Trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate - New fluorescent dye for testing of amyloid fibrils and study of their structure

We synthesized the benzothiazole dye trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) that is a new analogue of the widely used for amyloid fibrils detection fluorescent probe thioflavin T (ThT). The spectra of DMASEBT are shifted about 100 nm closer to the "transparent window" of biological tissues than that of ThT. Quantum-chemical calculations proved the molecular rotor nature of DMASEBT that underlies the similarity of its photophysical properties with ThT: high level of fluorescence anisotropy in aqueous solutions; fluorescence intensity and lifetime increase during their binding to amyloid fibrils. Using equilibrium microdialysis for sample preparation, two modes of DMASEBT binding to insulin amyloid fibrils, characterized by the different affinity and stoichiometry of interaction, as well as photophysiсal characteristics of the bound to fibrils dye were detected. The obtained results proved the change in DMASEBT photophysical properties when the dye binds to amyloid fibrils (what is critical point for a fluorescent probe), similar to ThT mechanism of the dye binding to fibrils and its improved spectral properties in comparison to ThT. These points make DMASEBT a perspective instrument for amyloid fibrils testing and examining their structure.