Thioflavin-T: A Quantum Yield-Based Molecular Viscometer for Glycerol-Monohydroxy Alcohol Mixtures

Area of Science:

• Photochemistry
• Physical Chemistry
• Materials Science

Background:

• Thioflavin T (ThT) is a molecular rotor dye that is nonfluorescent in low-viscosity solvents but highly fluorescent when bound to amyloid fibrils.
• This fluorescence change is due to viscosity-controlled rotation of its moieties in the excited state, enabling ThT quantum yield to assess environmental viscosity.

Purpose of the Study:

• To investigate the quantum yield of ThT (φ_ThT) in various compositions of six alcoholic solvent mixtures with glycerol.
• To propose an empirical model using φ_ThT to estimate interaction parameters and predict nonideality in solvent mixtures.
• To establish a relationship between ThT quantum yield and bulk viscosity and to propose a methodology for viscosity prediction in uncharacterized mixtures.

Main Methods:

• Measurement of ThT quantum yield (φ_ThT) in glycerol-alcohol solvent mixtures (methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol).
• Development of an empirical model correlating φ_ThT with glycerol mole fraction to estimate interaction parameters and mixture nonideality.
• Establishment of a power law relationship between ThT quantum yield and bulk viscosity for selected solvent mixtures.

Main Results:

• An empirical model was proposed to estimate interaction parameters and predict the nonideality of glycerol-alcohol solvent mixtures based on φ_ThT.
• A Förster-Hoffmann- and Loutfy-Arnold-type power law relationship was established between ThT quantum yield and bulk viscosity for methanol, ethanol, n-butanol, and tert-butanol mixtures with glycerol.
• A methodology was developed to quantify and predict bulk viscosity coefficients for n-propanol-glycerol and isopropanol-glycerol mixtures.

Conclusions:

• Thioflavin T's quantum yield can be effectively used to model and predict the properties and bulk viscosity of glycerol-alcohol solvent mixtures.
• The established power law relationship provides a reliable method for viscosity determination in various solvent compositions.
• This study offers a novel approach for quantifying viscosity in previously uncharacterized solvent mixtures.