Does aliphatic chain length influence carbocyanines' orientation in supported lipid multilayers?

Area of Science:

• Membrane biophysics
• Lipid bilayer organization
• Fluorescence spectroscopy

Background:

• Understanding lipid-protein interactions is crucial for membrane function.
• Carbocyanine dyes are widely used to probe membrane structure and dynamics.
• Lipid chain length and phase properties influence membrane behavior.

Purpose of the Study:

• To investigate the orientation of DiOC6(3) and DiOC16(3) in DPPC and DLPC lipid multilayers.
• To determine the localization of these carbocyanines within the lipid bilayer.
• To assess the influence of carbocyanine aliphatic chain length and lipid phase on probe organization.

Main Methods:

• UV-Vis linear dichroism spectroscopy to determine probe orientation.
• Fluorescence quenching studies to ascertain probe localization.
• Fluorescence anisotropy measurements to calculate partition constants.

Main Results:

• Similar orientational probability density functions were observed for both carbocyanines in DPPC and DLPC multilayers.
• Multimodal orientational distributions were found, with main peaks near the bilayer normal.
• Carbocyanines were localized at the membrane interface, irrespective of the lipid matrix.
• Partition constants (K(p)) for DiOC6(3) were determined in DPPC and DLPC.

Conclusions:

• Carbocyanine probe orientation and localization are minimally affected by lipid matrix composition and probe aliphatic chain length.
• The structural organization of these probes within lipidic bilayers is largely independent of specific lipid and dye variations.
• DiOC6(3) exhibits distinct partition constants in DPPC and DLPC, reflecting differential partitioning behavior.