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Observando la dinámica del estado excitado con sondas ópticas y de rayos X: La dinámica del estado excitado de la
Roseanne J Sension1,2, Taylor P McClain3, Ryan M Lamb1
1Department of Chemistry, University of Michigan, 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
Journal of the American Chemical Society
|June 16, 2023
Resumen
Las técnicas ultra rápidas de rayos X revelan los rápidos cambios atómicos y electrónicos en la vitamina B12 después de la exposición a la luz. Este estudio rastrea los cambios estructurales y los estados excitados en las cobalaminas, ofreciendo información sobre los complejos metálicos fotoactivos.
Área de la Ciencia:
- Fotoquímica y fotofísica
- Química de coordinación
- Espectroscopia ultrarrápida
Sus antecedentes:
- La vitamina B12 (cobalamina) es una biomolécula crucial con un centro de cobalto fotoactivo.
- Comprender los eventos fotoquímicos iniciales en las cobalaminas es vital para dilucidar sus funciones biológicas y diseñar sistemas artificiales.
- La dinámica femtosegunda de los complejos de metales de transición es difícil de resolver debido a su complejidad.
Objetivo del estudio:
- Investigar la dinámica atómica y electrónica secuencial de la hidroxocobalamina y la acuocobalamina después de la fotoexcitación.
- Para aclarar la evolución estructural y las vidas en estado excitado de los compuestos de vitamina B12 en escalas de tiempo de femtosegundos a picosegundos.
- Mostrar el poder de combinar la absorción de rayos X (XANES), la emisión de rayos X (XES) y la espectroscopia de absorción transitoria para el estudio de sistemas fotoactivos.
Principales métodos:
- Absorción de rayos X con resolución de tiempo de femtosegundos (XANES) en el borde K de cobalto.
- Emisión de rayos X con resolución temporal (XES) en las regiones de cobalto Kβ y valencia-núcleo.
- Espectroscopia de absorción transitorio de banda ancha con rayos UV.
- Utilizó espectros de diferencia polarizados XANES para rastrear cambios estructurales.
Principales resultados:
- Cambios estructurales secuenciales identificados que involucran ligandos ecuatoriales y axiales después de la fotoexcitación.
- Se observa un rápido alargamiento del enlace coherente del ligando axial seguido de un retroceso a un estado excitado relajado.
- El XES de resolución temporal y la absorción transitoria indicaron la formación de un estado excitado centrado en el metal con una vida útil de 2-5 ps.
Conclusiones:
- El enfoque espectroscópico combinado proporciona una visión sin precedentes de la dinámica ultrarrápida de la vitamina B12 fotoexcitada.
- El estudio revela una imagen detallada de la dinámica del ligando y la evolución del estado excitado en las cobalaminas.
- Esta metodología es muy eficaz para sondear la dinámica electrónica y estructural en varios complejos de metales de transición fotoactivos.
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