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La distribución del espín en las porfirinas de hierro de espín bajo

Mikael P Johansson¹, Dage Sundholm, Gary Gerfen

¹Department of Chemistry, P.O. Box 55 FIN-00014, University of Helsinki, Finland. mikael.johansson@helsinki.fi

Journal of the American Chemical Society

|September 26, 2002

Resumen

Los cálculos de la teoría de la densidad funcional revelan la deslocalización del espín en las porfirinas de hierro, reconciliando los datos de resonancia de espín de electrones (ESR) y resonancia magnética nuclear (RMN). Esta distribución de espín explica la aparente contradicción entre las técnicas experimentales.

Área de la Ciencia:

Química computacional es la química computacional.
Química biofísica y bioquímica.
Química Inorgánica La Química Inorgánica es la química inorgánica.

Sus antecedentes:

Las porfirinas de hierro de baja espina (S=1/2) exhiben estructuras electrónicas complejas.
La resonancia de espín de electrones (ESR) sugiere la localización de electrones no emparejados en el hierro.
La resonancia magnética nuclear (RMN) y ENDOR indican una deslocalización significativa de los electrones.

Objetivo del estudio:

Para resolver la discrepancia entre los hallazgos de ESR y NMR/ENDOR en las porfirinas de hierro.
Para dilucidar la distribución del espín dentro de los complejos de porfirina de hierro.
Para investigar la estructura electrónica del hemo a y la porfirina de hierro ligada con bis-imidazol.

Principales métodos:

Cálculos de la teoría de la densidad-funcional (DFT).
Modelado de porfirina de hierro ligada con hemo a y bis-imidazol.
Análisis de la densidad de giro integrada y la distribución de giro.

Principales resultados:

Los cálculos de DFT confirman la densidad de espín integrada cercana a uno en el átomo de hierro, alineándose con ESR.
Regiones significativas de densidad de espín opuesta (beta) encontradas a lo largo de los enlaces Fe-N.
Densidad de espín alfa adicional distribuida a través del anillo de porfirina, sustituyentes y ligandos.

Conclusiones:

La aparente contradicción entre ESR y NMR/ENDOR se explica por la distribución detallada de espín.
Se observa una densidad de espín bruto de aproximadamente 1,3 electrones.
La compleja interacción de las densidades de espín alfa y beta en diferentes regiones es un hallazgo novedoso.

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