title: High Affinity Macrocycle Threading by a Near-Infrared Croconaine Dye with Flanking Polymer Chains.
abstract: Croconaine dyes have narrow and intense absorption bands at ∼800 nm, very weak fluorescence, and high photostabilities, which combine to make them very attractive chromophores for absorption-based imaging or laser heating technologies. The physical supramolecular properties of croconaine dyes have rarely been investigated, especially in water. This study focuses on a molecular threading process that encapsulates a croconaine dye inside a tetralactam macrocycle in organic or aqueous solvent. Macrocycle association and rate constant data are reported for a series of croconaine structures with different substituents attached to the ends of the dye. The association constants were highest in water (Ka ∼ 10(9) M(-1)), and the threading rate constants (kon) increased in the solvent order H2O > MeOH > CHCl3. Systematic variation of croconaine substituents located just outside the croconaine/macrocycle complexation interface hardly changed Ka but had a strong influence on kon. A croconaine dye with N-propyl groups at each end of the structure exhibited a desirable mixture of macrocycle threading properties; that is, there was rapid and quantitative croconaine/macrocycle complexation at relatively high concentrations in water, and no dissociation of the preassembled complex when it was diluted into a solution of fetal bovine serum, even after laser-induced photothermal heating of the solution. The combination of favorable near-infrared absorption properties and tunable mechanical stability makes threaded croconaine/macrocycle complexes very attractive as molecular probes or as supramolecular composites for various applications in absorption-based imaging or photothermal therapy.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame , 236 Nieuwland Science Hall, Notre Dame, Indiana 46556, United States.
authors.forename: Wenqi
authors.initials: W
authors.lastname: Liu
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame , 236 Nieuwland Science Hall, Notre Dame, Indiana 46556, United States.
authors.forename: Evan M
authors.initials: EM
authors.lastname: Peck
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame , 236 Nieuwland Science Hall, Notre Dame, Indiana 46556, United States.
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Smith
mesh_terms: D004396:Coloring Agents / Q000737:chemistry*; D047028:Macrocyclic Compounds / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D013056:Spectrophotometry, Ultraviolet; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D004396:Coloring Agents; D047028:Macrocyclic Compounds; D011108:Polymers