IONIC TRANSPORT ACROSS LIPID BILAYERS ACTIVATED BY CRYPTANDS AND ALKYL-CRYPTANDS

The ionic flux of Na+ K+ ions across monoolein and lecithin bilayers, separating two aqueous electrolyte solutions, has been measured in the presence of 6,21-pentaoxa-1,10-diazabicyclo-(8,8,5)-tricosane, 5-decy l 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo (8,8,8)-hexacosane and the ir parent compounds 16,21-pentaoxa-1,10-diazabicyclo(8,8,5)-tricosane, ,24-hexaoxa-1,10-diaza-bicyclo-(8,8,8)-hexacosane. Under the effects of an electric field, a significant increase of the membrane conductan ce, proportional to the macrocycle and/or to the electrolyte concentra tion, was observed. In spite of the high ion selectivity of both class es of cryptands, related to the different stability constants of the m etal ion-macrobicyclic receptor complexes, alkyl cryptands show a grea ter efficiency to activate the ion transport across the lipid membrane s than their parent compounds. Such a result has been explained taking into account the different hydrophobicity of the macrobicyclic compou nds. Information on the ionic mobility and on the diffusion coefficien t of the ionic species moving across the membrane have been obtained a nalyzing the experimental data in terms of the carrier mechanism based on the Eyring theory. (C) 1998 Elsevier Science B.V. All rights reser ved.