Unbinding transition in lipid multibilayers induced by copper(II) ions

We describe our observations on an unbinding transition in a multilamellar dispersion of phosphatydilcoline (PC) vesicles induced by copper(II) ions. The small-angle X-ray measurements clearly show that the increasing amount of CuCl₂ in the millimolar concentration range continuously increases the amount of the unbound bilayers in the gel phase. Moreover, this phenomenon becomes more pronounced when the samples are heated above the so-called pretransition temperature between the gel and the ripple gel phase. The proposed reason for the latter is the increased repulsive electrostatic interaction due to the appearance of the surface modulation in the ripple gel phase. The observed effects reveal a new aspect of the unbinding phenomena since only the transition induced by the steric repulsion due to the layer fluctuations has been considered so far. Here, we show that the unbinding can also be triggered by the change in the electrostatic interactions. These findings are connected to the physical basis of the crucial role of copper(II) ions in biological processes such as neurodegenerative diseases and cell evolution.