The Effects of O-Substituents of Hexahomotrioxacalix [3] arene on Potentiometric Discrimination between Dopamine and Biological Organic/Inorganic Cations

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As an interesting type of molecular recognition at a membrane surface, the tri-O-acetic acid ester (host 2) of hexahomotrioxacalix [3] arene, when incorporated into poly (vinyl chloride) (PVC) liquid membranes, displays a high potentiometric selectivity for dopamine over, not only other catecholamines (noradrenaline, adrenaline), but also quaternary ammonium guests (tetramethylammonium, choline, and acetylcholine) and inorganic cations (Na^+, K^+, NH^+_4). Interestingly, changes in membrane potential based on the host-guest complexation of host 2 that were observed dopamine/inorganic cation selectivity were not displayed by the related hosts 3 and 4, which contain amide substituents. This paper describes our efforts to separately estimate the two factors contributing to the dopamine selectivities, i.e., the guest lipophilicity factor and the host-guest complexation factor, in an attempt to understand the effects of the O-substituents of these hosts. The potentiometric experiments showed that, although the guests had roughly equal lipophilicity, the electromotive force (EMF) response for dopamine by host 2 was excellent. Furthermore, host 2 displayed ca. a 20-fold stronger complexation for dopamine, compared to noradrenaline, adrenaline, K^+, and NH^+_4 cations. These results indicate that the high potentiometric selectivity of the ion-selective electrode for dopamine mainly reflect, not the guest lipophilicity factor but the host-guest complexation factor. On the other hand, host 3 displayed ca. a 3000-fold stronger binding to Na^+ than dopamine, thus explaining the reasons for the lower dopamine-selectivities of host 3 compared to host 2. It is interesting to note that the high potentiometric selectivities for dopamine were displayed by not only host 2 but also host 5, regardless of the simple structure of the O-substituents.
社団法人日本薬学会の論文
2007-03-01

The Effects of O-Substituents of Hexahomotrioxacalix [3] arene on Potentiometric Discrimination between Dopamine and Biological Organic/Inorganic Cations

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