Ternary Monolayers Research Articles

Designing a Useful Lipid Raft Model Membrane for Electrochemical and Surface Analytical Studies.

A model biomimetic system for the study of protein reconstitution or drug interactions should include lipid rafts in the mixed lipid monolayer, since they are usually the domains embedding membrane proteins and peptides. Four model lipid films composed of three components: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol (Chol) and sphingomyelin (SM) mixed in different molar ratios were proposed and investigated using surface pressure measurements and thermodynamic analysis of the monolayers at the air–water interface and imaged by Brewster angle microscopy. The ternary monolayers were transferred from the air–water onto the gold electrodes to form bilayer films and were studied for the first time by electrochemical methods: alternative current voltammetry and electrochemical impedance spectroscopy and imaged by atomic force microscopy. In excess of DOPC, the ternary systems remained too liquid for the raft region to be stable, while in the excess of cholesterol the layers were too solid. The layers with SM in excess lead to the formation of Chol:SM complexes but the amount of the fluid matrix was very low. The equimolar content of the three components lead to the formation of a stable and well-organized assembly with well-developed raft microdomains of larger thickness, surrounded by the more fluid part of the bilayer. The latter is proposed as a convenient raft model membrane for further physicochemical studies of interactions with drugs or pollutants or incorporation of membrane proteins.

The impact of fluoxetine and pH values on relaxation of the ternary lipid monolayers

Fluoxetine (FLX), used in the clinic to treat depression, is a well-known cationic amphiphilic antidepressant. To get a deeper insight into the effect of FLX on Langmuir monolayers, in this study the stability and relaxation of 1,2-dioctadecanoyl-sn-glycero-3-phophocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/cholesterol (DSPC/POPC/CHOL) monolayers without and with FLX at different pH values were studied. The experiments involved surface pressure-area (π-A) measurements, mean molecular area-time (A-t) measurements, and atomic force microscope (AFM) analysis. It was found that intermolecular interactions decreased after the addition of FLX in the subphase but increased with increasing pH values. The relaxation of the ternary lipid monolayers with FLX was dominated by dissolution steps, and the dissolution rates decreased with increasing pH values. These findings can be easily confirmed by the analysis of thermodynamic parameters calculated for the investigated films. The data obtained in this study help to understand the effect of drugs on the ternary lipid monolayers from the molecular point of view.

Anomalous Anisotropy of the Piezoelectric Response in 2D Copper‐Based Ternary Chalcogenides CuMX2

The development of 2D materials with excellent electronic properties and piezoelectric response is clearly critical for multifunctional piezoelectric devices. Herein, based on first‐principles calculations, the electronic, mechanical, and piezoelectric properties of a series of 2D copper‐based ternary chalcogenides, denoted as CuMX2 (M = Sb and Bi; X = S and Se) monolayers, are systematically studied, which can be obtained by exfoliating from their bulk counterparts. The calculations show that these ternary CuMX2 monolayers exhibit desirable dynamical and thermal stabilities and moderate bandgaps. The calculated piezoelectric coefficients and of these monolayers are in the range of 0.44–6.14 and 9.13–29.52 pm V−1, respectively, which exceed or approach those of most well‐studied 2D systems. Interestingly, as compared with other reported 2D systems, the CuMX2 monolayers exhibit an anomalous anisotropy of piezoelectric response, manifested as the larger coefficient than coefficient . The study demonstrates that the CuMX2 monolayers are potential 2D candidates in nanoelectric and nanopiezoelectric devices.

