Nonpolar Tail Research Articles

The Membrane Dipole Potential and the Roles of Interfacial Water and Lipid Hydrocarbon Chains.

Understanding membrane charge transport processes, including the actions of ion channels, pumps, carriers, and membrane-active peptides, requires a description of the electrostatics of the lipid bilayer. We have simulated a library of different lipid chemistries to reveal the impact of the headgroup, glycerol backbone, and hydrocarbon chains on the membrane dipole potential. We found a strong dependence of the potential on lipid packing, but this was not caused by the packing of lipid polar components, due to cancellation of their electric fields by electrolyte. In contrast, lipid tail contributions were determined by area per lipid, arising from two countering effects. Increased area per lipid leads to chain tilting that increases methylene dipole projections to strengthen the electric field within the bilayer, while at the same time decreasing the electric field from terminal methyl groups. Moreover, electric fields from some nonterminal groups and the terminal methyl group can extend beyond the bilayer center and be canceled by the opposing leaflet. This interleaflet field annulment explains the experimental reduction in dipole potential for unsaturated and branched lipid bilayers, by as much as ∼200 mV, as well as experiments that substitute chain carbons with sulfur. Replacing ester with ether groups (eliminating two carbonyl groups) causes a significant reduction in potential, also by ∼200 mV, in agreement with experiment. We show that the effect can be largely attributed to the loss of aligned water molecules in the glycerol backbone region, lowering the potential inside the bilayer core. When only one of the two carbonyls is removed (using a hybrid ester-ether lipid or a single-chain lipid), most of this reduction in potential was lost, with the single carbonyl group able to maintain full hydration in the interfacial region. While headgroup chemistry can have a major effect (by as much as ±100 mV relative to phosphatidylcholine), anionic headgroups either decrease or increase the dipole potential, with the variation involving perturbation in hydrogen-bonded water molecules and changes in packing of lipid tails. Overall, these results suggest that membrane electrostatics are dominated by aligned water molecules at the polar-hydrocarbon interface and, surprisingly, by the charge distribution of the nonpolar lipid tails, and not the packing of headgroup and glycerol carbonyl dipoles.

Substantial breakdown of the hydrogen-bonding network, local density inhomogeneities and fluid-liquid structural transitions in supercritical octanol-1: A molecular dynamics investigation.

Molecular dynamics simulations have been employed to explore the hydrogen-bonding structure and dynamics in supercritical octanol-1 at a near-critical temperature and up to high densities and pressures. A substantial breakdown of the hydrogen-bonding network when going from ambient-liquid to supercritical conditions is revealed. The fraction of the non-hydrogen bonded molecules significantly increases in supercritical octanol-1, and a substantial decrease in the intermittent hydrogen-bond lifetime is observed. This behavior is also reflected on the maximum local density augmentation, which is comparable to the values obtained for non-polar and non-hydrogen bonded fluids. The existence of a structural transition from an inhomogeneous fluid phase to a soft-liquid one at densities higher than 2.0 ρc is also revealed. At higher densities, a significant change in the reorientational relaxation process is observed, reflected on the significant increase in the ratio of the Legendre reorientational times τ1R/τ2R. The latter becomes much higher than the value predicted by the Debye model of diffusive reorientation and the corresponding ratio for ambient liquid octanol-1. The non-polar tail of octanol-1 under supercritical conditions reorients more slowly in comparison with the polar tail. Interestingly, the opposite behavior is observed for the ambient liquid, further verifying the strong effect of the breakdown of the hydrogen bonding network on the properties of supercritical octanol-1. In accordance with the above-mentioned findings, the static dielectric constant of supercritical octanol-1 is very low even at high densities and pressures, comparable to the values obtained for non-polar and non-hydrogen bonded fluids.

Stability of Cytoplasmic Membrane of Escherichia coli Bacteria in Aqueous and Ethanolic Environment.

