Supramolecular ligands: Monomer structure and protein ligation capability

The aim of this work was to define the chemical structure of compounds self -assembling in water solutions, which appear to interact with proteins as s ingle ligands with their supramolecular nature preserved. For this purpose the ligation to proteins of bis azo dyes, represented by Congo red and its derivatives with designed structural alterations, were tested. The three pa rameters which characterize the reactivity of supramolecular material were determined in the same conditions for all studied dyes. These were: A) stab ility of the assembly products; B) binding to heat-denatured protein (human IgG); and C) binding to native protein (rabbit antibodies in the immune co mplex) measured by the enhancement of hemagglutination. The structural diff erences between the Congo red derivatives concerned the symmetry of the mol ecule and the structure of its non-polar component, which occupies the cent ral part of the dye molecule and is thought to be crucial for self-assembly . Other dyes were also studied for the same purpose: Evans blue and Trypan blue, bis-ANS and ANS, as well as a group of compounds with a structural de sign unlike that of bis azo dyes. Compounds with rigid elongated symmetric molecules with a large non-polar middle fragment are expected to form a rib bon-like supramolecular organization in assembling. They appeared to have l igation properties related to their self-assembling tendency. The compounds with different structures, not corresponding to bis azo dyes, did not reve al ligation capability, at least in respect to native protein. The conditio ns of binding to denatured proteins seem less restrictive than the conditio ns of binding to native molecules. The molten hydrophobic protein interior becomes a new binding area allowing for complexation of even non-assembled molecules. (C) Societe francaise de biochimie et biologie moleculaire / Els evier, Paris.