Strain engineering and thermal conductivity of a penta-BCN monolayer: a computational study

Two-dimensional (2D) pentagonal nanostructures have been caught research attention down to their electronic, optical, mechanical and thermal transport properties. Among them, the newly proposed ternary penta-BCN monolayer shows a great potential for piezoelectric materials according to intrinsic piezoelectricity and spontaneous polarization. Nevertheless, the effect of strain toward these properties of the penta-BCN has not been elucidated. In this study, using density-functional theory with the Perdew–Burke–Ernzerhof (PBE) functional, we have investigated the impact of a uniform biaxial strain on the electronic structure and the thermal conductivity of the semiconducting penta-BCN single sheet. The strain-free penta-BCN monolayer is mechanically and dynamically stable with an indirect band gap of 1.70 eV. The sheet is rather soft as judged from the low in-plane Young’s moduli. The pentagonal structure is preserved up to the yielding point of 18.4%, beyond this point the irreversible transition into the dynamically unstable, honeycomb-like system is observed. In contrast, the penta-BCN has dynamically instability under the compressive strain as small as −4%. The PBE band gap of the penta-BCN monolayer could be tuned within a range of 1.36–1.70 eV, falling into the infrared spectrum. The calculated lattice thermal conductivity of penta-BCN is around 97 W m−1 K−1 at temperature of 300 K, and decreases with increasing temperature.

Analysis of Molecular Interactions between Components in Phospholipid-Immunosuppressant-Antioxidant Mixed Langmuir Films.

The study of Langmuir monolayers incorporating biomimetic and bioactive substances plays an important role today in assessing the properties and quality of the molecular films for potential biomedical applications. Here, miscibility of binary and ternary monolayers of phospholipid (dioleoyl phosphatidylcholine, DOPC), immunosuppressant (cyclosporine A, CsA), and antioxidant (lauryl gallate, LG) of varying molar fractions was analyzed by means of the Langmuir technique coupled with a surface potential (ΔV) module at the air–water interface. The surface pressure–area per molecule (π–A) isotherms provided information on the physical state of the films at a given surface pressure, the monolayer packing and ordering, and the type and strength of intermolecular interactions. Surface potential–area (ΔV–A) isotherms revealed the molecular orientation changes at the interface upon compression. In addition, the apparent dipole moment of the monolayer-forming molecules was determined from the surface potential isotherms. The obtained results indicated that the film compression provoked subsequent changes of CsA conformation and/or orientation, conferring better affinity for the hydrocarbon environment. The mutual interactions between the components were analyzed here in terms of the excess and total Gibbs energy of mixing, whose values depended on the stoichiometry of the mixed films. The strongest attraction, thus the highest thermodynamic stability, was found for a DOPC–CsA–LG mixture with a 1:1:2 molar ratio. Based on these results, a molecular model for the organization of the molecules within the Langmuir film was proposed. Through this model, we elucidated the significant role of LG in improving the miscibility of CsA in the model DOPC membrane and thus in increasing the stability of self-assembled monolayers by noncovalent interactions, such as H-bonds and Lifshitz–van der Waals forces. The above 1:1:2 combination of three components is revealed as the most promising film composition for the modification of implant device surfaces to improve their biocompatibility. Further insight into mechanisms concerning drug–membrane interactions at the molecular level is provided, which results in great importance for biocoating design and development as well as for drug release at target sites.

Anisotropic correlation between the piezoelectricity and anion-polarizability difference in 2D phosphorene-type ternary GaXY (X = Se, Te; Y = F, Cl, Br, I) monolayers

Inspired by the typical two-dimensional (2D) black-phosphorene-type structure with mm2 point-group symmetry, the structural stability, electronic structure, and intrinsic piezoelectricity of 2D ternary GaXY (X = Se and Te; Y = Cl, Br, and I) monolayers are systematically studied by the first-principles density functional theory. Our calculations show that these ternary monolayer compounds exhibit desirable dynamical and thermal stabilities and a large variety of bandgaps. The calculated piezoelectric coefficients d11 is as large as 15.57 pm/V for GaTeF, and the largest d12 reaches to 3.78 pm/V for GaSeI. It is worth noting that the eij and dij coefficients of GaXY monolayers display anisotropic periodic trends with respect to the constituent elements, which could be interpreted by a linear correlation between the piezoelectric coefficients and the differences in anionic polarizabilities $$\alpha_{X} \;{\text{or}}\;\alpha_{Y}$$ . It is found that d11 of GaXY monolayers is directly proportional to $$(\alpha_{X} - \alpha_{Y} )$$ , while d12 is inversely proportional to $$(\alpha_{X} - \alpha_{Y} )$$ . Such anisotropic correlation could be applicable to elucidate the origin of the piezoelectricity in other 2D ternary compounds.

