Ehrenberg B, Anderson J L, Foote C S
Department of Chemistry and Biochemistry, University of California, Los Angeles, USA.
Photochem Photobiol. 1998 Aug;68(2):135-40.
The spectroscopy and photophysics of the photosensitizer hypericin when in homogeneous solutions and when bound to liposomes were studied. Hypericin was found to partition efficiently into DMPC liposomes, with a binding constant of 58 (mg lipid/mL)-1. In these liposomes the singlet oxygen production quantum yield was 0.43 +/- 0.09. To determine the deactivation constant of singlet oxygen in lipid bilayers for the first time, we calculated extrapolated values from its quenching by DMPC and lecithin in homogeneous solutions and obtained decay times of 36.4 and 12.2 microseconds, respectively. We also measured the quenching of singlet oxygen, sensitized by hypericin in DMPC liposomes, by NaN3, diphenyl isobenzofuran and H2O:D2O mixtures and explained the results on the basis of singlet oxygen diffusing rapidly out of the lipid bilayer into the aqueous medium. The observed temperature effect on the lifetime of singlet oxygen of about 50% over a 15 degrees C range in liposome suspension contrasts with a 3% change in a homogeneous solution in 1-nonanol and is explained by the temperature effect on the diffusion out of the liposome. A strong pH effect was observed, indicating that the deprotonated species formed above about pH 10 is a much weaker photosensitizer of singlet oxygen than the native, protonated species.
研究了金丝桃素在均相溶液中以及与脂质体结合时的光谱学和光物理性质。发现金丝桃素能有效地分配到二肉豆蔻酰磷脂酰胆碱（DMPC）脂质体中，结合常数为58（mg脂质/mL）-1。在这些脂质体中，单线态氧产生的量子产率为0.43±0.09。为首次确定脂质双层中单线态氧的失活常数，我们根据其在均相溶液中被DMPC和卵磷脂猝灭的情况计算了外推值，分别得到36.4和12.2微秒的衰减时间。我们还测量了NaN3、二苯基异苯并呋喃和H2O:D2O混合物对DMPC脂质体中由金丝桃素敏化产生的单线态氧的猝灭作用，并基于单线态氧迅速从脂质双层扩散到水介质中对结果进行了解释。在脂质体悬浮液中观察到的温度对单线态氧寿命的影响在15℃范围内约为50%，这与在1-壬醇均相溶液中3%的变化形成对比，这是由温度对单线态氧从脂质体中扩散的影响所解释的。观察到了强烈的pH效应，表明在pH约10以上形成的去质子化物种作为单线态氧的光敏剂比天然的质子化物种弱得多。
