Tuning the selectivity/specificity of fluorescent metal ion sensors based on N2S2 pyridine-containing macrocyclic ligands by changing the fluorogenic subunit: spectrofluorimetric and metal ion binding studies

Aragoni, M.C., Arca, M., Bencini, A., Blake, A.J., Caltagirone, C., De Filippo, G., Devillanova, F.A., Garau, A., Gelbrich, T., Hursthouse, M.B., Isaia, F., Lippolis, V., Mameli, M., Mariani, P., Valtancoli, B. and Wilson, C. (2007) Tuning the selectivity/specificity of fluorescent metal ion sensors based on N2S2 pyridine-containing macrocyclic ligands by changing the fluorogenic subunit: spectrofluorimetric and metal ion binding studies. Inorganic Chemistry, 46 (11), 4548-4559. (doi:10.1021/ic070169e).

Abstract

Two new fluorescent chemosensors for metal ions have been synthesized and characterized, and their photophysical properties have been explored; they are the macrocycles 5-(2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L5) and 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L6). Both systems have a pyridyl-thioether-containing 12-membered macrocycle as a binding site. The coordination properties of these two ligands toward CuII, ZnII, CdII, HgII, and PbII have been studied in MeCN/H2O (1:1 v/v) and MeCN solutions and in the solid state. The stoichiometry of the species formed at 25 C have been determined from absorption, fluorescence, and potentiometric titrations. The complexes [CuL5](ClO4)2·1/2MeCN, [ZnL5(H2O)](ClO4)2, [HgL5(MeCN)](ClO4)2, [PbL5(ClO4)2], [Cu3(5-Cl-8-HDQH-1)(L6H-1)2](ClO4)3·7.5H2O (HDQ = hydroxyquinoline), and [Cu(L6)2](BF4)2·2MeNO2 have also been characterized by X-ray crystallography. A specific CHEF-type response of L5 and L6 to the presence of ZnII and CdII, respectively, has been observed at about pH 7.0 in MeCN/H2O (1:1 v/v) solutions.

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