Horizontal Monolayer Research Articles

Nanowire Electrode Structures Enhanced Direct Extracellular Electron Transport via Cell-Surface Multi-Heme Cytochromes in Desulfovibrio ferrophilus IS5

Extracellular electron transfer (EET) by sulfate-reducing bacteria (SRB), such as Desulfovibrio ferrophilus IS5, enables bacterial interactions with minerals, which are vital for biogeochemical cycling and environmental chemistry. Here, we explore the direct EET mechanisms through outer-membrane cytochromes (OMCs) using IS5 as a model SRB. We employed nanostructured electrodes arrayed with 0, 50, 200, and 500 nm long nanowires (NWs) coated with indium–tin–doped oxide to examine the impact of electrode morphology on the direct EET efficacy. Compared to flat electrodes, NW electrodes significantly enhanced current production in IS5 with OMCs. However, this enhancement was diminished when OMC expression was reduced. Differential pulse voltammetry revealed that NW electrodes specifically augmented redox peaks associated with OMCs without affecting those related to redox mediators, suggesting that NWs foster direct EET through OMCs. Scanning electron microscopy observations following electrochemical analyses revealed a novel vertical cell attachment and aggregation on NW electrodes, contrasting with the horizontal monolayer cell attachment on flat electrodes. This study presents the first evidence of the critical role of electrode nanoscale topography in modulating SRB cell orientation and aggregation behavior. The findings underscore the significant influence of electrode morphology on the direct EET kinetics, highlighting the potential impact of mineral morphology on mineral reduction and biogeochemical processes.

Adsorption capability and regenerability of carbon slit micropores for CO2 capture

To date, the exceptional performance of microporous carbon in CO2 capture has been widely acknowledged as a crucial step towards achieving global zero carbon emissions. In this molecular simulation study, we employ grand canonical Monte Carlo simulation (GCMC) to shed light on the significant influence of micropores on CO2 adsorption capability and regenerability, emphasizing the need for a rigorous selection of the swing adsorption process based on pore size. Our findings corroborate numerous experimental and numerical studies that the ultramicropore (pore size < 7 Å) is the appropriate range for CO2 capture, as it facilitates the formation of a horizontal monolayer of CO2 molecules. Furthermore, we highlight the importance of designing porous carbon materials with a large pore volume at the optimal ultramicropore sizes (approximately 5.8-6.4 Å depending on adsorption and desorption conditions) for obtaining high CO2 capture capacity and effective adsorbent regeneration. For the first time, taking into account the operational parameters of practical swing adsorption processes, our simulation study provides valuable guidance for selecting the most appropriate technology tailored to each specific range of micropore size in porous carbon. For porous carbon materials with an abundant volume of ultramicropores, pressure swing adsorption (PSA) and pressure-temperature swing adsorption (PTSA), as conventional and hybrid swing adsorption processes respectively, are the most effective practices, achieving high CO2 working capacity and regenerability exceeding 80%.

Multi-Responsive Peptide-Based Ultrathin Nanosheets Prepared by a Horizontal Monolayer Assembly.

In this study, peptide-based self-assembled nanosheets with a thickness of approximately 1 nm were prepared using a hierarchical covalent physical fabrication strategy. The covalent alternating polymerization of helical peptide E3 with an azobenzene (AZO) structure yielded copolymers CoP(E3-AZO), which physically self-assembled into ultrathin nanosheets in an unanticipated two-dimensional horizontal monolayer arrangement. This special monolayer arrangement enabled the thickness of the nanosheets to be equal to the cross-sectional diameter of a single linear copolymer, which is a rare phenomenon. Molecular dynamics simulations suggested that the synergistic effect of multiple molecular interactions drives the self-assembly of CoP(E3-AZO) into nanosheets and that various methods, including phototreatment, pH adjustment, the addition of additives, and introduction of cosolvents, can alter the molecular interactions and modulate the self-assembly of CoP(E3-AZO), yielding diverse nanostructures. Remarkably, the ultrathin nanosheets selectively inhibited cancer cells at certain concentrations.

Multi‐Responsive Peptide‐Based Ultrathin Nanosheets Prepared by a Horizontal Monolayer Assembly

AbstractIn this study, peptide‐based self‐assembled nanosheets with a thickness of approximately 1 nm were prepared using a hierarchical covalent physical fabrication strategy. The covalent alternating polymerization of helical peptide E3 with an azobenzene (AZO) structure yielded copolymers CoP(E3‐AZO), which physically self‐assembled into ultrathin nanosheets in an unanticipated two‐dimensional horizontal monolayer arrangement. This special monolayer arrangement enabled the thickness of the nanosheets to be equal to the cross‐sectional diameter of a single linear copolymer, which is a rare phenomenon. Molecular dynamics simulations suggested that the synergistic effect of multiple molecular interactions drives the self‐assembly of CoP(E3‐AZO) into nanosheets and that various methods, including phototreatment, pH adjustment, the addition of additives, and introduction of cosolvents, can alter the molecular interactions and modulate the self‐assembly of CoP(E3‐AZO), yielding diverse nanostructures. Remarkably, the ultrathin nanosheets selectively inhibited cancer cells at certain concentrations.

