Host–guest properties of NAD+/NADH models

The host–guest properties of four macrocyclic NAD+/NADH models in aqueous solutions have been investigated using 1H NMR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS). Compounds 1–3 have four nicotinamide units and compound 4 has two nicotinamide units linked by a chiral subunit and an aromatic spacer incorporated into the models. All four model compounds formed complexes with the dianion of terephthalate. The larger models 1–3 formed stronger complexes than the smaller model 4. The cavities of the models 1–3 are large enough to encapsulate a substrate and it is shown by NMR studies that the dianions of iso- and terephthalate are intercalated between the aromatic spacers of the hosts. ESI-MS revealed that isophthalate formed mostly 1:1 complexes but also to some extent 2:1 complexes with 1 and 2 at higher guest concentrations. In contrast, terephthalate formed only 1:1 complexes with the same model compounds.