Consequence of Variation in Topology of Naphthaquinone Derived Lariat Ethers on Uptake of Li+, Na+, K+, Ca2+ and Mg2+ Metal Ions

The condensation of 2,3-dichloro-1,4-naphthaquinone with series of substituted glycols has resulted in a new series of non-cyclic ionophores D3–D4a.. These ionophores vary with different end groups and chain length. The synthesized ionophores 2,3-bis[2-(2-ethoxyethoxy)ethoxy]naphthalene-1,4-dione (D3), 2,3-bis[2-(2-butoxyethoxy)ethoxy]naphthalene-1,4-dione (D3a), 2,3-bis[2-{2-(2-ethoxyethoxy)ethoxy}ethoxy]naphthalene-1,4-dione (D4), 2,3-bis[2-{2-(2-butoxyethoxy)ethoxy}ethoxy]naphthalene-1,4-dione (D4a) have been characterized by m.p., TLC and spectral analysis using 1H NMR, mass & IR spectroscopy. Their binding ability for Li+, Na+, K+, Ca2+, Mg2+ cations has been studied from two aspects: extraction and transport through an artificial bulk liquid membrane. The results show that Li+ and Na+ are extracted in highest amount by D3 while K+ is extracted maximum by D3a and D4. Whereas D3 and D4a proved to be the best extractant for Mg2+ and D3 for Ca2+ compared to other studied ionophores. The results of transport studies depicts that these lariat ethers possess highest carrier efficiency for Mg2+ than Li+, Na+, K+ and Ca2+. The ionophores contain quinone redox moiety which showed the enhancement in extraction and transport ability in reduced state compared to oxidized state. The results suggest that due to the presence of different end groups and chain lengths, the selectivity of non-cyclic ionophores towards metal ions is specified. The design and synthesis of new naphthaquinone derived ionophore is another potentiality to enhance the selectivity of ionophores which have potential applications in analytical, environmental, biomimetic chemistry and sensors.