Borges M L, Latterini L, Elisei F, Silva P F, Borges R, Becker R S, Maçanita A L
Instituto de Tecnologia Química e Biológica, Oeiras, Portugal.
Photochem Photobiol. 1998 Feb;67(2):184-91. doi: 10.1562/0031-8655(1998)067<0184:ppapao>2.3.co;2.
The larger photobiological activity of visnagin (VI) versus khellin (KH) toward several living organisms, including fungi, viruses, yeasts and bacteria, induced a detailed investigation of the photophysical properties of these naturally occurring furanochromones, using laser-flash-photolysis, photoacoustic calorimetry and fluorescence (steady-state and time-resolved) techniques in solvents with different polarity and content of water, including micelles and vesicles. The results have shown that the magnitude of all the three rate constants out of S1 (radiative, kf; internal conversion, kic and intersystem crossing, kisc) for VI and KH strongly depend on the solvent, namely on its hydrogen bonding ability and polarity. The changes of kf and kisc are due to the solvent-assisted mixing and/or inversion of the two first singlet excited states (1n, pi and 1 pi, pi), while kic increases with a decrease of the S0-S1 energy gap. As a consequence, the quantum yield of triplet formation (phi T) strongly decreases from values of approximately 0.8 in dioxane to < 0.05 in water for both compounds. The magnitude of solvent polarity/hydrogen bonding ability required, at which the state order is inverted and phi T starts to decrease, is greater for VI than for KH and consequently phi T (VI) >> phi T (KH) over a broad range of water content including that appropriate to the environment of the compounds in a living system. These facts account for the larger photobiological activity of VI with respect to KH, regarding both the fungus Fusarium culmorum L. and the wild strain of Escherichia coli, studied by us.
紫花前胡内酯（VI）对凯林（KH）在包括真菌、病毒、酵母和细菌在内的几种生物体内具有更大的光生物学活性，这促使我们利用激光闪光光解、光声量热法和荧光（稳态和时间分辨）技术，在具有不同极性和含水量的溶剂（包括胶束和囊泡）中，对这些天然存在的呋喃色酮的光物理性质进行了详细研究。结果表明，VI和KH的S1态的所有三个速率常数（辐射速率常数kf、内转换速率常数kic和系间窜越速率常数kisc）的大小强烈依赖于溶剂，即取决于其氢键能力和极性。kf和kisc的变化是由于溶剂辅助的两个第一单线态激发态（1n,π和1π,π）的混合和/或反转，而kic随着S0 - S1能隙的减小而增加。因此，两种化合物的三线态形成量子产率（φT）从二氧六环中的约0.8值急剧下降到水中的<0.05。对于VI，反转态序并使φT开始下降所需的溶剂极性/氢键能力的大小大于KH，因此在包括适合生物系统中化合物环境的广泛含水量范围内，φT（VI）>>φT（KH）。这些事实解释了VI相对于KH在我们研究的禾谷镰刀菌L.和大肠杆菌野生菌株方面具有更大的光生物学活性。
