Intravesicular and intervesicular interaction by orthogonal multivalent host–guest and metal–ligand complexation

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Abstract
Host vesicles composed of amphiphilic β-cyclodextrin CD1 recognize metal-coordination complexes of the adamantyl-functionalized ethylenediamine ligand L via hydrophobic inclusion in the β-cyclodextrin cavities at the vesicle surface. In the case of Cu(II) and L, the resulting coordination complex was exclusively CuL2, and the interaction with the host vesicles was intravesicular, unless the concentration of metal complex and vesicles was high (>0.1 mM). In the case of Ni(II) and L, a mixture was formed consisting of mainly NiL and NiL2, the interaction with the host vesicles was effectively intervesicular, and addition of the guest–metal complex resulted in aggregation of the vesicles into dense, multilamellar clusters even in dilute solution [1 μM Ni(II)]. The metal–L complex could be eliminated by a strong chelator such as EDTA, and the intervesicular interaction could be suppressed by a competitor such as unmodified β-cyclodextrin. The result from this investigation is that the strongest metal-coordination complex [Cu(II) with L] binds exclusively intravesicularly, whereas the weakest metal-coordination complex [Ni(II) with L] binds predominantly intervesicularly and is the strongest interfacial binder. These experimental observations are confirmed by a thermodynamic model that describes multivalent orthogonal interactions at interfaces.