Bilayer Formation Research Articles

Evaluation of the interactions between human stratum corneum and liposome formulations using QCM-D

The interactions between human stratum corneum (SC) and two liposomal formulations, azithromycin (AZM)- and nisin-loaded liposomal formulations designed for topical/intradermal application, were investigated using quartz crystal microbalance with dissipation (QCM-D) using. SC isolated from cadaver skin was affixed onto the QCM sensor’s surface. The liposome formulations were prepared using the thin film rehydration method. The particle sizes of the blank liposome, nisin-loaded, AZM-loaded, and combined-loaded liposomes were measured as 90.7 ± 0.58 nm, 100.8 ± 2.5 nm, 136.9 ± 6.5 nm, and 174.3 ± 9.8 nm, respectively. The frequency shifts when blank and drug-loaded liposomes were passed over the gold surface were ∼20 and ∼25 Hz, respectively as a result of the formation of bilayers in a two-step process, adsorption of intact vesicles followed by the formation of the bilayer upon rinsing with water. The frequency shifts for blank and drug-loaded liposomes on SC were ∼8 and ∼15 Hz, respectively. These results show that the liposomes are deposited as bilayers on SC with both the blank and drug-loaded liposomes. The increase in frequency shifts with drug-loaded liposomes indicate the deposition of drug along with lipids onto both the gold and SC surfaces. More significantly, the data showed much slower kinetics of liposome component spreading onto the SC than on gold. The changes in dissipation that accompanies these differences in frequency shifts show transformation of vesicle onto rigid bilayer on gold upon rinsing with water, but direct formation of lipid bilayers on SC. The findings of this study contribute to a better understanding of the interaction between SC and liposomes, such as adsorption, deformation, and rupture of liposomes on different substrates, paving the way for investigating topical and intradermal mechanisms of drug delivery and cosmetic products developed based on liposome formulations.

Mechanical characterization of freestanding lipid bilayers with temperature-controlled phase.

Coexistence of lipid domains in cell membranes is associated with vital biological processes. Here, we investigate two such membranes: a multi-component membrane composed of DOPC and DPPC lipids with gel and fluid separated domains, and a single component membrane composed of PMPC lipids forming ripples. We characterize their mechanical properties below their melting point, where ordered and disordered regions coexist, and above their melting point, where they are in fluid phase. To conduct these inquiries, we create lipid bilayers in a microfluidic chip interfaced with a heating system and optical tweezers. The chip features a bubble trap and enables high-throughput formation of planar bilayers. Optical tweezers experiments reveal interfacial hydrodynamics (fluid-slip) and elastic properties (membrane tension and bending rigidity) at various temperatures. For PMPC bilayers, we demonstrate a higher fluid slip at the interface in the fluid-phase compared to the ripple phase, while for the DOPC:DPPC mixture, similar fluid slip is measured below and above the transition point. Membrane tension for both compositions increases after thermal fluidization. Bending rigidity is also measured using the forces required to extend a lipid nanotube pushed out of the freestanding membranes. This novel temperature-controlled microfluidic platform opens numerous possibilities for thermomechanical studies on freestanding planar membranes.

One-pot fabrication of bio-inspired shape-morphing bilayer structures

Soft bilayer structures capable of shape morphing in response to external stimuli have been commonly adopted in the design of soft robots, flexible electronics and many other smart systems. However, existing methods to fabricate such structures generally require multiple steps and may end up a weak interface between the two layers. Here, we report a one-pot fabrication strategy to generate elastomer-based shape-morphing bilayer structures with a seamless interface. Our strategy leverages on a recently developed bioinspired polymer-NaCl particle composite system which can undergo significant osmotic swelling in water. Bilayer structures are readily formed after the precipitation of NaCl particles in liquid polymers under gravity and the crosslinking of the polymers. The shape-morphing behavior of the fabricated bilayer structures can be well controlled by tuning the particle precipitation kinetics, NaCl content, and crosslinking level of the polymer matrix. More importantly, the bilayer structures fabricated using this strategy exhibit more complex shape-morphing responses than typical bilayer structures. Considering the wide applicability of NaCl particle-induced osmotic swelling of polymer composites, our one-pot bilayer formation strategy will greatly benefit many shape-morphing applications with a simplified fabrication workflow and enhanced configurational versatility.

