Encapsulation of Cationic Fluorescent Dyes and Photosensitizers into the Nanoscopic Domains of Poly(ethylene Glycol)-b-poly(ε-caprolactone) Micelles

Abstract

This study describes an initial systematic investigation on the molecular determinants associated with the effective encapsulation (or lack thereof) of small cationic molecules into the nanoscopic domains of Poly(ethylene glycol)-b-poly(ε-caprolactone) micelles. Out of the seven model dyes investigated here (methylene blue, crystal violet, rhodamine 123, styryl 9M, HITC, DIR and Cardiogreen) only DiR and Cardiogreen were found to partition into the core region of the respective polymeric micelles with a high degree of efficiency. Evidences of weak interactions between styryl 9M and HITC with the corona region of these micelles were also found. No experimental evidences indicating any significant interaction involving methylene blue, crystal violet and rhodamine 123 with the nanoscopic regions of these micelles were found. The experimental observations described here are in keeping with the expected overall trend of enhanced encapsulation efficiencies associated with more lipophilic guest molecules as compared to those associated with more hydrophilic structural analogs (e.g. HITC vs DiR). Accordingly, the reduced form of crystal violet (i.e. leuco-crystal violet), a neutral and highly hydrophobic molecule, was found to partition into the core region of Poly(ethylene glycol)-b-poly(ε-caprolactone) micelles with a high degree of efficiency (comparable to those found for DiR and Cardiogreen), while no micellar interactions involving the respective parent cationic dye crystal violet were found.