Ions modulate stress-induced nano-texture in supported fluid lipid bilayers.

Most plasma membranes comprise a large number of different molecules including lipids and proteins. In the standard fluid mosaic model, the membrane function is effected by proteins whereas lipids are largely passive and serve solely in the membrane cohesion. Here we show, using supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers in different saline solutions, that ions can locally induce ordering of the lipid molecules within the otherwise fluid bilayer when the latter is supported. This nanoordering exhibits a characteristic length scale of ∼20 nm, and manifests itself clearly when mechanical stress is applied to the membrane. Atomic force microscopy (AFM) measurements in aqueous solutions containing NaCl, KCl, CaCl2, and Tris buffer show that the magnitude of the effect is strongly ion-specific, with Ca2+ and Tris, respectively, promoting and reducing stress-induced nanotexturing of the membrane. The AFM results are complemented by fluorescence recovery after photobleaching experiments, which reveal an inverse correlation between the tendency for molecular nanoordering and the diffusion coefficient within the bilayer. Control AFM experiments on other lipids and at different temperatures support the hypothesis that the nanotexturing is induced by reversible, localized gel-like solidification of the membrane. These results suggest that supported fluid phospholipid bilayers are not homogenous at the nanoscale, but specific ions are able to locally alter molecular organization and mobility, and spatially modulate the membrane’s properties on a length scale of ∼20 nm. To illustrate this point, AFM was used to follow the adsorption of the membrane-penetrating antimicrobial peptide Temporin L in different solutions. The results confirm that the peptides do not absorb randomly, but follow the ion-induced spatial modulation of the membrane. Our results suggest that ionic effects have a significant impact for passively modulating the local properties of biological membranes, when in contact with a support such as the cytoskeleton

Two‐Stage Polyelectrolyte Assembly Orchestrated by a Clock Reaction

Controlling the transient self‐assembly of (macro)molecular building blocks is of fundamental interest, both to understand the dynamic processes occurring in living systems and to develop new generations of functional materials. The subtle interplay between different types of physicochemical interactions, as well as the possible reaction pathways, are crucial when both thermodynamic and kinetic factors play substantial roles, as in the case of transient supramolecular assemblies. Clock reactions are a promising tool to achieve temporal control over self‐assembly in non‐living materials. Here, we report on the tunable association of poly(allylamine hydrochloride) (PAH) fueled by the formaldehyde‐sulfite clock reaction. The electrostatic interaction between the large macromolecules and the small, oppositely charged sulfite ions gives rise to micron‐sized coacervate‐like complexes. As the clock proceeds, sulfite is completely depleted and the complexes dissociate. However, under suitable conditions, a subsequent reaction between the polyelectrolyte and formaldehyde can lock‐in the preformed supramolecular structure, giving rise to covalently crosslinked colloidal particles

Two‐Stage Polyelectrolyte Assembly Orchestrated by a Clock Reaction

Controlling the transient self‐assembly of (macro)molecular building blocks is of fundamental interest, both to understand the dynamic processes occurring in living systems and to develop new generations of functional materials. The subtle interplay between different types of physicochemical interactions, as well as the possible reaction pathways, are crucial when both thermodynamic and kinetic factors play substantial roles, as in the case of transient supramolecular assemblies. Clock reactions are a promising tool to achieve temporal control over self‐assembly in non‐living materials. Here, we report on the tunable association of poly(allylamine hydrochloride) (PAH) fueled by the formaldehyde‐sulfite clock reaction. The electrostatic interaction between the large macromolecules and the small, oppositely charged sulfite ions gives rise to micron‐sized coacervate‐like complexes. As the clock proceeds, sulfite is completely depleted and the complexes dissociate. However, under suitable conditions, a subsequent reaction between the polyelectrolyte and formaldehyde can lock‐in the preformed supramolecular structure, giving rise to covalently crosslinked colloidal particles

Controlling the Formation of Polyelectrolyte Complex Nanoparticles Using Programmable pH Reactions

Enabling complexation of weak polyelectrolytes, in the presence of a programmable pH-modulation, offers a means to achieve temporal control over polyelectrolyte coassembly. Here, by mixing oppositely charged poly(allylamine hydrochloride) and poly(sodium methacrylate) in a (bi)sulfite buffer, nanoscopic complex coacervates are formed. Addition of formaldehyde initiates the formaldehyde-sulfite clock reaction, affecting the polyelectrolyte assembly in two ways. First, the abrupt pH increase from the reaction changes the charge density of the polyelectrolytes and thus the ratio of cationic and anionic species. Simultaneously, reactions between the polyamine and formaldehyde lead to chemical modifications on the polymer. Interestingly, core–shell polymeric nanoparticles are produced, which remain colloidally stable for months. Contrastingly, in the same system, in the absence of the clock reaction, aggregation and phase separation occur within minutes to days after mixing. Introducing an acid-producing reaction enables further temporal control over the coassembly, generating transient nanoparticles with nanoscopic dimensions and an adjustable lifetime of tens of minutes

Are the phase state or charge density of the phospholipids affecting protein adsorption onto the membrane?