Mechanical and Electrical Conductivity Properties of Graphene/Cu Interfaces: A Theoretical Insight.

For graphene/copper (Gr/Cu) composites, achieving high-quality interfaces between Gr and Cu (strong interfacial bonding strength and excellent electron transport performance) is crucial for enabling their widespread applications in electronic devices. This study employs first-principles calculations and the nonequilibrium Green's function method to systematically investigate the mechanical and electrical conductivity properties of Cu(111)/Gr/Cu(111) interfaces with various stacking sequences and different forms of Gr. For these interface systems, the binding energy, separation work, charge transfer, and electrical conductivity across the interface were obtained. The results show that the top-fcc interface exhibits superior interfacial properties, characterized by relatively high binding energy (-3.00 eV/C atom) and separation work (≥0.78 J/m2), a small interfacial distance (2.85 Å), and enhanced electron transport capacity (2.12 G0/nm2). A bilayer form of Gr significantly reduces electronic conductance across the Gr/Cu interface by nearly 2.46 orders of magnitude. Furthermore, point defects in Gr, especially single-vacancy defects, disrupt the traditional trade-offs between mechanical and electrical performance, simultaneously enhancing mechanical performance by 7.50-124.36% and electrical performance by 33.02%. Additionally, stress mechanisms have been proposed to further enhance the interfacial electrical conductivity of Gr/Cu composites. The present study provides a theoretical basis for exploring the engineering applications of Gr/Cu composite materials.

Electroformation of Giant Unilamellar Vesicles from Damp Films in Conditions Involving High Cholesterol Contents, Charged Lipids, and Saline Solutions.

Giant unilamellar vesicles (GUVs) are frequently used as membrane models in studies of membrane properties. They are most often produced using the electroformation method. However, there are a number of parameters that can influence the success of the procedure. Some of the most common conditions that have been shown to have a negative effect on GUV electroformation are the presence of high cholesterol (Chol) concentrations, the use of mixtures containing charged lipids, and the solutions with an elevated ionic strength. High Chol concentrations are problematic for the traditional electroformation protocol as it involves the formation of a dry lipid film by complete evaporation of the organic solvent from the lipid mixture. During drying, anhydrous Chol crystals form. They are not involved in the formation of the lipid bilayer, resulting in a lower Chol concentration in the vesicle bilayer compared to the original lipid mixture. Motivated primarily by the issue of artifactual Chol demixing, we have modified the electroformation protocol by incorporating the techniques of rapid solvent exchange (RSE), ultrasonication, plasma cleaning, and spin-coating for reproducible production of GUVs from damp lipid films. Aside from decreasing Chol demixing, we have shown that the method can also be used to produce GUVs from lipid mixtures with charged lipids and in ionic solutions used as internal solutions. A high yield of GUVs was obtained for Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) samples with mixing ratios ranging from 0 to 2.5. We also succeeded in preparing GUVs from mixtures containing up to 60 mol% of the charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) and in NaCl solutions with low ionic strength (<25 mM).

