title: Fluorescent zinc sensor with minimized proton-induced interferences: photophysical mechanism for fluorescence turn-on response and detection of endogenous free zinc ions.
abstract: A new fluorescent zinc sensor (HNBO-DPA) consisting of 2-(2'-hydroxy-3'-naphthyl)benzoxazole (HNBO) chromophore and a di(2-picolyl)amine (DPA) metal chelator has been prepared and examined for zinc bioimaging. The probe exhibits zinc-induced fluorescence turn-on without any spectral shifts. Its crystal structure reveals that HNBO-DPA binds a zinc ion in a pentacoordinative fashion through the DPA and HNBO moieties. Steady-state photophysical studies establish zinc-induced deprotonation of the HNBO group. Nanosecond and femtosecond laser flash photolysis and electrochemical measurements provide evidence for zinc-induced modulation of photoinduced electron transfer (PeT) from DPA to HNBO. Thus, the zinc-responsive fluorescence turn-on is attributed to suppression of PeT exerted by deprotonation of HNBO and occupation of the electron pair of DPA, a conclusion that is further supported by density functional theory and time-dependent density functional theory (DFT/TD-DFT) calculations. Under physiological conditions (pH 7.0), the probe displays a 44-fold fluorescence turn-on in response to zinc ions with a K(d) value of 12 pM. The fluorescent response of the probe to zinc ions is conserved over a broad pH range with its excellent selectivity for zinc ions among biologically relevant metal ions. In particular, its sensing ability is not altered by divalent transition metal ions such as Fe(II), Cu(II), Cd(II), and Hg(II). Cell experiments using HNBO-DPA show its suitability for monitoring intracellular zinc ions. We have also demonstrated applicability of the probe to visualize intact zinc ions released from cells that undergo apoptosis. More interestingly, zinc-rich pools in zebrafish embryos are traced with HNBO-DPA during early developmental stages. The results obtained from the in vitro and in vivo imaging studies demonstrate the practical usefulness of the probe to detect zinc ions.
authors.affiliation: Department of Materials Science & Engineering, Seoul National University, San 56-1, Sillim 9-dong, Gwanak-gu, Seoul 151-744, Korea.
authors.forename: Ji Eon
authors.initials: JE
authors.lastname: Kwon
authors.forename: Sumin
authors.initials: S
authors.lastname: Lee
authors.forename: Youngmin
authors.initials: Y
authors.lastname: You
authors.forename: Kyung-Hwa
authors.initials: KH
authors.lastname: Baek
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Jaeheung
authors.initials: J
authors.lastname: Cho
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Injae
authors.initials: I
authors.lastname: Shin
authors.forename: Soo Young
authors.initials: SY
authors.lastname: Park
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
mesh_terms: D000588:Amines / Q000737:chemistry*; D000818:Animals; D001583:Benzoxazoles / Q000737:chemistry*; D002614:Chelating Agents / Q000138:chemical synthesis*; D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D004579:Electron Transport; D004625:Embryo, Nonmammalian; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000138:chemical synthesis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D057054:Molecular Imaging; D015394:Molecular Structure; D010782:Photolysis; D010848:Picolinic Acids / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D015027:Zebrafish; D015032:Zinc / Q000032:analysis*
chemical_list: C501847:2,2'-dipicolylamine; D000588:Amines; D001583:Benzoxazoles; D002614:Chelating Agents; D005456:Fluorescent Dyes; D010848:Picolinic Acids; D011522:Protons; D015032:Zinc