Polyelectrolyte-lipid complexes as membrane mimetic systems

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.

Spectroscopic Characterization of Halorhodopsin Reconstituted into Nanodisks Using Native Lipids

Polyelectrolyte complexes (PECs) with nanocrystalline cellulose and ammonium polyphosphate (NCC/APP) were prepared by an accessibly oriented self-assembly method, and the morphology and ultrastructure were investigated with transmission electron micrographs, scanning electric microscopy, Fourier infrared, and X-ray diffraction. The prepared PECs were then used as a flame-retardant system in rice straw-HDPE composites (RPC), and the thermal degradation, flame retardancy, and mechanical properties were studied by thermogravimetry, cone calorimetry, limited oxygen index (LOI) and mechanical testing. The thermal stability and flame retardancy of RPC were significantly influenced with an incorporation of PECs. PECs can promote the thermal degradation of RPC that take place earlier and stabilize the char residues. PECs can significantly improve the LOI of RPC, and LOI increased to 24.8% and 25.0% in the presence of NCC1/APP and NCC5/APP. PECs had a slight effect on heat release rate. PECs can also improve the mechanical property of RPC, and the tensile and flexural strength were increased with the addition of PECs of NCC/APP.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComplexation of lecithin with cationic polyelectrolytes: "Plastic membranes" as models for the structure of the cell membrane?Markus Antonietti, Antje Kaul, and Andreas ThuenemannCite this: Langmuir 1995, 11, 7, 2633–2638Publication Date (Print):July 1, 1995Publication History Published online1 May 2002Published inissue 1 July 1995https://pubs.acs.org/doi/10.1021/la00007a050https://doi.org/10.1021/la00007a050research-articleACS PublicationsRequest reuse permissionsArticle Views393Altmetric-Citations98LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Ionically cross-linked polyelectrolyte complex (PEC) membranes of cationic chitosan (CS) and anionic poly(acrylic acid) (PAAc) were synthesized and assessed for applicability in fuel cells. CS and PAAc were blended in different weight ratios and the resulting membranes were posttreated to enable the formation of the polyelectrolyte complex. The ionic cross-linking occurring on blending the polyelectrolytes excludes the need of using other cross-linking agents. These membranes were extensively characterized for morphology, their intermolecular interactions, thermal stability, and physicomechanical properties using SEM, FTIR, DSC, sorption studies, and tensile testing, respectively. Methanol permeability and proton conductivity were estimated and compared with respective values for Nafion 117. PEC membranes exhibited high ion exchange capacity (IEC), high proton conductivity, low methanol permeability, and adequate thermal and mechanical stability. Among the blends synthesized, the membrane blend with 50 wt...

Thermal stability of nano-structure in polymeric Langmuir-Blodgett films studied by the energy transfer method

Construction and deconstruction of multilayer films containing polycarboxybetaine: Effect of pH and ionic strength

Substituted silicon phthalocyanine Langmuir-Blodgett film and its possible use in electronic devices

Thermal stability improvement of dielectric properties and non-ohmic characteristic of CaCu3+xTi4O12 ceramics via a Cu-nonstoichiometric approach

This study presents a comparative evaluation of four drying methods for carrot, red beet, and pumpkin pomace to produce natural functional food ingredients. The work addresses the valorization of 35-45% vegetable processing waste-a rich source of bioactive compounds-aligning with circular bioeconomy principles and Kazakhstan's goals for deep processing of agricultural raw materials. The compared methods were convective drying (CD), ultrasound pretreatment + convective drying (US + CD), vacuum-microwave drying (VMD), and ultrasound pretreatment + vacuum-microwave drying (US + VMD). Drying kinetics, water activity, physicochemical and functional properties of powders, retention of bioactive compounds, color characteristics, thermal stability, and sensory attributes were assessed. Kinetics were fitted using Midilli et al., Page, and Weibull models. US + VMD provided the highest drying acceleration (6-11 times faster than CD), reaching final moisture of 5.1-5.9%, water activity aw 0.27-0.31 in 80-170 min, and bioactive compound retention of 90-95% (carotenoids 92-95%, betalains 90-94%). It also delivered superior flowability (Carr's index 22.5-30.4%), dispersibility (80-88% in 30 s), and thermal stability (75-85% at 200 °C). Acceleration varied by raw material: maximum for beet (up to 11×) due to soluble sugars and nitrates, minimum for pumpkin (5.5-8×) due to dietary fibers and pectins, and intermediate for carrot (6-9×) influenced by carotenoids' dielectric properties. The results highlight US + VMD's strong potential for producing functional powders to replace synthetic additives in food systems. Effective method selection and parameter optimization require consideration of raw material type and rheological characteristics.