Influence of hydrogen-bonded 3-mercaptopropionic acid bilayers on binary self-assembled monolayer formation

The influence of the monolayer order, defect density, and bilayer formation on the formation of binary self-assembled monolayers (SAMs) was investigated via the solution-phase displacement of 3-mercaptopropionic acid (MPA) by 1-decanethiol (DT). The ultrahigh vacuum scanning tunneling microscopy results confirm that well-ordered, pristine MPA SAMs are displaced at slower rates than MPA SAMs with less long-range order and greater defect density. Furthermore, MPA samples containing regions of an MPA bilayer displayed the slowest rates of displacement with DT. For pristine MPA samples and MPA samples with regions of an MPA bilayer, displacement with DT resulted in the formation of the low-density, lying down phase of DT. Our results suggest that the presence of an MPA bilayer, the result of hydrogen bonding between carboxylic acid groups in MPA, significantly lowers the rate of total displacement of MPA by DT compared to moderately defected MPA SAMs. These results highlight the importance of the structure, composition, and intermolecular forces, such as hydrogen bonding, when considering binary SAM formation via solution-phase displacement methods.

Aggregation Characteristics of Biobased Anionic Surfactant, Hydroxy Alkane Sulfonate in Aqueous CaCl2 Solutions: Vesicle and Supported Bilayer Formation.

Vesicles are known to spontaneously adsorb onto solid-liquid interfaces and to form supported bilayers in aqueous solution. Cationic surfactants have typically been used to generate supported bilayers because solid surfaces in water are often negatively charged. The present study investigated the aggregation behavior of an anionic surfactant, hydroxy alkane sulfonate having a C18 alkyl chain (C18HAS) in aqueous CaCl2 solutions. These assessments were performed by acquiring data related to equilibrium surface tension, the solubilization of an oil-soluble dye, UV-visible transmittance, pyrene fluorescence and dynamic light scattering together with freeze-fracture transmission electron microscopy observations. The results suggest that C18HAS can form vesicles in aqueous CaCl2 solutions under certain surfactant concentrations. Specifically, this aggregation behavior is greatly affected by C18HAS/CaCl2 molar ratio. At the C18HAS/CaCl2 molar ratio is less than an equivalence point (that is, less than 2:1), phase separation occurs with the formation of a vesicle above solubility limit of the C18HAS Ca salt. On the other hand, in the case that the C18HAS/CaCl2 molar ratio is above an equivalence point (that is, above 2:1), the Na salt of C18HAS forms micelles above the critical micelle concentration (cmc), causing solubilization of vesicles. Analyses by high-speed atomic force microscopy demonstrated that the C18HAS vesicles can spontaneously form a supported bilayer on a negatively charged mica surfaces, similar to the behavior of cationic surfactant vesicles, even though C18HAS is an anionic surfactant. These results suggest that C18HAS could serve as a detergent component but also as a surface modifier when the C18HAS/CaCl2 molar ratio is optimized.

Capillary-Assisted Assembly of Polymer Gel-Supported Lipid Bilayers.

The polymer-supported lipid bilayer represents an attractive supramolecular assembly in numerous biophysical and bioanalytical applications. The assembly of polymer-supported membranes with a polymer layer thickness of just a few nanometers is now well-established, but bilayer properties in such a membrane architecture are still influenced by the nearby solid substrate. Polymer-supported lipid bilayer systems with a several micrometers thick polymer layer will overcome this shortcoming. However, formation of a fluid lipid bilayer on a fully hydrated, micrometer thick polymer film using traditional methods (e.g., vesicle fusion and lipid monolayer deposition techniques) remains a challenging task due to the rather unfavorable interfacial conditions for bilayer formation in such a system. Here, we report for the first time on the facile capillary-assisted formation of a lipid bilayer on the surface of a fully hydrated, several micrometers thick polyacrylamide (PAA) gel, in which forced molecular crowding of lipids at the air-water interface of the capillary results in monolayer instability and collapse, thereby forming a lipid bilayer on the top of the polymer gel inside the capillary. Stable bilayer attachment on the surface of the polymer gel can be achieved via physisorption or specific chemical linkages (tethering) on both cross-linked and non-cross-linked PAA films. Unlike the traditional solid-supported lipid bilayer (SLB), the lipid lateral diffusion in the polymer gel-supported lipid bilayer is not anymore perturbed by a solid substrate. Instead, more like a plasma membrane, it is mainly influenced by the properties of the underlying polymer and the nature/distribution of polymer-bilayer attachments. Polymer gel-supported lipid bilayers built using the capillary-assisted assembly approach show attractive self-healing properties, resulting in superior long-term stability relative to the SLB. We hypothesize that the described capillary-assisted assembly method can be applied to a wide range of polymeric materials and lipid compositions, opening exciting opportunities as an advanced model membrane system.

