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Eu(III) and Tb(III) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: a spectroscopic and thermodynamic study

Abstract

In the present contribution, four classes of Ln(III) complexes (Ln = Eu and Tb) have been synthesized and characterized in aqueous solution. They differ by charge, Ln(bpcd)+ [bpcd2- = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate] and Ln(bQcd)+ (bQcd2- = N,N′-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate) being positively charged and Ln(PyC3A) (PyC3A3- = N-picolyl-N,N’,N’-trans-l,2-cyclohexylenediaminetriacetate) and Ln(QC3A) (QC3A3- = N-quinolyl-N,N’,N’-trans-l,2-cyclohexylenediaminetriacetate) being neutral. Combined DFT, spectrophotometric and potentiometric studies reveal the presence, in physiological condition (pH 7.4), of a couple of equally and highly stable isomers differing by the stereochemistry of the ligands (trans-N,N and trans-O,O for bpcd2- and bQcd2-; trans-O,O and trans-N,O for PyC3A3- and QC3A3-). Their high logβ values (9.97 < logβ < 15.68), the presence of an efficient antenna effect and the strong increase of the Ln(III) luminescence intensity as a function of the hydrogen carbonate concentration in physiological solution, candidate these complexes as very promising optical probes for a selective detection of HCO3- in cellulo or in extracellular fluid. This particularly applies to the cationic Eu(bpcd)+, Tb(bpcd)+ and Eu(bQcd)+ complexes, which are capable to guest up to two hydrogen carbonate anions in the inner coordination sphere of the metal ion, so that they show an unprecedented affinity towards HCO3- (logK for the formation of the adduct in the 4.6-5.9 range).

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Publication details

The article was received on 07 Sep 2018, accepted on 07 Nov 2018 and first published on 08 Nov 2018


Article type: Paper
DOI: 10.1039/C8DT03621G
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Eu(III) and Tb(III) complexes of 6-fold coordinating ligands showing high affinity for the hydrogen carbonate ion: a spectroscopic and thermodynamic study

    F. PICCINELLI, C. De Rosa, A. Melchior, G. Faura, M. Tolazzi and M. Bettinelli, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT03621G

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