The mechanism of action of any antibacterial agent or disinfectant depends largely on their interaction with the bacterial membrane. Herein, we use the SPICA (surface property fitting coarse graining) force-field and develop a coarse-grained (CG) model for the structure of the cytoplasmic membrane of Escherichia coli (E. coli) and its interaction with water and ethanol. We elucidate the impact of different concentrations of ethanol on the cytoplasmic membrane bilayers and vesicles of E. coli using the CG molecular dynamics (CG MD) simulations. Our modeling approach first focuses on the parametrization of the required force-field for POPG lipid and its interaction with water, ethanol, and POPE lipid. Subsequently, the structural stability of the E. coli bacterial membrane in the presence of high and low concentrations of ethanol is delineated. Both flat bilayers as well as vesicles of E. coli membrane were considered for the CG MD. Our results reveal that, at low ethanol concentrations (<30 mol %), the size of the E. coli vesicles increases with discernible deformations in their shapes. Because of ethanol-induced interdigitation, thinning of the E. coli vesicular membrane is also observed. However, at higher ethanol concentrations (>30 mol %), the integrity of the vesicles is lost because of deteriorating invasion of ethanol molecules into the vesicle bilayer and significant weakening of lipid-lipid interactions. At higher ethanol concentrations (40 and 70 mol %), both the multivesicle and single-vesicle bacterial membranes exhibit a similar rupturing pattern wherein the extraction of lipids from the membrane and formation of aggregates of the component lipids are observed. These aggregates consist of polar head groups of 3-5 POPE/POPG lipids with intertwined nonpolar tails.

Insight into the flame-retardant mechanism of different organic-modified layered double hydroxide for epoxy resin

Aiming to enhance the flame-retardant efficiency of layered double hydroxide (LDH) in epoxy resin (EP), positively charged LDH was modified by incorporating various anionic modifiers, resulting in a series of organically modified LDH. These modifiers were selected based on the length of nonpolar tails with and without aromatic ring such as sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS) and sodium benzene sulfonate (SBS). The chemical composition, structure and hydrophobicity of organic-modified LDH were characterized and the flame-retardant efficiency of organic-modified LDH in EP were investigated. The incorporation of organic-modified LDH into EP resulted in improved Tg and flame retardancy, which depended on the type of modifiers used as well as the structure and loading amount of LDH. Particularly, LDH@DBS exhibited higher improvement efficiency in flame retardancy and Tg than that of LDH@BS and LDH@DS due to the enlarged interlayer spacing, which facilitated the homogeneous dispersion and compatibility in the epoxy matrix. These results demonstrated that good compatibility between organic-modified LDH and polymer was advantageous to enhance the flame-retardancy efficiency and thermal mechanical properties of polymer.

Molecular Design of Competitive Solvation Electrolytes for Practical High‐Energy and Long‐Cycling Lithium‐Metal Batteries

AbstractElectrolytes with high stability against both Li anode and high‐voltage cathode are critical for high‐energy and long‐cycling lithium metal batteries (LMBs). However, the free active solvents in common electrolytes are susceptible to decomposition at both Li anode and high‐voltage cathode. Although recently developed locally high‐concentration electrolytes (LHCEs) have largely restricted active solvents via Li+ coordination, the free molecules are still released upon the desolvation of Li+ at the surface of electrodes, causing continuous decomposition during long‐cycling processes. Here, a molecule competitive solvation electrolyte (MCE) is shown to stabilize high‐voltage LMBs by introducing a well‐designed and newly synthetic bipolar solvent molecule with one ion‐dissociative polar head and the other highly fluorinated nonpolar tail. The bipolar molecules competitively dissociate Li+ via weak coordination interactions, drastically reducing the ratio of active solvents in electrolytes and the detrimental decomposition at electrodes during the desolvation processes. Consequently, the MCE enables a 1.4‐Ah Li metal pouch cell with a stack energy density of 450 Wh kg−1 along with exceptional operation stability over 400 cycles (retention: 81%). Furthermore, the MCE also maintains the stable operation of a 2.5‐Ah Li‐S pouch cell with an excellent energy density of 417 Wh kg−1 for 70 cycles under practical conditions.

