Rigid-rod beta-barrels as lipocalin models: Probing confined space by carotenoid encapsulation

Herein, we describe the design, synthesis, structure, and function of synth etic, supramolecular beta-barrel models. Assembly of octi(p-phenylene)s wit h complementary -Lys-Leu-Lys-NH2 and Glu-Leu-Glu-NH2 side chains yielded wa ter-soluble rigid-rod beta-barrels of precise length and with flexible diam eter. A hydrophobic interior was evidenced by guest encapsulation. Host-gue st complexes with planarized, monomeric beta-carotene within tetrameric rig id-rod beta-barrels, and disc micellar astaxanthin J-aggregates surrounded by about dodecameric rigid-rod "bicycle tires" were prepared from mixed mic elles by dialytic detergent removal. The significance of these findings for future bioorganic chemistry in confined, intratoroidal space is discussed in comparison with pertinent biological examples.