A variety of lipophilic amines incorporated in liquid membranes exhibit potentiometric responses to neutral phenols

A variety of lipophilic amines incorporated in PVC matrix liquid membranes exhibited anionic potentiometric responses to phenolic compounds at the pH conditions under which the phenols exist mainly or exclusively in their undissociated, neutral forms. The examined lipophilic amines include a macrocyclic pentaamine, tri(decyl)amine, 4,7-dephenyl-1,10-phenanthroline (bathophenanthroline), 4-octadecylpyridine, and sapphyrin. The potentiometric selectivities of the membranes based on lipophilic aliphatic amines (B) reflected the acidity (hydrogen bond donor activity) and lipophilicity (extractability) of the phenols (ArOH), similarly as membranes based on lipophilic quaternary ammonium salts (Q^+X^-). The anionic responses were explained on the basis of a decrease in the charge separation of protonated amines (BH^+) and their counteranions (X^-) across the membrane interface. Possible processes leading to a decrease in the charge separation between BH^+ and X^- are (i) complexation between ArOH and BH^+X^-, followed by proton dissociation and ejection of HX into the aqueous phase, as well as (ii) complexation between ArOH and B. The membrane based on sapphyrin showed a high potentiometric selectivity to catechol, possibly due to geometrical discrimination of the ortho dihydroxy structure of catechol by the nitrogen(s) on the rigid macrocyclic structure of sapphyrin

脂溶性Ｎ4及びＮ5大環状ポリアミンを感応素子とする陰イオン選択性液膜の電位応答挙動の比較

人工合成ホスト化合物である2種額の脂溶性大環状ポリアミン(C16H33-[16]aneN5:1,C16H33-[14]-aneN4:2)を感応素子とした電位応答型の高分子支持液膜型陰イオン選択性電極を作製し,電荷の集中度が異なる一連のジカルボン酸ジ陰イオン類の異性体,又電荷の大きさの異なるATP^4-,ADP^3-,AMP^2-に対する電位応答を測定した。いずれのシリーズのゲストに関しても,両電極による選択性の序列は同じで,二つの負電荷がより集中しているもの,あるいはより大きな負電荷を持つものに高い選択性を示した。電位変化の濃度依存性はホスト1を含む電極のほうがホスト2を含む電極よりも大きく,ネルンストの理論値に近い値を示した。これは,高い塩基性を示すホスト1は膜界面で2に比べてより多くのプロトンを取り込むことができ,その結果生じたホストポリ陽イオンはゲスト陰イオンとより強くホスト－ゲスト錯体を形成することができるためと考えられる