Influence of External NaCl Salt on Membrane Rigidity of Neutral DOPC Vesicles

Abstract

Sodium chloride (NaCl) is a very common molecule in biotic and abiotic aqueous environments. In both cases, variation of ionic strength is inevitable. In addition to the osmotic variation posed by such perturbations, the question of whether the interactions of monovalent ions Na+ and Cl–, especially with the neutral head groups of phospholipid membranes are impactful enough to change the membrane rigidity, is still not entirely understood. We investigated the dynamics of 1,2-di-(octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) vesicles with zwitterionic neutral head groups in the fluid phase with increasing external salt concentration. At higher salt concentrations, we observe an increase in bending rigidity from neutron spin echo (NSE) spectroscopy and an increase in bilayer thickness from small-angle X-ray scattering (SAXS). We compared different models to distinguish membrane undulations, lipid tail motions, and the translational diffusion of the vesicles. All of the models indicate an increase in bending rigidity by a factor of 1.3–3.6. We demonstrate that even down to t > 10 ns and for Q > 0.07 Å–1, the observed NSE relaxation spectra are influenced by translational diffusion of the vesicles. For t < 5 ns, the lipid tail motion dominates the intermediate dynamic structure factor. As the salt concentration increases, this contribution diminishes. We introduced a time-dependent analysis for the bending rigidity that highlights only a limited Zilman–Granek time window in which the rigidity is physically meaningful.

Fusion‐Induced Growth of Biomimetic Polymersomes: Behavior of Poly(dimethylsiloxane)‐Poly(ethylene oxide) Vesicles in Saline Solutions Under High Agitation

“…We rarely detected 1-3 μm multilamellar (Figure S21, Supporting Information) and larger multivesicular vesicles (Figures S22 and S23, Supporting Information), while the majority of the polymer constituted long multilamellar tubes (Figure S24, Supporting Information) and polymer beads (Figure S25, Supporting Information). Such an increase in lamellarity with increasing NaCl concentration was previously observed for DOPC vesicles [33] and multilamellar tubes were formed upon contact with water. [34]…”

“…[ 47 ] On the other side, small‐angle X‐ray scattering evidenced that the bilayer thickness of zwitterionic DOPC vesicles increased in presence of NaCl. [ 33 ] In regard to the present case, we recently observed increase in the membrane thickness of PDMS‐ g ‐PEO/phosphatidylcholine (70:30 molar ratio) mixtures in presence of KCl via cryo electron microscopy: in absence of salt the thickness was 4.9 nm, [ 14 ] while in buffer containing 150 m m KCl it was 6.1 nm. [ 16 ] Thus, the fusion in the present case is attributed to PEO expansion upon interaction with salts, contrary to the previously assumed corona contraction in the case of PBd‐ b ‐PEO, [ 23 ] which expansion in turn softens the membrane and thus lowers the energetic barriers during fusion‐related deformations.…”

Experimental platform for the functional investigation of membrane proteins in giant unilamellar vesicles

“…70 Second, both buffers and ions can affect the bending rigidity of the membrane, 71,72 but effects depend on the membrane composition. 73…”

“…78 The difference observed for Pt wire GUVs with and without NaCl is unclear, but could also be due to alteration of membrane properties, such as the bending rigidity, in the presence of salt. 72,73,79…”

Lamellar-to-MLV transformation in SDS/octanol/brine examined by microfluidic-SANS and polarised microscopy

“…5,19 Experimentally, the formation of MLVs has been described by the emergence of intermediate multilamellar cylinder (MLC) phase [20][21][22] in continuous shear flow or a direct emergence of MLVs with oscillatory flows. 4 Numerous experimental reports have considered the effect of shear field, stress and rate, on various model systems (nonionic, 4,21,23,24 cationic 25,26 and anionic 27,28 ), the effect of added co-surfactants 3,29 and salt, 30,31 and the effect of oscillatory shear flows. 4,28,32 Predominant analytical techniques include rheology, 33,34 scattering, 21,22,34,35 optical microscopy 35,36 and 2 H NMR.…”