Effect of aromatic ring on surface and self‐assembly properties of synthesized heterocyclic‐based surfactants

AbstractHeterocyclic‐based cationic surfactants with dodecyl tail group bridged to the head group either via aromatic ether [3‐(4‐dodecyloxybenzyl)‐1‐methyl‐imidazolium bromide (Ar‐I) and 4‐(4‐dodecyloxybenzyl)‐4‐methyl‐morpholinium bromide (Ar‐M)] or via aliphatic ether [3‐(2‐dodecyloxyethyl)‐1‐methyl imidazolium bromide (Al‐I) and 4‐(2‐dodecyloxyethyl)‐4‐methyl morpholinium bromide (Al‐M)] were synthesized and characterized using different spectral techniques. For the synthesis of Ar‐I and Ar‐M, 4‐hydroxybenzoic acid was esterified initially, followed by O‐alkylation, reduction, bromination and finally quaternization either with 1‐methylimidazole or with 4‐methylmorpholine. For the synthesis of aliphatic analogues (Al‐I and Al‐M), ethylene glycol was initially alkylated, followed by tosylation, bromination and quaternization either with 1‐methylimidazole or with 4‐methylmorpholine. Synthesized surfactants were evaluated for surface and self‐assembly properties. Impact of the presence or absence of phenyl ring bridging the polar head and nonpolar tail of the surfactant and also type of heterocyclic moiety in the head group region on micellization and surface properties such as wetting, foaming and emulsification was studied. Surfactants with the bridged aromatic ether moiety were observed to display lower critical micelle concentration than those with the bridged aliphatic ether moiety irrespective of type of heterocyclic molecule in the head group region. Foam volume and stability of the aromatic ether‐bridged surfactant were observed to be superior to their corresponding aliphatic analogs. Similar trend was observed in stabilizing the emulsion. However, aromatic ether‐bridged surfactant depicted poor wetting ability compared to their aliphatic analog. Aliphatic ether bridged surfactant showed higher aggregation number compared to their aromatic counterparts, but depicted similar micellar core polarity.

A Nonflammable Electrolyte for High-Voltage Lithium Metal Batteries

The electrochemical instability of the polar solvents in electrolytes often causes reduction/oxidation at the surface of both Li anodes and nickel-rich cathodes in high-voltage lithium metal batteries (LMBs). Here, we design a bipolar molecule-regulated electrolyte with a capsule-like solvation structure and nonflammability to stabilize high-voltage LMBs. The key enabler is to design and synthesize a nonflammable bipolar molecule with a ion-dissociative polar head and a perfluorinated nonpolar tail. The bipolar solvent promotes the formation of capsule-like solvation sheaths via weak coordination and encapsulates the polar molecules inside the primary solvation shell, drastically reducing the detrimental decomposition of solvents. Finally, the assembled high-voltage cell provides high capacity retention (Li||LiNi0.8Co0.1Mn0.1O2: >90%) during 200 charge/discharge cycles under strict conditions. The capsule-like electrolyte also enables a 420 mAh pouch cell with a cell-level energy density of 440 Wh kg–1 along with long cycling stability over 150 cycles (retention: 92%).

Biomimetic lipid-fluorescein probe for cellular bioimaging.

Fluorescence probe is one of the most powerful tools for cellular imaging. Here, three phospholipid-mimicking fluorescent probes (FP1-FP3) comprising fluorescein and two lipophilic groups of saturated and/or unsaturated C18 fatty acids were synthesized, and their optical properties were investigated. Like in biological phospholipids, the fluorescein group acts as a hydrophilic polar headgroup and the lipid groups act as hydrophobic non-polar tail groups. Laser confocal microscope images illustrated that FP3, which contains both saturated and unsaturated lipid tails, showed great uptake into the canine adipose-derived mesenchymal stem cells.

