A preparative, spectroscopic and equilibrium study of some phenyl-2-thiazoline fluorophores for aluminium(III) detection

Abstract

As part of a study of fluorophores for selective Al³⁺ detection and of potential use in the study of intracellular Al³⁺, the preparative, UV–visible and fluorescence spectroscopic, and Al³⁺ coordination characteristics of five ligands containing the conjugated phenolic substituted thiazoline chromophore of the natural siderophore, pyochelin, 2-[2-(2-hydroxyphenyl)-4,5-dihydro-1,3-thiazol-4-yl]-3-methyl-1,3-thiazolane-4-carboxylic acid) 1, are reported. The five ligands are 2-(2-hydroxyphenyl)-4,5-dihydro-1,3-thiazole-4-carboxylic acid, 2, 2-(4,5-dihydro-1,3-thiazol-2-yl)phenol, 3, 4-bromo-2-(4,5-dihydro-1,3-thiazol-2-yl)phenol, 4, 2-(4,5-dihydro-1,3-thiazol-2-yl)-5-nitrophenol, 5, and 2-(4,5-dihydro-1,3-thiazol-2-yl)-4-nitrophenol, 6. All form stable binary Al³⁺ complexes in 75% methanol and 25% water in the case of 2, and 73.2% methanol, 24.4% water and 2.4% N,N-dimethylformamide in the case of 3–6, and exhibit substantial UV–visible absorbance changes on coordination. However, while 2, 3 and 4 fluoresce strongly when coordinated to Al³⁺, 5 and 6 do not, probably because their fluorescence is quenched through a twisted intramolecular charge transfer process. All five ligands show selectivity in complexing for Al³⁺ over other metal ions and, in the case of 2, 3 and 4, represent an initial stage in the development of Al³⁺ specific fluorophores for biological use.