Dissanayake Komadhie C, Walid Mohammad K I, Austin Madelyn, Smith Emily A, Winter Arthur H
Department of Chemistry, Iowa State University Ames Iowa 50014 USA
Chem Sci. 2025 Mar 5;16(15):6418-6424. doi: 10.1039/d5sc00204d. eCollection 2025 Apr 9.
Photocages are protecting groups that can be unmasked with light irradiation and provide spatiotemporal control over the activity of a biomolecule. Ideally, photocages have high quantum yields for deprotection and good water solubility. Small photocages are preferred in applications where minimal biological perturbations of the photocage are desired or where large photocage structures stymie needed binding or activity, such as in the incorporation of unnatural photocaged amino acids into proteins. Here, we report -methyl-3-oxypicolinium ester, by molecular weight the smallest photocage reported to date. The photocage is smaller (by MW) than even the parent nitrobenzyl photocage, but has improved properties, including being more water soluble as a result of its zwitterionic character, a higher quantum yield of release of 0.32 at pH 7 for release of the mediocre leaving group AcOH, and a superior chromophore within a single benzene ring ( = 320 nm, = 402 nm) that matches the absorbance wavelength of the larger 7-hydroxy coumarin photocage. The zwitterionic character aids in water solubility, red-shifts the chromophore absorption and emission by raising the HOMO and lowering the LUMO, and improves the quantum yield of release. Cell studies show that the photocage crosses the HEK293 cell membrane and shows no observable toxicity (trypan blue exclusion assay, 25 μM), while mechanistic studies indicate a singlet photoheterolysis mechanism that is supported by ultrafast transient absorption spectroscopy, oxygen sensitivity studies, computational investigations, and photoproduct analysis.
光笼是一种保护基团，可通过光照射去除保护，从而对生物分子的活性进行时空控制。理想情况下，光笼具有高的脱保护量子产率和良好的水溶性。在希望光笼对生物的干扰最小的应用中，或者在大的光笼结构阻碍所需的结合或活性的情况下（例如将非天然的光笼化氨基酸掺入蛋白质中），较小的光笼更受青睐。在此，我们报道了一种甲基 - 3 - 氧代吡啶鎓酯，按分子量计算它是迄今为止报道的最小的光笼。该光笼甚至比母体硝基苄基光笼还小（按分子量），但具有改进的性能，包括由于其两性离子特性而具有更高的水溶性，在pH 7时对于释放中等离去基团乙酸的释放量子产率为0.32，并且在单个苯环内具有优越的发色团（λabs = 320 nm，λem = 402 nm），与较大的7 - 羟基香豆素光笼的吸收波长相匹配。两性离子特性有助于提高水溶性，通过提高最高占据分子轨道（HOMO）和降低最低未占据分子轨道（LUMO）使发色团吸收和发射发生红移，并提高释放量子产率。细胞研究表明，该光笼可穿过HEK293细胞膜且未显示出可观察到的毒性（台盼蓝排斥试验，25 μM），而机理研究表明其为单重态光异裂机理，超快瞬态吸收光谱、氧敏感性研究、计算研究和光产物分析均支持这一机理。
