Moyano Fernando, Biasutti M Alicia, Silber Juana J, Correa N Mariano
Departamento de Química, Universidad Nacional de Río Cuarto, Agencia Postal # 3, X5804ZAB Río Cuarto, Argentina.
J Phys Chem B. 2006 Jun 22;110(24):11838-46. doi: 10.1021/jp057208x.
The behavior of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) was studied in homogeneous media and in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC), using absorption, emission, depolarization, and time-resolved spectroscopies. In homogeneous media, the Kamlet and Taft solvatochromic comparison method quantified solute-solvent interactions from the absorption and emission PRODAN bands. These studies demonstrate that the absorption band is sensitive to the polarity-polarizability (pi) and the hydrogen bond donor ability (alpha) parameters of the media. PRODAN in the excited state is even more sensitive to these parameters and to the hydrogen bond acceptor ability (beta) of the media. The transition energy (expressed in kcal/mol) for both absorption and emission bands gives a linear correlation with the well-known polarity parameter E(T30). The results from the absorption and emission bands also reveal that PRODAN aggregates in water. The monomer has two fluorescence lifetimes, 2.27 and 0.65 ns, while the aggregate has a lifetime of 14.6 ns. Using steady-state anisotropy measurements, the calculated volumes of the aggregate and the monomer are 5590 and 222 mL mol(-1), respectively. In DOPC LUVs, PRODAN undergoes a partition process between the water bulk and the DOPC bilayer. We show that the partition constant (K(p)) value is large enough that only at [DOPC] below 0.15 mg/mL PRODAN in water can be detected. PRODAN dissolved in LUVs at [DOPC] > 1 mg/mL exists completely incorporated in its monomer form and senses two different microenvironments within the bilayer: a polar region in the interface near the water and a less polar and also less viscous environment, between the phospholipid tails. These environments were characterized by their fluorescence lifetimes (tau), showing that PRODAN in the polar microenvironment has a tau value of approximately 4 ns while in the less polar region gives a value of 1.2 ns. Moreover, this probe also senses the micropolarity of these two different regions of the bilayer and yields values similar to that of methanol and tetrahydrofuran.
使用吸收光谱、发射光谱、去极化光谱和时间分辨光谱，研究了6-丙酰基-2-二甲基氨基萘（PRODAN）在均相介质以及磷脂1,2-二油酰基-sn-甘油-3-磷脂酰胆碱（DOPC）的大单层囊泡（LUVs）中的行为。在均相介质中，Kamlet和Taft溶剂化显色比较方法通过PRODAN的吸收光谱带和发射光谱带来量化溶质 - 溶剂相互作用。这些研究表明，吸收光谱带对介质的极性 - 极化率（π）和氢键供体能力（α）参数敏感。处于激发态的PRODAN对这些参数以及介质的氢键受体能力（β）更为敏感。吸收光谱带和发射光谱带的跃迁能量（以kcal/mol表示）与著名的极性参数E(T30)呈线性相关。吸收光谱带和发射光谱带的结果还表明，PRODAN在水中会聚集。单体有两个荧光寿命，分别为2.27和0.65 ns，而聚集体的寿命为14.6 ns。通过稳态各向异性测量，计算出的聚集体和单体的体积分别为5590和222 mL mol⁻¹。在DOPC LUVs中，PRODAN在水相和DOPC双层之间经历分配过程。我们表明，分配常数（K(p)）值足够大，以至于只有在[DOPC]低于0.15 mg/mL时才能检测到水中的PRODAN。当[DOPC] > 1 mg/mL时，溶解在LUVs中的PRODAN完全以单体形式存在，并感知双层内的两种不同微环境：靠近水的界面处的极性区域以及磷脂尾部之间极性较小且粘性也较小的环境。这些环境通过它们的荧光寿命（τ）来表征，表明处于极性微环境中的PRODAN的τ值约为4 ns，而在极性较小的区域中该值为1.2 ns。此外，该探针还能感知双层这两个不同区域的微极性，并产生与甲醇和四氢呋喃相似的值。
