Salt and bile salt accelerate self-assembly behavior of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) probed by curcumin fluorescence

Abstract

Understanding self-assembly aspects of block copolymers is of great importance due to their utility in a wide range of applications whether in chemistry, pharmacy, or medicine. In this work, properties of poly(ethylene oxide) -block- poly(propylene oxide) -block- poly(ethylene oxide) (F108) are studied in solution using fluorescence technique and curcumin as the molecular probe. Fluorescence of curcumin has been tracked in solutions of different concentrations of F108. The CMC (critical micellar concentration) and CMT (critical micellar temperature) have been found to be 23.2 μM and 35 °C respectively. First time curcumin fluorescence-based method has been proven to be useful to estimate CMT. Furthermore, fluorescence quenching technique using hydrophobic cetyl pyridinium bromide and hydrophilic KI quenchers has established the position of curcumin is located near the hydrophobic pocket of Stern-layer of F108 micelle. New insight on effect of ionic strength and bile salt on the CMC and CMT values of F108 is evaluated through curcumin probing. CMC has decreased with the increase in the concentration of the three salts except for NaC. The effect has been arranged in decreasing order as follows: NaDC > NaCl > NaC. On the other hand, the effect of the three salts on the CMT of F108 has been found to be less remarkable, with a 1-fold decrease for NaCl and NaDC and almost no change for NaC.