Toward the Detection of Cellular Copper(II) by a Light-Activated Fluorescence Increase

Abstract

A new type of Cu 2+ fluorescent sensor, coucage, has been prepared with a photosensitive nitrophenyl group incorporated into the backbone of a coumarin-tagged tetradentate ligand. Coucage provides a selective fluorescence response for Cu 2+ over other biologically relevant metal ions. Coordination of Cu 2+ dims the fluorescence output until irradiation with UV light cleaves the ligand backbone, which relieves the copper-induced quenching to provide a turn-on response. Experiments in live MCF-7 cells show that coucage can be used for detecting changes in intracellular Cu 2+ upon the addition of excess exogenous copper. If improvements can be made to increase its affinity for copper, this new type of turn-on sensor could be used as a tool for visualizing the cellular distribution of labile copper to gain insight into the mechanisms of copper trafficking.Copper, the third most abundant transition metal in the human body, plays a critical role in many fundamental physiological processes; however, it also catalyzes the production of highly reactive oxygen species that damage biomolecules.1 Due to copper's dual nature, cells have developed strict regulatory processes to control its cellular distribution.1 Alterations in copper homeostasis are linked to neurodegenerative diseases such as Menkes and Wilson diseases, Alzheimer's, familial amyotrophic lateral sclerosis, and prion diseases. 2 Being able to visualize the cellular distribution of copper in both its physiological oxidation states, Cu + and Cu 2+ , would offer insight into how cells acquire, maintain, and utilize copper while suppressing its toxicity. Whereas reliable fluorescence sensors exist for Cu + , there are fewer options for detecting Cu 2+ in living cells.3 A common strategy in designing fluorescent probes for metal ions is to link a ligand to a fluorophore such that metal binding causes an increase in fluorescence only in response to the target ion. Cell permeable fluorescent sensors have proven useful for investigating intracellular metal ion distribution, particularly for Ca 2+ ,4 Zn 2+, 5 and Cu + .6 The development of this type of "turn-on" sensor for Cu 2+ , however, is hampered by the fluorescence quenching effect of this paramagnetic metal ion. As a consequence, many Cu 2+ sensors have a "turn-off" mechanism,7 which is generally less sensitive, gives false-positive results, and offers limited spatial resolution. Several examples of turn-on sensors have appeared recently,3 , 8 but limitations include sensing mechanisms that operate only in organic solvent or at non-physiological pH,8a-d low quantum yields in aqueous solution,8e or potential off-target responses.8f-i Therefore, there is a need to develop new strategies that provide a fluorescent turn-on response in order to investigate intracellular Cu 2+ . We present here coucage, a new type of fluorescent sensor that uses UV light to uncage a Cu 2+ -dependent fluorescence response.Katherine.franz@duke.edu. Supporting Information Available: Full experimental details, including synthesis...

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“…Akkaya e colaboradores reportaram a detecção de metais promovida por aza-BODIPY's, substituídos nas posições 1 e 7 por grupamentos 2-piridinicos, que desempenharam papel quelante de íons metálicos 51 . A sonda apresentou boa seletividade para íons Hg 2+ , evidenciado pelo deslocamento de emissão de fluorescência, de 682 para 719 nm (Figura O Cobre é um elemento-traço, presente em organismos biológicos com participação em processos celulares importantes 54,55 . Contudo em altas concentrações pode ser tóxico e o aumento de sua utilização em vários segmentos, em especial agricultura, provoca contaminação ambiental que pode acarretar em doenças neurodegenerativas 56 e por este motivo, métodos robustos de sua detecção são importantes.…”

Optical Sensing of Copper and Its Removal by Different Environmental Technologies

“…Moreover, the probe can be used for bio‐imaging studies in living cells. Ciesienski, et al . also synthesized a coumarin based fluoro probe for copper that can also acts good on living cells.…”

Coumarin-Derived Fluorescent Chemosensors

“…Mechanism studies suggest that 26 forms a complex with Cu 2+ in a 1:2 metal-to-ligand ratio, and a 50-fold fluorescence enhancement is observed when the complex simultaneously undergoes Cu 2+ -promoted hydrolysis (N. . Sensor 27 relies on a coumarin-tagged ligand that selectively binds Cu 2+ over other biometals to induce fluorescence quenching, which is subsequently relieved upon UV irradiation to provide the turn-on response (Ciesienski et al, 2010). For chemosensor 28 the mechanism of fluorescence is based on ICT, which is modified by the introduction of an electron-donating diethylamino group making it chromogenic and increasing the binding affinity (Helal et al, 2011).…”