Hexagons on rectangles: Epitaxial graphene on Ru[formula omitted]

Ruthenium is emerging as a promising candidate to replace copper in highly integrated electronics by enabling barrierless metallization in ultrathin interconnects. From this perspective, the study of graphene growth on such surface templates is of paramount importance as a platform for graphene integration in electronic devices. In particular, graphene growth on the Ru(101‾0) surface allows selective growth of different graphene orientations, one-dimensional structures, and reduced substrate interaction compared to the well-established hexagonal Ru(0001) substrate. Real-time growth observations using low-energy electron microscopy and micro-diffraction highlight the influence of substrate symmetry on graphene growth, leading to the formation of rectangular islands with distinct zigzag- or armchair-terminated edges. Bilayer formation on Ru(101‾0) occurs by nucleation of graphene nanoribbons under the monolayer. Micro-spot angle-resolved photoemission spectroscopy shows significantly less charge-transfer doping in these freestanding, zigzag-terminated bilayer graphene nanoribbons, indicating reduced graphene-substrate interaction and hence more effective decoupling as compared to graphene/Ru(0001). Our results show that the growth of graphene on non-hexagonal substrates opens new pathways for tailoring the graphene-substrate interaction at the interface, and thus the properties of graphene beyond the limits imposed by hexagonal substrates.

(Invited) Spironanographenes: Chemospecific Scholl Reaction, Unexpected Formation of Bilayers and Donor-Acceptor Behavior

Bottom-up benchtop synthesis of nanometric fragments of graphene, molecular nanographenes (NGs), allows the design and monodisperse preparation of molecules with structures, and thus properties, at will. The most commonly employed methodology has mainly consisted in the π-extension of a central scaffold followed by a graphitization step, in which the honeycomb pattern of the final molecular nanographene is formed. The vast majority of syntheses involving molecular nanographenes, employ the Scholl reaction as graphitization step. This dehydrogenative C–C coupling, first described by Roland Scholl in 1910, has now become one of the most powerful reactions in NGs synthesis, although its mechanism pathway is still under debate.In this connection, in early 2023, we reported a chemospecific Scholl reaction depending on the electronic nature of the central scaffold. The formation of stabilized trityl cations using anthracene as central scaffold, led to the formation of spirocycles under Scholl reaction conditions, without interrupting the graphitization process, for the first time (Figure a).1 In contrast, the destabilization of the trityl cation by including fluorine atoms afforded helically arranged NGs (Figure b).2 Furthermore, in order to study the electronic communication in spironanographenes, recently we have extended the π-system of spirobifluorene yielding to two-fold chiral spironanographenes (Figure c). Surprinsingly, the π-π interactions of the graphitic moieties avoid their orthogonal disposition yielding a bilayer that could lead to important electronic features due to the overlap of the two fragments (Figure d).3 [1] P. Izquierdo-García, J. M. Fernández-García, J. Perles, I. Fernández, N. Martín. Angew. Chem. Int. Ed. 2023, 62, e202215655[2] P. Izquierdo-García, J. M. Fernández-García, I. Fernández, J. Perles, N. Martín. J. Am. Chem. Soc. 2021, 143, 11864–11870.[3] P. Izquierdo-Garcia, J. M. Fernandez-Garcia, S. Medina Rivero, M. Samal, J. Rybacek, L. Bednarova, S. Ramirez-Barroso, F. J. Ramirez, R. Rodriguez, J. Perles, D. Garcia-Fresnadillo, J. Crassous, J. Casado, I. G. Stara, N. Martin, J. Am. Chem. Soc. 2023, 145, 11599. Figure 1

