Monoolein cubic phase containing acidic proteinoid: pH-dependent release

Objective: Monoolein (MO) cubic phase containing acidic proteinoid was prepared for a pH-dependent release. Methods: The acidic proteinoid was prepared by a thermal-condensation reaction of Asp and Leu (9.85/0.15 in molar ratio). To prepare MO cubic phase, molten MO was hydrated with the proteinoid solution in distilled water. For pH-dependent release experiment, amaranth was included as an anionic dye, and either auramine O or methylene blue was contained as a cationic dye. Results: The release of amaranth from the cubic phase was promoted under neutral and alkali conditions, possibly because of electrostatic repulsions between the anionic dye and the ionized carboxylic group of the acidic proteinoid. On the contrary, the releases of auramine O and methylene blue were suppressed under neutral and alkali conditions, probably because of electrostatic interactions between the cationic dyes and the ionized carboxylic group. Conclusion: The acidic proteinoid is believed to control the releases in response to change in pH.