Are the phase state or charge density of the phospholipids affecting protein adsorption onto the membrane? . 7.International Colloids Conferenc

Pulling lipid tubes from supported bilayers unveils the underlying substrate contribution to the membrane mechanics

International audienc

Impact of poly(ethylene glycol) functionalized lipids on ordering and fluidity of colloid supported lipid bilayers

Colloid supported lipid bilayers (CSLBs) are highly appealing building blocks for functional colloids. In this contribution, we critically evaluate the impact on lipid ordering and CSLB fluidity of inserted additives. We focus on poly(ethylene glycol) (PEG) bearing lipids, which are commonly introduced to promote colloidal stability. We investigate whether their effect on the CSLB is related to the incorporated amount and chemical nature of the lipid anchor. To this end, CSLBs were prepared from lipids with a low or high melting temperature (Tm), DOPC, and DPPC, respectively. Samples were supplemented with either 0, 5 or 10 mol% of either a low or high Tm PEGylated lipid, DOPE-PEG2000 or DSPE-PEG2000, respectively. Lipid ordering was probed via differential scanning calorimetry and fluidity by fluorescence recovery after photobleaching. We find that up to 5 mol% of either PEGylated lipids could be incorporated into both membranes without any pronounced effects. However, the fluorescence recovery of the liquid-like DOPC membrane was markedly decelerated upon incorporating 10 mol% of either PEGylated lipids, whilst insertion of the anchoring lipids (DOPE and DSPE without PEG2000) had no detectable impact. Therefore, we conclude that the amount of incorporated PEG stabilizer, not the chemical nature of the lipid anchor, should be tuned carefully to achieve sufficient colloidal stability without compromising the membrane dynamics. These findings offer guidance for the experimental design of studies using CSLBs, such as those focusing on the consequences of intra- and inter-particle inhomogeneities for multivalent binding and the impact of additive mobility on superselectivity. Graphical abstract: Impact of poly(ethylene glycol) functionalized lipids on ordering and fluidity of colloid supported lipid bilayer

Assembly of Dynamic Supramolecular Polymers on a DNA Origami Platform

Contains fulltext : 231421.pdf (publisher's version ) (Open Access

Reversibly Programmable Photonics via Responsive Polyelectrolyte Multilayer Cladding

Reversibly programmable photonic integrated circuits (PICs) that can facilitate multifunctionality have been long sought after to deliver user-level design flexibility. Issues like complicated control, continuous power consumption, and high optical losses hinder their large-scale adaptation. In this work, a novel approach toward programmable photonics using a responsive polyelectrolyte multilayer (PEM) cladding is presented. Reversible (de)swelling of PEMs by consecutive exposure to acidic and neutral pH solutions yields highly contrasting refractive index changes in the dry film. Utilizing this effect, an easily applied technique for programming photonic integrated devices with two different approaches, complete and area-selective deposition, for several reversible cycles is demonstrated. These devices operate at two distinct states that are virtually lossless and nonvolatile. This proof-of-concept demonstration is suitable for various photonic integration platforms to facilitate reconfigurable photonic processors, static memories, and fine-tuning of fabrication related limitations. Therefore, these results are the first step toward PEM-assisted reversibly programmable multipurpose PICs for low-cost mass production

Reversibly Programmable Photonics via Responsive Polyelectrolyte Multilayer Cladding

Reversibly programmable photonic integrated circuits (PICs) that can facilitate multifunctionality have been long sought after to deliver user-level design flexibility. Issues like complicated control, continuous power consumption, and high optical losses hinder their large-scale adaptation. In this work, a novel approach toward programmable photonics using a responsive polyelectrolyte multilayer (PEM) cladding is presented. Reversible (de)swelling of PEMs by consecutive exposure to acidic and neutral pH solutions yields highly contrasting refractive index changes in the dry film. Utilizing this effect, an easily applied technique for programming photonic integrated devices with two different approaches, complete and area-selective deposition, for several reversible cycles is demonstrated. These devices operate at two distinct states that are virtually lossless and nonvolatile. This proof-of-concept demonstration is suitable for various photonic integration platforms to facilitate reconfigurable photonic processors, static memories, and fine-tuning of fabrication related limitations. Therefore, these results are the first step toward PEM-assisted reversibly programmable multipurpose PICs for low-cost mass production