Ultrafast torsional dynamics of Thioflavin-T in an anionic cyclodextrin cavity

• Ultrafast torsional dynamics of Thioflavin-T is investigated under supramolecular confinement.
• Anionic Sulphobutylether β-cyclodextrin induces a significant retardation in the torsional dynamics of Thioflavin-T.
• Electrostatic interaction is predominant between the guest and the anionic host.
• The confinement effect is significantly larger for the anionic β-cyclodextrin derivative as compared with the native β-cyclodextrin.

Using sub-picosecond fluorescence upconversion spectroscopy, the effect of supramolecular confinement on the ultrafast excited state torsional dynamics of an amyloid fibril sensing dye, Thioflavin-T (ThT), is investigated in a novel cyclodextrin derivative, Sulphobutylether β-cyclodextrin (SBE-β-CD). The encapsulation of ThT inside the nanocavity of SBE-β-CD results in a significant increase in the emission intensity and the excited state lifetime of ThT when compared with native β-CD. Detailed analysis of the time-resolved emission spectra (TRES) shows that the time dependent changes in the integrated area, mean frequency and the width of the emission spectra are appreciably slower as compared with bulk water and native β-CD. These features suggest a significant confinement effect on the ultrafast torsional dynamics of ThT. The ionic strength of the medium significantly affects the complexation of ThT with SBE-β-CD, which indicates that the interaction between the host and the guest is predominantly electrostatic in nature. The results further suggest that the hydrophobic interaction in SBE-β-CD, although minor in contribution in the present case, is comparatively stronger than the native β-CD.

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