Anion binding to neutral and positively-charged lipid membranes

Abstract

Aqueous anion binding to bilayer membranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated by using deuterium and phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy. Only those anions that exhibit chaotropic properties showed significant binding to POPC membranes. A detailed investigation of thiocyanate binding to neutral POPC and to positively charged mixed POPC/dihexadecyldimethylammonium bromide (DHDMAB) (8:2 mol/mol) membranes revealed changes in the 2H NMR quadrupole splittings from POPC specifically deuteriated at either the alpha-segment or the beta-segment of the choline head group which were consistent with a progressive accumulation of excess negative charge at the membrane surface with increasing SCN- concentration. Both the 2H and 31P NMR spectra indicated the presence of fluid lipids in a bilayer configuration up to at least 1.0 M NaSCN with no indication of any phase separation of lipid domains. Calibration of the relationship between the change in the 2H NMR quadrupole splitting and the amount of SCN- binding provided thiocyanate binding isotherms. At a given SCN- concentration the positively charged membranes bound levels of SCN- 3 times that of the neutral membranes. The binding isotherms were analyzed by considering both the electrostatic and the chemical equilibrium contributions to SCN- binding. Electrostatic considerations were accounted for by using the Gouy-Chapman theory. For 100% POPC membranes as well as for mixed POPC/DHDMAB (8:2 mol/mol) membranes the thiocyanate binding up to concentrations of 100 mM was characterized by a partition equilibrium with an association constant of K approximately 1.4 +/- 0.3 M-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The Chaotropic Effect as an Assembly Motif in Chemistry

“…Numerous examples for unspecific interactions of chaotropic anions with biological membranes are also known;7, 162, 168, 169, 170, 171, 172, 173, 174 in particular, their membrane‐disrupting properties are noteworthy 171, 172. Gabel and co‐workers investigated the interaction between dodecaborate cluster dianions and lipid bilayers;34, 35, 36, 175 at high salt concentrations they observed changes in the morphology of liposomes as well as bilayer leakage (see Figure 8 for an example).…”

Ion Dynamics in Cationic Lipid Bilayer Systems in Saline Solutions

“…Instead, ions can interact with the bilayer and modify its structural, interfacial, and electrostatic properties. Experiments have shown that anionic 4, [22][23][24][25] and cationic 26,27 membranes interact readily with their counterions (especially divalent ones), whereas the interactions of zwitterionic lipid bilayers with salt ions appear rather sensitive to the size and valency of ions. [28][29][30][31][32][33][34][35][36][37][38][39][40][41] As for molecular-level computational studies, the increase in computing power in the past few years has made it possible to extend computer simulations beyond the relatively long relaxation times of tens to hundreds of nanoseconds required for equilibration of ions in lipid/water systems.…”

Characterization of lipid bilayer formation in aligned nanoporous aluminum oxide nanotube arrays

“…Specifically, in phosphate solutions, many PO 3 − anions gather on the outer parts of the film. It has been shown that charged anions affect the absolute value of the CSA by decreasing it (shifting the σ ⊥ peak to the left) [20,21]. We propose that charges remaining from the preparation of the AAO substrate interact with the lipid bilayer and cause a slight shift in the 31 P NMR spectrum of AAO substrate bound lipids, not an increase in motional dynamics.…”