Fluorimetric Detection of Zn 2+ , Mg 2+ , and Fe 2+ with 3-Hydroxy-4-Pyridylisoquinoline as Fluorescent Probe
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ORIGINAL ARTICLE
Fluorimetric Detection of Zn2+, Mg2+, and Fe2+ with 3-Hydroxy-4-Pyridylisoquinoline as Fluorescent Probe Gabriel E. Gomez Pinheiro 1 & Heiko Ihmels 1 Received: 29 September 2020 / Accepted: 7 December 2020 # The Author(s) 2020
Abstract The suitability of 3-hydroxy-4-pyridylisoquinoline to operate as fluorescent chemosensor for the detection of metal ions was investigated. For that purpose, the interactions of the title compound with selected metal ions were investigated by absorption and emission spectroscopy. The complexation of Zn2+, Fe2+, Mg2+ with 1:1 and 2:1 stoichiometry leads to characteristic optical responses that depend significantly on the employed solvents, thus allowing for the fluorimetric identification and detection of particular metal cations in a matrix-based pattern analysis or by fluorimetric titrations. Keywords Isoquinoline . Metal ion complexes . Fluorescent probe . Chemosensor
Introduction The concentration of metal cations in biological media or in the environment is an essential parameter that determines – among others – the vital function of a bio- or ecosystem [1–4]. Thus, anomalous concentrations of particular cations may lead to harmful effects such as serious diseases as well as contamination and pollution. As a result, the development of sensitive and selective optical probes, also named chemosensors, for cation detection has attracted much attention in recent years [5–10]. Specifically, the development of sensitive and easyto-use fluorimetric probes for biologically abundant metal cations, such as Zn2+ and Fe2+, has a special importance as imbalances in their levels may lead to serious health problems [11–19]. To this end, numerous fluorescent ligands, whose emission changes signficantly on cation complexation, have been developed and employed for the detection of metal ions in biological and environmental samples [5–10]. For example, aromatic 2-hydroxy-substituted Schiff bases (1) [11, 13, 18, 20–35] and hydroxyphenyl and hydroxynaphthylpyridines (2, Scheme 1) [17, 36–38] have been shown to act as colorimet-
* Heiko Ihmels [email protected] 1
Department of Chemistry and Biology, and Center of Micro- and Nanochemistry and Engineering (Cμ), University of Siegen, Adolf-Reichwein-Str. 2, 57068 Siegen, Germany
ric, fluorimetic and electrochemical probes for metal ions, because they form complexes with particular cations with high selectivity, which in turn leads to a significant change of their optical or electrochemical properties. In this context, we have recently observed that the absorption and emission properties of the structurally resembling 4pyridyl-3-hydroxyisoquinoline (3) and its derivatives are highly dependent on their environment in solution [39], and others have assessed these properties theoretically [40]. Namely, the changes in solvent polarity and pH affect the tautomeric equilibrium of 3 which in turn leads to changes of the emission color and intensity. Considering the fact, that the 4-pyridyl-3-hydroxyisoquinoline (3) has the same 2-
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