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Transferencia concertada y gradual de electrones acoplados por protones para la oxidación del triptófano derivado con

Astrid Nilsen-Moe¹, Andrea Rosichini¹, Starla D Glover¹

¹Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden.

Journal of the American Chemical Society

|April 13, 2022

Resumen

Se investigaron las reacciones de transferencia de electrones-protones (CEPT) para el triptófano. Este estudio demuestra que CEPT es clave para la transferencia de electrones y protones en sistemas acuosos, desafiando los modelos de transferencia secuencial anteriores.

Área de la Ciencia:

Química Física
Biofísica y Química
La fotoquímica

Sus antecedentes:

Las reacciones concertadas de transferencia de electrones y protones (CEPT) ofrecen una vía para la transferencia de redox y radicales, evitando los intermedios cargados.
El papel del triptófano en las cadenas de transferencia de radicales está establecido, pero su mecanismo de transferencia de protones, especialmente con el agua, ha sido debatido.
Estudios anteriores sugirieron una transferencia secuencial de electrones seguida de una transferencia de protones para la oxidación del triptófano en agua, con resultados contradictorios sobre la dependencia del pH y los efectos cinéticos de los isótopos.

Objetivo del estudio:

Investigar el mecanismo de transferencia de electrones acoplados a protones (PCET) para los derivados del triptófano utilizando fotosensibilizadores.
Aclarar si la CEPT o la transferencia secuencial de electrones (ET) seguida de la transferencia de protones (PT) rige la oxidación del triptófano en entornos acuosos.
Proporcionar pruebas sólidas a favor o en contra de la CEPT en sistemas biológicos y sintéticos que involucren triptófano.

Principales métodos:

Se utilizaron estudios de apagado de flash láser para medir las constantes de velocidad PCET entre los derivados de triptófano y los fotosensibilizadores oxidados de Ru- y Zn-porfirina.
Se emplearon métodos alternativos de apagado y fotooxidación para eludir las complicaciones de estudios previos.
Protegió grupos de aminas y ácidos carboxílicos de triptófano para aislar la desprotonación del grupo indol y su papel en la PCET.

Principales resultados:

Se han observado reacciones limitadas en la transferencia de electrones (ET) a pH < 4 y tasas débilmente dependientes del pH a pH > 5 para los derivados del triptófano.
Constantes de velocidad identificadas significativamente más altas (más de 100 veces) que las velocidades iniciales de transferencia de electrones, descartando un mecanismo de electrones primero.
Se demostró que la cinética observada es intrínseca al PCET del grupo indol con agua como aceptor de protones.

Conclusiones:

El estudio proporciona pruebas sólidas que apoyan un mecanismo de transferencia concertada de electrones y protones (CEPT) para la oxidación del triptófano en el agua.
Estos hallazgos desafían la noción de que el triptófano se somete exclusivamente a la transferencia secuencial de electrones y protones con el agua.
Los resultados tienen implicaciones significativas para la comprensión de la CEPT en medios acuosos y las reacciones radicales mediadas por PCET que involucran triptófano en sistemas biológicos.

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