title: Zinc-specific intramolecular excimer formation in TQEN derivatives: fluorescence and zinc binding properties of TPEN-based hexadentate ligands.
abstract: Zn(2+)-induced fluorescence enhancement of the TPEN (N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine)-based ligand, N,N-bis(1-isoquinolylmethyl)-N',N'-bis(pyridylmethyl)ethylenediamine (N,N-1-isoBQBPEN, 1b), has been investigated. Upon Zn(2+) binding, 1b shows a fluorescence increase (ϕZn = 0.028) at 353 and 475 nm. The fluorescence enhancement at longer wavelengths is due to intramolecular excimer formation of two isoquinolines and is specific for Zn(2+); Cd(2+) induces very small fluorescence at 475 nm (ICd/IZn = 10%). The excimer formation of the [Zn(1b)](2+) complex in the excited state is supported by the time-dependent DFT calculation. Neither long-wavelength fluorescence nor excimer formation is observed in the Zn(2+) complex of N,N'-1-isoBQBPEN (2b). The quinoline analog N,N-BQBPEN (1a) exhibits similar but significantly smaller excimer formation. Thermodynamic and kinetic comparisons of Zn(2+) binding properties of ethylenediamine-based hexadentate ligands with pyridines and (iso)quinolines are comprehensively discussed.
authors.affiliation: KYOUSEI Science Center, Nara Women's University, Nara 630-8506, Japan. mikata@cc.nara-wu.ac.jp.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Mikata
authors.forename: Saaya
authors.initials: S
authors.lastname: Takeuchi
authors.forename: Eri
authors.initials: E
authors.lastname: Higuchi
authors.forename: Ayaka
authors.initials: A
authors.lastname: Ochi
authors.forename: Hideo
authors.initials: H
authors.lastname: Konno
authors.forename: Kazuma
authors.initials: K
authors.lastname: Yanai
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Sato
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005029:Ethylenediamines / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007546:Isoquinolines / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D005029:Ethylenediamines; D007546:Isoquinolines; D008024:Ligands; D011725:Pyridines; C031234:ethylenediamine; D015032:Zinc; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine