Solubilization, micellar transition and biocidal assay of loaded antioxidants in Tetronic® 1304 micelles

The current study scrutinizes the solubilization behaviour of pharmaceutically active antioxidants, namely hydrocinnamic acid (HCA), cinnamic acid (CA) and phenyl propiolic acid (PPA), in the micelles of polyethylene oxide-polypropylene oxide (PEO-PPO) based star-block copolymer: Tetronic (R) 1304 (T1304). A correlation between the molecular orbital energy levels of PEO-PPO units of T1304 and the active parts of the antioxidants are well explained using a simulation study. The antioxidants modulate core-shell micelles of T1304 with enhanced solubilization dependent on their unsaturation and hydrophobicity, as depicted from UV-visible spectroscopy. Antioxidants as an additive induce micellization in 5% w/v T1304 thereby modulating the phase behaviour, as indicated by the decrease in the cloud point. The cloud point results are well complemented by steady state fluorescence spectroscopy findings, depicting a decrease in critical micelle temperature due to the solubilization of antioxidants into the T1304 micelles. A significant difference between the hydrodynamic diameter (D-h) of unloaded and loaded polymer micelles with antioxidants is observed from dynamic light scattering, ensuring the solubilization of the antioxidants in T1304 micelles. These results can apparently be attributed to the interaction and the charge induced by the antioxidants on non-ionic T1304 micelles which increase the micellar size. Furthermore, the role of unsaturation and hydrophobicity of the employed antioxidants in 5% T1304 demonstrates the solution viscosity (eta) change as a function of temperature. In addition, small-angle neutron scattering depicts the shape transition (spherical to ellipsoidal to polymersomes) with temperature. The antioxidant loaded 5% T1304 micellar systems exhibit brilliant biocidal activity against the tested microbes, suggesting their antimicrobial application. (c) 2019 Society of Chemical Industry