Chiral Fluorescent Uranyl-Salen Oligomer for Enantiomeric Supramolecular Recognition of Tryptophan

A new chiral oligomer based on oligo-(pphenyleneethynylene), having many Lewis acid metal centers (uranyl ions), able to efficiently recognize tryptophan (Trp), is herein reported. The presence of a conjugated oligomeric scaffold allows for obtaining the first fluorescent uranyl-oligomer, with a significant limit of detection (sub-ppm). This oligomer has been found to show high enantioselectivity for the L-enantiomer of Trp (more than 40:1) relative to the D-form, with high selectivity relative to other amino acid derivatives. Oligomers, having a length of around 10 nm, exhibited increased size due to the formation of non-covalent host-guest interactions with Trp, leading to micrometer-sized structures, as observed by DLS measurements. This is the first example of a fluorescent uranylsalen oligomer able to recognize Trp.