Photophysical and Structural Characterization of Intrinsically Fluorescent Sterol Aggregates

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Cholesterol self-association into aggregates and crystals is a key factor in atherosclerosis development.
• Intrinsically fluorescent sterols like dehydroergosterol (DHE) are valuable tools for studying sterol aggregation.
• A comprehensive understanding of DHE's photophysical and structural properties in aggregated states is lacking.

Purpose of the Study:

• To investigate the photophysical and structural properties of dehydroergosterol (DHE) aggregates.
• To elucidate the mechanisms behind fluorescence quenching and spectral changes in aggregated DHE.
• To provide insights into the behavior of fluorescent sterol analogues for atherosclerosis research.

Main Methods:

• Evaporation of DHE from ethanol solutions to form aggregates.
• Atomic Force Microscopy (AFM) to determine aggregate morphology and size.
• Fluorescence spectroscopy to analyze changes in DHE's optical properties.
• Electronic structure calculations and Molecular Dynamics (MD) simulations to model aggregation behavior and intermolecular interactions.

Main Results:

• DHE forms submicron, compact oblate-shaped aggregates (<100 nm) upon evaporation, mirroring cholesterol's aggregation.
• DHE fluorescence intensity decreases significantly in aggregates compared to monomers, accompanied by spectral shifts.
• Frenkel-type exciton coupling in DHE dimers and tight packing in aggregates contribute to reduced fluorescence and molecular brightness.

Conclusions:

• DHE exhibits cholesterol-like aggregation behavior, forming stable nanostructures with altered photophysical properties.
• Intermolecular interactions, including exciton coupling and tight packing, are crucial for DHE aggregation and fluorescence modulation.
• These findings support the use of DHE and similar fluorescent sterols for studying sterol solubility and aggregation in biological contexts.