Synthesis, aggregation, and binding behavior of synthetic amphiphilic receptors

Amphiphilic bowl-shaped receptor molecules have been synthesized starling R om diphenylglycoluril: Upon dispersion in water, these molecules self-assem ble to form vesicles that bind neutral guests and alkali metal ions. In the case of bis(alkylester)-modified receptor compound 4,electron microscopy r eveals that an increase in the size of the alkali metal ion (from Na+ or K to Rb+ and to Cs+) leads to a change in the shape of the aggregates, viz. from vesicles to tubules. Monoplayer experiments suggest that this behavior is due to a change in the conformation of this amphiphilic receptor. In wa ter, molecules of 4 have an elongated conformation that changes to a-sandwi ch-like one upon binding of alkali metal ions. Binding studies with vesicle s from the bis ammonium receptors 6 and 9 and the guest 4-(4-nitrophenylazo )resorcinol (Magneson) reveal that below the critical aggregation concentra tion (CAC) of the amphiphile 1:1 host-guest complexes are formed with high host-guest association constants. Above the CAC, a host-guest ratio of 2:1 was observed that indicates that,only the cavities on the outside of the ve sicle can be occupied. In the rase of the naphthalene walled compound 8 cha nges in the vesicle structure are induced by the organic guest Magneson.