Mini review: Fluorescent heteroditopic ligands of metal ions

In addition to being a covalent linker in molecular conjugation chemistry, the function of a 1,2,3-triazolyl moiety resulting from the copper(I)-catalyzed azide-alkyne cycloaddition reaction as a ligand for metal ions is receiving considerable attention. In this work, we characterize the thermodynamic and kinetic effects of incorporating a 1,2,3-triazolyl group in a multidentate ligand scaffold on metal coordination in the context of fluorescent zinc(II) indicator development. Ligands L14, BrL14, and FL14 (1,4-isomers) contain the 1,4- disubstituted-1,2,3-triazolyl group that is capable of binding with zinc(II) in conjunction with a di(2-picolylamino) (DPA) moiety within a multidentate ligand scaffold. The 1,2,3-triazolyl in the 1,4-isomers is therefore “integrated” in chelation. The 1,5-isomers L15, BrL15, and FL15 contain 1,2,3-triazolyls that are excluded from participating in zinc(II) coordination. These 1,2,3- triazolyls are “passive linkers”. Zinc(II) complexes of 2:1 (ligand/metal) stoichiometry are identified in solution using 1H NMR spectroscopy and isothermal titration calorimetry (ITC), and in one case, characterized in the solid state. The 1:1 ligand/zinc(II) affinity ratio of L14 over L15, which is attributed to the affinity enhancement of a 1,2,3-triazolyl group to zinc(II) over that of the solvent acetonitrile, is quantified at 18 (−1.7 kcal/mol at 298 K) using an ITC experiment. Fluorescent ligands FL14 and FL15 are evaluated for their potential in zinc(II) sensing applications under pH neutral aqueous conditions. The 1,4-isomer FL14 binds zinc(II) both stronger and faster than the 1,5-isomer FL15. Visualization of free zinc(II) ion distribution in live HeLa cells is achieved using both FL14 and FL15. The superiority of FL14 in staining endogenous zinc(II) ions in live rat hippocampal slices is evident. In summation, this work is a fundamental study of 1,2,3-triazole coordination chemistry, with a demonstration of its utility in developing fluorescent indicators.

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“…These observations are expected for indicators operating via a metal binding affected photoinduced electron transfer (PET) process. 70 …”

Section: Resultsmentioning

confidence: 99%

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

et al. 2013

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“…11) [97]. When a metal ion encounters the ligand, it associates with the high-affinity binding site (the rectangle in Fig.…”

Section: Avbs In Fluorescent Heteroditopic Ligandsmentioning

confidence: 99%

5-Arylvinylene-2,2′-bipyridyls: Bright “push–pull” dyes as components in fluorescent indicators for zinc ions

Zhu

Younes

Zhao

et al. 2015

Journal of Photochemistry and Photobiology A: Chemistry

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This article reviews the zinc(II)-dependent photophysical properties of arylvinylbipyridines (AVBs), a class of fluoroionophores in which 2,2′-bipyridyl and an aryl moiety are electronically conjugated. Zinc(II) binding of an AVB may lead to an emission bathochromic shift of the fluoroionophore without diminishing its fluorescence quantum yield. This observation can be explained using the excited state model of electron donor–π bridge–electron acceptor “push–pull” fluorophores, in which the bipy moiety acts as an electron acceptor, and zinc(II)-coordination strengthens its electron affinity. The spectral sensitivity of bipy-containing fluoroionophores, such as AVBs, to zinc(II) can be exploited to prepare fluorescent indicators for this ion. In several cases, AVB moieties are incorporated in fluorescent heteroditopic ligands, so that the variation of zinc(II) concentration over a relatively large range can be correlated to fluorescence changes in either intensity or color. AVB fluoroionophores are also used to introduce an intramolecular Förster resonance energy transfer (FRET) strategy for creating zinc(II) indicators with high photostability and a narrow emission band, two desired characteristics of dyes used in fluorescence microscopy.

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“…Addition of Zn II quenches the anthryl fluorescence due to the formation of a weakly-emissive complex (f f ¼ 0.03). The fact that fluorescence quenching upon Zn II -coordination occurs without a significant change in the absorption band of the fluorophore (anthryl) led us to hypothesise that an intramolecular PET pathway is open in the excited state of Zn II complex of clickate 2, which is supported by the frontier MO analysis and cyclic voltammetric data (57). Coordination of Zn II to the clickate lowers the reduction potential of the clickate moiety, which provides the thermodynamic driving force for PET from the LUMO of the excited anthryl to the LUMO of the Zn II -coordinated clickate (58,59).…”

Section: Supramolecular Chemistry 703mentioning

confidence: 96%

Zn^II and Pb^II coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of ‘clickate’–appended anthracene

Younes

Clark

Zhu

2012

Supramolecular Chemistry

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2012) Zn II and PbII coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of 'clickate'-appended anthracene, Supramolecular Chemistry, 24:9, 696-706,The effect of metal coordination of 2-(1-(9-anthryl)methyl-1,2,3-triazol-4-yl)-6-(1-n-octyl-1,2,3-triazol-4-yl)pyridine (2) on the emission of the appended anthryl group was investigated in acetonitrile. The tridentate 2,6-bis(1,2,3-triazol-4-yl)pyridyl ligand included in 2 is referred herein as 'clickate'. Titrating zinc(II) perchlorate or zinc(II) chloride into the solution of fluorescent ligand 2 results in quenching, which is attributed to the formation of a dark 1:1 Zn II complex of 2. Frontier molecular orbital analysis and cyclic voltammetric data support the occurrence of photoinduced electron transfer from the excited state of the anthryl group to the Zn II -bound clickate moiety, which relaxes the excited fluorophore non-radiatively, i.e. quenches fluorescence. Fluorescence quenching of clickate 2 upon forming the Pb II complex was also observed. The Zn II /Pb II -coordination chemistry of clickate was characterised via X-ray crystallography, isothermal titration calorimetry, 1 H NMR spectroscopy and absorption spectroscopy using the symmetrically substituted clickate 2,6-bis(1-n-octyl-1,2,3-triazol-4 yl)pyridine (1).

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Mini review: Fluorescent heteroditopic ligands of metal ions

Cited by 25 publications

References 124 publications

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

5-Arylvinylene-2,2′-bipyridyls: Bright “push–pull” dyes as components in fluorescent indicators for zinc ions

Zn^II and Pb^II coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of ‘clickate’–appended anthracene

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Mini review: Fluorescent heteroditopic ligands of metal ions

Cited by 25 publications

References 124 publications

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

Integrated and Passive 1,2,3-Triazolyl Groups in Fluorescent Indicators for Zinc(II) Ions: Thermodynamic and Kinetic Evaluations

5-Arylvinylene-2,2′-bipyridyls: Bright “push–pull” dyes as components in fluorescent indicators for zinc ions

ZnII and PbII coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of ‘clickate’–appended anthracene

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Zn^II and Pb^II coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of ‘clickate’–appended anthracene