Sortino S, De Guidi G, Giuffrida S, Monti S, Velardita A
Dipartimento di Scienze Chimiche, Università di Catania, Italy.
Photochem Photobiol. 1998 Feb;67(2):167-73. doi: 10.1562/0031-8655(1998)067<0167:peotsa>2.3.co;2.
The spectroscopic and photochemical behavior of Enoxacin (ENX), 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- 1,8-naphthyridine-3-carboxylic acid, has been investigated in aqueous solutions between pH 3.5 and pH 12. The absorption and emission properties of ENX are strongly affected by pH. The fluorescence quantum yield, 4 x 10(-3) at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH. The photodegradation quantum yield also depends on pH, being maximum in neutral conditions (ca 0.04). Nanosecond flash photolysis experiments confirm that the yield of absorbing transients is maximum at neutral pH while it decreases to zero at acid and alkaline pH. These results indicate that both the dissociation of the carboxylic group and the protonation of the piperazinyl residues are key steps for the formation of the photochemically active form of ENX. Loss of F by heterolytic cleavage of the C-F bond is proposed to occur from the triplet state of the zwitterion with formation of a carbocation. A path for the evolution of this intermediate to the final product is also proposed.
已对依诺沙星（ENX），即1-乙基-6-氟-1,4-二氢-4-氧代-7-(1-哌嗪基)-1,8-萘啶-3-羧酸，在pH值为3.5至12的水溶液中的光谱和光化学行为进行了研究。依诺沙星的吸收和发射特性受pH值的强烈影响。荧光量子产率在pH值为3.5时为4×10⁻³，在变为中性pH值时增加了一倍，而在碱性pH值下则观察到强烈降低。光降解量子产率也取决于pH值，在中性条件下最大（约为0.04）。纳秒级闪光光解实验证实，吸收瞬态的产率在中性pH值时最大，而在酸性和碱性pH值时降至零。这些结果表明，羧基的解离和哌嗪基残基的质子化都是形成依诺沙星光化学活性形式的关键步骤。有人提出，通过碳正离子的形成，两性离子的三重态会发生C-F键的异裂从而导致氟的损失。还提出了这种中间体演变成最终产物的途径。
