A phenol-based compartmental ligand as a potential chemosensor for zinc(ii) cations

Abstract

O ligante compartimental 2,6-bis(2-hidroxibenzil-2-hidroxietilamino) metil-4-metilfenol (L) foi sintetizado como um sensor químico em potencial para íons Zn 2+ . A base L coordena dois cátions Zn 2+ em metanol-água, formando um complexo dinuclear cuja formulação foi confirmada por espectrometria de massas com ionização por "electrospray" (ESI-MS) e pelo gráfico de Job. A fluorescência de L é notavelmente aumentada por Zn 2+ em comparação com os íons K + , Ca 2+ , Mg 2+ , Cu 2+ , Pb 2+ , Mn 2+ , Fe 3+ , Fe 2+ , Co 2+ , Cd 2+ e Ni 2+ . Isto se deve ao fato de que a complexação do íon Zn 2+ a L interrompe o processo de transferência eletrônica fotoinduzida e aumenta a rigidez do esqueleto molecular de L. Observou-se ainda que a fluorescência de L é fortemente dependente da acidez e da polaridade dos solventes. Este composto poderá ser utilizado como uma sonda sensível a íons Zn 2+ em solventes polares próticos, após uma modificação estrutural adequada.An "end-off"-type compartmental Lewis base, 2,6-bis(2-hydroxybenzyl-2-hydroxyethylamino) methyl-4-methylphenol (L), was synthesized as a potential chemosensor for Zn 2+ ions. L coordinates two Zn 2+ cations in methanol-water solution, forming a dinuclear complex whose formulation was confirmed by ESI-MS spectroscopy and Job's plot. The fluorescence of L is remarkably enhanced by Zn 2+ as compared with K + , Ca 2+ , Mg 2+ , Cu 2+ , Pb 2+ , Mn 2+ , Fe 3+ , Fe 2+ , Co 2+ , Cd 2+ and Ni 2+ ions. The fluorescence enhancement is attributed to the complexation of Zn 2+ with L, which interrupts the photoinduced electron transfer process and rigidifies the molecular skeleton of L. The fluorescence of L is greatly dependent on the acidity and polarity of the solvents. This compound may be used as a probe to sense Zn 2+ ion in polar protic solvents after proper modification.Keywords: chemosensor, fluorescence mechanism, phenol derivative, solvent effects, zinc(II) IntroductionZinc(II) ions play vital roles in a wide range of physiological processes. Deficiency or imbalance of Zn 2+ within the human body can lead to a variety of diseases. 1 Hence the development of selective zinc chemosensors is of great importance for tracking the Zn 2+ status in biological systems. 2 Fluorescence chemosensors based on photoinduced electron transfer (PET), 3 intramolecular charge transfer (ICT), 4 excited-state intramolecular proton transfer (ESIPT), 5 and fluorescence resonance energy transfer (FRET) mechanisms have been developed for this purpose in the past years. 2,6-10 Nevertheless, none of them completely satisfies the criteria for a biosystemoriented chemosensor. Therefore, efforts to design novel zinc probes are still needed.Structural factors, such as molecular rigidity, could produce significant influence on the fluorescence efficiency of a chemosensor. An increase in planarity and a decrease in torsion may benefit the chemosensor to enhance its fluorescence. 11 As a metal ion binds to a chemosensor, the molecular rigidity is enhanced and the above mentioned transfer processes are poss...

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