Potential Dependence of Surfactant Adsorption at the Graphite Electrode/Deep Eutectic Solvent Interface.

Atomic force microscopy and cyclic voltammetry are used to probe how ionic surfactant adsorbed layer structure affects redox processes at deep eutectic solvent (DES)/graphite interfaces. Unlike its behavior in water, sodium dodecyl sulfate (SDS) in DESs only adsorbs as a complete layer of hemicylindrical hemimicelles far above its critical micelle concentration (CMC). Near the CMC it forms a tail-to-tail monolayer at open-circuit potential (OCP) and positive potentials, and it desorbs at negative potentials. In contrast, cetyltrimethylammonium bromide (CTAB) adsorbs as hemimicelles at low concentrations and remains adsorbed at both positive and negative potentials. The SDS horizontal monolayer has little overall effect on redox processes at the graphite interface, but hemimicelles form an effective and stable barrier. The stronger solvophobic interactions between the C16 versus C12 alkyl chains in the DES allow CTAB to self-assemble into a robust coating at low concentrations and illustrate how the structure of the DES/electrode interface and electrochemical response can be engineered by controlling surfactant structure.

Investigation of intercalation of diphenhydramine into the interlayer of smectite by XRD, FTIR, TG-DTG analyses and molecular simulation

Diphenhydramine (DPH) is one of the pharmaceuticals commonly found in the effluent stream after wastewater treatment, and the cause of its environmental persistence needs to be addressed urgently. Smectite minerals are common soil components with large surface area, expandable interlayer, and high cation exchange capacity (CEC), thus are capable of adsorbing or intercalating inorganic or organic cations on the surface or in the interlayer. In this study the intercalation of DPH in the interlayer of a Ca-smectite was characterized by X-ray diffraction, infra-red, and thermogravimetric analyses supported by molecular dynamic simulation. At the low (0.2–0.3 CEC) and high (0.6–0.7 CEC) adsorption levels, the intercalated DPH might take a horizontal monolayer or a bilayer configuration, resulting in a d001 expansion to 15 or 17Å, respectively. As the amount of DPH intercalation increased, a gradual, yet systematic, dehydration due to removal of hydrated inorganic cation Ca2+ from the interlayer was observed. In addition, the intercalated DPH had a slightly higher thermal stability due to the shield effect of the host mineral smectite against heat. The uptake of DPH by the smectite was attributed to both electrostatic interactions between the negatively charged mineral surfaces and the positively charged tertiary amine and cation exchange interactions between DPH+ and hydrated Ca2+. Thus, smectite minerals could serve as a sink to remove dissolved DPH from water on the one hand, and as a carrier to transport intercalated DPH in the environment on the other hand.

Edge Structure of through Pore in Lipid Membrane

Theoretical model of edge structure of through pore in lipid membrane was developed. We assumed that membrane monolayers are not necessary in close contact with each other everywhere; instead, hydrophobic void can appear between monolayers of the membrane near the pore edge. If formed, the void is supposed to be filled by organic solvent or low-polarity impurities, which are usually present in artificial and cell membranes. The monolayer of pore edge was divided to three regions: almost vertical monolayer, almost horizontal monolayer, and horizontal monolayer of bilayer part of the membrane. All three regions were assumed continuously conjugated. Pore line tension was calculated in the framework of theory of elasticity of liquid crystals adapted to lipid membranes, by taking into account splay and tilt deformations. Line tension depends on the value of surface tension at the boundary of lipid tails with the void. For sufficiently high surface tension the void collapses. Calculated values of pore edge line tension are in good agreement with available experimental data both for membranes containing and lacking organic solvent or low-polarity impurities.

