The synthesis of homo- and heterocyclodextrin (CD) dimers, containing two CD moieties that are linked through their secondary sides by aliphatic or 2,2'-bipyridyl spacers is described. In these dimers, the glucose units to which the spacers are linked have been transformed into altrose units. The dimers with an octamethylene spacer show self-complexation of the spacer in one of the CD moieties in aqueous solution, as revealed by H-1 and C-13 NMR spectroscopy. Using high-resolution (600 and 800 MHz) NMR spectroscopy and a variety of 2D NMR techniques, an assignment of nearly all of the H-1 NMR signals of two of the CD dimers was made, affording detailed information about the structure of these compounds in water. The self-inclusion of the spacers leads to lower binding affinities for ditopic guest molecules like p-toluidino-6-naphthalene sulfonate (TNS) derivatives and porphyrins. When a rigid 2,2'-bipyridyl group is used to connect the two CD moieties, self-inclusion of the spacer is not possible. This results in the formation of different complexes with ditopic guest molecules, for example, a 2:2 complex with a porphyrin. The CD heterodimers described in this paper contain an alpha-CD and a beta-CD moiety. These dimers display site-specific binding of guest molecules.
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