Region Of Bilayer Research Articles

Activating the delivery of a model drug to lipid membrane by encapsulation of cyclodextrin: Combined experimental and molecular docking studies

Drug delivery science is always an important topic as it studies the delivery of therapeutic payloads to the desired target cells without affecting the healthy tissues/cells, thus minimizing drug-induced toxicity. Aiming towards the targeted drug delivery, the present project deals with the delivery of a polarity-sensitive solvatochromic model drug, namely, salt of 8-anilinonaphthalene-1-sulphonic acid (ANSA) to the model bio-membrane (which mimic several aspects of the real cell membrane), more precisely at the lipid-water interface of L–α-Dipalmitoylphosphatidylcholine (DPPC) phospholipid. The drug delivery process has been activated through the binding of dye with cyclodextrin, acting as a drug transporter. Detailed steady-state and time-resolved spectroscopic studies including molecular docking analysis imply the targeted drug delivery of dye, ANSA, towards the lipid-water interface region of lipid bilayers through encapsulation within the cyclodextrin void. Stronger binding interaction of the dye with the lipid bilayers relative to β-cyclodextrin (β-CD) is the foremost reason for the targeted delivery. The present biophysical interaction studies of drug-lipid interaction, thus, may provide a cordial approach for drug formulation and drug delivery.

Sparsely tethered bilayer lipid membranes formed by self-assembly of bicelles: Spectroelectrochemical characterization and incorporation of transmembrane protein

Many biochemical processes related to proper homeostasis take place in cell membranes. The key molecules involved in these processes are proteins, including transmembrane proteins. These macromolecules still challenge the understanding of their function within the membrane. Biomimetic models that mimic the properties of the cell membrane can help understand their functionality. Unfortunately, preserving the native protein structure in such systems is problematic. A possible solution to this problem involves the use of bicelles. Their unique properties make integrating bicelles with transmembrane proteins manageable while preserving their native structure. Hitherto, bicelles have not been used as precursors for protein-hosting lipid membranes deposited on solid substrates like pre-modified gold. Here, we demonstrated that bicelles can be self-assembled to form sparsely tethered bilayer lipid membranes and the properties of the resulting membrane satisfy the conditions suitable for transmembrane protein insertion. We showed that the incorporation of α-hemolysin toxin in the lipid membrane leads to a decrease in membrane resistance due to pore formation. Simultaneously, the insertion of the protein causes a drop in the capacitance of the membrane-modified electrode, which can be explained by the dehydration of the polar region of the lipid bilayer and the loss of water from the submembrane region.

Imaging of short-wavelength spin waves in a nanometer-thick YIG/Co bilayer

We report the imaging of short-wavelength spin waves in a continuous nanometer-thick YIG film with a Co stripe patterned on top. Dynamic dipolar coupling between the YIG film and the Co stripe lowers the spin-wave wavelength when spin waves enter the YIG/Co bilayer region from the bare YIG film, causing partial reflection at the YIG/Co edge. We use time-resolved scanning transmission x-ray microscopy to image the mode conversion process down to a wavelength of 280 nm and extract the spin-wave dispersion, decay length, and magnetic damping in the YIG/Co bilayer. We also analyze spin-wave reflection from the YIG/Co edge and its dependence on the wavelength of incoming and transmitted spin waves.

Single-Molecule Electrical Currents Associated with Valinomycin Transport of K+

A quantitative description of ionophore-mediated ion transport is important in understanding ionophore activity in biological systems and developing ionophore applications. Herein, we describe the direct measurement of the electrical current resulting from K+ transport mediated by individual valinomycin (val) ionophores. Step fluctuations in current measured across a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) bilayer suspended over a ∼400 nm radius glass nanopore result from dynamic partitioning of val between the bilayer and torus region, effectively increasing or decreasing the total number of val present in the membrane. In our studies, approximately 30 val are present in the membrane on average with a val entering or leaving the bilayer approximately every 50 s, allowing measurement of changes in electrical current associated with individual val. The single-molecule val(K+) transport current at 0.1 V applied potential is (1.3 ± 0.6) × 10-15 A, consistent with estimates of the transport kinetics based on large val ensembles. This methodology for analyzing single ionophore transport is general and can be applied to other carrier-type ionophores.

