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Temperature dependence study of the self-diffusion coefficient of Cs(+) ion in dibenzo-18-crown-6 (DB18C6) modified Nafion-117 (Cs-Naf-CR) was carried out in the temperature range of 50-65 °C. Temperature dependence of water diffusion in Cs-Naf-CR was also studied to understand the mechanism of cation and water transport in the membrane. Because of the very slow kinetics of isotopic exchange, self-diffusion measurement of Na(+) in Na-Naf-CR was carried out only at 60 °C. The result indicates that self-diffusion behavior is governed by the nature of the cation in which the crown ether was loaded in the membrane matrix. The activation energy of diffusion for Cs(+) ion and water in Cs-Naf-CR was found to be much higher than that in the pure Cs(+) form of Nafion (Cs-Naf). Water uptake of the membrane was also found to have reduced compared to Cs/Na-Naf. The results point to the binding of the ions by DB18C6 and the destruction of the water channels in the crown ether loaded membrane. The differential scanning calorimetry (DSC) data supports these observations.

A theoretical study to understand molecular structures and coordination modes of neptunium complexes with three different substituent hydroxamates viz., acetohydroxamate (AHA), benzhydroxamate (BHA) and salicylhydroxamate (SHA) was carried out using density functional theory (DFT). The geometries for different complexes reported in literature M x L y H z (x:y:z) viz 1:1:1, 1:2:2 and 1:2:0 were optimized and interaction energies (DE) for complexation process were calculated to obtain the most probable structures of complexes. The DE value revealed, the complex stability order as NpO 2 + -SHA > NpO 2 -AHA > NpO 2 -BHA which is in agreement with the reported experimental data. Higher negative charge on AHA compared to BHA leads to its higher interaction with NpO 2 which in turn reflects in shorter Np-O eq (ligand) bond distances. In 1:1:1 complex of NpO 2 -SHA, the binding mode involving ortho hydroxyl group and -NHO À oxygen atom (seven membered ring) shows most negative interaction energy.However, for binding of second ligand in 1:2:2 NpO 2 -SHA complex, steric effects dominate and the mode involving five membered ring through oxygen atoms of -CONHO À is most stable.

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