Miskoski S, Sánchez E, Garavano M, López M, Soltermann A T, Garcia N A
Dto. de Química y Fica, Universidad Nacional de Río Cuarto, 5800 R io Cuarto, Argentina.
J Photochem Photobiol B. 1998 May 15;43(2):164-71. doi: 10.1016/S1011-1344(98)00104-3.
Members of the biologically active series tetracyclines (TCs) suffer visible light-promoted photodynamic degradation to different extents, depending on their respective chemical structures and reaction conditions (solvent polarity and pH). The photo-oxidation is accompanied by a partial loss of the antimicrobial power. The photodamage is very fast in the alkaline pH range and less aggressive. although not negligible in kinetic terms, in the physiological pH region. Photo-oxidation quantum efficiencies, evaluated for eight TC derivatives, through singlet molecular oxygen [O2(1Delta(g))] phosphorescence detection, spectrophotometric and polarographic methods, range from 0.12 to 0.65 as upper limits in alkaline medium. The photo-oxidation essentially proceeds via a O2(1Delta(g)) mediated process, with rose bengal or eosine as dye-sensitizers, Nevertheless, as a minor reactive pathway,the excited triplet state of the dye sensitizers interacts with TCS in a competitive process with O2(1Delta(g) generation. The O2(1Delta(g)-mediated photo-oxidation of TCs appears to be a plausible mechanism to account for their phototransformations in biological media, in the presence of visible-absorbing pigments. In both highly and moderately polar media, the quenching of the excited oxygen species is mainly represented by a reactive interaction. It is exerted by the TC molecule through a cooperative effect from the different contributions of several nuclear and extranuclear O2(1Delta(g)-sensitive substituents, as discussed in detail in this paper. The TC lower than 0.03 in the most favourable cases. Nevertheless, the TC photoproduct, formed through direct irradiation, efficiently generates O2(1Delta(g) with Phi(Delta)=0.24. This important finding constitutes the first direct evidence of Type II sensitization by TC photoproducts, and could contribute to the elucidation of the mechanism of TC phototoxicity.
具有生物活性的四环素（TCs）系列成员会受到可见光促进的光动力降解，降解程度因各自的化学结构和反应条件（溶剂极性和pH值）而异。光氧化伴随着抗菌能力的部分丧失。在碱性pH范围内，光损伤非常快且攻击性较小，尽管从动力学角度来看在生理pH区域中也不可忽略。通过单重态分子氧[O₂(¹Δg)]磷光检测、分光光度法和极谱法对八种TC衍生物评估的光氧化量子效率，在碱性介质中的上限范围为0.12至0.65。光氧化基本上通过O₂(¹Δg)介导的过程进行，以孟加拉玫瑰红或曙红作为染料敏化剂。然而，作为次要的反应途径，染料敏化剂的激发三重态在与O₂(¹Δg)生成的竞争过程中与TCs相互作用。在存在可见光吸收色素的情况下，TCs的O₂(¹Δg)介导的光氧化似乎是解释其在生物介质中光转化的合理机制。在高极性和中等极性介质中，激发态氧物种的猝灭主要由反应性相互作用表示。如本文详细讨论的那样，它是由TC分子通过几个核内和核外对O₂(¹Δg)敏感的取代基的不同贡献的协同作用来施加的。在最有利的情况下，猝灭常数低于0.03。然而，通过直接照射形成的TC光产物能有效地产生O₂(¹Δg)，其量子产率（ΦΔ）为0.24。这一重要发现构成了TC光产物II型敏化的首个直接证据，并可能有助于阐明TC光毒性的机制。