Photoemission study of twisted monolayers and bilayers of WSe2 on graphite substrates

Using microfocused angle-resolved photoemission spectroscopy we investigated microstructures containing regions of single-layer (SL) and bilayer (BL) ${\mathrm{WSe}}_{2}$ on graphite substrates at different twist angles between SL ${\mathrm{WSe}}_{2}$ and graphite and within the BL ${\mathrm{WSe}}_{2}$. Fermi level electrons emitted from the graphite are sharply focused near their $K{}_{gr}$ points in the Brillouin zone, and, when passing through the ${\mathrm{WSe}}_{2}$, get diffracted to form band replicas readily observed in experimental Fermi surface maps from twisted SL ${\mathrm{WSe}}_{2}$/graphite. We investigated two twisted BL ${\mathrm{WSe}}_{2}$ at twist angles $\ensuremath{\sim}{28}^{\ensuremath{\circ}}$ and $\ensuremath{\sim}{10}^{\ensuremath{\circ}}$ and found no evidence of hybridization gaps at the interlayer band-crossing points, that could be precursors of the flat bands at smaller twist angles. Similarly, no such gaps were found for SL ${\mathrm{WSe}}_{2}$/graphite. Experimental results are complemented by theoretical density functional theory calculations, which suggest that a formation of hybridization gaps in the ${\mathrm{WSe}}_{2}$/graphene (which approximates the experimental ${\mathrm{WSe}}_{2}$/graphite system) sensitively depends on the ${\mathrm{WSe}}_{2}$ band character at the crossing point with the graphene Dirac band.

Local dielectric function of hBN-encapsulated WS2 flakes grown by chemical vapor deposition

Hexagonal boron nitride (hBN), sometimes referred to as white graphene, receives growing interest in the scientific community, especially when combined into van der Waals (vdW) homo- and heterostacks, in which novel and interesting phenomena may arise. hBN is also commonly used in combination with two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs). The realization of hBN-encapsulated TMDC homo- and heterostacks can indeed offer opportunities to investigate and compare TMDC excitonic properties in various stacking configurations. In this work, we investigate the optical response at the micrometric scale of mono- and homo-bilayer WS2 grown by chemical vapor deposition and encapsulated between two single layers of hBN. Imaging spectroscopic ellipsometry is exploited to extract the local dielectric functions across one single WS2 flake and detect the evolution of excitonic spectral features from monolayer to bilayer regions. Exciton energies undergo a redshift by passing from hBN-encapsulated single layer to homo-bilayer WS2, as also confirmed by photoluminescence spectra. Our results can provide a reference for the study of the dielectric properties of more complex systems where hBN is combined with other 2D vdW materials into heterostructures and are stimulating towards the investigation of the optical response of other technologically-relevant heterostacks.

NMR and EPR study of the interaction of tris(3-hydroxy-4-pyridinonato) Ga(III) complexes with liposomes that mimic plant membranes

We performed an NMR and EPR study of the interaction of four [Ga(3,4-HPO)3] chelates with liposomes derived from a soybean extract (SEL) and simpler formulations using POPC (100%) and POPE:POPC (50%). Parent [Fe(3,4-HPO)3] chelates are eligible to prevent Iron Deficiency Chlorosis and we took advantage of the likenesses of the ions Fe (III) and Ga (III), and the fact their metal ion complexes are isostructural, to perform a combined NMR and EPR study to get information about the permeation properties of the complexes.The results demonstrate the presence of liposomes loaded with Ga-chelates and that the distribution of complexes alongside the bilayer is dependent on their structure. Two compounds, [Ga(mpp)3] and [Ga(etpp)3], have a higher affinity for the polar region of the liposome bilayer thus suggesting that their structure facilitates their permanence at the root-rhizosphere interface. Chelates [Ga(dmpp)3] and [Ga(mrb13)3] interact with all types of protons of the lipid bilayer thus implying that they travel all along the bilayer structure indicating their higher permeation properties through soybean membranes.The results obtained for compound, [Ga(mrb13)3], which has been included in this work but was not yet tested in plant supplementation experiments, encourage its testing in in vivo plant studies once this study revealed that it interacts strongly with the model membranes. If the results of the future experiments in plants are positive and consistent with the present membrane-interaction studies the latter could constitute a good screening test for future compounds thus saving reagents and time.

