APTRA‐Based Luminescent Lanthanide Complexes Displaying Enhanced Selectivity for Mg²⁺

Abstract

A series of three europium(III) complexes has been created in which an APTRA moiety has been integrated into the sensitising chromophore (APTRA=o-aminophenol-N,N,N-triacetate). The constitutionally isomeric complexes EuL and EuL feature the APTRA unit linked to a metal-bound pyridine ring through an alkynyl unit, differing according to the disposition of the APTRA substituents relative to the C≡C unit (para-N and para-O). In EuL , the APTRA ring is directly bonded to the Eu-coordinated pyridine (para-O). The metal binding affinities for magnesium, calcium and zinc ions have been measured by using emission and excitation spectroscopy. The pyridylalkynylaryl systems, EuL and EuL , offer superior affinity and selectivity for Mg . The Mg affinities are surprisingly very different from prior studies on structurally related systems that incorporate organic fluorophores as reporters, as opposed to the macrocyclic Eu complex moiety. A much-reduced affinity for calcium and zinc-possibly arising from the lower donor ability of the aryl N or O atoms arising from extended conjugation-means that magnesium ion concentrations can be measured directly in serum for the first time, by using such an approach. An apparent dissociation constant for magnesium binding of K =2.4 mm was calculated in the serum background.

Tuning Mg(II) Selectivity: Comparative Analysis of the Photophysical Properties of Four Fluorescent Probes with an Alkynyl‐Naphthalene Fluorophore

“…Levy et al have previously demonstrated that bi-aryl systems containing an APTRA binding group display ar atiometric response to Mg 2 + andC a 2 + (L 5 ,F igure 1). [26,27] Ligand L 1 features an APTRAm oiety bound to a1 -naphthylalkynylf luorophore, and L 2 is constitutionally isomeric with L 1 , differing in the positiono ft he oxygen and nitrogen donor atoms aroundt he aromatic ring. [17] The developmento ft wo new phosphi-nate-based fluorescent indicators in particulari sd escribed, L 3 and L 4 ,a sa na lternative to the carboxylate-based APTRA binding chelate used in the literature.…”

“…It also enabled the fluorescent systems to act as modelsf or lanthanide(III)-based complexes created in parallel work, to be reported elsewhere, in which pyridylalkynylaryl chromophores are also integratedt os ensitise lanthanide(III) emission efficiently. [26,27] Ligand L 1 features an APTRAm oiety bound to a1 -naphthylalkynylf luorophore, and L 2 is constitutionally isomeric with L 1 , differing in the positiono ft he oxygen and nitrogen donor atoms aroundt he aromatic ring. Ligand L 3 is ap hosphinate analogue of L 1 ,containing apentadentate APDAP binding chelate.…”

The design of responsive luminescent lanthanide probes and sensors

“…Typically, they lead to intensity enhancements of a factor of three or so, when exciting at the isosbestic wavelength. Thus, examples have been reported of the detection of millimolar potassium in aqueous samples of a Eu complex with a remote phenanthridine sensitiser, 103 of millimolar magnesium levels in calf serum with a pyridyl arylalkynyl Eu complex 104 and of zinc at the micromolar level with a terbium complex. 105 In each case, the lanthanide emission lifetime is not changed.…”

A fluorescent probe for the discrimination of oxidation states of palladium

“…Small molecule-based uorescent probes are versatile tools which are frequently explored as metal sensors. [14][15][16] Although probes with novel structures or improved properties are routinely developed, it remains a very active research area. For example, two uorescent rotaxane probes have been recently identied in Goldup's group as a selective Zn 2+ and Pt 2+ sensor.…”