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

Self-assembly of bile salts and their mixed aggregates as building blocks for smart aggregates

The present communication offers a comprehensive overview of the self-assembly of bile salts emphasizing their mixed smart aggregates with a variety of amphiphiles. Using an updated literature survey, we have explored the dissimilar interactions of bile salts with different types of surfactants, phospholipids, ionic liquids, drugs, and a variety of natural and synthetic polymers. While assembling this review, special attention was also provided to the potency of bile salts to alter the size/shape of aggregates formed by several amphiphiles to use these aggregates for solubility improvement of medicinally important compounds, active pharmaceutical ingredients, and also to develop their smart delivery vehicles. A fundamental understanding of bile salt mixed aggregates will enable the development of new strategies for improving the bioavailability of drugs solubilized in newly developed potential hosts and to formulate smart aggregates of desired morphology for specific targeted applications. It enriches our existing knowledge of the distinct interactions exerted in mixed systems of bile salts with variety of amphiphiles. By virtue of this, researchers can get innovative ideas to construct novel nanoaggregates from bile salts by incorporating various amphiphiles that serve as a building block for smart aggregates for their numerous industrial applications.

A Novel Study on the Self-Assembly Behavior of Poly(lactic-co-glycolic acid) Polymer Probed by Curcumin Fluorescence

Understanding the self-assembly behavior of block copolymers is of great importance due to their usefulness in a wide range of applications. In this work, the physical properties of poly(lactic-co-glycolic acid) (PLGA polymer) are studied for the first time in solution using the fluorescence technique and curcumin as a molecular probe. First, curcumin at a concentration of 2 μM was added to different concentrations of PLGA, and the fluorescence of curcumin was tracked. It was found that the critical micellar concentration (CMC) was equal to 0.31 g/L and the critical micellar temperature (CMT) was obtained to be 25 °C. Furthermore, an insight on the effect of NaCl salt on the CMC value of PLGA is assessed through curcumin probing. A decrease in the CMC has been observed with the increase in the concentration of NaCl, which could be due to the salting out effect. Moreover, in order to understand the aggregation behavior of PLGA in different solutions, CMC experiments were investigated using chloroform as a solvent. Results showed that the solvent does not affect the CMC value of the polymer; however, it only affects the shape of the obtained micelle forming a reversed micelle. Finally, fluorescence quenching of curcumin with hydrophobic cetyl-pyridinium bromide (CPB) and hydrophilic KI quenchers was established, where it was proved that curcumin is located near the hydrophobic pocket of the Stern layer of the PLGA micelle.

Optical spectroscopy study of the interaction between curcumin and acrylic polymers

This paper presents the results of a study conducted on the interaction between curcumin, a compound with several biomedical applications in traditional and modern medicine, and the acrylic polymers poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate), through photophysical experiments in curcumin/acrylic polymers casting films. Optical absorption intensity at ~340 nm increases relatively to its maximum at ~417 nm when the amount of curcumin in the polymeric film decreases, due to a significant change in the concentration of the isomers cis- or trans-form of curcumin, regardless of the acrylic polymer. Fluorescence (FL) spectra of the films depend on the curcumin concentration in the matrix with well-resolved line shape. They show two distinct bands, one at ~525 nm, for higher curcumin concentration (5.00 mmol.L^-1), related to the aggregated curcumin species, and another at ~465 nm, for lower concentration of curcumin (0.10 mmol.L^-1), related to the effects of the solvent on the conformational structure of the curcumin molecule and the presence of the trans-form of curcumin. The parameter K_agg, related to the contribution of the aggregated curcumin, shows the influence of the polymeric lateral chain length of the matrix in the de-aggregation of the curcumin. The Huang-Rhys factor indicates that curcumin aggregated species are conformationally more stable, and that the isolate species depends on the chemical environment and the matrix/curcumin interaction, decreasing its conformational degrees of freedom. Arrhenius plots, obtained via FL experiment in function of the sample temperature, show that, for higher curcumin concentration, the value for the relaxation energy process is not well defined, due the decrease in the interaction between the matrix and the curcumin molecules. With these results, it is possible to infer that the interaction matrix/curcumin must occur via lateral chemical alkyl groups.