Interaction of neutral and protonated Tamoxifen with the DPPC lipid bilayer using molecular dynamics simulation

Tamoxifen as an antiestrogen is successfully applied for the clinical treatment of breast cancer in pre- and post-menopausal women. Due to the side effects related to the oral administration of Tamoxifen (such as deep vein thrombosis, pulmonary embolism, hot flushes, ocular disturbances and some types of cancer), liposomal drug delivery is recommended for taking this drug. Drug encapsulation in a liposomal or lipid drug delivery system improves the pharmacokinetic and pharmacodynamic properties. In this regard, we carried out 200-ns molecular dynamics (MD) simulations for three systems (pure DPPC and neutral and protonated Tamoxifen-loaded DPPC). Here, DPPC is a model lipid bilayer to provide us with conditions like liposomal drug delivery systems to investigate the interactions between Tamoxifen and DPPC lipid bilayers and to estimate the preferred location and orientation of the drug molecule inside the bilayer membrane.Properties such as area per lipid, membrane thickness, lateral diffusion coefficient, order parameters and mass density, were surveyed. With insertion of neutral and protonated Tamoxifen inside the DPPC lipid bilayers, area per lipid and membrane thickness increased slightly. Also, Tamoxifen induce ordering of the hydrocarbon chains in DPPC bilayer. Analysis of MD trajectories shows that neutral Tamoxifen is predominantly found in the hydrophobic tail region, whereas protonated Tamoxifen is located at the lipid–water interface (polar region of DPPC lipid bilayers).

Conformational dynamics of A30G α-synuclein that causes familial Parkinson disease

The first gene shown to be responsible for autosomal-dominant Parkinson’s disease (PD) is the SNCA gene, which encodes for alpha synuclein (α-Syn). Recently, a novel heterozygous A30G mutation of the SNCA gene associated with familial PD has been reported. However, little research has been done on how the A30G mutation affects the structure of α-Syn. So, using atomistic molecular dynamics (MD) simulation, we demonstrate here the key structural characteristics of A30G α-Syn in the free monomer form and membrane associated state. From the MD trajectory analysis, the structure of A30G α-Syn was noticed to exhibit rapid conformational change, increase in backbone flexibility near the site of mutation and decrease in α-helical propensity. The typical torsion angles in residues (Val26 and Glu28) near the mutation site were observed to deviate significantly in A30G α-Syn. In the case of membrane bound A30G α-Syn, the regions that were submerged in the lipid bilayer (N-helix (3-37) and turn region (38-44)) found to contain higher helical content than the elevated region above the lipid surface. The bending angle in the helix-N and helix-C regions were noticed to be relatively higher in the free form of A30G α-Syn (38.50) than in the membrane bound form (370). The A30G mutation in α-Syn was predicted to have an impact on the stability and function of the protein based on ΔΔG values obtained from the online servers. Our results demonstrate that the A30G mutation in α-Syn altered the protein’s α-helical structure and slightly altered the membrane binding. Communicated by Ramaswamy H. Sarma

On the relationship between the properties of planar structures of non-ionic surfactants and their vesicular analogues – Niosomes

