Zn2+/Cd2+ optical discrimination by fluorescent chemosensors based on 8-hydroxyquinoline derivatives and sulfur-containing macrocyclic units

Aragoni, M. Carla, Arca, Massimiliano, Bencini, Andrea, Caltagirone, Claudia, Garau, Alessandra, Isaia, Francesco, Light, Mark E., Lippolis, Vito, Lodeiro, Carlos, Mameli, Marta, Montis, Riccardo, Mostallino, M. Cristina, Pintus, Anna and Puccioni, Stefano (2013) Zn2+/Cd2+ optical discrimination by fluorescent chemosensors based on 8-hydroxyquinoline derivatives and sulfur-containing macrocyclic units. Dalton Transactions, 42 (40), 14516-14530. (doi:10.1039/c3dt51292d).

Abstract

Four new fluorescent chemosensors for metal ions based on 8-hydroxyquinoline (8-HDQ) derivatives and sulfur-containing macrocyclic units were synthesized and characterized, namely 1-(5-chloro-8-hydroxy-7-quinolinylmethyl)-1-aza-4,7,10-trithiacyclododecane (L1), 1-(5-chloro-8-hydroxy-7-quinolinylmethyl)-1-aza-4,13-dithia-7,10-dioxacyclopentadecane (L2), 1-(8-hydroxy-2-quinolinylmethyl)-1-aza-4,7,10-trithiacyclododecane (L3), and 1-(8-hydroxy-2-quinolinylmethyl)-1-aza-4,13-dithia-7,10-dioxacyclopentadecane (L4). Preliminary fluorimetric titrations indicated L1 as the only member of the family of ligands to give a selective CHEF-type response to the presence of Zn2+ in MeCN–H2O (1 : 1, v/v) solutions, which allowed imaging of this metal ion in Cos-7 cells in vitro. The other ligands either did not show any fluorescence response (L3, L4) to any of the metal ions considered (Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+) or gave (L2) a CHEF-type response also to the presence of Cd2+. The coordination properties of L1 towards Zn2+ were, therefore, fully investigated by potentiometric measurements and absorption and emission spectroscopy at different pH values, which indicated that the formation of 2 : 1 L1/Zn2+ complexes is responsible for the CHEF-type effect observed. The complexes [Zn(L1)2H2O](BF4)2 and [Zn(L3)](ClO4)2 were characterized in the solid state by X-ray crystallography, and DFT calculations were performed to understand the origin of the Zn2+/Cd2+ optical discrimination of the 8-HDQ-based “conjugate” fluorescent chemosensors reported.

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Contributors

Author: Mark E. Light

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