Electrochemical behaviors of protonated diamines at the micro-water/1,2-dichloroethane interface

The simple ion transfer (IT) and facilitated ion transfer (FIT) of a series of protonated diamines ([H3N(CH2)(n)NH3](2+) (DA(2+)) or [H2N(CH2)(n)NH3](+) (DA(+)), n = 2,3, 4, 6, 8) at the micro-water/1,2-dichloroethane (mu-W/DCE) interface supported at the tip of a micropipette are reported. The effect of pH on both transfer processes has been studied in detail. For the IT process at low pH, DA(2+) is dominated whereas at high pH it is mostly due to the DA(+) transfer. The experimental results also demonstrate that dibenzo-18-crown-6 (DB18C6, L) can facilitate the transfer of protonated diamines at such interface. The complexation between ion and ligand is 1:1 at all experimental pH when C-DA(z+) >> CL (where z can be 0, 1 or 2 depending on the pH of solutions). For C-DA(z+) << C-L, the ion to ligand stoichiometry is 1:1 when pH is high, and is 1:2 when pH is low. The association constants for both cases are also calculated. Among these five diamines, the association constant for protonated 1,3-propanediamine has the biggest values. (C) 2014 Elsevier B.V. All rights reserved.