In recent years, the study of niosomes as nanocarriers alternative to liposomes has received increasing attention. In contrast to well-studied liposome membranes, many aspects of the behavior of analogous niosome bilayers have not been studied. This paper considers one of these aspects related to the communication between the physicochemical properties of planar and vesicular objects. We present the first results of comparative studies of Langmuir monolayers of binary and ternary (with cholesterol) mixtures of non-ionic surfactants based on sorbitan esters and niosomal structures assembled from the same materials. The Thin-Film Hydration (TFH) method in the gentle shaking version was used to produce the particles of large sizes, while small unilamellar high quality vesicles with a unimodal distribution of particles were prepared by TFH using ultrasonic treatment and extrusion. An analysis of the structural organization and phase state of monolayers based on compression isotherms and supplemented by thermodynamic calculations, as well as the results of determining the particle morphology, polarity and microviscosity of niosome shells, made it possible to obtain fundamental data on the intermolecular interactions of the components and their packing in shells and to relate these data to the properties of niosomes. This relationship can be used to optimize the composition of niosome membranes and predict the behavior of these vesicular systems. It was shown that cholesterol excess creates regions of bilayers with increased rigidity (like “lipid rafts”), which hinders the process of folding film fragments into small niosomes.

Er intercalation and its impact on transport properties of epitaxial graphene

Intercalation of atomic species is a practicable method for epitaxial graphene to adjust the electronic band structure and to tune the coupling between graphene and SiC substrate. In this work, atomically flat epitaxial graphene is prepared on 4H-SiC(0001) using the flash heating method in an ultrahigh vacuum system. Scanning tunneling microscopy, Raman spectroscopy and electrical transport measurements are utilized to investigate surface morphological structures and transport properties of pristine and Er-intercalated epitaxial graphene. It is found that Er atoms are intercalated underneath the graphene layer after annealing at 900 °C, and the intercalation sites of Er atoms are located mainly at the buffer-layer/monolayer-graphene interface in monolayer domains. We also report the different behaviors of Er intercalation in monolayer and bilayer regions, and the experimental results show that the diffusion barrier for Er intercalated atoms in the buffer-layer/monolayer interface is at least 0.2 eV higher than that in the first/second graphene-layer interface. The appearance of Er atoms is found to have distinct impacts on the electronic transports of epitaxial graphene on SiC(0001).

Disorder within disordered regions of protein-free lipid bilayers.

Optical microscopy-based reports on protein-free lipid bilayers with heterogeneous compositions generally consider observed phase separations as thermodynamic endpoints; while MD simulations indicate kinetic characteristics of domain formations. Here, we study GUVs of POPC:DOPE (9:1) and POPC:DPPC (9:1), labeled with disordered-phase probe Liss-RhodPE (1/1000 w/w), using confocal imaging. In addition to confirming previously well-reported disorder and/or phase-separations in vesicular membranes of above compositions, we report the discovery of non-uniform probe distributions within disordered phases, indicating varying degrees of disorder (VDD) for the same vesicular membrane. We further examine dynamics of probe distributions in VDD regions of vesicular membranes. Regression analysis of time-dependent changes in average pixel intensities of probe molecules (avPIs) in different regions of interest (ROIs) allowed quantitative characterization of local (within ROIs) and global (overall vesicular membrane) motion of probe molecules within disordered phases. Optics-related artifacts (e.g., photobleaching, excitation and/or emission fluctuations) were ruled out by noting negligible variations in whole-vesicle avPIs with time. However, avPIs within certain ROIs showed considerable changes with time. In fact, in the same vesicular membrane, avPIs in different ROIs within disordered phases show (a) linear dependence on time (indicating diffusive motion), (b) dependence on square of time (indicating convective motion), and (c) other dependencies on time (e.g., logarithmic, exponential, power, 1/time etc.) - all clubbed together as non-diffusive-non-convective motions. Thus, we rigorously establish existence of further (at least three) levels of heterogeneity, based on dynamics of probe molecules, within disordered phases of protein-free lipid bilayers. Such heterogeneity has previously been ascribed only to biologically active membranes due to presence of membrane proteins. Interestingly, while diffusive motion may be linked to overall membrane viscosity, convective motion may be linked to concepts such as line-tension resulting from heterogeneous compositions.

Retarded Diffusion and Confinement of Membrane-Bound Molecules in a Patterned Hybrid Membrane of Phospholipid Bilayers and Monolayers.