Drug delivery system for an anticancer agent, chlorogenate-Zn/Al-layered double hydroxide nanohybrid synthesised using direct co-precipitation and ion exchange methods

A nano-structured drug-inorganic clay hybrid involving an active anticancer compound, which is chlorogenic acid (CA) intercalated into Zn/Al-layered double hydroxide, has been assembled via ion-exchange and co-precipitation methods to form a nanohybrid CZAE (a chlorogenic acid-Zn/Al nanohybrid synthesised using an ion-exchange method) and CZAC (a chlorogenic acid-Zn/Al nanohybrid synthesised using a direct method), respectively. The X-ray diffraction (XRD) results confirmed that the CA-LDH had a hybrid structure in which the anionic chlorogenate is arranged between the interlayers as a horizontal monolayer at 90 and 20° angles from the x axis for CZAE and CZAC, respectively. Both nanohybrids have the properties of mesoporous materials. The high loading percentage of chlorogenic acid (approximately 43.2% for CZAE and 45.3% for CZAC) with basal spacings of 11.7 and 12.6Å for CZAE and CZAC, respectively, corroborates the successful intercalation of chlorogenic acid into the interlayer gallery of layered double hydroxides. Free chlorogenic acid and the synthesised nanocomposites (CZAE, CZAC) were assessed for their cytotoxicity against various cancer cells. The Fourier transform infrared data supported the formation of both nanohybrids, and a thermal analysis showed that the nanohybrids are more thermally stable than their counterparts. The chlorogenate shows a sustained release, and the release rate of chlorogenate from CZAE and CZAC nanohybrids at pH 7.4 is remarkably lower than that at pH 4.8 due to their different release mechanisms. The release rate of chlorogenate from both nanohybrids can be described as pseudo-second order. The present investigation revealed the potential of the nanohybrids to enhance the in vitro anti-tumour effect of chlorogenic acid in liver and lung cancer cells in vitro.

Sorption and desorption of tetracycline on layered manganese dioxide birnessite

Birnessite is one of the most common manganese oxides in the clay-sized fraction (<2 μm) of soils and has high cation exchange capacity and larger surface area. Birnessite was previously studied for decomposition of selected antibiotics from water. In this study, the removal of tetracycline (TC) by birnessite from aqueous solution was investigated as a function of initial tetracycline concentration, solution pH, temperature, and equilibrium time. Changes in solid phase after TC adsorption and desorption were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared analyses. Desorption of exchangeable cations accompanying TC removal and partial desorption of TC from birnessite by AlCl3 confirmed that cation exchange was responsible for TC removal at low initial concentrations. Both the external and internal surface areas were readily available for TC uptake by birnessite. The intercalated TC formed a horizontal monolayer configuration in the interlayer of birnessite as deduced from XRD analyses.

Mechanism of amitriptyline adsorption on Ca-montmorillonite (SAz-2)

The uptake of amitriptyline (AMI) from aqueous environment by Ca-montmorillonite (SAz-2) was studied in a batch system under different physicochemical conditions. The adsorbent was characterized by X-ray diffraction and Fourier transform infrared (FTIR) analyses. The AMI adsorption on SAz-2 obeyed the Langmuir isotherm with a capacity of 330mg/g (1.05mmol/g) at pH 6–7. The adsorption kinetics was fast, almost reaching equilibrium in 2h, and followed a pseudo-second-order kinetic model. Desorption of exchangeable cations correlated with the AMI adsorption well, indicating that cation exchange was the major mechanism. X-ray diffraction patterns showing significant expansions of the d001 spacing and characteristic FTIR band shifts toward higher frequencies after AMI adsorption onto SAz-2 indicated that the adsorbed AMI molecules were intercalated into the interlayers of the mineral. Thermodynamic parameters based on partitioning coefficients suggested that the AMI adsorption was an endothermic physisorption at high adsorption levels. At low and higher AMI adsorption levels, the intercalated AMI molecules take a horizontal monolayer and bilayer conformation, respectively. The higher adsorption capacity suggested that SAz-2 could be a good candidate to remove AMI from wastewater and would be an important environmental sink for the fate and transport of AMI in soils and groundwater.

Differential capacity and chronocoulometry studies of a quaternary ammonium surfactant adsorbed on Au(111)

AbstractThe adsorption of a model quaternary ammonium surfactant, octyltrimethylammonium triflate, on Au(111) has been studied using capacity and chronoculometry methods. The surfactant adsorbs on the metal surface as a non‐dissociated ion pair at moderate potentials but can be desorbed by either positive or negative polarization. Within the adsorption region, two states are observed which correspond to a horizontal monolayer and a higher coverage vertically oriented film. Measurements of capacity transients upon potential steps reveal a slow organization of the molecular film. Although it is possible to equate the transients to known surfactant film aggregate geometries, the results are in disagreement with thermodynamic results. In comparison with other studies, the results indicate that the states of surfactant adsorption depend on surfactant chain length and electrode crystallography. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Influence of the gravity on the discharge of a silo

