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Caracterización de la estructura electrónica y propiedades de un modelo complejo de Bis (histidina) hemo
Dayle M A Smith1, Michel Dupuis, Erich R Vorpagel
1Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Journal of the American Chemical Society
|February 27, 2003
Resumen
Este estudio explora cómo los estados de espín influyen en la transferencia de electrones en las proteínas hemo. Los hemes de alto espín muestran enlaces de hierro-imidazol más débiles, lo que sugiere que los entornos proteicos regulan los estados de espín para la transferencia de electrones.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química computacional es la química computacional.
- Química Física es la química física.
Sus antecedentes:
- Los hemes férricos y ferrosos en las proteínas de transferencia de electrones exhiben estados de espín estrechamente espaciados.
- Comprender el estado de espín, la geometría y la transferencia de electrones es crucial para la función del citocromo.
Objetivo del estudio:
- Investigar la relación entre el estado de espín, la geometría y la transferencia de electrones en modelos hemo.
- Modele la interacción del hemo con los residuos de histidina utilizando complejos de hierro-porfirina.
Principales métodos:
- Se empleó la teoría funcional de densidad (DFT) con la funcional híbrida B3LYP.
- Energías relativas calculadas, estructura electrónica y geometrías optimizadas.
- Estructura electrónica validada utilizando parámetros de Mössbauer y geometrías comparadas con cristalografía de rayos X.
Principales resultados:
- El doblete de hierro es 8.4 kcal/mol menor que el sexteto; el singlete de hierro es 6.7 kcal/mol más estable que el quinteto.
- Las afinidades de electrones adiabáticas (AEAs) se calcularon como 5.24 eV (espín alto) y 5.17 eV (espín bajo).
- Los hemes de alto espín exhiben enlaces de hierro-imidazol más largos y una disociación de ligando más fácil, lo que indica la influencia de la proteína en el estado de espín.
Conclusiones:
- El orbital de hierro d(pi) es clave en la transferencia de electrones entre hemisferios.
- Las AEAs calculadas sugieren un atrapamiento eficiente de electrones.
- Los entornos proteicos, modelados por los imidazoles, regulan significativamente los estados de espín hemo e influyen en las propiedades de transferencia de electrones.
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