Ibuprofen molecular aggregation by direct back-face transmission steady-state fluorescence

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Materials Science

Background:

• Studying the aggregation of molecules like ibuprofen is crucial for understanding solution behavior.
• Traditional fluorescence methods face challenges with highly concentrated or poorly fluorescent samples due to re-absorption.

Purpose of the Study:

• To apply direct back-face transmission steady-state fluorescence for studying ibuprofen and ibuprofenate anion aggregation.
• To develop a robust methodology for characterizing aggregation in challenging sample conditions.

Main Methods:

• Utilized direct back-face transmission steady-state fluorescence spectroscopy.
• Employed the differential reabsorption model and closed association model for data analysis.
• Validated results with time-resolved fluorescence, 1H-NMR, and scattering techniques.

Main Results:

• Successfully determined critical aggregation concentrations and mean aggregation numbers for ibuprofenate.
• Observed changes in fluorescence quantum yield dependent on the counterion (e.g., sodium vs. 1-butyl-3-methylimidazolium).
• Demonstrated the method's efficacy for samples with high absorbance where conventional methods fail.

Conclusions:

• Direct back-face transmission fluorescence is a powerful tool for characterizing molecular aggregation.
• The developed methodology overcomes limitations of standard fluorescence techniques for concentrated and poorly fluorescent systems.
• This approach offers a promising strategy for analyzing aggregation in diverse chemical and material science applications.