Spectral Properties of Thioflavin T in Solvents with Different Dielectric Properties and in a Fibril-Incorporated Form
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- 作者：Alexander A. Maskevich ; Vitali I. Stsiapura ; Valeriy A. Kuzmitsky ; Irina M. Kuznetsova ; Olga I. Povarova ; Vladimir N. Uversky ; Konstantin K. Turoverov
- 刊名：Journal of Proteome Research
- 出版年：2007
- 出版时间：April 2007
- 年：2007
- 卷：6
- 期：4
- 页码：1392 - 1401
- 全文大小：413K
- 年卷期：v.6,no.4(April 2007)
- ISSN：1535-3907
文摘
The increase in the solvent polarity induces a significant shift of the long-wavelength absorption bandof the thioflavin T (ThT) to the shorter wavelengths. This is due to the fact that the positive charge ofthe ThT molecule (Z = +1e) is unequally and very differently distributed between the benzthiazole andaminobenzene rings in the ground and excited states. Therefore, ThT ground state is stabilized by theorientational interactions of the polar solvent dipoles with the positively charged ThT fragments, whereasthe configuration of the solvation shell of the ThT molecule in the excited Franck-Condon state islikely far from being equilibrium. ThT absorption spectrum has the shortest (412 nm) and the longest(450 nm) wavelengths in water and in water being incorporated to the amyloid fibrils, respectively.Intriguingly, the position of the ThT fluorescence spectrum depends on the polarity of solvent to asignificantly lesser degree than its absorption spectrum: being excited at 440 nm, ThT has emissionwith maxima at 493 and 478 nm in water and fibrils, respectively. This can be due to the fact that, inthe excited state, the rotational oscillations of the ThT fragments relative to each other preventestablishing equilibrium with the solvent and fluorescence occurs from the partially equilibrium excitedstated to the partially equilibrium ground state. For the fibril-incorporated ThT, the maximum of thefluorescence excitation spectrum coincides with the maximum of the long wavelength absorption band(450 nm), whereas for ThT in aqueous and alcohol solutions, additional short-wavelength bands offluorescence and fluorescence excitation spectra were described (Naiki et al. Anal. Biochem. 1989, 177,244-249; Le Vine Methods Enzymol. 1999, 309, 274-284). These bands could result either from somefluorescent admixtures (including free benzthiazole and aminobenzene) or from the specific ThTconformers in which benzthiazole and aminobenzene rings, being oriented at 
angle close to 90 or270
, serve as independent chromophores. On the basis of the results of the quantum-chemicalcalculations, it is proposed that at = 90 (270), the relatively low barrier (only 700 cm-1) of the internalrotation of the benzthiazole and aminobenzene rings relative to each other gives rise to a subpopulationof ThT molecules possessing a violated system of the 
-conjugated bonds of the benzthiazole andaminobenzene rings.
angle close to 90 or270, serve as independent chromophores. On the basis of the results of the quantum-chemicalcalculations, it is proposed that at = 90 (270), the relatively low barrier (only 700 cm-1) of the internalrotation of the benzthiazole and aminobenzene rings relative to each other gives rise to a subpopulationof ThT molecules possessing a violated system of the -conjugated bonds of the benzthiazole andaminobenzene rings.