Self-propelled cellular translocation of Janus-shaped graphene quantum dots: A molecular dynamics simulation and thermodynamic analysis

Although spatially heterogeneous oxidation is pivotal to the cellular translocation process of graphene quantum dots (GQDs), the dynamical road to the thermodynamically stable translocation conformation remains hazy. In this study, we illuminate the bio-interface doctrine involving the cellular translocation of Janus-shaped oxidized GQDs by performing multi-dimensional pathway computations predicated on coupled microsecond-long molecular dynamics and well-tempered metadynamics simulations. The oxidation nanodomains of Janus-shaped GQDs spontaneously yield hydrogen-bonds with polar lipid heads, while their pristine graphene nanodomains hydrophobically associate with nonpolar lipid tails, and thus respond as self-propelled nanomotors across biological membranes. Hydrophobic-associations and hydrogen-bondings are found to be competitively coordinated, which dictates the dynamic pathway and thermodynamic states for cellular translocation, particularly modulating the adaptive self-propelling activity. The translocational phase diagram is drawn, demonstrating that GQDs with moderately square-patterned oxidation and thin thickness facilitate excellent translocation and minimal biological nanotoxicity. Importantly, intermolecular mechanochemistry is discovered to play a crucial role in energy transduction and nanomechanical interactions, which in turn affect the spatial rotation pathways of GQDs, as well as the membrane perturbations. Overall, this study provides an intuitive insight into the dynamics and thermodynamics of spontaneously translocating GQDs, opening up brand-new avenues for developing GQD-enabled nanocarriers or antibiotics.

Emulsification of low viscosity oil in alkali-activated materials

This research aims to understand the mechanisms enhancing the fixation of low viscosity mineral oils, including tailings, in reactive inorganic matrices, by emulsification. To this purpose, significant amounts of a model low viscosity pure mineral oil (20%vol) are immobilized in alkali-activated materials (AAM), either based on metakaolin or blast furnace slag. In such case, Portland cement-based matrices are not adequate (emulsification delicate to manage and excessive setting retardation). Various surfactants are used to ease the oil emulsion.Visual observation and rheology evidence two distinct groups of surfactants. One contributes to structuring the oil/AAM fresh mix, with greater viscosity than without surfactant; the other includes non-structuring surfactants, without change in viscosity. Each group depends on the AAM considered.Whatever the AAM and the surfactant, the oil droplet size decreases significantly, without consistent correlation with the interfacial tension between oil/activating solution (AS). Interfacial tension alone does not explain the reduction in oil droplet size. Characterization of diluted ternary suspensions (solid particles – oil – AS) relates the structuring effect to interactions between oil and solid particles, through the surfactant polar head groups and non-polar hydrocarbon tails. A detailed mechanism explaining the oil stabilization and the mix structuring is discussed.

Ethosomes: A carrier for Transdermal Drug Delivery System

In our five sense organs skin is the biggest organ which prevents entry of different foreign particles into the systemic circulation. For our body drug is also considered as a foreign particle hence it is difficult task to reach the drug into systemic circulation through the transdermal route without invasion. Now a day’s many novel formulations are present in the market which allows the transfer of drug through the transdermal route without invasion like liposomes, phytosomes, neosomes and ethosomes. But with the help of ethosome formulation it becomes very easy to transfer the drug into systemic circulation through the transdermal route. Large drug molecules can be delivered to site of action by ethosomes. Ethosomes are the bilayer lipid vesicles which allow the transfer of drug into the deep skin layers and into the blood. It contains large amount of ethanol and penetration enhancers are incorporated into it to enhance the rate of penetration. It contains the phospholipid bilayer with polar head and nonpolar tail. At the center ethanolic cavity is present which is filled with the hydroethanolic solution. We can incorporate all types of drug into the ethosome i.e., lipophilic, hydrophilic, and amphiphilic and this property makes it unique from other dosage forms. Further we can formulate cream, gel or patches of ethosomes. Cellutight EF, Nanominox, Noicellex, Supravir cream these are some examples of marketed ethosomal formulations. This review summarizes the types of ethosomes i.e., classical ethosomes, binary ethosomes and transethosomes. And also includes advantages, disadvantages, therapeutic applications, methods of preparation and characterization of the ethosomes.

