title: Supramolecular chirogenesis in zinc porphyrins: interaction with bidentate ligands, formation of tweezer structures, and the origin of enhanced optical activity.
abstract: The complexation behavior, binding properties, and spectral parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral bidentate guests (diamines and amino alcohols) have been studied by means of UV-vis, CD, fluorescence, (1)H NMR, and ESI MS techniques. It was found that the guest structure plays a decisive role in the chirogenesis pathway. The majority of bidentate ligands (except those geometrically unsuitable) exhibit two major equilibria steps: the first guest ligation leading to formation of the 1:1 host-guest tweezer structure (K(1)) and the second guest molecule ligation (K(2)) forming the anti bis-ligated species (1:2). The second ligation is much weaker (K(1) >> K(2)) due to the optimal geometry and stability of the 1:1 tweezer complex. The enhanced conformational stability of the tweezer complex ensures an efficient chirality transfer from the chiral guest to the achiral host, consequently inducing a remarkably high optical activity in the bis-porphyrin.
authors.affiliation: Entropy Control Project, ICORP, JST, 4-6-3 Kamishinden, Toyonaka-shi, Osaka 560-0085, Japan. victrb@inoue.jst.go.jp
authors.forename: Victor V
authors.initials: VV
authors.lastname: Borovkov
authors.forename: Juha M
authors.initials: JM
authors.lastname: Lintuluoto
authors.forename: Guy A
authors.initials: GA
authors.lastname: Hembury
authors.forename: Makiko
authors.initials: M
authors.lastname: Sugiura
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Arakawa
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D008024:Ligands; D008665:Metalloporphyrins / Q000737:chemistry*; D009904:Optical Rotation; D013057:Spectrum Analysis; D013237:Stereoisomerism
chemical_list: D008024:Ligands; D008665:Metalloporphyrins; C017802:zinc hematoporphyrin