Enhanced properties in Si3N4/Cu AMB joints through regulating interfacial reaction modes induced by Mo-particle additives

Si3N4 ceramics are the new package materials for large-power electronics and devices, which are required to be bonded to the high-thermal-and-electrical-conductivity metal, Cu. Among the methods to join Si3N4 and Cu, active metal brazing (AMB) is widely used, but the joint still faces the challenge of interface bonding reliability for harsh services. Here, a novel approach for enhancement of the Si3N4 AMB joint by regulating interfacial products to be a unitary nanograined TiN layer was proposed. To achieve this, the Si3N4/Cu AMB joint was obtained with an Ag–Cu–In–Ti foil whose formation mechanism was investigated, and the detailed morphology of TiN + Ti5Si3 bilayer was observed at brazing temperatures from 740 to 800 °C. Based on the bilayer formation process, adding different Mo contents from 5 to 20 wt % to hinder the formation of Ti5Si3, obtaining a nanograined TiN layer at the interface with hard-to-observed Ti5Si3 particles around. In the seam, Ag and Cu solid solutions and Cu2InTi were refined after adding Mo, but Cu4Ti and Cu3Ti2 were not generated in the seam, only with CuTi distributed dispersedly. Although the fractures both occurred at the Si3N4/filler interface, the joint with Mo additions had higher strength than those with Mo-free. This was because the reduced CTE of the filler alleviated the residual stress during brazing, the refinement in microstructure as a consequence of nucleation-points Mo functioned, and the unitary TiN layer allowed the joints to bear more load particularly. As a result, the maximum strength of joints with Mo additions reached 424 MPa, 115 MPa higher than those brazed with a foil, and significantly more reliable than joints reported by other literature.

Two-dimensional platinum borides: A Dirac nodal line quantum electrocatalyst for efficient hydrogen evolution reaction

Two-dimensional (2D) catalysts exhibiting high carrier mobility, near-zero Gibbs free energy (ΔGH*), and an active basal plane are highly desirable for optimizing the hydrogen evolution reaction (HER). However, fusing these attributes within a solitary material encounters profound difficulties. Utilizing density functional theory (DFT) calculations, we have identified the PtB2 monolayer is such a candidate, demonstrating exceptional dynamical, thermal, and mechanical stability. The band structure analysis reveals that the PtB2 monolayer features double Dirac points along its high-symmetry lines. The estimated Fermi velocity of the PtB2 monolayer is as high as 7.8×105m/s, close to that of graphene. By scanning the Dirac points in the first Brillouin Zone, the Dirac points constitute a nodal-line semimetal with a loop centered at the Γ point. This nodal line is anticipated to facilitate charge transfer between the catalyst surfaces and reaction intermediates, potentially enhancing catalytic efficiency. Importantly, PtB2 monolayer boasts superior HER performance, with a nearly zero ΔGH* of 0.057 eV at its boron-dominant sites. The application of a subtle 1% strain serves to reduce its ΔGH* to an even more favorable −0.003 eV, suggesting significantly improved HER capabilities. When layered in a bilayer form, the PtB2 exhibits van der Waals (vdW) type interlayer interactions. Remarkably, we found that varying the stacking order can effectively alter the nodal line's shape and, accordingly, the PtB2 layer's catalytic properties. The distinctive combination of a Dirac nodal line, ideal Gibbs free energy, and expansive active sites positions the PtB2 monolayer as a competitive 2D quantum catalyst for hydrogen production.

