Unveiling the pH dependent interaction between bolaamphiphiles (dicarboxylic acids) and C₁₀TAB...

Development of stable self-assembled nanostructures (especially vesicles and liposomes), and understanding their physicochemical behaviors in aqueous solution is a long-standing topic of interest in chemical and biochemical research. In this progressive area, we report for the first-time formation of mixed micelles (at pH 12), and vesicles of anionic bolaamphiphiles (dicarboxylic acids viz. [Formula: see text] , with moderate values of n 10, 11, 12, and 14) in combination with a cationic surfactant decyltrimethylammonium bromide (C₁₀TAB) in buffered aqueous medium at different pH (6.0, 6.5, 6.8, and 8.0 for bola 10, 11, 12, and 14, respectively). Three pH dependent states of the solutions are observed: clear (high pH > 8), turbid and translucent (mid pH ≈ 6-8), and viscous inhomogeneous oil-like state (low pH < 6). The micelle size varies from 6.24 to 7.43 nm at pH 12, for vesicles the values are large (220-296 nm), and small (∼30-70 nm) in the pH range of 6.0-8.0. The self-assembly formation properties of their mixtures are herein investigated using different techniques viz. UV-vis spectroscopy, fluorescence spectroscopy, dynamic light scattering, laser confocal scanning microscopy, and isothermal titration calorimetry. The formed vesicles are fairly polydisperse, and show overall spherical shape. Formation of the bilayer assemblies, and their conversion to mixed micelles by the temperature effect are observed from steady state fluorescence anisotropy measurements. Micellization of the mixed bola-C₁₀TAB species is endothermic and fairly entropy controlled; their formation/deformation is pH sensitive. They have spherical morphologies, and once formed at the right pH they are found to be very stable in terms of time. Thus, these vesicles have prospects for encapsulation and delivery of materials like drugs, and other substrates by controling the acid-base conditions of the system environment. The formed mixed micelles, and vesicles are expected to be low toxic, and thus green materials in nature with wider application possibilites.