Photo-Curable Lacquer Sap Resin Based on Urushiol-Mimicking, Tyrosine-Containing Additive.

Oriental lacquer sap is attracting considerable attention as a renewable and eco-friendly natural resin with high durability, heat resistance, insulation, insect repellency, and antiseptic and antibacterial properties. However, to ensure excellent coating performance, it is necessary to improve the drying/curing process of lacquer sap with a time-consuming drying time at high humidity [relative humidity (RH), 70-90%] and ambient temperature (20-30 °C). Drawing on an understanding of the polymerization mechanism of urushiol, the main component of the lacquer sap consisted of a water-in-oil (W/O) emulsion, and this study presents an eco-friendly additive that mimics the structure-function of urushiol composed of a polar catechol head group and a nonpolar hydrocarbon tail. A photo-curable lacquer sap was thus developed by adding a tyrosine amino acid-based lipid agent (denoted as Y-ADDA), which allows faster and more effective drying/curing at lower humidity while maintaining the nature-derived properties of lacquer sap. Y-ADDA easily coassembles with urushiol in the W/O emulsion droplets, thereby significantly accelerating the formation of a polymer network along with urushiol during water evaporation leading to fast drying/curing under ultraviolet (UV) light irradiation at low humidity (∼50% RH). The UV-cured lacquer sap resins showed higher performance in terms of film processing and physicochemical properties compared with that of the lacquer containing only tyrosine amino acids without aliphatic tail conjugation, N-(9-fluorenylmethoxycarbonyl)-O-tert-butyl-l-tyrosine Fmoc-Tyr(tBu)-OH. Furthermore, the drying and curing times, film morphology, transmittance, hardness, and adhesion strength of the UV-cured lacquer were markedly superior compared to those of shellac, a general eco-friendly fast-drying primer. The study provides useful strategies and insights to promote the industrial application of lacquer sap resins by employing biocompatible nanoagents developed with an understanding of the curing mechanism of natural resins and from the viewpoint of green and sustainable chemistry perspective.

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.

Molecular characterization of CTNSmutations in Tunisian patients with ocular cystinosis.

BackgroundOcular cystinosis is a rare autosomal recessive disorder characterized by intralysosomal cystine accumulation in renal, ophthalmic (cornea, conjunctiva), and other organ abnormalities. Patients with ocular cystinosis are mostly asymptomatic and typically experience mild photophobia due to cystine crystals in the cornea observed accidently during a routine ocular examination. The ocular cystinosis is associated with different mutations in CTNS gene. Cysteamine therapy mostly corrects the organ abnormalities.MethodsThis study was performed in collaboration with the department of ophthalmology of Farhat Hached Hospital. The Optical Coherence Tomography (OCT) of the cornea and retinal photography were used to search cystine crystals within the corneas and conjunctiva in eight Tunisian patients. Screening for the common 57-kb deletion was performed by standard multiplex PCR, followed by direct sequencing of the entire CTNS gene.ResultsThe studied patients were found to have cystine crystal limited anterior corneal stroma and the conjunctiva associated with retinal crystals accumulation. CTNS gene sequencing disclosed 7 mutations: three missense mutations (G308R, p.Q88K, and p.S139Y); one duplication (C.829dup), one framshift mutation (p.G258f), one splice site mutation (c.681 + 7delC) and a large deletion (20,327-bp deletion). Crystallographic structure analysis suggests that the novel mutation p.S139Y is buried in a first transmembrane helix closed to the lipid bilayer polar region, introducing a difference in hydrophobicity which could affect the hydrophobic interactions with the membrane lipids. The second novel mutation p.Q88K which is located in the lysosomal lumen close to the lipid membrane polar head region, introduced a basic amino acid in a region which tolerate only uncharged residue. The third missense mutation introduces a positive change in nonpolar tail region of the phospholipid bilayer membrane affecting the folding and stability of the protein in the lipid bilayer.ConclusionsOur data demonstrate that impaired transport of cystine out of lysosomes is the most common, which is obviously associated with the mutations of transmembrane domains of cystinosine resulting from a total loss of its activity.

