21 research outputs found
Specific binding of chloride ions to lipid vesicles and implications at molecular scale
Biological membranes composed of lipids and proteins are in contact with electrolytes like aqueous NaCl solutions. Based on molecular dynamics studies it is widely believed that Na(+) ions specifically bind to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes, whereas Cl(â) ions stay in solution. Here, we present a careful comparison of recent data from electrophoresis and isothermal titration calorimetry experiments as well as molecular dynamics simulations suggesting that in fact both ions show very similar affinities. The corresponding binding constants are [Formula: see text] M(â1) for Na(+) and [Formula: see text] M(â1) for Cl(â) ions. This is highlighted by our observation that a widely used simulation setup showing asymmetric affinities of Na(+) and Cl(â) for POPC bilayers overestimates the effect of NaCl on the electrophoretic mobility of a POPC membrane by an order of magnitude. Implications for previous simulation results on the effect of NaCl on polarization of interfacial water, transmembrane potentials, and mechanisms for ion transport through bilayers are discussed. Our findings suggest that a range of published simulations results on the interaction of NaCl with phosphocholine bilayers have to be reconsidered and revised and that force field refinements are necessary for reliable simulation studies of membranes at physiological conditions on a molecular level
A Quantitative Analytical Method to Test for Salt Effects on Giant Unilamellar Vesicles
Today, free-standing membranes, i.e. liposomes and vesicles, are used in a multitude of
applications, e.g. as drug delivery devices and artificial cell models. Because current
laboratory techniques do not allow handling of large sample sizes, systematic and
quantitative studies on the impact of different effectors, e.g. electrolytes, are limited.
In this work, we evaluated the Hofmeister effects of ten alkali metal halides on giant
unilamellar vesicles made of palmitoyloleoylphosphatidylcholine for a large sample size by
combining the highly parallel water-in-oil emulsion transfer vesicle preparation method with
automatic haemocytometry. We found that this new quantitative screening method is highly
reliable and consistent with previously reported results. Thus, this method may provide a
significant methodological advance in analysis of effects on free-standing model
membranes