Aggregation features and fluorescence of Hoechst 33258.

Area of Science:

• Biophysical chemistry
• Molecular biology
• Fluorescent probes

Background:

• The bisbenzimide Hoechst 33258 is widely used for DNA quantification.
• Understanding its solution behavior is crucial for biological applications.

Purpose of the Study:

• To investigate the dimerization of Hoechst 33258.
• To determine how concentration and ionic strength affect monomer-dimer equilibrium.

Main Methods:

• Isothermal titration calorimetry
• Absorbance and fluorescence spectroscopy
• Differential scanning calorimetry
• T-jump kinetic measurements

Main Results:

• Dimer/monomer ratio is dependent on dye concentration and ionic strength.
• Dimerization constant (KD) is 3 × 10^4 M⁻¹ under physiological conditions.
• At 10 μM, dimer predominates above 0.08 M ionic strength; monomer prevails at lower ionic strength.

Conclusions:

• Micromolar concentrations are needed for significant monomer presence.
• Ionic strength critically influences the monomer-dimer ratio and fluorescence.
• Dimer is more fluorescent than the monomer, impacting intensity measurements.