The biological membrane is a complex two-dimensional fluid, in which various molecular interactions regulate the lateral diffusion of membrane-associated molecules. Pinning of membrane proteins or lipids by extra-membrane proteins impedes the diffusion. In addition, coupling between two monolayer leaflets within a phospholipid bilayer via interdigitation plays important roles, though this effect remains elusive. Here, we fabricate a substrate-supported model membrane with patterned bilayer/monolayer regions to explore the influences of interleaflet coupling. A patterned monolayer of polymerized diacetylene phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC), was lithographically generated and used to form patterned lipid bilayers and monolayers. A phospholipid monolayer was formed on top of the polymerized monolayer. The bilayer/monolayer hybrid membrane was continuous and fluid, but lateral diffusion in the monolayer region was significantly retarded, suggesting the influences of interleaflet coupling. We reconstituted photoreceptor rhodopsin (Rh) and G-protein transducin (Gt) as model transmembrane and peripheral proteins. Rh diffused laterally only in the bilayer region, whereas Gt diffused in both bilayer and monolayer regions. The patterned hybrid bilayer/monolayer membrane reproduces the retarded diffusion and confinement of membrane-bound molecules in a controlled manner and provides insight into the physicochemical and functional roles of semipermeable corrals in the cell membrane.

Antimicrobial peptide magainin 2-induced rupture of single giant unilamellar vesicles comprising E. coli polar lipids

Most antimicrobial peptides (AMPs) damage the cell membrane of bacterial cells and induce rapid leakage of the internal cell contents, which is a main cause of their bactericidal activity. One of the AMPs, magainin 2 (Mag), forms nanopores in giant unilamellar vesicles (GUVs) comprising phosphatidylcholine (PC) and phosphatidylglycerol (PG), inducing leakage of fluorescent probes. In this study, to elucidate the Mag-induced pore formation in lipid bilayer region in E. coli cell membrane, we examined the interaction of Mag with single GUVs comprising E. coli polar lipids (E. coli-lipid-GUVs). First, we investigated the Mag-induced leakage of a fluorescent probe AF488 from single E. coli-lipid-GUVs, and found that Mag caused rupture of GUVs, inducing rapid AF488 leakage. The rate constant of Mag-induced GUV rupture increased with the Mag concentration. Using fluorescence microscopy with a time resolution of 5 ms, we revealed the GUV rupture process: first, a small micropore was observed in the GUV membrane, then the pore radius increased within 50 ms without changing the GUV diameter, the thickness of the membrane at the pore rim concomitantly increased, and eventually membrane aggregates were formed. Mag bound to only the outer monolayer of the GUV before GUV rupture, which increased the area of the GUV bilayer. We also examined the physical properties of E. coli-lipid-GUVs themselves. We found that the rate constant of the constant tension-induced rupture of E. coli-lipid-GUVs was higher than that of PG/PC-GUVs. Based on these results, we discussed the Mag-induced rupture of E. coli-lipid-GUVs and its mechanism.

Effects of a single vacancy on electronic properties of a Ca2N electride bilayer

We present the optimized geometric and electronic structures of a defective Ca2N bilayer with a monovacancy. Using first-principles calculations, we investigate effects of a vacancy on the electronic properties of interlayer anionic electrons (IAEs) and surface anionic electrons (SAEs) in defect-free and defected structures. The electron density is non-uniform in the interlayer region of the defective Ca2N bilayer. In the absence of Ca atoms, electrons at a specific position of the interlayer decrease by about 40% compared with a defect-free bilayer. Besides, we obtain simulated images for scanning tunneling microscopy (STM) to explain the SAE states of the 2D electride bilayer. The STM simulation can determine which atom is missing from the STM images. We hope that our study will enable one to understand how defects affect the properties of electrides.

