Chiral induction, memory, and amplification in porphyrin homoaggregates based on electrostatic interactions.

Supramolecular chirality in two configurational homoaggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D- and L-alanine in acidic water (see picture). The chirality can be further memorized and enforced through strong electrostatic interactions between TPPS aggregates and achiral poly(allylamine) [PAA].Supramolecular chirality in two configurational homoaggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D- and L-alanine (Ala) in acidic water, respectively. The induced supramolecular chirality can be further memorized and enforced, even after complete removal of Ala or in the presence of excess Ala with the opposite configuration, through strong electrostatic interactions with achiral poly(allylamine) [PAA]. The ionic chiral interactions between TPPS and Ala or PAA are characterized by means of UV/Vis absorption and circular dichroism spectrometry. Fluorescence spectroscopy and atomic force microscopy are used as complementary techniques. On the basis of the comprehensive experimental results, a possible mechanism for chiral induction, memory, and amplification of TPPS homoaggregates by chiral amino acids and achiral PAA is proposed. Thus, we demonstrate a novel strategy to realize chiral memory in supramolecular systems by polyelectrolytes through hierarchical electrostatic self-assembly.