pH-sensitive transformation of the peptidic bolaamphiphile self-assembly: Exploitation for the pH-triggered chemical reaction

Control of the macroscopic self-assembled structure of the amphiphilic molecule has been a challenging issue in micro/nanotechnologies. In this study, the microtubular self-assembly of a novel peptidic bolaamphiphile, bis(N-a-amido-glycylglycine)-1,10-decene dicarboxylate, which undergoes reversible structural transformation between microtubes and precipitates as a function of pH, was exploited for pH-triggered chemical release. At neutral and basic conditions above a pH of 6, the peptidic bolaamphiphilic molecule self-assembled to form tubular structures several hundreds of micrometers in length. When the solution became acidic below a pH of 4, the tubular assembly disintegrated to form aggregated precipitates. The reversible transformation of precipitate to microtube was achieved by raising the pH above 6. From the Raman spectroscopy results, it was revealed that the hydrogen bonds of the amide group and carboxylate were enhanced under the acidic conditions. These variation of the hydrogen bonds resulted in precipitation of peptidic bolaamphiphilic molecules while rupturing the microtubular structure. The pH-sensitive microscopic structural transformation was exploited for release of a chemical in which the pH-triggered release of a model chemical, a fluorescence dye of ANS, was demonstrated. The ANS dye was released gradually with decreasing pH, which suggests gradual disintegration of the microtubular self-assembly. Furthermore, this pH-triggered release of a chemical was exploited for the chemical reaction of gold ion reduction to produce solid clusters. This study demonstrated the reversible transformation of peptidic bolaamphiphile and its application as a pH-sensitive host matrix. (C) 2013 Elsevier B.V. All rights reserved.