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Estabilización del zwitterión en fase gaseosa mediante una dication metálica
Robert C Dunbar1, Nick C Polfer, Jos Oomens
1Chemistry Department, Case Western Reserve University, Cleveland, Ohio 44106, USA. rcd@po.cwru.edu
Journal of the American Chemical Society
|November 8, 2007
Resumen
Los aminoácidos en fase gaseosa generalmente favorecen las estructuras canónicas sobre los zwitteriones. Sin embargo, este estudio confirma experimentalmente la forma zwitteriónica del puente de sal (SB) en complejos de bario de doble carga de triptófano, descartando otras estructuras.
Área de la Ciencia:
- Química Física es la química física.
- La espectroscopia es una técnica de espectroscopia.
- Química biofísica y bioquímica.
Sus antecedentes:
- Los aminoácidos existen como zwitteriones en solución, pero típicamente adoptan formas canónicas en la fase gaseosa.
- La complejación de iones metálicos puede estabilizar formas zwitteriónicas, pero esta no es generalmente la configuración más estable para complejos de carga única.
- Los estudios computacionales sugirieron una mayor estabilidad zwitteriónica en complejos de doble carga, pero faltaba la verificación experimental.
Objetivo del estudio:
- Para investigar experimentalmente la estructura de la fase gaseosa de los complejos metálico-aminoácidos doblemente cargados.
- Para verificar la estabilidad mejorada predicha de la forma zwitteriónica (puente de sal) en tales complejos.
- Para caracterizar la estructura del complejo bario-triptófano utilizando espectroscopia infrarroja.
Principales métodos:
- Se utilizó la espectroscopia de disociación infrarroja de fotones múltiples (MP-IRPD).
- Empleado el láser de electrones libres FELIX para excitación infrarroja precisa.
- Se analizaron las frecuencias vibracionales características (estiramiento de CO carboxilato antisimetrico y modo paraguas NH3) para identificar estructuras iónicas.
Principales resultados:
- Se confirmó experimentalmente que el complejo de bario (Ba2+) del triptófano existe en la forma zwitteriónica del puente de sal (SB).
- Se descartó definitivamente la presencia de la forma solvata de carga no zwitteriónica.
- Se identificaron firmas espectroscópicas clave, incluido un tramo de CO de 1600 cm-1 y un modo paraguas NH3 de 1400 cm-1, para la estructura SB.
Conclusiones:
- Los complejos metálicos de doble carga pueden estabilizar la forma zwitteriónica (puente de sal) de los aminoácidos en la fase gaseosa.
- Esta evidencia experimental valida las predicciones computacionales con respecto a la estabilidad SB mejorada.
- La espectroscopia infrarroja proporciona una poderosa herramienta para distinguir entre estructuras de iones en fase gaseosa zwitteriónica y no zwitteriónica.
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