Phase transition affects energy transfer efficiency in phospholipid vesicles.

Area of Science:

• Biochemistry
• Biophysics
• Physical Chemistry

Background:

• Small unilamellar vesicles (SUVs) composed of dipalmitoylphosphatidyl-choline (DPPC) are widely used model systems for studying lipid bilayer properties.
• Fluorescence quenching is a sensitive technique to probe molecular interactions and microenvironments within lipid bilayers.
• PRODAN and LAURDAN are fluorescent probes sensitive to membrane polarity and fluidity.

Purpose of the Study:

• To investigate the fluorescence quenching of PRODAN and LAURDAN by ORB in DPPC SUVs.
• To understand the influence of membrane phase state (gel vs. fluid) on dye incorporation and quenching efficiency.
• To elucidate the mechanisms of quenching, including static quenching and association processes.

Main Methods:

• Steady-state fluorescence spectroscopy was employed to measure fluorescence quenching.
• The study utilized a model membrane system of DPPC SUVs.
• Experiments were conducted at two different temperatures (25°C - gel phase, 50°C - fluid phase) to represent distinct bilayer states.

Main Results:

• Non-linear Stern-Volmer behavior was observed for both PRODAN and LAURDAN in both gel and fluid phases.
• Quenching was attributed to a combination of static quenching and association between the fluorophores and quencher.
• The relative quenching efficiencies indicated that PRODAN and LAURDAN are incorporated more deeply into the lipid bilayer in its fluid phase compared to its gel phase.

Conclusions:

• The phase state of the lipid bilayer significantly influences the incorporation depth and quenching efficiency of PRODAN and LAURDAN.
• Deeper incorporation in the fluid phase suggests altered membrane structure or dynamics affecting probe partitioning.
• Findings provide insights into the behavior of fluorescent probes within model lipid membranes under different phase conditions.