Amino acids recognition by water-soluble uncharged porphyrin tweezers: Spectroscopic evidences in high optical density solutions

Small angle X-ray measurements on concentrated solutions of Cobalt-bis-porphyrins showed, at all theinvestigated concentration values, the presence of small aggregates which possess a sphere-like shapewith a homogeneous electron density distribution. Such an aggregation, however, is proven not to affectthe binding properties of the molecules with amino acids. Indeed, the Cobalt ion of the bis-porphyrins areavailable for coordinating the nitrogen atom of the amino acid to form a stable complex, as indicated byUV–vis and circular dichroism spectroscopy. The ability of these uncharged water-soluble bis-porphyrinsto act as molecular sensors of amino acids in a wide concentration range takes great relevance in biosen-sing applications for which high concentration might be required.