Comparison of lattice thermal conductivity using ab-initio DFT, machine learning interatomic potentials, and temperature dependent effective potential: a case study of hexagonal BN and BP bilayer

Discovering high thermal conductivity materials is essential for various practical applications, particularly in electronic cooling. The significance of two-dimensional (2D) materials lies in their unique properties that emerge due to their reduced dimensionality, making them highly promising for a wide range of applications. Hexagonal boron nitride (BN), both monolayer and bilayer forms, has garnered attention for its fascinating properties. In this work, we focus on bilayer boron phosphide (BP), which is isostructural to its BN analogue. The lattice thermal conductivity of both bilayer BN and BP have been calculated using ab-initio density functional theory, machine learning with the moment tensor potential method, and the temperature-dependent effective-potential method (TDEP). The TDEP approach gives more accurate results for both BN and BP materials. The lattice thermal conductivity of bilayer BP is lower than that of bilayer BN at room temperature, attributed to increased phonon anharmonicity. This study highlights the importance of understanding phonon scattering mechanisms in determining the thermal conductivity of 2D materials, contributing to the broader understanding and potential applications of these materials in future technologies.

Droplet Polymer Bilayers for Bioelectronic Membrane Interfacing.

Model membranes interfaced with bioelectronics allow for the exploration of fundamental cell processes and the design of biomimetic sensors. Organic conducting polymers are an attractive surface on which to study the electrical properties of membranes because of their low impedance, high biocompatibility, and hygroscopic nature. However, establishing supported lipid bilayers (SLBs) on conducting polymers has lagged significantly behind other substrate materials, namely, for challenges in membrane electrical sealing and stability. Unlike SLBs that are highly dependent on surface interactions, droplet interface bilayers (DIBs) and droplet hydrogel bilayers (DHBs) leverage the energetically favorable organization of phospholipids at atomically smooth liquid interfaces to build high-integrity membranes. For the first time, we report the formation of droplet polymer bilayers (DPBs) between a lipid-coated aqueous droplet and the high-performing conducting polymer poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). The resulting bilayers can be produced from a range of lipid compositions and demonstrate strong electrical sealing that outcompetes SLBs. DPBs are subsequently translated to patterned and planar microelectrode arrays to ease barriers to implementation and improve the reliability of membrane formation. This platform enables more reproducible and robust membranes on conducting polymers to further the mission of merging bioelectronics and synthetic, natural, or hybrid bilayer membranes.

Wafer-scale porous germanium bilayer structure formation by fast bipolar electrochemical etching

Recently, porous Germanium (PGe) structures have gained significant attention as a promising engineering material for a broad range of applications due to the versatility of its intrinsic physical and chemical properties. The Conventional Bipolar Electrochemical Etching (CBEE) technique favours a cost-effective and controlled synthesis of PGe layers, to tune the structural properties. However, some challenges still persist. Specifically, the etch rate of these layers remains low limited, resulting in extended process times. Achieving low porosity layers (< 40 %) remains unclear, and addressing the development of a non-sponge morphology is necessary for various fields, such as batteries. In this work, we investigate the impact of the anodic current density and electrolyte ratio on tubular single PGe layer (T-PGe) morphology with low porosities using a Fast Bipolar Electrochemical Etching (FBEE) process. We have demonstrated T-PGe structures with no parasitic sponge-like layer on top, providing insights to control their occurrence. We establish the feasibility of such layers as a template for the formation of tubular bilayers on the wafer's scale. This approach emphasizes the fast synthesis of promising T-PGe structures with low porosities (< 40 %).

