pH-dependent self-assembling behavior of imidazole-containing polyaspartamide derivatives

A series of pH-sensitive polyaspartamide derivatives were prepared by grafting 1-(3-aminopyl)imidazole (API) and O-(2-aminoethyl)-O'- methylpolyethylene glycol (MPEG, Mw:5000), as a pH sensitive moiety and hydrophilic group, respectively. The effect of the polymer composition was examined. The UV transmittance of the polymer solutions showed a sharp pH-dependence around pH 7 as a result of protonation or unprotonation of the imidazole rings, and a high buffering capacity between pH 5.5 and 7. Reversible pH-dependent aggregation and deaggregation behavior was observed. The mean size of the prepared polymer aggregates with increasing degree of substitution (DS) of API ranged from 180 and 220 nm, while that of the octadecylamine-conjugated polyaspartamide ones approximately 100 nm. The CAC of MPEG/ API-grafted polyasparamides decreased with increasing DS of API and that of the octadecylamine-conjugated polyaspartamide aggregates increased with decreasing pH. These pH-sensitive polyaspartamide derivatives are expected to have many applications in areas, such as an intracellular or tumor targeting drug-delivery carrier that is triggered by very small changes in pH.