Mersol J V, Wang H, Gafni A, Steel D G
Department of Physics, University of Michigan, Ann Arbor 48109.
Biophys J. 1992 Jun;61(6):1647-55. doi: 10.1016/S0006-3495(92)81968-9.
Dipole-dipole energy transfer between suitable donor and acceptor chromophores is an important luminescence quenching mechanism and has been shown to be useful for distance determination at the molecular level. In the rapid diffusion limit, where the excited-state lifetime of the donor is long enough to allow the donor and acceptor to diffuse many times their average separation before deexcitation, it is usually assumed that the relative dipolar orientation is completely averaged due to rotational Brownian motion. Under this simplifying assumption, analytical expressions have been derived earlier for the energy transfer rate between donor and acceptor characterized by different geometries. Most such expressions, however, are only approximate because complete angular averaging is permitted only in a geometry that possesses spherical symmetry surrounding each chromophore. In this paper analytical expressions that correctly account for incomplete angle averaging due to steric hindrance are presented for several geometries. Each of the equations reveals a dependence of the energy transfer rate on chromophore orientation. It is shown that correctly accounting for this effect can lead to improvements in estimates of the distance of closest approach from measured quenching rates based on energy transfer experiments.
合适的供体和受体发色团之间的偶极-偶极能量转移是一种重要的发光猝灭机制,并且已被证明对于分子水平的距离测定是有用的。在快速扩散极限情况下,即供体的激发态寿命足够长,使得供体和受体在去激发之前能够扩散许多倍它们的平均间距,通常假定由于旋转布朗运动,相对偶极取向被完全平均化。在这个简化假设下,先前已经推导出了以不同几何形状为特征的供体和受体之间能量转移速率的解析表达式。然而,大多数这样的表达式只是近似的,因为只有在每个发色团周围具有球对称性的几何形状中才允许完全角度平均化。本文针对几种几何形状给出了能够正确考虑由于空间位阻导致的不完全角度平均化的解析表达式。每个方程都揭示了能量转移速率对发色团取向的依赖性。结果表明,正确考虑这种效应可以改进基于能量转移实验从测量的猝灭速率来估计最接近距离的方法。