We performed a series of experiments to investigate the flow of an assembly of non-cohesive spherical grains in both high and low gravity conditions (i.e. above and under the Earth’s gravity). In high gravity conditions, we studied the flow of glass beads out of a cylindrical silo and the flow of metallic beads out of a vertical Hele-Shaw rectangular silo. Both silos were loaded in one of the gondolas of the large diameter centrifuge facility (located at ESTEC) in which an apparent gravity up to 20 times the Earth’s gravity can be established. To simulate low gravity conditions, we submitted a horizontal monolayer of metallic beads to the centrifuge force of a small rotation device (located at University of Liege). The influences of both gravity and aperture size on the mass flow were analysed in these various conditions. For the three systems (cylindrical silo, the Hele-shaw silo and the monolayer of beads), we demonstrated that (i) the square root scaling of the gravity found by Beverloo is relevant and (ii) the critical aperture size below which the flow is jammed does not significantly increase with the apparent gravity. Moreover, we studied in more details the Hele-Shaw silo in high gravity because this configuration allowed to determine local properties of the flow at the level of the aperture. We measured the velocity profiles and the packing fraction profiles for the various aperture sizes and apparent high gravities. We demonstrate the existence of a slip length for the flow at the level of the aperture. This later fact seems to result from the geometrical configuration of the silo.

Preparation and characterization of spermine-exchanged montmorillonite and interaction with the herbicide fluometuron

We studied the interaction between the naturally occurring polycation spermine (SPERM) and Na-exchanged SWy-2 Wyoming montmorillonite (Na-SWy-2 Mt) and between spermine-exchanged montmorillonite (Mt-SPERM) and the herbicide fluometuron. Mt-SPERM with spermine contents ranging between 0 and 1.2 times the cation exchange capacity (CEC) of Na-SWy-2 were studied by XRD, FTIR and TGA analysis. Spermine was intercalated stoichiometrically into Na-SWy-2 up to the CEC of the clay mineral, resulting in basal spacing of 1.29nm. TGA analysis indicated that intercalation of spermine into Na-SWy-2 increased the thermal stability of the organic cations and affected the dehydroxylation temperature of the clay mineral. FTIR measurements of Mt-SPERM samples showed the involvement of NH and CH groups of spermine in the interaction with the clay mineral. The intensity of the spermine NH and CH deformation vibrations increased linearly with the amount of spermine incorporated into Na-SWy-2 up to an amount close to the CEC of the montmorillonite. Structural modeling suggested that the arrangement of spermine cations formed a horizontal monolayer within the interlayer space of SWy-2 with strong interaction between the NH3+ and NH2+-groups of spermine and the montmorillonite surface oxygen atoms. Mt-SPERM showed pronounced affinity for the herbicide fluometuron.

Influence of Chain Lengths and Loading Levels on Interlayer Configurations of Intercalated Alkylammonium and Their Transitions in Rectorite

There have been extensive studies on intercalation of alkylammonium into swelling clay minerals for the purpose of surface charge determination of the clay minerals, as well as their interlayer configurations in the clay minerals. The most accepted findings are that the intercalated alkylammonium molecules adopted horizontal monolayer, bilayer, pseudotrilayer, and vertical paraffin-like configurations in the interlayer space of the swelling clay minerals depending on the chain length and loading level of the alkylammonium used. This study examined the interlayer configurations of intercalated alkyltrimethylammonium and their transition structure as a function of alkylammonium inputs and chain lengths. As the amount of alkylammonium intercalation increased, the bilayer configuration of the intercalated alkylammonium was absent during a transition from a horizontal monolayer to a pseudotrilayer intercalation. Instead, the transition structure involved a mixed layer made of rectorite intercalated with one layer and rectorite intercalated with pseudotrilayer of alkylammonium molecules. When intercalated in horizontal monolayer, the alkylammonium molecules took a random, more gauche-like arrangement. On the other hand, as alkylammonium molecules adopted a pseudotrilayer, particularly the vertical paraffin-like arrangement, a more ordered all-trans configuration was achieved. As layer charge is one of the most important properties of swelling clay minerals, commonly determined by intercalation of n-alkylammonium ions, the identification of mixed-layer transition structure in this study may suggest a need for further investigations on principles of layer charge determination of swelling clays by the alkylammonium method.

One-phase synthesis of small gold nanoparticles coated by a horizontal porphyrin monolayer

One-pot reduction of HAuCl4 in a DMF solution containing a porphyrin-cored tetradentate passivant gives horizontal porphyrin monolayer-coated gold nanoparticles, whose particle size is significantly smaller than that made by using monodentate passivants under identical conditions.