Liposome Loaded Prostaglandin E2 (PGE2) for Muscle Regeneration

Prostaglandin E2 (PGE2) is an FDA approved lipid signaling molecule for range of disorders. Also, it has a significant therapeutic potential for tissue repair and regeneration. However, to date there are no applications of PGE2 specifically designed for the muscle repair and regeneration. Liposome systems offer several advantages for PGE2 delivery, improved drug stability, reduced side effects, and tissue-specific targeting. Our hypothesis is that encapsulating PGE2 in liposome system will significantly enhance its bioavailability and maintain an effective therapeutic level. The research was designed to optimize PGE2 concentration in muscle cells, study its effect on cells differentiation, use the optimized PGE2 concentration for liposome-loading and testing the delivery system in-vitro and in-vivo using muscle injury models. We further investigated the molecular mechanism and signaling pathways triggered by the intracellular elevation of PGE2 in muscle cells. Optimization results revealed that nM concentration of PGE2 was beneficial while μM concentrations were detrimental. All our studies reported here were conducted with 50nM PGE2. 50nM PGE2 significantly enhances proliferation and myogenic differentiation as indicated by increased fusion index ( p=0.02) compared to a control. Scanning Electron Microscopy (SEM) images confirmed the lipid bi-layer formation with core-shell structure of 3μm liposomes containing PGE2. In-vitro studies on the C2C12 muscles cells showed that PGE2-liposome system significantly increased the intracellular concentration of PGE2 compared to a PGE2-vehicle (DMSO) control ( p=0.019), confirming the effcacy of this delivery system. Additionally, 50nM PGE2 significantly regulated myogenic signaling pathways and genes associated with calcium homeostasis, mitochondrial biogenesis, cellular hypertrophy, and oxidative stress. These findings support the notion that PGE2 induces the acceleration of myogenic differentiation which is supported by our initial signaling pathway analysis. Our in-vitro muscle damage model indicated that 50nM PGE2 can significantly attenuate the muscle damage and regenerate myotubes within 48 hours compared to 4 days in normal control. In conclusion, the findings suggest that liposome-PGE2 delivery system can positively influence myogenic differentiation, muscle properties, and cellular signaling pathways, offering promise for improving the delivery of PGE2 to injured skeletal muscles to assist in their regeneration process. This work was directly supported by NIH-National Institutes of Aging P01AG039355 (MB) and the George W. and Hazel M. Jay and Evanston Research Endowments (MB). Authors were supported by NIH Grants: National Institutes of Aging (NINDS) 2-R01NS105621; NIA-R01AG056504, NIA-2R01AG060341, National Institutes of Diabetes, Digestive, and Kidney Diseases Kidney (NIDDK)-1R01DK119066 to MB, and National Institutes of Neurological Disorders and Stroke (NINDS) 2-R01NS105621 to MB. Also, NIH/NIDC 1R01DE031872-01 (VV). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Unveiling the electronic properties of BiP[formula omitted] triphosphide from bulk to graphene-based heterostructures by first-principles calculations

In our study, we investigated the structural and electronic properties of bismuth triphosphide (BiP3) in its bulk, few-layer, and monolayer forms. We found that BiP3 in bulk exhibits a metallic stable layered structure. The exfoliation energy of 1.07 J/m2 indicates ease exfoliation, comparable to other triphosphides. The band gap varies with thickness, transitioning from semiconductor–metal between four to five layers, influenced by interlayer coupling and quantum confinement. We also investigated the heterostructure created by depositing graphene (G) on few-layer BiP3. In monolayer (G/m-BiP3) and bilayer (G/2L-BiP3) forms, a metal–semiconductor junction is formed, characterized by weak vdW interactions at the interface and exhibiting p-type Schottky contacts. We observed that the Schottky Barrier Height (SBH) can be modulated by altering the interlayer distance between G and BiP3. This adjustment allows transitions between n-type and p-type Schottky contacts in G/m-BiP3 and the formation of an ohmic contact in G/2L-BiP3. Furthermore, applying an electric field affects the SBH, leading to similar transitions and the development of an ohmic contact. Additionally, our study shows that n-doping in graphene increases with the number of BiP3 layers and external electric field application. These properties position BiP3 few-layer as a promising material for nanoelectronic, optoelectronic, and graphene-based devices.

