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1,3-Dimethoxy- p - tert -butyldihomooxacalix[4]arene-crown-6 ( 4 ) was synthesized for the first time. 4 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements ( 1 H, 13 C, COSY and NOESY). Conformational behaviour of 4 and p - tert -butyldihomooxacalix[4]-crown-5 ( 2 ) and crown-6 ( 3 ) was studied by dynamic 1 H NMR and by MD/MM calculations. Two-phase (water/CH 2 Cl 2 ) picrate extraction studies and transport experiments with the same salts through a CH 2 Cl 2 membrane were performed to evaluate the binding properties of these ligands towards alkali and alkaline earth metal cations. 2 and 3 are poor phase transfer agents for all cations, while 4 is a reasonable extractant for the alkali cations, showing preference for Cs + . However, all three calixcrowns are good carriers for the alkali cations and display a very selective transport for Ba 2+ . |
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