Selective bulk liquid membrane carrier facilitated transport of Mg2+ over Li+, Na+, K+ and Ca2+ metal ions using naphthaquinone derived redox-switchable ionophores

When the redox-switchable ionophores switch between their oxidized and reduced forms, they demonstrate different ligating abilities in these forms. The redoxswitchable naphthaquinone-derived ionophores (D-1-D-5) are designed and synthesized in this study, with the aim of investigating their cation transport abilities and selectivities across a bulk liquid membrane (BLM) transport system. The biologically significant cations include Li+, Na+, K+, Ca2+, and Mg2+. The selectivity trend shown by D-1, D-3, D-3a, and D-5 is expressed as Mg2+ >> Na+ > K+ approximate to Ca2+, whereas that of D-2, D-4, and D-4a is given by Mg2+ >> Na+ > Ca2+ approximate to K+. The selective transport of Mg2+ over Li+, Na+, K+, and Ca2+ by all the ionophores is also observed. The presence of quinone redox moiety in the ionophores leads to their enhanced carrier ability in a reduced state. Ultimately, any variation in the topology of the ionophores lead to variations in their cation-binding strengths and selectivities. The intrinsic abilities of these ionophores to selectively bind and transport Mg2+ is demonstrated. Moreover, the good and selective transport of Mg2+ by D-1 reveals its scope in molecular devices, whereas the poor but selective transport of Mg2+ by D-4a and D-5 demonstrate their application in sensors.