Graphene Oxide‐Assisted Molecular Crystal Co‐Assembly for Large‐Scale Freestanding 2D Photoresponse Heterostructures with Synaptic Plasticity

Abstract2D van der Waals heterostructures (2D vdWHs) have been gaining significant attention in neuromorphic electronics. However, the facile synthesis of large‐scale, high‐quality freestanding 2D vdWHs remains challenge, particularly for organic counterparts due to susceptible nucleation behaviors and weak intermolecular interactions. Here, the study reports a graphene oxide (GO)‐assisted molecular crystal co‐assembly method for one‐step growth of centimeter‐scale freestanding heterostructures. This co‐assembly involves the simultaneous assembling of organic and GO precursors at the liquid–liquid interface, where the amphiphilic nature of GO nanosheets facilitates the diffusion of organic molecules and 2D nucleation of organic crystals, and the nanosheets also become enriched to grow a quasi‐solid film for the bilayer formation. Owing to integrated photosensitive and charge‐trapping properties as well as type II band structure, this heterostructure exhibits exceptional photonic synaptic behaviors, with a paired‐pulse facilitation index of 141% and image recognition of 91%.

Molecular Transportation Conversion of Membrane Tension Using a Mechanosensitive Channel in Asymmetric Lipid-Protein Vesicles.

Giant lipid vesicles composed of a lipid bilayer form complex membrane structures and enzyme network reactions that can be used to construct well-defined artificial cell models based on microfluidic technologies and synthetic biology. As a different approach to cell-mimicking systems, we formed an asymmetric lipid-amphiphilic protein (oleosin) vesicle containing a lipid and an oleosin monolayer in the outer and inner leaflets, respectively. These asymmetric vesicles enabled the reconstitution and function of β-barrel types of membrane proteins (OmpG) and the fission of vesicles stimulated by lysophospholipids. These applications combine the advantages of the high stability of lipids and oleosin leaflets in asymmetric lipid-oleosin vesicles. In this study, to evaluate the versatility of this asymmetric lipid-oleosin vesicle, the molecular transport of the mechanosensitive channel of large conductance (MscL) with an α-helix was evaluated by changing the tension of the asymmetric vesicle membrane with lysophospholipid. A nanopore of MscL assembled as a pentamer of MscLs transports small molecules of less than 10 kDa by sensing physical stress at the lipid bilayer. The amount and maximum size of the small molecules transported via MscL in the asymmetric lipid-oleosin vesicles were compared to those in the lipid vesicles. We revealed the existence of the C- and N-terminal regions (cytoplasmic side) of MscL on the inner leaflet of the asymmetric lipid-oleosin vesicles using an insertion direction assay. Furthermore, the change in the tension of the lipid-oleosin membrane activated the proteins in these vesicles, inducing their transportation through MscL nanopores. Therefore, asymmetric lipid-oleosin vesicles containing MscL can be used as substrates to study the external environment response of complex artificial cell models.

The Chemical Reactivity of Membrane Lipids.

It is well-known that aqueous dispersions of phospholipids spontaneously assemble into bilayer structures. These structures have numerous applications across chemistry and materials science and form the fundamental structural unit of the biological membrane. The particular environment of the lipid bilayer, with a water-poor low dielectric core surrounded by a more polar and better hydrated interfacial region, gives the membrane particular biophysical and physicochemical properties and presents a unique environment for chemical reactions to occur. Many different types of molecule spanning a range of sizes, from dissolved gases through small organics to proteins, are able to interact with membranes and promote chemical changes to lipids that subsequently affect the physicochemical properties of the bilayer. This Review describes the chemical reactivity exhibited by lipids in their membrane form, with an emphasis on conditions where the lipids are well hydrated in the form of bilayers. Key topics include the following: lytic reactions of glyceryl esters, including hydrolysis, aminolysis, and transesterification; oxidation reactions of alkenes in unsaturated fatty acids and sterols, including autoxidation and oxidation by singlet oxygen; reactivity of headgroups, particularly with reactive carbonyl species; and E/Z isomerization of alkenes. The consequences of reactivity for biological activity and biophysical properties are also discussed.