Synthesis of diverse reverse self-assembled structures including reverse vesicles in cyclohexane using lecithin and bulky organic salts

초록

The reverse self-assembly of lecithin in nonpolar solvents typically results in the formation of reverse spherical micelles. In this study, we examined the effects of organic salts (bulkier in size, R4N+X¯; non-metallic salt) with varying molecular weights with purely aliphatic and aliphatic-aromatic moieties, such as tetramethylammonium chloride (TMACl), tetraethylammonium chloride (TEACl), and trimethylphenylammonium chloride (TPACl), on the reverse self-assembly of lecithin in dilute solutions. These bulkier organic salts (OS) do not dissolve in nonpolar solvents, such as cyclohexane; however, lecithin/OS mixtures readily dissolve in such solvents because of the ionic interactions between the OS and lecithin headgroups. Systematically increasing the salt concentration resulted in a structural transition, beginning with the formation of reverse spherical micelles, progressing to reverse cylindrical micelles, and eventually leading to the formation of reverse bilayer structures such as reverse vesicles. Importantly, the capacity of these salts to drive structural transitions followed the order: TPACl > TEACl > TMACl, correlating with the increasing size of the salts such as methyl, ethyl, and phenyl groups. This transition was confirmed by fitting and indirect Fourier transform (IFT) analysis of small-angle X-ray scattering (SAXS) data. Additionally, hydrophilic dye, methylene blue (MB), can be encapsulated within reverse micelles and vesicles, with MB expected to localize in the hydrophilic core of the reverse micelles or within the hydrophilic bilayer of the reverse vesicles. These findings suggest the potential of these structures for controlled solute delivery in the wide range applications from biology to medicine.

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