Formation of supramolecular structures of chiral porphyrin-bile salt conjugates

Porphyrin derivatives play a fundamental role in supramolecular chemistry thanks to their unique physical-chemical and structural characteristics, which make them versatile building blocks for construction of systems with broad interesting scientific and technological applications. Supramolecular chirality, one of the most fascinating aspects of supramolecular chemistry1, allows the transfer of asymmetry information, within multimolecular systems through noncovalent interactions. It has profound implications in the field of nanotechnology and in the construction of sensor devices with stereoselective properties2. The proposed project is aimed at the synthesis and characterization of chiral porphyrin derivatives, obtained through covalent conjugation with bile salts. In addition to inducing chirality, conjugation allows to impart amphiphilic characteristics to the aromatic macrocycle, important for their aggregation. Bile salts, natural surfactants with an important biological role, in fact show a rigid and chiral amphiphilic molecular structure, typical of steroids, which gives them specific auto-associative characteristics. These properties can be effectively exploited for the construction of highly organized supramolecular systems in aqueous solvents, characterized by a high degree of asymmetry3. Circular dichroism studies have shown the presence of highly organized supramolecular structures, in water/organic solvent mixtures in different ratio, characterized by intense chirality, detectable by very intense CD signals. Morphological studies (SEM, AFM) have shown the high regularity of the morphology of the structures obtained, well-formed tubules, with a hierarchical fine structure (Fig. 1), were imaged, whose size (from nano to micro scale) depends on the selected conditions. Slight variations in solvents composition can strongly affect the kinetic of aggregation.