Role of Co in the Electrocatalytic Activity of Monolayer Ternary NiFeCo-Double Hydroxide Nanosheets for Oxygen Evolution Reaction.

Monolayer nanosheets have gained significant attention as functional materials and also in photo/electrocatalysis due to their unique physical/chemical properties, abundance of highly exposed coordination sites, edges, and corner sites, motivating the pursuit of highly active monolayer nanosheets. NiFe-based layered double hydroxide (NiFe-LDH) nanosheets have been regarded as the most efficient electrocatalysis for oxygen evolution. However, the limited catalytic active site and the stacking layer limited the performance. Therefore, by introducing highly electroactive Co ions into monolayer NiFe-LDH, the obtained ternary NiFeCo-LDH monolayer structure possessed an increased concentration of defect (oxygen and metal vacancies), providing enough unsaturated coordination sites, benefitting the electrocatalytic water oxidation, as also explained by the density functional theory (DFT). This work reported an efficient strategy for the synthesis of ternary monolayer LDH in the application of energy conversion and storage.

Strain-mediated unusual bandgap bowing in continuous composition tuned monolayer Mo1−xWxS2 ternary alloys

Band gap engineering via 2D alloying is a vital strategy for three-atom-thick transition metal dichalcogenides based optoelectronics, valleytronics and nanophotonics. Here we demonstrate the growth of Mo1−xWxS2 ternary alloy monolayers and precise compositional tuning for the entire range of x from 0 to 1 using the gas-phase precursor approach. By means of Raman spectroscopy we show that W alloying in MoS2 lattice can lead to a tensile strain of ∼0.8%. The alloying-induced tensile strain plays a key role in observing redshift in optical absorption and photoluminescence (PL) bands and resulted an unusual bandgap bowing. The coupling of tensile strain and alloying effect allowed us to tune the overall PL emission energy to as large as 185 meV. Our optical spectroscopy results indicate three different phase-regions for the Mo1−xWxS2 alloy system. For x < 0.37, the alloys exhibit MoS2-like nature, whereas, WS2-like behavior is observed for x > 0.64, and a mixed behavior for 0.37 ≤ x ≤ 0.64.

The coexistence of superior intrinsic piezoelectricity and thermoelectricity in two-dimensional Janus α-TeSSe

A new group-VI Janus ternary compounds α-TeSSe monolayer exhibits outstanding piezoelectric and thermoelectric performances, which has broad application prospects in the fields of piezoelectrics and thermoelectrics.

The impact of electron-phonon coupling on the figure of merit of Nb2SiTe4 and Nb2GeTe4 ternary monolayers.

We have comprehensively demonstrated the thermal transport properties of Nb2SiTe4 and Nb2GeTe4 ternary monolayers by employing first-principles calculations and the semi-classical Boltzmann transport theory, including the electron-phonon coupling. The appealing features uncovered here for the monolayers are their colossal Seebeck coefficient and power factor at a higher carrier concentration. For example, the room temperature Seebeck coefficient lasts as high as 200 μV K-1 even at an increased hole (electron) concentration 6.32 × 1020 cm-3 (5.17 × 1019 cm-3) and 1.47 × 1020 cm-3 (5.18 × 1019 cm-3) for Nb2SiTe4 and Nb2GeTe4 monolayers, respectively. Our findings disclose similar band structures and moderate indirect bandgaps of 0.55 eV and 0.41 eV for Nb2SiTe4 and Nb2GeTe4 monolayers. The absence of imaginary frequencies in phonon band dispersion confirms the dynamic stability of both monolayers. The lowest value of lattice thermal conductivity turns out to be 14.30 W m-1 K-1 (12.30 W m-1 K-1) for Nb2SiTe4 and 11.70 W m-1 K-1 (8.34 W m-1 K-1) for Nb2GeTe4 in the x(y) direction. Besides, both monolayers express tremendous potential to further reduced lattice thermal conductivity by nano-structuring without requiring a diminished sample size that is technically challenging to synthesize.

