Norlin N, Håkansson P, Westlund P-O, Johansson L B-A
Department of Chemistry, Biophysical Chemistry, Umeå University, Umeå, S-901 87, Sweden.
Phys Chem Chem Phys. 2008 Dec 14;10(46):6962-70. doi: 10.1039/b810661d. Epub 2008 Oct 14.
An extended Förster theory (EFT) is derived and outlined for electronic energy migration between two fluorescent molecules which are chemically identical, but photophysically non-identical. These molecules exhibit identical absorption and fluorescence spectra, while their fluorescence lifetimes differ. The latter means that the excitation probability becomes irreversible. Unlike the case of equal lifetimes, which is often referred to as, donor-donor energy migration (DDEM), the observed fluorescence relaxation is then no longer invariant to the energy migration process. To distinguish, the present case is therefore referred to as partial donor-donor energy migration (PDDEM). The EFT of PPDEM is described by a stochastic master equation (SME), which has been derived from the stochastic Liouville equation (SLE) of motion. The SME accounts for the reorienting as well as the translational motions of the interacting chromophores. Synthetic fluorescence lifetime and depolarisation data that mimics time-correlated single photon counting experiments have been generated and re-analysed. The rates of reorientation, as well as the orientational configurations of the interacting D-groups were examined. Moreover the EFT of PPDEM overcomes the classical "kappa(2)-problem" and the frequently applied approximation of kappa(2) = 2/3 in the data analyses. An outline for the analyses of fluorescence lifetime and depolarisation data is also given, which might prove applicable to structural studies of D-labelled macromolecules, e.g. proteins. The EFT presented here brings the analyses of PDDEM data to the same level of molecular detail as that used in ESR- and NMR-spectroscopy.
本文推导并概述了一种扩展的福斯特理论（EFT），用于描述两个化学性质相同但光物理性质不同的荧光分子之间的电子能量迁移。这些分子具有相同的吸收光谱和荧光光谱，但荧光寿命不同。后者意味着激发概率变得不可逆。与通常所说的等寿命情况下的供体-供体能量迁移（DDEM）不同，此时观察到的荧光弛豫不再对能量迁移过程保持不变。为了区分，因此将当前情况称为部分供体-供体能量迁移（PDDEM）。PPDEM的EFT由一个随机主方程（SME）描述，该方程是从运动的随机刘维尔方程（SLE）推导出来的。SME考虑了相互作用发色团的重排和平移运动。已经生成并重新分析了模拟时间相关单光子计数实验的合成荧光寿命和去极化数据。研究了重排速率以及相互作用的D基团的取向构型。此外，PPDEM的EFT克服了经典的“kappa(2)问题”以及数据分析中经常应用的kappa(2)=2/3近似。还给出了荧光寿命和去极化数据分析的概述，这可能适用于D标记大分子（如蛋白质）的结构研究。本文提出的EFT将PDDEM数据的分析提升到了与电子自旋共振（ESR）和核磁共振（NMR）光谱相同的分子细节水平。
