Molecular level investigation on the interaction of pluronic F127 and human intestinal bile salts using excited state prototropism of 1-naphthol

• Bile salts show efficient micellar aggregation with CMC values of 12.6 mM for NaTC and 12.7 mM for NaC.
• With increase in concentration of bile salts the sol–gel phase transition temperature of PF127 decreases.
• Bile salts induced appreciable dehydration of the hydrophilic corona as well as core region PF127 hydrogel.
• Micropolarity of the hydrogel microenvironment decreases with increase in concentration of the bile salts.

Pluronic F127 (PF127), a surfactant polymer is used as a drug delivery system and has been introduced recently in the food research to delay lipid digestion process. In this context study the interaction of this polymer with human intestinal bile salts assumes important. The studies involving interaction of PF127 with human intestinal bile salts sodium taurocholic acid (NaTC) and sodium cholate acid (NaC) by using differential scanning calorimetry (DSC) and 1-naphthol as a fluorescent molecular probe show that the bile salts induce decrease of sol–gel phase transition temperature of the PF127 to lower temperature, from ~ 21 °C to ~ 18 °C. Variation of neutral form fluorescence intensity of 1-naphthol with bile salts in water confirmed efficient micellar aggregation with critical micellar concentration (CMC) values of 12.6 mM for NaTC and 12.7 mM for NaC. Fluorescence parameters like fluorescence intensity and fluorescence lifetime of the two excited state prototropic forms {neutral form emission (λem = 370 nm), anion form emission (λem = 470 nm)} of 1-naphthol suggested that the NaTC (below critical micellar concentration 12 mM) and NaC (above critical micellar concentration 12 mM) induce appreciable dehydration of the hydrophilic corona as well as core region PF127 hydrogel. The micropolarity of the hydrogel microenvironment decreases with increase in concentration of both the bile salts.

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