Transfer of electronic excitation energy between thioflavin t and its styryl derivatives incorporated into amyloid fibrils

Abstract

The spectral and luminescent properties of the styryl derivative of thiofl avin T (ThT) 2-{(1E,3E)-4-[4-(dimethylamino) -2,6-dimethylphenyl]buta-1,3-dien-1-yl}-3-ethyl-1,3-benzothiazolium-3 tosylate (Th-C23) were studied. The fl uorescence decay kinetics of Th-C23 incorporated into amyloid fi brils (AF) were not exponential and could be represented as a unimodal distribution of fl uorophores over duration α(t). ThT and Th-C23 were shown to form an eff ective donor–acceptor (D–A) pair when incorporated into the AF structure. The degree of polarization of the acceptor fl uorescence was high (~0.4) within the entire spectrum, despite the energy transfer, and was explained by the special orientation of D–A pairs, parallel and antiparallel. The measured fl uorescence spectrum of the donor (ThT) and absorption spectrum of the acceptor (Th-C23) were used to calculate the critical energy-transfer radius R0, which could take values from 54 to 68 Å depending on the mutual orientation and quantum yield of the donor and acceptor.