Solution complexation behaviour of 1,3,5-trioxycyclohexane based ligands and their evaluation as ionophores for Group IA/IIA metal cations

Abstract

A new series of cis,cis-cyclohexane-1,3,5-triol derivatives bearing one, two and three carbamoylalkyl substituents is reported. Ring interconversion promoted by intramolecular hydrogen bonding is observed for the mono- and di-alkylated derivatives 3 and 4 depending on solvent polarity. ¹H NMR parameters obtained have allowed the calculation of the Gibbs free energy change (ΔG⁰) for the trioxa-equatorial ⇆ trioxa-axial equilibrium, modelling the conformational changes promoted by ion binding. Selectivity coefficients have been assessed electrochemically using fixed interference methods for the detection of biologically relevant IA/IIA metal cations. Ionophore 4 displays a Nernstian response towards the detection of Ca²⁺ and logK_Ca,M^pot values are calculated. Solution NMR studies confirm the formation of 1∶1 complexes for 4 with lithium, while 2∶1 complexation is favoured with Ca²⁺. Detailed ES-MS studies performed under controlled conditions revealed similar trends in ion binding.