Conde F R, Churio M S, Previtali C M
Departamento de Química, FCEyN, Universidad Nacional de Mar del Plata, Argentina.
J Photochem Photobiol B. 2000 Jul;56(2-3):139-44. doi: 10.1016/s1011-1344(00)00066-x.
The photostability and photophysical parameters of an aqueous solution of the mycosporine-like amino acid (MAA) porphyra-334 have been determined. The excited-singlet state lifetime, measured by time-correlated single photon counting, was 0.4 ns. Laser flash photolysis experiments at 355 nm did not show any transient species. The triplet state of porphyra-334 was sensitized by triplet-triplet energy transfer. The T-T absorption spectrum was determined and the maximal absorption coefficient at 440 nm was estimated to be 1 x 10(4) M(-1) cm(-1). In this way an upper limit for the intersystem crossing quantum yield was determined. The very low quantum yield of fluorescence (phiF = 0.0016) and triplet formation (phiT < 0.05) together with a photodecomposition quantum yield of 2-4 x 10(-4), in the absence and the presence of oxygen respectively, can be explained by a very fast internal conversion process. These results support the photoprotective role assigned to this MAA in living systems.
已测定了类菌孢素氨基酸（MAA）紫菜-334水溶液的光稳定性和光物理参数。通过时间相关单光子计数测量的激发单重态寿命为0.4纳秒。355纳米处的激光闪光光解实验未显示任何瞬态物种。紫菜-334的三重态通过三重态-三重态能量转移被敏化。测定了T-T吸收光谱，估计440纳米处的最大吸收系数为1×10⁴ M⁻¹ cm⁻¹。通过这种方式确定了系间窜越量子产率的上限。荧光量子产率非常低（φF = 0.0016）且三重态形成量子产率（φT < 0.05），在分别无氧和有氧的情况下光分解量子产率为2 - 4×10⁻⁴，这可以用非常快速的内转换过程来解释。这些结果支持了这种MAA在生命系统中所赋予的光保护作用。