Preparation of stable, free-standing elastic film with hydrophobic surface from water-dispersible polyurethanes (WDPUs) is a challenging task. Here, we have prepared WDPUs from polybutadiene-based diols and the resulting PU films are satisfying the requisites. Two types of diols, namely, hydroxyl-terminated polybutadiene (HTPB) and terminal-functionalized HTPB with dinitrobenzene (DNB) [HTPB-DNB], were used to make WDPUs and the effects of diol structures were investigated. The synthesized WDPUs displayed particle morphology with size in the range of ∼130–270 nm and more than 1 year storage stability. WDPUs yielded stable and free-standing films upon curing and the resulting films showed high thermal and mechanical stabilities. The contact angle of the films is in the range of ∼80–100°, attributing the hydrophobic nature of the surface. Hard segment content of the PU varied from 30 to 40% (by weight) to tune the properties of WDPUs and the resulting films.

G-protein-coupled receptors (GPCRs) are a pivotal superfamily of seven-helix transmembrane receptors responsible for the transduction of stimuli across cellular membranes. They are the targets of ~30% of the pharmaceuticals currently in the market. Understanding how the soft membrane matter (membrane Lipids and Cellular Water) influences the structural changes during the activation of GPCRs is crucial to discovering and developing novel GPCR-targeted drugs. Their dynamic conformational ensembles encompassing various inactive and active states can be biased by the lipids and surrounding aqueous environments [1]. By using different polyethylene glycol (PEG) solutions, we explored the effect of osmotic pressure and lipid bilayer composition on the metarhodopsin equilibrium of the archetypical GPCR rhodopsin in native membranes and POPC recombinant membranes [2]. Our results show a flood of ~80 water molecules into the rhodopsin interior during photoactivation, forming a solvent-swollen Meta-II active state [3]. Under applied osmotic pressure, the overall equilibrium generally shifted to Meta-I. Dehydrating conditions favor Meta-I through the efflux of water from the protein interior while increasing bilayer thickness and the monolayer spontaneous curvature favor Meta-II. The osmotic effect on the protein is more significant than the effect of the lipid bilayer. However, small osmolytes favored the Meta-II state at lower concentrations because they can penetrate the protein core giving a lower excluded volume, decreasing the osmotic effect on the protein and favoring the Meta-II state. Furthermore, the metarhodopsin equilibrium was shifted towards the Meta-I state in POPC recombinant membranes compared to the native membrane environment. Analysis of transducin C-terminal peptide-binding isotherms revealed that the binding affinity is significantly decreased when the lipid environment is changed from the native lipids to POPC lipids. The POPC lipid membrane has zero-spontaneous curvature that shifts the equilibrium towards the more compact, inactive Meta-I state. By contrast, the native lipid membrane environment has a negative spontaneous curvature that favors the more expanded state of Meta-II. Our results delineate the crucial role of soft matter in regulating the metarhodopsin equilibrium in a membrane environment. [1] M.F. Brown (2017) Annu. Rev. Biophys. 46, 379-410. [2] N. Weerasinghe et al. (2018) Biophys. J. 114, 274a. [3] U. Chawla et al. (2020) Angew. Chem. Int. Ed. doi: https://doi.org/10.1002/ange.202003342.

A property of cell membranes which is intimately bound up with electrical double layers is that of the frequency-dependent membrane impedance. The aim of this paper is to outline the basics of the Fourier transform method of measuring impedance across a spectrum of frequencies simultaneously, and to describe practical experimental techniques which the author has used in obtaining these measurements across the intact membranes of two very different kinds of cell.

The need for functional polymers derived from plant-based materials has increased from a carbon-neutral perspective. Herein, six different semialicyclic isosorbide-containing diamine-based polyimides (ISSD-PIs) are synthesized by incorporating isosorbide (ISS), which is a D-glucose derivative, into the diamine moiety to investigate the relationship between the chemical structure and optical, thermal, and dielectric properties. Compared with the conventional fully aromatic PIs, such as Kapton, the as-prepared ISSD-PIs demonstrate excellent optical transparency, low refractive indices (1.554-1.633), low birefringence (0.0084-0.0348) at 1310nm, and low dielectric constants (2.93-3.36) with moderate dissipation factors (0.0112-0.0267) at 10GHz. They also exhibit excellent thermal stability, with glass transition temperatures exceeding 250°C and 5% thermal decomposition temperatures exceeding 400°C. The chirality of the ISS skeleton remains intact, displaying characteristic circular dichroism. This study shows that the incorporation of ISS into PI chains enhances their optical and dielectric properties while maintaining thermal stability by increasing the free volume and reducing intermolecular interactions. In addition, the physical properties of the ISSD-PIs are more dependent on the rigidity of the dianhydride moiety, which directly affects the molecular packing of the PI chains, rather than that of the diamine moiety.

Synthesis of azopolymers with controlled structure and photoinduced birefringence in their LB films