Bioorganic chemistry à la baguette: studies on molecular recognition in biological systems using rigid-rod molecules.

Initial studies using rigid-rod molecules or "baguettes" to address bioorganic topics of current scientific concern are reported. It is illustrated how transmembrane oligo(p-phenylene)s as representative model rods can be tuned to recognize lipid bilayer membranes either by their thickness or polarization. The construction of otherwise problematic hydrogen-bonded chains along transmembrane rods yields "proton wires," which act by a mechanism that is central in bioenergetics but poorly explored by means of synthetic models. Another example focuses on multivalent ligands assembling rigid-rod cell-surface receptors into transmembrane dynamic arene arrays. The potassium transport mediated by these ligand-receptor complexes provides experimental support for the potential biological importances of the controversial cation-pi mechanism. More complex supramolecular architecture is portrayed in the first artificial beta-barrels. It is shown how programmed assembly of toroidal rigid-rod supramolecules in detergent-free water permits control of diameter of the chemical nature of their interior. Reversed rigid-rod beta-barrels are assembled to function as self-assembled ionophores, ion channel models, and transmembrane nanopores. The potential of future intratoroidal chemistry is exemplified by encapsulation and planarization of beta-carotene in water and the construction of transmembrane B-DNA at the center of a second-sphere host-guest complex à al baguette.