Biophysical interactions of phenolic acids from yerba mate tea with lipid membranes

Yerba mate (Ilex paraguariensis) tea is a well know source of phenolic antioxidants compounds. Caffeoyl derivatives are the primary constituents that account for the antioxidant capacity of this beverage. It was proposed that the interaction of polyphenols with lipid bilayers of various cell types provides the molecular rationale for their hallmark antioxidant and anti-inflammatory activities. In this study, atomistic molecular dynamics (MD) simulations were carried out in order to outline a detailed picture of the molecular interactions between three caffeoyl acids derivatives and two different lipid bilayers. We show that the three phenolic acids are able to interact at the upper regions of lipid bilayers, confining their action to the membrane surface; moreover, the strength of these interactions relay on the probability of metabolite protonation once inserted in the bilayer.

Molecular dynamics simulations of a central nervous system-penetrant drug AZD3759 with lipid bilayer.

AZD3759 is an epidermal growth factor receptor inhibitor with good blood-brain barrier permeability, demonstrating encouraging activity against central nervous system metastases. However, the underlying mechanism was still unclear. In this study, the interaction between AZD3759 and membrane was studied with 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer as a model lipid. Both the cationic and neutral state of AZD3759 were considered in the simulations, and the results show that cationic AZD3759 forms more hydrogen bonds with bilayer than neutral AZD3759, and Coulombic interaction has great effects in the transmembrane process of cationic AZD3759. AZD3759 prefers to reside in the interface between the hydrophilic headgroup region and hydrophobic region of bilayer, and the chloroflurobenzene moiety plays a crucial role in the insertion of AZD3759. PMF results suggest that the hydrophobic region of DMPC bilayer is permeable by AZD3759. Understanding the transmembrane mechanism of AZD3759 at molecular level may provide useful information to the design and optimization of anti-tumor drugs with improved BBB penetration. • The penetration mechanism of AZD3759 with DMPC bilayer was studied by molecular dynamics simulations. • Neutral AZD3759 could penetrate deeper into DMPC bilayer than protonated AZD3759. • The chloroflurobenzene moiety plays a significant role in the insertion of AZD3759 into DMPC bilayer. • The electrostatic interaction is the driving force for the initial binding of AZD3759 to DMPC bilayer. • Our findings may enhance the mechanism understanding of drugs with good BBB permeability.

Combined in-silico and in-vitro experiments support acid-base equilibrium as a tool to estimate the localization depth of 4-nitrophenol within a phospholipid bilayer

The interaction and location of 4-nitrophenol (PNP) in biomembranes are relevant in the bioaccumulation and potentiation of the intensive toxic effects of this persistent organic pollutant. In this work, in-silico analyses predicted that, in a fluid phospholipid bilayer, the minimum energy of the protonated (PNPH) and deprotonated (PNP−) species is located within the glycerol and choline region, respectively. This was experimentally confirmed by acid-base equilibrium experiments and theory, allowing the estimation of the mean location of PNP within a bilayer region with a dielectric constant D = 50.6 compatible with the phosphate/choline moiety of egg-yolk phosphatidylcholine unilamellar (EPC) vesicles. The comparison with the D = 43.2 value obtained in Triton X-100 micelles allow predicting a mean surface potential of ψ = 25.37 mV for the EPC-water interface. Changes in the chemical shifts and longitudinal relaxation times of EPC hydrogens by 1H NMR confirm the deeper location of the PNPH within the glycerol region and at the choline region (PNP−) at higher pH. Intermolecular PNP−EPC dipolar interactions within the choline region was also demonstrated at pH 10.2 using ROESY experiments. Additional information was obtained trough 31P NMR, that detected an increase in the anisotropy at the membrane interface after insertion of PNP which probably act as a bridge between choline moieties rigidizing the crystalline structure at that spot. Concluding, here we provide experimental support to the “pH-piston hypothesis” proposed some decades ago in the pharmaceutical field, and that reinforce the importance of the environmental conditions (e.g. pH) to modulate the bioavailability of this highly toxic pollutant.

