Phototriggers are useful molecular tools to initiate reactions in enzymes by light for the purpose of photoenzymatic design and mechanistic investigations. Here, we incorporated the non-natural amino acid 5-cyanotryptophan (W5CN) in a polypeptide scaffold and resolved the photochemical reaction of the W5CN–W motif using femtosecond transient UV/Vis and mid-IR spectroscopy. We identified a marker band of ∼2037 cm−1 from the CN stretch of the electron transfer intermediate W5CN·− in the transient IR measurement and found UV/Vis spectroscopic evidence for the W·+ radical at 580 nm. Through kinetic analysis, we characterized that the charge separation between the excited W5CN and W occurs in 253 ps, with a charge-recombination lifetime of 862 ps. Our study highlights the potential use of the W5CN–W pair as an ultrafast phototrigger to initiate reactions in enzymes that are not light-sensitive, making downstream reactions accessible to femtosecond spectroscopic detection.

中文翻译：

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β-发夹肽中 Trp5CN-Trp 基序的超快光触发

光触发剂是有用的分子工具，可通过光引发酶中的反应，用于光酶设计和机理研究。在这里，我们将非天然氨基酸 5-氰基色氨酸 (W5CN) 掺入多肽支架中，并使用飞秒瞬态 UV/Vis 和中红外光谱解决了 W5CN-W 基序的光化学反应。我们在瞬态 IR 测量中从电子转移中间体 W5CN·− 的 CN 延伸中识别出一个 ~2037 cm−1 的标记带，并在 580 nm 处发现了 W·+ 自由基的 UV/Vis 光谱证据。通过动力学分析，我们发现激发的 W5CN 和 W 之间的电荷分离发生在 253 ps 内，电荷复合寿命为 862 ps。