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Alkali metal ion complexation of adamantane functionalized diaza-bibracchial lariat ethers

A series of adamantane functionalized diaza-lariat ethers 1–6 have been prepared and alkali metal picrate extraction profiles determined. The ability of aza-crown ethers 1–6 to extract the alkali metal picrates was compared with that of diaza-18-crown-6 (7) and N, N’-dibenzodiaza-18-crown-6 (8). Na+ and K+ transport across bulk liquid membrane was also measured. The results of alkali metal cation extraction experiments showed that lariat ethers 2 and 3, in which the adamantane molecule is linked to the diaza-18-crown-6 by amine bond, have better complexation abilities for all cations compared to the parent crown ethers 7 and 8, as well as a significantly higher selectivity for K+ than diaza-18-crown-6. However, diaza-lariat ether 1 showed reduced, and 4–6 negligible extractability towards any of the alkali cations. Monte Carlo conformational analysis pointed to the importance of conformational flexibility of the investigated compounds for their extraction ability of alkali cations.

diaza-bibracchial lariat ethers; adamantane functionalized crown ethers; metal ion complexation; metal ion transport; Monte Carlo conformational search

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