Band gap engineering of monolayer ZrGeTe4 via strain: A first-principles study

Modulating the bandgap of two-dimensional (2D) semiconductors is of particular importance for electronics, optoelectronics, and sensors applications in the nanoscale. Here, based on first-principles calculations, we report the modulation of electronic, mechanical, and optical properties of a ternary transition metal chalcogenide ZrGeTe4 monolayer with the applied external strain. The perfect 2D ZrGeTe4 crystal is a semiconductor with a direct bandgap of 1.21 eV, exhibiting anisotropic elastic and optical response. Both external compression and tensile strain can reduce its bandgap linearly, resulting in the modulation of its optical absorption edge. In particular, a semiconductor-to-metal transition observed in ZrGeTe4 monolayer under a compression strain. The flexibility and significantly strain-tunable electronics properties in 2D ZrGeTe4 monolayer render its great potential in the nanoscale electronic and optoelectronic applications.

Penta-BCN: A New Ternary Pentagonal Monolayer with Intrinsic Piezoelectricity.

Going beyond conventional hexagonal sheets, pentagonal 2D structures are of current interest due to their novel properties and broad applications. Herein, for the first time, we study a ternary pentagonal BCN monolayer, penta-BCN, which exhibits intrinsic piezoelectric properties. Based on state-of-the-art theoretical calculations, we find that penta-BCN is stable mechanically, thermally, and dynamically and has a direct band gap of 2.81 eV. Due to its unique atomic configuration with noncentrosymmetric and semiconducting features, penta-BCN displays high spontaneous polarization of 3.17 × 10-10 C/m and a prominent piezoelectricity with d21 = 0.878 pm/V, d22 = -0.678 pm/V, and d16 = 1.72 pm/V, which are larger than those of an h-BN sheet and functionalized pentagraphene. Since B, C, and N are rich in resources, light in mass, and benign to the environment, the intrinsic polarization and piezoelectricity make the penta-BCN monolayer promising for technological applications. This study expands the family of 2D pentagonal structures with new features.

Ligand Distribution and Lipid Phase Behavior in Phospholipid-Coated Microbubbles and Monolayers.

Phospholipid-coated targeted microbubbles are ultrasound contrast agents that can be used for molecular imaging and enhanced drug delivery. However, a better understanding is needed of their targeting capabilities and how they relate to microstructures in the microbubble coating. Here, we investigated the ligand distribution, lipid phase behavior, and their correlation in targeted microbubbles of clinically relevant sizes, coated with a ternary mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), with PEG40-stearate and DSPE-PEG2000. To investigate the effect of lipid handling prior to microbubble production in DSPC-based microbubbles, the components were either dispersed in aqueous medium (direct method) or first dissolved and mixed in an organic solvent (indirect method). To determine the lipid-phase behavior of all components, experiments were conducted on monolayers at the air/water interface. In comparison to pure DSPC and DPPC, the ternary mixtures had an additional transition plateau around 10–12 mN/m. As confirmed by infrared reflection absorption spectroscopy (IRRAS), this plateau was due to a transition in the conformation of the PEGylated components (mushroom to brush). While the condensed phase domains had a different morphology in the ternary DPPC and DSPC monolayers on the Langmuir trough, the domain morphology was similar in the coating of both ternary DPPC and DSPC microbubbles (1.5–8 μm diameter). The ternary DPPC microbubbles had a homogenous ligand distribution and significantly less liquid condensed (LC) phase area in their coating than the DSPC-based microbubbles. For ternary DSPC microbubbles, the ligand distribution and LC phase area in the coating depended on the lipid handling. The direct method resulted in a heterogeneous ligand distribution, less LC phase area than the indirect method, and the ligand colocalizing with the liquid expanded (LE) phase area. The indirect method resulted in a homogenous ligand distribution with the largest LC phase area. In conclusion, lipid handling prior to microbubble production is of importance for a ternary mixture of DSPC, PEG40-stearate, and DSPE-PEG2000.