Sugar-sugar interactions in oil suspensions containing surfactants and effects on macroscopic phenomena

Surfactants are used in confectionery production to control the viscosity and yield value of molten chocolate. To develop a deeper understanding of the structure–function relationship of surfactants in food-related particle suspensions, the apparent viscosity, yield value, sedimentation, and particle interactions of 10 wt% confectioner’s sugar-in-canola oil suspensions were investigated in the presence of up to 1 wt% commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of monoacylglycerols (CITREM) or ammonium phosphatides (AMP). Atomic force microscopy (AFM) was used to measure attractive forces at the nano-Newton scale between a sugar substrate and a sugar crystal-functionalized AFM cantilever in an oil environment. For all but PGPR, addition of surfactant reduced the adhesion force between sugar surfaces up to a critical concentration above which the force increased, implying the presence of additional interactions. This critical concentration was assumed to be when monolayer coverage of the sugar surfaces by surfactant occurred (0.05 wt% for lecithin, 0.10 wt% for CITREM and AMP). No critical concentration was found for PGPR, with its greatest effect for each analysis occurring at the highest concentrations tested (0.60 and 1.00 wt%). The significance of these interactions on macroscopic phenomena such as apparent viscosity and sedimentation was also assessed. Like with the AFM data, there was an optimal concentration of added surfactant above which viscosity increased. Sedimentation rate greatly decreased with addition of PGPR while being only slightly affected by addition of lecithin, CITREM and AMP. An argument regarding their efficacy was made based on the relative sizes of the polar headgroup and nonpolar tail groups of the molecules, which contributed to how they adsorbed to the sugar surface. Overall, these results suggested that surfactant properties such as molecular weight and head group properties played an important role in modifying the interactions between sugar crystals in an oil-continuous environment.

Rheological Studies of Anionic Surfactants in Presence of Urea Derivatives and Monohydric Alcohols at Constant Temperature

Surfactants are adaptable amphiphilic compounds have an especially distinctive polar hydrophilic head and non-polar hydrophilic tail group. The surfactant is extensively used in each walk of life such as care products, domestic cleaners, pharmaceuticals, oil recovery, food handling, and nanotechnologies due to decreasing the interfacial tension,. The Micellization of anionic surfactants such as potassium dodecyl sulphate (KDS), sodium dodecyl sulphate (NaDS), sodium dodecyl benzene sulphonate (NaDBS) in presence of urea derivatives (2.0 M) in 2.5% alkanol-water systems at constant temperature (35ºC) are measured using the Agla micrometer syringe. The conclusion of this study gives the Critical Micelles Concentration (CMC) values of anionic surfactants decreased with the increase in methyl group of urea derivatives, monohydric alcohols (methanol, propanol butanol) and water systems at 35ºC.

Polarization in partitioning: quantifying the effects of induced dipoles on amino acid sidechain analogs in a POPC membrane

The cell membrane is a semi-permeable barrier that regulates the exchange of materials between the cell and its surroundings. Arising from the amphiphilic nature of individual lipids, the bilayer has a characteristic dielectric gradient from the polar headgroups and water interface to the nonpolar tails deep in the membrane interior. This gradient is crucial in different biological processes, such as small molecule partitioning and membrane protein folding and function. While much is known about the composition and function of membranes, the atomistic details of small molecule partitioning and protein folding are not fully understood.

