A new class of ditopic receptor molecules have been synthesized and structurally characterized. The unique structural features of these molecules are: (a) a very lipophilic unit that consists of two 3,5-di- t -butylsalicylideneimine moieties that form a square O 2 N 2 coordination site and (b) a relatively hydrophilic benzo-18-crown-6 unit capable of binding to alkali metal ions and hydrogen bonding with ammonium functional groups. These molecules are totally insoluble in water but very soluble in non-polar solvents. By virtue of their hydrophilic end, they are able to invade the water-organic solvent interface and retrieve hydrophilic molecules from water solution that subsequently are extracted into the organic solvent. Procedures are described for the syntheses of the {H 2 - t Bu 4 -salphen-18-cr-6 and also 15-crown-5 and 12-crown-4 derivatives. With dibenzo-crown ethers 2:1 t Bu 4 -salphen:crown ether molecules have been obtained with 18-crown-6, 24-crown-8 and 30-crown-10 ‘bridges’. A variety of metal ions (Mn 3+ , Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ and Cu 2+ ) have been incorporated within the N 2 O 2 cavity of the salphen subunits in the 18-crown-6 and 24-crown-8 hybrids. An account of structural features and transport characteristics for some of these molecules are reported. The results of a detailed study of the transport of tryptophan and serotonin across CHCl 3 bulk liquid membranes are discussed for these processes that follow Michaelis–Menten kinetics.
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Coucouvanis et al. (2003) studied this question.
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