Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
Analytical Science Centre for Doctoral Training, Senate House, University of Warwick, Coventry CV4 7AL, UK.
Molecules. 2022 Mar 31;27(7):2272. doi: 10.3390/molecules27072272.
Mycosporine-like amino acids are a prevalent form of photoprotection in micro- and macro-organisms. Using a combination of natural product extraction/purification and femtosecond transient absorption spectroscopy, we studied the relaxation pathway for a common mycosporine-like amino acid pair, usujirene and its geometric isomer palythene, in the first few nanoseconds following photoexcitation. Our studies show that the electronic excited state lifetimes of these molecules persist for only a few hundred femtoseconds before the excited state population is funneled through an energetically accessible conical intersection with subsequent vibrational energy transfer to the solvent. We found that a minor portion of the isomer pair did not recover to their original state within 3 ns after photoexcitation. We investigated the long-term photostability using continuous irradiation at a single wavelength and with a solar simulator to mimic a more real-life environment; high levels of photostability were observed in both experiments. Finally, we employed computational methods to elucidate the photochemical and photophysical properties of usujirene and palythene as well as to reconcile the photoprotective mechanism.
菌氨酸类似物是微生物和宏观生物中普遍存在的一种光保护形式。我们采用天然产物提取/纯化和飞秒瞬态吸收光谱相结合的方法，在光激发后的最初几纳秒内研究了一种常见的菌氨酸类似物对，即尿卟啉和其几何异构体棕酮的弛豫途径。我们的研究表明，这些分子的电子激发态寿命仅持续几百飞秒，然后激发态种群通过能量上可及的锥形交叉，并随后通过振动能量转移到溶剂中。我们发现，在光激发后 3 ns 内，有一小部分异构体对没有恢复到原来的状态。我们使用单波长连续辐照和太阳模拟器进行了长期光稳定性研究，以模拟更真实的环境；在这两种实验中都观察到了高水平的光稳定性。最后，我们采用计算方法阐明了尿卟啉和棕酮的光化学和光物理性质，并协调了光保护机制。
