The behavior of monocationic chlorin in water and aqueous solutions of non-ionic surfactant Tween 80 and potassium iodide

Abstract We have studied the behavior of monocationic chlorin (compound 1 ) which is considered as an appropriate agent for both antimicrobial and antitumor photodynamic therapy in water, aqueous solutions of KI and non-ionic surfactant Tween 80 with the dynamic light scattering (DLS), UV–Vis and fluorescence spectroscopy techniques. Our results do indicate that the solute reveals a tendency to form aggregates both in diluted (~10 −5  mol/kg) and rather concentrated aqueous solutions (~10 −3  mol/kg). For diluted aqueous solutions UV–Vis spectra appear to show the appearance of small associates, so-called H-aggregates, whereas for more concentrated solutions the DLS study reveals formation of large aggregates containing both chlorin and water molecules. The addition of surfactants or polymers such as Tween 80 or polyvinylpyrrolidone (PVP) leads to monomerisation of a potential drug for all cases. The spectrophotometric titration of aqueous solutions of compound 1 with Tween 80 demonstrates the strong interaction between surfactant and chlorin molecules, the binding constants and stoichiometry of complex formation being dependent of a solute concentration. The comparison of fluorescence quenching by KI in water and surfactant solutions indicates that solute molecules mainly occupy intermediate positions within Tween 80 micelles nearby the hydrophilic head groups of the surfactant.