Second-Chance Forward Isomerization Dynamics of the Red/Green Cyanobacteriochrome NpR6012g4 from Nostoc punctiforme
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- 作者：Peter W. Kim ; Lucy H. Freer ; Nathan C. Rockwell ; Shelley S. Martin ; J. Clark Lagarias ; Delmar S. Larsen
- 刊名：The Journal of the American Chemical Society
- 出版年：2012
- 出版时间：January 11, 2012
- 年：2012
- 卷：134
- 期：1
- 页码：130-133
- 全文大小：323K
- 年卷期：v.134,no.1(January 11, 2012)
- ISSN：1520-5126
文摘
The primary ultrafast Z-to-E isomerization photodynamics of the phytochrome-related cyanobacteriochrome NpR6012g4 from Nostoc punctiforme was studied by transient absorption pump鈥揹ump鈥損robe spectroscopy. A 2 ps dump pulse resonant with the stimulated emission band depleted 21% of the excited-state population, while the initial photoproduct Lumi-R was depleted by only 11%. We observed a red-shifted ground-state intermediate (GSI) that we assign to a metastable state that failed to isomerize fully. Multicomponent global analysis implicates the generation of additional Lumi-R from the GSI via crossing over the ground-state thermal barrier for full isomerization, explaining the discrepancy between excited-state and Lumi-R depletion by the dump pulse. This second-chance ground-state dynamics provides a plausible explanation for the unusually high quantum yield of 40% for the primary isomerization step in the forward reaction of NpR6012g4.