Selective urea transport by macrocyclic carriers through a supported liquid membrane

Wilma F. van Straaten-Nijhuis, Arie R. van Doorn, Arjen M. Reichwein, Feike de Jong, David N. Reinhoudt

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    Synthetic metallomacrocyclic receptor molecules (1-4) transport urea through a supported liquid membrane by encapsulation of the guest in the molecular cavity. The ring size of the macrocycle has a large effect on the rate of transport; C!irriers that have the dptimal complementary shape for complexing urea are the most effective. The membrane stability is improved by the enhanced hydrophobicity of receptors with binaphthyl (5,6) or calixarene (7,8) moieties. The binaphthylcarrier 5 shows a selective transport of urea versus KCl04 and N-methylurea in competition experiments. A mathematical model for the diffusion-limited, carrier-mediated transport of neutral compounds through a supported liquid membrane describes the fluxes in single transport well. From this model the extraction constants as well as the diffusion coefficients of the complexes can be calculated. Binaphthyl carrier 5 shows the same extraction constant for urea as calixsalophene carrier 7. The higher urea flux for the former carrier is caused by a faster diffusion. The fluxes in competition experiments can be accurately predicted from Kex and Dm values obtained in single transport
    experiments, which show that for binaphthyl carrier 5 the extraction constant for urea is 10 times higher than for N-methylurea.
    Original languageEnglish
    Pages (from-to)2265-2271
    JournalJournal of organic chemistry
    Issue number8
    Publication statusPublished - 1993


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