Simple ApproximaTion for Aggregation Number Determination by Isothermal Titration Calorimetry: STAND-ITC

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Biophysical Chemistry

Background:

• Isothermal titration calorimetry (ITC) is a powerful technique for studying molecular interactions.
• Determining aggregation numbers from ITC dilution experiments is crucial for understanding self-assembly processes.
• Existing methods may have limitations in accuracy or scope.

Purpose of the Study:

• To introduce and validate a new method for calculating aggregation numbers from ITC dilution experiments.
• To simultaneously determine other thermodynamic parameters related to self-assembly and dilution.
• To assess the applicability of the method to various surfactant systems and potentially biomolecules.

Main Methods:

• Utilized isothermal titration calorimetry (ITC) dilution experiments.
• Applied newly developed equations to analyze calorimetric isotherms.
• Tested the method with aqueous solutions of dodecyl trimethyl ammonium bromide, dodecyl methylimidazolium chloride, dodecyl methylimidazolium sulfonate, and didecyl methylimidazolium chloride at varying temperatures.
• Validated results against fluorescence measurements and literature data.
• Implemented a computational code for automated parameter determination and uncertainty analysis.

Main Results:

• Successfully obtained aggregation numbers for tested surfactant systems.
• Simultaneously determined molar free energy of transfer, enthalpy of self-assembly, molar heat of dilution, and an offset parameter.
• Demonstrated the method's sensitivity to aggregation numbers, even for small assemblies.
• Validated the new equations against previous proposals and analyzed parameter impact on calorimetric profiles.

Conclusions:

• The proposed method provides a robust approach to determine aggregation numbers from ITC dilution experiments.
• The method offers simultaneous quantification of key thermodynamic parameters governing self-assembly.
• The approach is suitable for diverse calorimetric profiles and shows potential for quantifying biomolecular oligomerization states.