Electrochemical genosensor for Klotho detection based on aliphatic and aromatic thiols self-assembled monolayers

Changes in expression of Klotho gene are associated with chronic kidney disease and its potential as early biomarker is being studied. We report, for the first time, the detection of Klotho gene by a biosensor platform. Self-assembled mixed monolayers (SAMs) as DNA immobilization method in screen-printed gold electrodes and a sandwich format detection were used in the development of an electrochemical genosensor for the detection of a 100-mer DNA fragment, copy of the partial region of the mRNA Klotho gene. The use of different binary and ternary SAMs based on aliphatic (mercaptohexanol, MCH, and hexanedithiol, HDT) and aromatic (mercaptophenylacetic acid, MPAA) thiol diluents and capture probe (CP) as sensing phases was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. Multiple configurations were studied, changing the order of component addition and comparing co-immobilization and two-step immobilization processes. The procedure for binary SAM preparation consisting of sequential addition of a thiol diluent followed by CP was found to have the least detrimental impact on electrochemical performance. The signal-to-blank ratios increased considerably in the case of thioaromatic binary DNA monolayers, MPPA/CP, compared to the values obtained for aliphatic SAMs. Ternary monolayers formed by MCH and HDT rendered good fractional coverage levels and generated more reversible redox reactions at the surface, mostly when CP was firstly immobilized, CP/HDT/MCH. A significant reduction of the blank and non-specific (non-complementary sequence) signals was obtained with this ternary SAM, compared to binary SAMs and an increase of 2.42-fold of the S/B ratio (10 nM of target) compared with MPAA/CP SAMs. A linear response in the range of 5·10−10 to 5·10−8 M was obtained with CP/HDT/MCH monolayer, with a detection limit of 0.5 nM and RSD of 8.10%.

Quantifying the composition dependency of the ground-state structure, electronic property and phase-transition dynamics in ternary transition-metal-dichalcogenide monolayers

Structural and electronic transition in the ternary TMD monolayer via doping.

Electronic, elastic and piezoelectric properties of boron-V group binary and ternary monolayers

Electronic, elastic, and piezoelectric properties of two-dimensional (2D) boron-V group binary and ternary monolayers are investigated by a density-functional theory (DFT) first-principle calculation. All calculated 2D monolayers show excellent piezoelectric coefficients, comparable with the frequently used bulk α-quartz (2.3 pm/V), α-SiO2 (2.06 pm/V), and wurtzite GaN (3.1 pm/V). In particular, the e12 of ternary BN0.5P0.5 and BN0.5As0.5 (−3.71 × 10−10 C/m and −4.66 × 10−10 C/m, respectively) are significantly larger than their reference binary monolayers BN (−1.35 × 10−10 C/m) and BP (−2.42 × 10−10 C/m), and BAs (−2.65 × 10−10 C/m). Our calculation not only expand the family of piezoelectric nano-materials, but also instruct to design new 2D piezoelectric monolayers with higher piezoelectric response by atom substitution, and to design new nano-devices that integrate piezoelectric and unique physical properties of B–V group compounds.

The pesticide picloram affects biomembrane models made with Langmuir monolayers

Cell membrane models are useful to obtain molecular-level information on the interaction of biologically-relevant molecules such as pesticides whose activity is believed to depend on its effects on the membrane. In this study, we investigated the interaction between the widely used pesticide picloram with Langmuir monolayers of binary and ternary mixtures comprising 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), sphingomyelin (SM) and cholesterol (Chol), which could be taken as representative of ocular membranes in humans. Picloram expanded the molecular area of DOPC/SM and DOPC/SM/Chol monolayers as the pesticide penetrated the hydrophobic region of the mixtures. A clear correlation was also found between the compressibility modulus (Cs−1) and the presence of cholesterol in the ternary monolayer. Data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) confirmed that picloram interacts with both the acyl chains and headgroups. Spectral shifts and band broadening were induced by picloram, particularly for the phosphate and choline groups, probably owing to its H-bonding ability. The effects reported here on the lipid monolayers may be evidence of the possible activity of picloram on mammalian cell membranes, which highlights the importance of strict control of the level of exposure of humans dealing with pesticides.

