A fluorescent heteroditopic ligand responding to free zinc ion over six orders of magnitude concentration range

Zhang, Lu; Murphy, Christopher S.; Kuang, Gui‐Chao; Hazelwood, Kristin L.; Constantino, Manuel H.; Davidson, Michael W.; Zhu, Lei

doi:10.1039/b918729d

Cited by 22 publications

(17 citation statements)

References 35 publications

(33 reference statements)

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“…If the three coordination states of the ligand (free, mono-, and di-coordinated) have distinct fluorescence spectra, the emission intensity and/or wavelength of the ligand upon single-wavelength excitation is a function of [Zn 2+ ] over the collective response range of two coordination sites. 16 In this paper, a new design of fluorescent heteroditopic ligands is reported, which shows a continuous emission color change from blue to orange over a concentration gradient of Zn 2+ in the organic solvent acetonitrile. A limitation of the selected rhodamine spirolactam ring-opening chemistry in the new design is also described, which at this point prevents the reported prototype structure from being applied as an indicator in aqueous-based systems.…”

Section: Introductionmentioning

confidence: 99%

“…12–14 Our group has focused on developing indicators for Zn 2+ with a concentration coverage appropriate for the uniquely broad range of “free” Zn 2+ ions 15 in mammalian cellular systems. 16,17 Most known indicators for Zn 2+ report concentration variations within three orders of magnitude under physiological conditions. This rather limited range originates from the species distribution makeup of a monotopic (one binding site) indicator, and it is inadequate to cover the entire physiological range of Zn 2+ observed in mammalian cells.…”

Section: Introductionmentioning

confidence: 99%

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Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

2012

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The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2′-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn(ClO4)2 in acetonitrile. Coordination of Zn2+ stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn(ClO4)2, the non-fluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn2+-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e. from blue to green to orange as [Zn2+] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn2+ coordination.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

2012

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“…33 We hypothesized that the protonation of the electron-donating tertiary amino groups reduces the efficiency of PET, which results in high background fluorescence (Figure 2). Therefore, decreasing the pK a of the amino groups by strategically installing electron-withdrawing components in proximity shall increase the efficiency of PET, hence lowering the background fluorescence.…”

Section: Resultsmentioning

confidence: 99%

“…33 Compound 1 contains a phenylvinyl-bipyridyl fluorophore whose fluorescence is quenched via intramolecular photoinduced electron transfer (PET) 34 from the amino groups in the high-affinity pentadentate metal coordination site (boxed in blue). Zinc(II)-coordination at the high-affinity site lowers the rate of PET, hence allowing the fluorescence to occur.…”

Section: Introductionmentioning

confidence: 99%

Balance between Fluorescence Enhancement and Association Affinity in Fluorescent Heteroditopic Indicators for Imaging Zinc Ion in Living Cells

et al. 2011

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A fluorescent heteroditopic indicator for zinc(II) ion possesses two different zinc(II) binding sites. The sequential coordination of zinc(II) at the two sites can be transmitted into distinct fluorescence changes. In the heteroditopic ligand system that our group developed, the formations of mono- and di-zinc(II) complexes along an increasing gradient of zinc(II) concentration lead to fluorescence enhancement and emission bathochromic shift, respectively. The extents of these two changes determine the sensitivity, and ultimately, the effectiveness of the heteroditopic indicator in quantifying zinc(II) ion over a large concentration range. In this work, a strategy to increase the degree of fluorescence enhancement upon the formation of the mono-zinc(II) complex of a heteroditopic ligand under simulated physiological conditions is demonstrated. Fluorination of the pyridyl groups in the pentadentate N,N,N′-tris(pyridylmethyl)ethyleneamino group reduces the apparent pKa value of the high-affinity site, which increases the degree of fluorescence enhancement as the mono-zinc(II) complex is forming. However, fluorination impairs the coordination strength of the high-affinity zinc(II) binding site, which in the triply-fluorinated ligand reduces the binding strength to the level of the low-affinity 2,2′-bipyridyl. The potential of the reported ligands in imaging zinc(II) ion in living cells was evaluated. The subcellular localization properties of two ligands in five organelles were characterized. Both benefits and deficiencies of these ligands were revealed which provides directions for the near future in this line of research.

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“…233,234 Compound 32 (Scheme 11) undergoes a more than 5-fold fluorescence enhancement followed by emission bathochromic shift over a range of 0.1 nM to 0.1 mM of free Zn(II). 234 The deficiency of this compound is still the emission band separation, which is too small (32 nm) for the two bands to be captured by two different emission filter sets, for example, blue (i.e., 420 – 480 nm) and green (i.e., 510 – 560 nm).…”

Section: Zn(ii) Coordination Chemistrymentioning

confidence: 99%

Zn(ii)-coordination modulated ligand photophysical processes – the development of fluorescent indicators for imaging biological Zn(ii) ions

et al. 2014

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Molecular photophysics and metal coordination chemistry are the two fundamental pillars that support the development of fluorescent cation indicators. In this article, we describe how Zn(II)-coordination alters various ligand-centered photophysical processes that are pertinent to developing Zn(II) indicators. The main aim is to show how small organic Zn(II) indicators work under the constraints of specific requirements, including Zn(II) detection range, photophysical requirements such as excitation energy and emission color, temporal and spatial resolutions in a heterogeneous intracellular environment, and fluorescence response selectivity between similar cations such as Zn(II) and Cd(II). In the last section, the biological questions that fluorescent Zn(II) indicators help to answer are described, which have been motivating and challenging this field of research.

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A fluorescent heteroditopic ligand responding to free zinc ion over six orders of magnitude concentration range

Abstract: A fluorescent heteroditopic ligand useful in live-cell imaging studies responds to free zinc ion concentration over a range of six orders of magnitude in a buffered aqueous solution via dual-channel fluorescence.

Cited by 22 publications

References 35 publications

Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

Balance between Fluorescence Enhancement and Association Affinity in Fluorescent Heteroditopic Indicators for Imaging Zinc Ion in Living Cells

Zn(ii)-coordination modulated ligand photophysical processes – the development of fluorescent indicators for imaging biological Zn(ii) ions

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