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Cambiar el mecanismo redox: modelos para la transferencia de electrones acoplados a protones de la tirosina y el
Martin Sjödin1, Stenbjörn Styring, Henriette Wolpher
1Department of Physical Chemistry, BMC, Uppsala University, PO Box 579, SE-751 23 Uppsala, Sweden.
Journal of the American Chemical Society
|March 18, 2005
Resumen
La transferencia de electrones acoplados a protones (PCET) en sistemas modelo puede ocurrir a través de mecanismos escalonados (ETPT) o concertados (CEP). Los investigadores identificaron factores que controlan estas vías, encontrando que la CEP es probable para ciertas reacciones.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química Física es la química física.
- La fotoquímica es la fotoquímica.
Sus antecedentes:
- La transferencia de electrones acoplados a protones (PCET) es crucial en sistemas biológicos como el fotosistema II.
- Comprender los mecanismos de la PCET es clave para descifrar la función de las proteínas radicales.
Objetivo del estudio:
- Para investigar la PCET en modelos complejos que involucran tirosina o triptófano oxidados.
- Analizar la competencia entre las vías de reacción gradual (ETPT) y concertada (CEP).
Principales métodos:
- Se utilizó la fotólisis de flash láser para generar un oxidante de trisbipiridina-Ru (III).
- Aplicó la teoría de Marcus para la transferencia de electrones para analizar datos cinéticos.
- Manipula el pH de la solución, la fuerza del oxidante y la identidad del aminoácido para controlar los mecanismos de reacción.
Principales resultados:
- Condiciones identificadas que favorecen los mecanismos ETPT o CEP.
- Parámetros cuantificados que influyen en el dominio de cada vía.
- Se observó una mayor energía de reorganización y efecto de isótopo cinético para el CEP en comparación con el ETPT.
Conclusiones:
- La PCET concertada es una vía probable, especialmente para las reacciones exoergónicas débiles.
- La interacción entre la fuerza motriz y la energía de reorganización dicta el mecanismo dominante.
- Los efectos de isótopos cinéticos confirman el movimiento significativo de protones en el paso que determina la velocidad del CEP.
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