Enhanced creation of dispersive monolayer phonons in Xe∕Pt(111) by inelastic helium atom scattering at low energies

Conditions likely to lead to enhanced inelastic atomic scattering that creates shear horizontal (SH) and longitudinal acoustic (LA) monolayer phonons are identified, specifically examining the inelastic scattering of (4)He atoms by a monolayer solid of XePt(111) at incident energies of 2-25 meV. There is strong inelastic scattering for both dispersive phonon branches (SH and LA) of the monolayer at incident energies below 8 meV. Several improvements enable more complete wave packet calculations of the inelastic scattering than in previous work. Long propagation times are made feasible by adding an absorbing potential at large distance. The times now extend to beyond 100 ps and enable a clarification of processes involving transient trapping of the He atoms. The wave packet is made more monochromatic by significantly increasing the spatial width of the initial Gaussian shape. The narrower energy distribution in the incident beam then enables a demonstration of strong energy dependence of the scattering over a scale of less than 0.3 meV.

Nonequilibrium steady states in a vibrated-rod monolayer: tetratic, nematic, and smecticcorrelations

We study experimentally the nonequilibrium phase behaviour of a horizontal monolayer ofmacroscopic rods. The motion of the rods in two dimensions is driven by vibrations in thevertical direction. In addition to varying packing fraction and aspect ratio asin most studies on hard-particle systems, we take advantage of our ability tovary the precise shape of these macroscopic particles to investigate the effect ofshape on their nonequilibrium steady states. We find that the shape plays animportant role in determining the nature of the orientational ordering at high packingfraction. Cylindrical particles show substantial tetratic correlations over a rangeof aspect ratios where spherocylinders have previously been shown to undergotransitions between isotropic and nematic phases. Particles that are thinner atthe ends (rolling pins or bails) show nematic ordering over the same range ofaspect ratios, with a well established nematic phase at large aspect ratio anda defect-ridden nematic state with large-scale swirling motion at small aspectratios. Finally, long-grain, basmati rice, whose geometry is intermediate betweenthe two shapes above, shows phases with strong indications of smectic order.

Complete Nonlinear Theory of Longitudinal-to-Transverse Dust Lattice Mode Coupling in a Single-Layer Dusty Plasma Crystal

A comprehensive nonlinear model is put forward for coupled longitudinal-to-transverse displacements in a horizontal dust mono-layer, levitated under the combined influence of gravity and an electric and/or magnetic sheath field. A set of coupled nonlinear evolution equations are obtained in a discrete description, and a pair of coupled (Boussinesq-like) PDEs are obtained in the continuum approximation. Finally, the amplitude modulation of the coupled modes is discussed, pointing out the importance of the coupling. All these results are generic, i.e. valid for any assumed form of the inter-grain interaction potential U and the sheath potential Φ

Compressional and shear wakes in a two-dimensional dusty plasma crystal.

Wakes composed of compressional and shear waves were studied experimentally in a two-dimensional screened-Coulomb crystal. Highly charged microspheres suspended in a plasma settled in a horizontal monolayer and arranged in a triangular lattice with a repulsive interparticle potential. Wakes were excited by a moving spot of Ar+ laser light. Depending on the laser spot speed, compressional waves formed a Mach cone and multiple lateral or transverse wakes, similar to ship wakes on the water surface, due to a combination of acoustic and dispersive properties. Shear waves, however, formed only a Mach cone, due to their nearly acoustic, i.e., dispersionless character. The experimental results show agreement with a recently developed theory and with molecular dynamics simulations, which assume a binary Yukawa interparticle potential. A generally useful method is presented for calculating the real part of the dispersion relation of the compressional waves based on the analysis of the spatial structure of a phonon wake. Fitting the resulting dispersion relation provides an independent measure of the interparticle potential, parametrized by the screening parameter kappa and particle charge Q.

Receptor-mediated transport of insulin across endothelial cells.

Hormones such as insulin are transported from the interior to the exterior of blood vessels. Whether endothelial cells, which line the inner walls of blood vessels have a role in this transport of hormones is not clear, but it is known that endothelial cells can internalize and release insulin rapidly with little degradation. The transport of iodine-125-labeled insulin was measured directly through the use of dual chambers separated by a horizontal monolayer of cultured bovine aortic endothelial cells. In this setting, endothelial cells took up and released the labeled insulin, thereby transporting it across the cells. The transport of insulin across the endothelial cells was temperature sensitive and was inhibited by unlabeled insulin and by antibody to insulin receptor in proportion to the ability of these substances to inhibit insulin binding to its receptor. More than 80 percent of the transported insulin was intact. These data suggest that insulin is rapidly transported across endothelial cells by a receptor-mediated process.