Incorporation of triazole into a quinoline-rhodamine conjugate imparts iron(iii) selective complexation permitting detection at nanomolar levels

Abstract

Two new rhodamine based probes 1 and 2 for the detection of Fe³⁺ were synthesized and their selectivity towards Fe³⁺ ions in the presence of other competitive metal ions tested. The probe 1 formed a coloured complex with Fe³⁺ as well as Cu²⁺ ions and revealed the lack of adequate number of coordination sites for selective complexation with Fe³⁺. Incorporation of a triazole unit to the chelating moiety of 1 resulted in the probe 2, that displayed Fe³⁺ selective complex formation even in the presence of other competitive metal ions like Li⁺, Na⁺, K⁺, Cu²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺. The observed limit of detection of Fe³⁺ ions (5 × 10⁻⁸ M) confirmed the very high sensitivity of 2. The excellent stability of 2 in physiological pH conditions, non-interference of amino acids, blood serum and bovine serum albumin (BSA) in the detection process, and the remarkable selectivity for Fe³⁺ ions permitted the use of 2 in the imaging of live fibroblast cells treated with Fe³⁺ ions.