Coumarin-Based Chemosensors for Zinc(II):  Toward the Determination of the Design Algorithm for CHEF-Type and Ratiometric Probes

Abstract

The synthesis of a series of coumarin-based chemosensor assemblies for zinc is detailed, using established and novel synthetic pathways. Variations of the nature of the chelating unit (DPA or cyclen), position of the attachment point of the chelating unit (3- or 4-position), and nature of the 7-substituent (-OH, -OAc, or -NR2) on the coumarin play a crucial role in whether, and to what extent, a CHEF-type or ratiometric response of the chemosensor is observed. Solvent effects are also discussed. The chemosensors were shown to be competent for detecting zinc pools in cultured rat pituitary (GH3) and hepatoma (H4IIE) cell lines. The work further defines the design algorithms for zinc-selective CHEF-type and ratiometric chemosensors.

Coumarin-Derived Fluorescent Chemosensors

“…Another series of coumarin-derived chemosensors 39-42 belong to the CHEF-type and have been showed to Table 3. Structures and references of coumarin-derived chemosensors for Zn(II) ions be competent for detecting zinc pools in cultured rat pituitary (GH3) and hepatoma (H4IIE) cell lines (N. C. Lim et al, 2005). Coumarin 44 is a fluorescent sensor for Zn 2+ and exhibits lower background fluorescence due to intramolecular PET but upon mixing with Zn 2+ in aqueous ethanol, a turn-on fluorescence emission is observed (Su et al, 2010).…”

Fe(III)-Induced FRET-On: Energy Transfer from Rhodamine 6G to Nile Red

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excimer/exciplex formation, 4 imine isomerization, 5 chelationenhanced fluorescence (CHEF), 6 and fluorescence resonance energy transfer (FRET).7 Among them, at present, the FRET is an active field in chemistry and biochemistry due to its potential practical benefits in cell physiology, optical therapy, as well as selective and sensitive sensing toward target molecular or ionic species. FRET arises from an excited-state energy interaction between two fluorophores in which a donor fluorophore, in its excited-state, transfers energy to an acceptor fluorephore.

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“…excimer/exciplex formation, 4 imine isomerization, 5 chelationenhanced fluorescence (CHEF), 6 and fluorescence resonance energy transfer (FRET).…”

“…The design of fluorescent chemosensors is mainly based on photo-induced electron/energy transfer (PET), 1 metal-ligand charge transfer (MLCT), 2 intramolecular charge transfer (ICT), 3 excimer/exciplex formation, 4 imine isomerization, 5 chelationenhanced fluorescence (CHEF), 6 and fluorescence resonance energy transfer (FRET). 7 Among them, at present, the FRET is an active field in chemistry and biochemistry due to its potential practical benefits in cell physiology, optical therapy, as well as selective and sensitive sensing toward target molecular or ionic species.…”

“…9,45.3,61.6,69.8,96.5,105.4,106.9,Notes 109.8,118.4,124.9,126.2,128.1,131.3,134.3,140.0,147.1,151.0,152.3,161.5,183.4 13 C NMR (100 MHz) δ 12. 6, 21.7, 45.1, 65.6, 68.0, 96.2, 105.2, 106.3, 109.6, 118.3, 124.7, 126.1, 127.8, 128.0, 129.9, 131.1, 132.8, 134.0, 145.1, 146.9, 150.8, 152.1, 160.5, 183 6.31 (1H, s), 4.38 (2H, t, J = 4.9 Hz), 3.70 (2H, t, J = 4.9 Hz), 3.48 (4H, q, J = 7.1 Hz), 1.27 (6H, t, J = 7.1 Hz).…”