Blocking effect of a phospholipid monolayer on ion transfer at a liquid | liquid interface and its electrochemical control

Compact poly-pyrrole layers formed at a liquid|liquid interface

“…At the beginning the layer is very thin and the layer structure can be destroyed by the transferring ion. Similar sharp peaks of ion transfer are observed when the transfer reaction is blocked by an adsorbed layer of the phospholipid complex with a multiple-charged cation (e.g., Ce 4+ ) and can proceed only at more positive potentials where the adsorbed layer is destroyed [1,2].…”

“…A typical example is stabilization of the phospholipid monolayer in the presence of multiply charged cations in the aqueous phase. However, at positive potentials the formed complex decomposes and the protonated phospholipid desorbs from the interface due to its positive charge [1,2]. Another example of a followup reaction is the formation of a chemical bond between the adsorbed molecules.…”

Cation adsorption at a distearoylphosphatidic acid layer adsorbed at a liquid/liquid interface

“…This can be explained considering that the accumulation and organisation of DSPA molecules at the liquid-liquid interface are taking place throughout the time. Since the aqueous electrolyte contains a structuring cation (Li + ), the interaction between the negative polar head group of DSPA and this cation is strong [11,[24][25][26][27][28], leading to a highly ordered film, after few minutes. As it can be seen, and as it was already pointed out, profile (4) shows that TEA + transfer process is almost blocked, indicating the hydrophobic nature and the high compactness of this film, after 20 min.…”

“…On the other hand, negative charged phospholipids desorb at negative potential, with respect to E pzc [7,11,[29][30][31]. In spite the fact polar head group of DSPA is anionic, the film becomes neutral in the presence of Li + cations, due to electrostatic interactions.…”

“…have been reported [1,[9][10][11]. This kind of adsorption occurs spontaneously, without applying a potential difference, but the film stability depends on the interfacial potential difference and the coverage may change during the experiment.…”