Organization and dynamics in micellar structural transition monitored by pyrene fluorescence

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Biophysical Chemistry

Background:

• Structural transitions in charged micelles are crucial for cellular physiology.
• These transitions, like sphere-to-rod changes in SDS micelles, can be triggered by altering ionic strength.
• Understanding micellar organization and dynamics is key for applications like drug delivery.

Purpose of the Study:

• To investigate the structural and dynamic changes in SDS (sodium dodecyl sulfate) micelles during the sphere-to-rod transition.
• To quantify the changes in micellar polarity using pyrene fluorescence.
• To explore the implications of these transitions for micellar properties and cellular processes.

Main Methods:

• Utilizing pyrene fluorescence spectroscopy to monitor micellar organization and dynamics.
• Analyzing the ratio of pyrene vibronic peak intensities (I(1)/I(3)) to estimate the apparent dielectric constant.
• Measuring the pyrene excimer/monomer ratio to assess changes in micelle aggregation.

Main Results:

• The apparent dielectric constant of SDS micelles decreased from ~32 (spherical) to ~22 (rod-shaped) with increasing NaCl concentration.
• This reduction in dielectric constant indicates a change in micellar polarity during the sphere-to-rod transition.
• The pyrene excimer/monomer ratio increased with NaCl concentration, suggesting more pyrene molecules per micelle as they transition to rods.

Conclusions:

• The study provides early estimates of polarity in rod-shaped SDS micelles.
• The sphere-to-rod transition significantly alters micellar organization, dynamics, and polarity.
• Findings are relevant to micellar drug solubilization, delivery, and understanding membrane morphology changes.