Van der Meer B W, Cheng K H, Chen S Y
Department of Physics and Astronomy, Western Kentucky University, Bowling Green, Kentucky 42101.
Biophys J. 1990 Dec;58(6):1517-26. doi: 10.1016/S0006-3495(90)82496-6.
It is shown that fluorescence anisotropy from lipidlike probes in the hexagonal HII phase gives information of (a) orientational order parameters, (b) the wobbling diffusion constant, and (c) the hopping diffusion constant of the probe, DH, equals DL/R2, the lateral diffusion constant over the square of the radius of the hexagonal tubes. Here we consider only lipidlike probes having the absorption transition movement and/or the emission transition moment along the long axis of the molecule. Three models are introduced for analysis of time-resolved data: the "WOBHOP," the "reduced WOBHOP," and the "P2P4HOP" model. The fluorescence anisotropy in response to a very short excitation pulse in each of the three models is a constant plus a number of exponentials. The WOBHOP and reduced WOBHOP models have 3 and 2 exponentials, respectively, and both contain four fitting parameters: r0 (the fundamental anisotropy), (P2) (the second rank orientational order parameter), DW (the wobbling diffusion constant), and DH (the hopping diffusion constant). The P2P4HOP model has eight exponentials and five fitting parameters: the four parameters listed above and (P4) (the fourth rank orientational order parameter). Analysis of fluorescence anisotropy data in the hexagonal HII phase using one of these models allows for obtaining the hopping diffusion constant, and, if the lateral diffusion constant is known, the radius of the hexagonal tubes. Substitution of DH = 0 in each of the three models yields an expression for the fluorescence anisotropy that is used in the literature for lamellar (L alpha or L beta) phases. The fluorescence anisotropy in coexisting L alpha/HII phases is discussed.
结果表明，六方HII相中类脂探针的荧光各向异性可提供以下信息：(a) 取向序参数；(b) 摆动扩散常数；(c) 探针的跳跃扩散常数DH，其等于DL/R2，即六边形管半径平方上的横向扩散常数。这里我们仅考虑分子长轴方向上具有吸收跃迁运动和/或发射跃迁矩的类脂探针。引入了三种模型来分析时间分辨数据：“WOBHOP”模型、“简化WOBHOP”模型和“P2P4HOP”模型。在这三种模型中，对极短激发脉冲响应的荧光各向异性是一个常数加上若干指数项。WOBHOP模型和简化WOBHOP模型分别有3个和2个指数项，且都包含四个拟合参数：r0（基本各向异性）、(P2)（二阶取向序参数）、DW（摆动扩散常数）和DH（跳跃扩散常数）。P2P4HOP模型有8个指数项和5个拟合参数：上述四个参数以及(P4)（四阶取向序参数）。使用这些模型之一分析六方HII相中的荧光各向异性数据，可得到跳跃扩散常数，并且如果已知横向扩散常数，则可得到六边形管的半径。在这三种模型中令DH = 0，可得到一个用于文献中层状（Lα或Lβ）相的荧光各向异性表达式。还讨论了共存Lα/HII相中的荧光各向异性。
