Analytical Sciences

Fluorescent Iminodiacetamide Derivatives as Potential Ionophores for Optical Zinc Ion-selective Sensors

Nikoleta URBANOVÁ,* Mihály KÁDÁR,** Klára TÓTH,** Botond BOGÁTI,** Vasil ANDRUCH,* and István BITTER***

*Department of Analytical Chemistry, P. J. Šafárik University, Moyzesova 11, SK-04154 Košice, Slovak Republic
**Research Group for Technical Analytical Chemistry of the Hungarian Academy of Sciences, Szent Gellért tér 4., H-1111 Budapest, Hungary
***Department for Organic Chemistry and Technology, Budapest University of Technology and Economics, Budafoki út 6-8., H-1111 Budapest, Hungary

Fluorescent sensor molecules were synthesized by conjugation of iminodiacetamide derivatives with fluorescent moieties of different structures and their UV-visible and fluorescent properties were characterized in acetonitrile solvent. The fluorescent measurements revealed that the N-(2-naphthyl) and N-phenyl derivatives exhibit a distinct zinc ion-selectivity over alkali and alkaline earth metal ions, while N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives do not possess any ion-selectivities. In contrast to the fluorescent measurements, all ligands show Zn²⁺ selectivity over Ca²⁺ and Mg²⁺ ions in plasticized PVC membranes using potentiometric signal transduction. This observation found for N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives can be ascribed to the more hindered interaction between the signalling group of the ionophore and the central metal ion in PVC membranes than in acetonitrile solution upon complexation. From the fluorescent measurements it can also be concluded that the ligands with metal ions form complexes mainly with 2:1 stoichiometry (L₂M). On complex formation a considerable decrease in the fluorescent intensity was observed for all ligands except the N-(anthrylmethyl) derivative, where a 25 - 30 fold fluorescence enhancement was found, which is explained by the photoinduced electron transfer (PET) mechanism. All ionophores exhibited serious hydrogen ion interference, therefore complexation-induced spectral changes were measured in aprotic acetonitrile solution.

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