túnel de átomos de hidrógeno

Sergey V Ryazantsev^1,2, Vladimir I Feldman¹, Leonid Khriachtchev²

¹Department of Chemistry, Lomonosov Moscow State University , Moscow 119991, Russia.

Journal of the American Chemical Society

|June 20, 2017

Resumen

Los investigadores observaron el primer fotoscambio conformacional en una especie de cáscara abierta, el radical carboxilo (HOCO). Descubrieron que las matrices de nitrógeno estabilizan el conformador cis, lo que permite las conversiones trans-cis a través de la excitación vibratoria y el túnel de átomos de hidrógeno.

Área de la Ciencia:

Química Física
Espectroscopia
Física Química

Sus antecedentes:

El radical carboxilo (HOCO) existe en los conformadores cis y trans, siendo el trans la forma de menor energía.
Las técnicas de aislamiento de matriz que utilizan argón y nitrógeno se emplean para estudiar las especies radicales.
Comprender la estabilidad del conformador y la interconversión es crucial para la dinámica de la reacción.

Objetivo del estudio:

Investigar el comportamiento conformacional del radical carboxilo (HOCO) y su isotopólogo deuterado (DOCO) en matrices de argón y nitrógeno.
Para explorar la posibilidad de conformación fotoswitching en una especie radical de cáscara abierta.
Para aclarar el mecanismo de interconversión entre cis y trans conformers.

Principales métodos:

Se utilizó espectroscopia infrarroja (IR) para estudiar HOCO y DOCO en matrices de argón y nitrógeno.
Se aplicó excitación vibratoria selectiva para inducir cambios conformacionales.
Se utilizó luz infrarroja de banda ancha para observar las interconversiones espontáneas.

Principales resultados:

En las matrices de argón, solo se observó el conformador trans-HOCO, mientras que los conformadores cis y trans de DOCO estaban presentes.
Las matrices de nitrógeno estabilizaron el conformador cis de mayor energía tanto para HOCO como para DOCO.
La primera instancia de conmutación conformacional para una especie de cáscara abierta se logró a través de la excitación vibratoria selectiva.
El túnel de átomos de hidrógeno fue identificado como el mecanismo para el decaimiento cis-trans en matrices de nitrógeno, apoyado por efectos de isótopos cinéticos.

Conclusiones:

Las matrices de nitrógeno estabilizan significativamente el conformador cis de HOCO y DOCO en comparación con las matrices de argón.
Se puede lograr el fotointercambio conformacional de HOCO y DOCO, lo que demuestra el control de las conformaciones radicales.
El túnel de átomos de hidrógeno proporciona una vía única para la conversión cis-trans en especies de caparazón abierta, con distintos efectos de isótopos cinéticos observados en diferentes matrices.

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