Photophysics in Biomembranes: Computational Insight into the Interaction between Lipid Bilayers and Chromophores

Area of Science:

• Biophysics
• Computational Chemistry
• Spectroscopy

Background:

• Visible light absorption by biomolecules is limited, necessitating the use of optical probes (chromophores).
• Chromophore optical properties are sensitive to their environment, making them useful for studying biosystems.
• Time-resolved spectroscopic studies offer nondestructive insights into molecular-scale dynamics.

Purpose of the Study:

• To present a multiscale computational strategy for analyzing chromophore behavior in biological systems.
• To demonstrate the necessity of theoretical studies for explaining and predicting fluorescence experiments.
• To explore the capabilities of chromophores in discriminating lipid bilayer properties and their environmental dependencies.

Main Methods:

• Multiscale computational strategy over eight years.
• Analysis of three archetypal chromophores: diphenylhexatriene (DPH), Laurdan, and azobenzene.
• Nonadiabatic QM/MM surface hopping (QM/MM-SH) analyses for azobenzene photoisomerization.

Main Results:

• DPH conformational changes are crucial for its orientation and spectral properties in different lipid phases (Lo, Ld, So).
• Laurdan's two conformers exhibit distinct behaviors in lipid membranes, acting as a molecular rotor.
• Azobenzene shows dual trans-to-cis photoisomerization mechanisms and a "pedal-like" cis-to-trans mechanism, influenced by surrounding lipid chains.

Conclusions:

• Computational simulations are essential for understanding and predicting fluorescence experiments.
• Chromophores like DPH, Laurdan, and azobenzene possess unexplored abilities to probe lipid bilayer characteristics.
• The study highlights the importance of considering molecular conformation and environmental interactions for accurate interpretation of spectroscopic data.