Facilitated SO
42- transfers by hydrogen bond-forming ionophores are investigated across the nitrobenzene (NB)-water interface by using polarography with a dropping electrolyte electrode. Bis-thiourea
1,
α,
α′-bis(
N′-
p-nitrophenylthioureylene)-
m-xylene, is found to significantly facilitate the transfer of the highly hydrophilic SO
42- whereas its counterpart,
N-(
p-nitrophenyl)-
N′-propylthiourea (ionophore
2), cannot. In contrast to the predominant formation of a 1:1 complex with SO
42- in the bulk NB phase, the SO
42- transfer assisted by
1 is indeed based on the formation of a 1:2 complex between SO
42- and ionophore, even under the condition of [SO
42-]
aq » [
1]
org. Such an exclusive formation of the 1:2 (SO
42- to ionophore) complex at the NB-water interface is not observed with structurally similar bis-thiourea
3,
α,
α′-bis(
N′-phenylthioureylene)-
m-xylene, where
p-nitrophenyl moietes of bis-thiourea
1 are simply replaced by phenyl groups. The facilitated transfer of SO
42- with bis-thiourea
1 is further compared to that of HPO
42- and H
2PO
4- across the NB-water interface, which was previously shown to be assisted by
1 through the formation of the 1:1 and 2:1 (anion to ionophore) complexes, respectively. On the basis of these examinations, unique binding behaviors of hydrogen bond-forming ionophores at the NB-water interface are discussed, with a view towards development of ionophore-based anion-selective chemical sensors.
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