Selective Ion Transfer Accompanied by a Respiration Mimetic Reaction at an Aqueous/Organic Solutions Interface

Abstract

It is well known that the selective transport of ions through a mitochondrial inner membrane is attained when the oxygen supplied by the respiration oxidizes glycolysis products in mitochondria. 1 The energy which enables ion transport has been attributed to that supplied by electron transport through the membrane due to a redox reaction occurring at the aqueous/membrane interface accompanied by respiration. 1-3 A quantitative understanding of the energetics involved in the coupling of ion transport with electron transport is considered to be very important for elucidating physiological reactions in a living system as well as to develop novel biomimetic separation methods of ions. Since real bio-systems contain substances such as enzymes and proteins, the functions of which have not been fully analyzed, the present stage is far from a quantitative understanding.In the present work, selective ion transfer coupled with respiration mimetic electron transfer was realized at an interface between aqueous and organic solutions which did not contain any enzymes or proteins; also, the reaction process of the selective ion transfer and the energetic relation in the coupling of ion transfer with electron transfer were elucidated with the aid of controlled potential electrolysis and polarography for charge (ion or electron) transfer at an aqueous/organic solutions interface 4-6 , respectively. Experimental Polarographic measurementThe electron or ion transfer at the interface between aqueous (W) and nitrobenzene (NB) solutions was investigated by current-scan polarography at an electrolyte solution dropping electrode. 4 The procedure used to measure the polarogram, the polarographic cell, the potentiostat, the galvanostat, the function generator, the X-Y recorder and the apparatus for IR drop compensation employed were identical with those described in previous papers. 4,7 The potential difference at the W/NB interface was measured as the potential of a silver/silver chloride electrode (SSE) set in W with reference to a tetraphenylborate ion-selective electrode (TPhBE) set in NB. 4 As supporting electrolytes (SE) in polarographic measurements, 0.1 M Li 2 SO 4 and 0.05 M tetrapentylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]-borate, TPenA + TFPB -, were added in W and NB, respectively. A phosphate buffer of lithium salts (0.02 M) was added in W when necessary. Controlled potential electrolysisThe glass cell illustrated in Fig. 1 was used to investigate the CO 2 evolution accompanied by a redox reaction between flavin mononucleotide (FMN) in W and bis(1,2,3,4,5-pentamethylcyclopentadienyl)iron (DMFC) in NB at the W/NB interface, to which a definite potential difference was applied. In the cell, W (20 ml) contained FMN (Nacalai, guaranteed grade, lot no. M8T1283), pyruvic acid, phosphate buffer and SE (Li 2 SO 4 ), and NB (20 ml) contained DMFC (Aldrich, lot no. 03302HR) and SE (TPenA + TFPB -). During electrolysis, O 2 was bubbled into W, and both the W and NB phases were stirred at about 200 rpm. The electrolysis was c...

Biomimetic Charge Transfer Reactions at the Aqueous/Organic Solution Interface or through Artificial Membrane

“…The energy which enables the ion transport has been attributed to that supplied by electron transport through the membrane due to a redox reaction occurring at the W/membrane interface accompanied by respiration. 34 In this section, an example of selective ion transfers accompanied by a respiration mimetic reaction at the W/NB interface realized by present authors 35 is introduced.…”