Saijo Ryosuke, Murakami Hiroyuki, Tsunekawa Saori, Imanishi Souhei, Shirai Naohiro, Ikeda Shin-Ichi, Odashima Kazunori
Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.
Chem Pharm Bull (Tokyo). 2007 Mar;55(3):417-21. doi: 10.1248/cpb.55.417.
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+, NH4+). 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 NH4+ 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.
作为膜表面一种有趣的分子识别类型，六同型三氧杂杯[3]芳烃的三-O-乙酸酯（主体2）在掺入聚氯乙烯（PVC）液膜后，对多巴胺表现出高电位选择性，不仅高于其他儿茶酚胺（去甲肾上腺素、肾上腺素），还高于季铵客体（四甲基铵、胆碱和乙酰胆碱）以及无机阳离子（Na+、K+、NH4+）。有趣的是，基于主体2与多巴胺/无机阳离子选择性的主客体络合所观察到的膜电位变化，在含有酰胺取代基的相关主体3和4中并未出现。本文描述了我们为分别估算影响多巴胺选择性的两个因素，即客体亲脂性因素和主客体络合因素所做的努力，旨在了解这些主体的O-取代基的影响。电位实验表明，尽管客体的亲脂性大致相等，但主体2对多巴胺的电动势（EMF）响应却非常出色。此外，与去甲肾上腺素、肾上腺素、K+和NH4+阳离子相比，主体2对多巴胺的络合能力大约强20倍。这些结果表明，离子选择性电极对多巴胺的高电位选择性主要反映的不是客体亲脂性因素，而是主客体络合因素。另一方面，主体3对Na+的结合能力比对多巴胺强约3000倍，从而解释了主体3与主体2相比多巴胺选择性较低的原因。值得注意的是，不仅主体2，而且主体5都对多巴胺表现出高电位选择性，无论O-取代基的结构多么简单。
