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

•The IT and FIT of a series of protonated diamines (DA+ and DA2+) were studied.•DA2+ is dominated at low pH whereas at high pH it is mostly due to the DA+ transfer.•Some basic thermodynamic parameters for both processes have been calculated.•The mechanism for facilitated ion transfer (FIT) has also been evaluated.

The simple ion transfer (IT) and facilitated ion transfer (FIT) of a series of protonated diamines ([H3N(CH2)nNH3]2+ (DA2+) or [H2N(CH2)nNH3]+ (DA+), n = 2, 3, 4, 6, 8) at the micro-water/1,2-dichloroethane (μ-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, DA2+ 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 CDAz+≫CLCDAz+≫CL (where z   can be 0, 1 or 2 depending on the pH of solutions). For CDAz+≪CL,CDAz+≪CL, 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.