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The transfer of streptothricin antibiotics containing a β-lysine monomer (ST-F), trimer (ST-D), and tetramer (ST-C) at a polarizable nitrobenzene (NB) | water (W) interface was studied by cyclic voltammetry. Under acidic conditions, the streptothricins existed in fully protonated forms, as ST-F 2 + , ST-D 4 + and ST-C 5 + cationic species. Within the potential range tested, ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer across the NB | W interface. The formal potentials, Δ O W ϕ 0 S ’ T , of ST-D 4 + and ST-C 5 + ions were determined. In the presence of a neutral ligand (L), dibenzo-18-crown-6, in NB, ST-F 2 + , ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer assisted by the formation of ST-FL 2 2 + , ST-DL 4 4 + and ST-CL 5 5 + complexes with the ligand in NB. Using the Δ O W ϕ 0 S ’ T -values, association constants between the NH 3 + -groups of ST-D 4 + and ST-C 5 + ions and the crown ether in NB were determined. The association constants were in agreement with each other. By assuming that the association constant of ST-F 2 + was equal to those of the ST-D 4 + and ST-C 5 + ions, the Δ O W ϕ 0 S ’ T of the ST-F 2 + ion was estimated. Interestingly, the determined Δ O W ϕ 0 S ’ T -value was increasingly negative in the order of ST-F 2 + (~ 0.24 V) > ST-D 4 + (0.199 V) > ST-C 5 + (0.194 V), indicating that the lysine oligomer affected the phase-transfer characteristics of streptothricin. [ABSTRACT FROM AUTHOR]

We present the availability of a fluorous solvent, 1,1,1,2,3,4,4,5,5,5-decafluoropentane (C5F10), for the non-aqueous medium in liquid-liquid electrochemistry. The solvent is immiscible, and forms stable interface with water (W). The solvent dissolved a high concentration of a hydrophobic electrolyte, tetrabutylammonium bis(nona fluorobutanesulfonyl)imide (TBABNSI), and the TBABNSI (C5F10) solution gave a high conductivity. The TBABNSI (C5F10)| LiCl (W) interface gave a polarizable potential window. Within the potential window, tetramethylammonium ion gave a reversible voltammetric wave due to its transfer across the C5F10 | W interface. The potential window became wider by replacement of the supporting electrolytes in C5F10- and W-phases. The results indicate that various ion-transfer reactions at the C5F10 | W interface can be studied voltammetrically. [ABSTRACT FROM AUTHOR]