Phospholipids dock SARS-CoV-2 spike protein via hydrophobic interactions: a minimal in-silico study of lecithin nasal spray therapy.

Understanding the physical and chemical properties of viral infections at molecular scales is a major challenge for the scientific community more so with the outbreak of global pandemics. There is currently a lot of effort being placed in identifying molecules that could act as putative drugs or blockers of viral molecules. In this work, we computationally explore the importance in antiviral activity of a less studied class of molecules, namely surfactants. We employ all-atoms molecular dynamics simulations to study the interaction between the receptor-binding domain of the SARS-CoV-2 spike protein and the phospholipid lecithin (POPC), in water. Our microsecond simulations show a preferential binding of lecithin to the receptor-binding motif of SARS-CoV-2 with binding free energies significantly larger than k_mathrm{B}T. Furthermore, hydrophobic interactions involving lecithin non-polar tails dominate these binding events, which are also accompanied by dewetting of the receptor binding motif. Through an analysis of fluctuations in the radius of gyration of the receptor-binding domain, its contact maps with lecithin molecules, and distributions of water molecules near the binding region, we elucidate molecular interactions that may play an important role in interactions involving surfactant-type molecules and viruses. We discuss our minimal computational model in the context of lecithin-based liposomal nasal sprays as putative mitigating therapies for COVID-19.Supplementary InformationThe online version supplementary material available at 10.1140/epje/s10189-021-00137-3.

Study on the cell-collector-bubble interfacial interactions during microalgae harvesting using foam flotation

Foam flotation is an economical and efficient technology for microalgae harvesting. However, the mechanism of cell-collector-bubble interfacial interactions remains to be elucidated. There are two distinct hypotheses regarding the mechanism of microalgae foam flotation. In this study, the cationic surfactant N-cetyl-N-N-N-trimethylammonium bromide (CTAB), which acts as a partition between Chlorella sorokiniana cells and bubbles, is quantified and the zeta potential response of cells and bubbles after adsorption of CTAB is calculated to reveal the interfacial mechanism of the cells-collector-bubble interfacial interactions. The results indicated that more than 90% of CTAB was preferentially adsorbed on the bubbles, which reversed the surface charge of bubbles from negative (−20 mV) to positive (6.1 mV). However, only 0%–3% CTAB was observed on the microalgae cells, suggesting its limited influence on the negatively charged microalgae cells (from −22.3 to −18.6 mV). During microalgae foam flotation, the nonpolar tails of CTAB were first inserted into the bubble through hydrophobic interactions, leaving the positively charged polar heads outside; further, the CTAB-covered positively charged bubbles captured the negatively charged cells by electrostatic attraction. A feasible mechanism was proposed to understand the interfacial interaction of the microalgae cell-CTAB-bubble. By understanding the mechanism of foam flotation, efficient and cost-effective collectors and devices for microalgae harvesting using foam flotation can be developed.

Inhibition of jack bean urease by amphiphilic peptides

In the current study, amphiphilic peptides were designed and screened against Jack bean urease by using computer aided drug discovery approach. The result showed that out of thirty-eight amphiphilic peptides 1, 3, 12, 18, 30, and 33 exhibit stronger binding affinity with the active site of the enzyme through chelation of charged amino acids with the nickel ions i.e., Ni+2 841 and Ni+2 842 as well as hydrophobic contacts of the nonpolar tail with the nonpolar residues in the active site. The selected amphiphilic peptides were synthesized by solid-phase peptide synthesis strategy, characterized by fast atomic bombardment mass spectroscopy (FAB-MS) and nuclear magnetic resonance spectroscopy (1H and 13C-NMR) and in vitro urease inhibitory activity of amphiphilic peptides was studied. Amphiphilic peptides 12 and 33 showed excellent urease inhibitory activity, (p < 0.001) with IC50 values 20.5 ± 0.01, and 28.1 ± 0.03 µM respectively, which was considerably better than thiourea used as positive control.