Statistically designed novel ranolazine-loaded ethosomal transdermal gel for the treatment of angina pectoris

Ranolazine (RZ) is a newer novel anti-anginal drug with poor solubility and high permeability features. The current research work focused on the statistical design and development of RZ-loaded ethosome as a novel carrier through entrapment and in silico binding affinity studies using molecular docking. The study investigates the prospect of ethosomes as lipid nano-carrier in the form of vesicles for the transdermal enhancement of RZ. The affinity studies of RZ with Phospholipon 90H (PL90H) and a copolymer cholesterol signified the importance of cholesterol in the entrapment of drug in polar region of lipid bilayer in ethosomal vesicle with binding affinity −10.2 kcal/mol that enhanced drug solubility and absorption. In the absence of copolymer, the drug entrapped in non-polar tail with significantly less binding affinity −1.9 kcal/mol. Based on this finding the effective RZ-loaded ethosome compositions were designed and optimized. The Box-Behnken Design (BBD) was applied to fabricate ethosomes with changing amounts of phospholipon PL90H, hydroethanol, and cholesterol. The influence of independent variables PL90H (A), hydroethanol solution (B), and cholesterol (C) on vesicle size (nm), and % entrapment efficiency (%EE) was studied. The optimized ethosome formulation (R4) containing drug in ethosomal vesicle, evaluated using FTIR and XRD techniques, revealed a change in its physical state. Results demonstrated composition R4 with PL90H (100 mg) and hydroethanol (40% w/v) was embedded into Carbopol 934P gel to screen drug permeation and skin irritation. The ethosomal suspension (R4) was demonstrated with ethosome size 165.71 ± 2.73 nm, zeta potential −36.63 ± 2.78 mV, and %EE 80.21 ± 1.27. The optimized ethosomal suspension recorded release of RZ through dialysis membrane against RZ-loaded plain gel; was superior sustained over 24 h. The drug release from ethosomal gel followed a combination of Higuchi and Peppas model. RZ ethosomal gel tested using MTT assay manifested enhanced cytotoxic potential of RZ on H9C2-mouse cardiomyoblast cell line. Incorporation of vesicles into the gel leads to significant improvement in its stability. The present study demonstrates the prospective of ethosomal vesicles in delivering RZ across transdermal layers with the least skin irritation potential proclaiming its better safety, efficacy, and patient compliance.

Efficient Quantification of Lipid Packing Defect Sensing by Amphipathic Peptides: Comparing Martini 2 and 3 with CHARMM36

In biological systems, proteins can be attracted to curved or stretched regions of lipid bilayers by sensing hydrophobic defects in the lipid packing on the membrane surface. Here, we present an efficient end-state free energy calculation method to quantify such sensing in molecular dynamics simulations. We illustrate that lipid packing defect sensing can be defined as the difference in mechanical work required to stretch a membrane with and without a peptide bound to the surface. We also demonstrate that a peptide’s ability to concurrently induce excess leaflet area (tension) and elastic softening—a property we call the “characteristic area of sensing” (CHAOS)—and lipid packing sensing behavior are in fact two sides of the same coin. In essence, defect sensing displays a peptide’s propensity to generate tension. The here-proposed mechanical pathway is equally accurate yet, computationally, about 40 times less costly than the commonly used alchemical pathway (thermodynamic integration), allowing for more feasible free energy calculations in atomistic simulations. This enabled us to directly compare the Martini 2 and 3 coarse-grained and the CHARMM36 atomistic force fields in terms of relative binding free energies for six representative peptides including the curvature sensor ALPS and two antiviral amphipathic helices (AH). We observed that Martini 3 qualitatively reproduces experimental trends while producing substantially lower (relative) binding free energies and shallower membrane insertion depths compared to atomistic simulations. In contrast, Martini 2 tends to overestimate (relative) binding free energies. Finally, we offer a glimpse into how our end-state-based free energy method can enable the inverse design of optimal lipid packing defect sensing peptides when used in conjunction with our recently developed evolutionary molecular dynamics (Evo-MD) method. We argue that these optimized defect sensors—aside from their biomedical and biophysical relevance—can provide valuable targets for the development of lipid force fields.