How does bile salt penetration affect the self-assembled architecture of pluronic P123 micelles? – light scattering and spectroscopic investigations

Abstract

The triblock copolymer of the type (PEO)20-(PPO)70-(PEO)20 (P123) forms a mixed supramolecular aggregate with different bile salts, sodium deoxycholate (NaDC) and sodium taurocholate (NaTC), having different hydrophobicity. These mixed micellar systems have been investigated through dynamic light scattering (DLS) and other various spectroscopic techniques. DLS measurements reveal that the bile salts penetrate into the core-corona region of the P123 micelle and further addition of bile salts causes formation of a new supramolecular aggregate. Further CONTIN analysis confirms existence of two types of complexes at higher molar ratios of bile salt-P123 (>1 : 3). Due to the bile salt penetration, the polarity of the core-corona region of bile salt-P123 mixed micelle increases which results in red shift in the absorption and emission spectra of coumarin 153 (C153) and coumarin 480 (C480). The rotational diffusion of the hydrophobic probe C153 and a hydrophilic probe C480 has been investigated in these bile salt-P123 mixed systems and for both the probes a decrease in the average reorientation time has been observed. The reason behind this decrease in the average reorientation time is the increase in both polarity and hydration of the core-corona region in these mixed micelles. Moreover, these bile salt-P123 mixed micelles are characterized by fluorescence correlation spectroscopy (FCS) techniques. As hydrophobic solute 4-(dicyanomethylene)-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM) resides in the core region of the bile salt-P123 mixed micelles, the translational diffusion of DCM becomes faster in these mixed micelles compared to that in pure P123 micelle. However, for cationic probe rhodamine 6G perchlorate (R6G), a totally opposite trend in the translational diffusion coefficients has been observed. Both anisotropy and FCS measurements confirm that bile salts affect the core region of the P123 micelle more than the corona region. Besides, all these characterizations confirm that more hydrophobic NaDC interacts in a better way than NaTC with the P123 micelle.

Bile salts in digestion and transport of lipids

“…Hydrophobic association is the main driving force for the interactions between non-ionic Pluronic and anionic BS to occur, corroborated by the larger extent of interaction with the relatively more hydrophobic Pluronic F127, and additional experiments performed under high ionic strength conditions, screening electrostatic interactions of NaTDC [87]. Later studies performed with Pluronic P123 micelles and two BS, NaDC and NaTC, have corroborated the greater intensity of the interactions with the more hydrophobic NaDC [88]. In addition, the combination of DLS and spectroscopic techniques used in this study shed light on how BS molecules penetrate into the core of the Pluronic micelle, increasing the polarity at low BS concentrations.…”

An investigation of Pluronic P123–sodium cholate mixed system: micellization, gelation and encapsulation behavior

“…43 However, little emphasis has been given to the mixed micellization of bile salts with Pluronics. Very recently, Roy et al 44 investigated the role of NaTc (sodium taurocholate) and NaDc (sodium deoxycholate) on the self-assembled architecture of P123 micelles. The study revealed that the bile salts reside at the core-corona interface of the P123 micelle, thereby increasing the polarity of the bile salt-P123 mixed micelle.…”

Sustained release of sodium deoxycholate from PLGA–PEG–PLGA thermosensitive polymer

“…The interaction between the different copolymer and surfactants has been studied. It has been reported that NaDC with Pluronic P-123 micelles and sodium dodecyl sulphate with Pluronic F127 micelles interacted together and formed mixed micelles [20]. Castro et al reported such changes in the size of diblock copolymer micelles with SDS [33].…”

“…In this work, a sustained-release system for NaDCbased injectable polymer solution of PLGA-PEG-PLGA copolymer was developed to fulfil the localized fat therapy. Due to the interconnections between the triblock copolymers and both ionic and non-ionic surfactants, they can mix together and form mixed micelles which are potentially promising in the pharmaceutical applications [20]. For this purpose, the copolymer was synthesized and characterized, then the properties of the NaDC-loaded PLGA-PEG-PLGA were investigated.…”