Pulsed thermal deposition of binary and ternary transition metal dichalcogenide monolayers and heterostructures

The application of transition metal dichalcogenides in optoelectronic, photonic, or valleytronic devices requires the growth of continuous monolayers, heterostructures, and alloys of different materials in a single process. We present a facile pulsed thermal deposition method which provides precise control over the number of layers and the composition of two-dimensional systems. The versatility of the method is demonstrated on ternary monolayers of Mo1−xWxS2 and on heterostructures combining metallic TaS2 and semiconducting MoS2 layers. The fabricated ternary monolayers cover the entire composition range of x = 0…1 without phase separation. Bandgap engineering and control over the spin–orbit coupling strength are demonstrated by absorption and photoluminescence spectroscopy. Vertical heterostructures are grown without intermixing. The formation of clean and atomically abrupt interfaces is evidenced by high-resolution transmission electron microscopy. Since both the metal components and the chalcogen are thermally evaporated, complex alloys and heterostructures can thus be prepared.

Phase-Controlled Synthesis of Monolayer Ternary Telluride with a Random Local Displacement of Tellurium Atoms.

Alloying 2D transition metal dichalcogenides has opened up new opportunities for bandgap engineering and phase control. Developing a simple and scalable synthetic route is therefore essential to explore the full potential of these alloys with tunable optical and electrical properties. Here, the direct synthesis of monolayer WTe2 x S2(1- x ) alloys via one-step chemical vapor deposition (CVD) is demonstrated. The WTe2 x S2(1- x ) alloys exhibit two distinct phases (1H semiconducting and 1T ' metallic) under different chemical compositions, which can be controlled by the ratio of chalcogen precursors as well as the H2 flow rate. Atomic-resolution scanning transmission electron microscopy-annular dark field (STEM-ADF) imaging reveals the atomic structure of as-formed 1H and 1T ' alloys. Unlike the commonly observed displacement of metal atoms in the 1T ' phase, local displacement of Te atoms from original 1H lattice sites is discovered by combined STEM-ADF imaging and ab initio molecular dynamics calculations. The structure distortion provides new insights into the structure formation of alloys. This generic synthetic approach is also demonstrated for other telluride-based ternary monolayers such as WTe2 x Se2(1- x ) single crystals.

The impact of selected Polycyclic Aromatic Hydrocarbons (PAHs) on the morphology, stability and relaxation of ternary lipid monolayers imitating soil bacteria membrane

Polycyclic Aromatic Hydrocarbons (PAHs) are the organic compounds of strong human and environmental toxicity. Highly important aspect of cytotoxicity of these substances is related to a direct effect of PAHs on membranes, where they can incorporate and accumulate. The latter is highly problematic also from the point of view of the harmful influence of these compounds on the colony of the soil microorganisms and the negative effect of PAHs on biodegradation processes. Since the exact effect of PAHs on the organisation of lipid membrane is not fully explored, in this work the investigations on the influence of pyrene, tetracene and Naphtho[1,2,3,4-def]chrysene (chrysene) on ternary lipid monolayers imitating gram(+) Bacillus subtilis soil bacteria were performed. Our intention was to gain insight into the alterations induced by selected PAHs at the level of model bacteria membrane and to discuss the results in the context of PAH toxicity. The experiments involved the surface pressure-area measurements, Brewster Angle Microscopy studies and the analysis of the relaxation of the systems. It was found that PAH molecules tend to be excluded from model membrane, however, they alter its morphology and destabilize the system. Although the mechanism of desorption of the monolayer material depends on the kind of PAH molecule, its concentration is also of great importance. Based on the collected results it can be summarized that the effect of PAH on membrane organisation can be important step in the mechanism of toxicity of these compounds.