Charged Substrates Research Articles

Internal resonance in a MEMS levitation force resonator

In this work, we explore internal resonances in a levitation force microelectromechanical system-based actuator assuming flexible cantilever and clamped–clamped microbeam configurations. The levitation force is generated through a special arrangement of two-side stationary charged substrates and a central grounded stationary strip. The design assumes as well an upper flexible microbeam strip. The DC part of the excitation voltage pushes up the moving microbeam away from its lower stationary electrode. A superimposed harmonic AC voltage lets the flexible strip vibrate around its equilibrium position. Energy exchange among the computed lower vibration frequencies and their respective frequency and force response curves are explored for possibilities of principal parametric and internal resonances interactions. The generated responses are computed using the bifurcation toolbox MatCont. The effect of Von Karman nonlinearity to power the energy exchange within vibration modes is explored and dominant factors in the MEMS design for resonances are found from a two-parameter bifurcation analysis. Our results allow optimizing the micro-actuator device performance for future applications.

Electrogenic reaction step and phospholipid translocation pathway of the mammalian P4-ATPase ATP8A2.

ATP8A2 is a mammalian P4-ATPase (flippase) that translocates the negatively charged lipid substrate phosphatidylserine from the exoplasmic leaflet to the cytoplasmic leaflet of cellular membranes. Using an electrophysiological method based on solid supported membranes, we investigated the electrogenicity of specific reaction steps of ATP8A2 and explored a potential phospholipid translocation pathway involving residues with positively charged side chains. Changes to the current signals caused by mutations show that the main electrogenic event occurs in connection with the release of the bound phosphatidylserine to the cytoplasmic leaflet and support the hypothesis that the phospholipid interacts with specific lysine and arginine residues near the cytoplasmic border of the lipid bilayer during the translocation and reorientation required for insertion into the cytoplasmic leaflet.

First-principles study on the design of metal-decorated N-doped γ-graphyne as a high capacity CH4 adsorbent

Nitrogen doping γ-graphyne (γ-NGY) is a recently synthesized carbon nitride two-dimensional material with a large specific surface area and unique structure. Based on the first-principles method, the CH4 adsorption properties of γ-NGY are calculated, and a substrate structure Ti-decorated γ-NGY is designed. The results show that the center of the rhombus hole of γ-NGY is the best CH4 adsorption position, and the adsorption energy is −0.145 eV. The most stable binding position of the Ti atom on γ-NGY is also the rhombus hole. The binding energy of a Ti atom is −5.737 eV, and the average binding energy of two Ti atoms is −4.88 eV. Ti-γ-NGY successfully adsorbs 24 CH4 molecules on both sides with an average adsorption energy of −0.184 eV and the storage capacity of 69.12 wt. %. After doping N atoms, the hole size increases, and the negative charges are concentrated on N atoms. The adsorption of CH4 by γ-NGY is mainly the intermolecular force, and the adsorption energy is slightly increased. After the Ti atom transfers the negative charge to the substrate, a strong electric field is formed between the positively charged Ti atom and the negatively charged substrate. The adsorption energy of CH4 molecules near the Ti atom is greatly increased, and the Coulomb attraction between CH4 and Ti atom is dominant. The adsorption energy of the CH4 molecule far away from the Ti atom is also improved, and the intermolecular force between negatively charged substrates and polarized CH4 molecules plays a dominant role in the adsorption.

Human Vimentin Layers on Solid Substrates: Adsorption Kinetics and Corona Formation Investigations.

Adsorption kinetics of human vimentin on negatively charged substrates (mica, silica, and polymer particles) was analyzed using atomic force microscopy (AFM), quartz microbalance (QCM), and the laser doppler velocimetry (LDV) method. AFM studies realized under diffusion conditions proved that the adsorbed protein layer mainly consisted of aggregates in the form of compact tetramers and hexamers of a size equal to 11–12 nm. These results were consistent with vimentin adsorption kinetics under flow conditions investigated by QCM. It was established that vimentin aggregates efficiently adsorbed on the negatively charged silica sensor at pH 3.5 and 7.4, forming compact layers with the coverage reaching 3.5 mg m–2. Additionally, the formation of the vimentin corona at polymer particles was examined using the LDV method and interpreted in terms of the electrokinetic model. This allowed us to determine the zeta potential of the corona as a function of pH and the electrokinetic charge of aggregates, which was equal to −0.7 e nm–2 at pH 7.4 in a 10 mM NaCl solution. The anomalous adsorption of aggregates exhibiting an average negative charge on the negatively charged substrates was interpreted as a result of a heterogeneous charge distribution. These investigations confirmed that it is feasible to deposit stable vimentin layers both at planar substrates and at carrier particles with well-controlled coverage and zeta potential. They can be used for investigations of vimentin interactions with various ligands including receptors of the innate immune system, immunoglobulins, bacterial virulence factors, and spike proteins of viruses.

Metal clusters trapped on opaque substrate particles prepared using pulsed laser ablation in liquid

Gold clusters trapped on opaque substrate particles were produced using pulsed laser ablation. The ablation laser irradiated the target Au plate in a liquid dispersed with opaque substrate particles. It was found that the rate of thermal diffusion from the smaller particle that absorbed laser energy was greater than that from the larger particle; therefore, it is less likely to increase the temperature. Subsequently, the Au target was ablated more efficiently than the opaque substrate particles dispersed in the liquid. Therefore, the opaque particles were barely miniaturized and remained intact. The interaction mechanism of the deposition of the Au particle produced by laser ablation on the substrate particles was investigated by measuring the zeta potential of the substrate particles. The positively charged Au particles were adsorbed by ion exchange with positively charged Y2O3 substrate particles. In contrast, they interacted via electrostatic interactions with negatively charged α-quartz and ZSM-5 zeolite particles.

Exquisite manipulation of two-dimensional laminar graphene oxide (GO) membranes via layer-by-layer self-assembly method with cationic dyes as cross-linkers

Herein, we propose one novel strategy by layer-by-layer (LBL) self-assembly method to prepare two-dimensional (2D) laminar membranes assembled between sulfonated graphene oxide (S-GO) nanosheets and various cationic dyes on the polyethyleneimine (PEI) -modified Nylon-6 (PA6) substrate. The membrane performances are manipulated exquisitely by the charge of substrate, the assembled dye type, dye size, self-assembly layer number etc. The water permeance positively correlates with the height of assembled cationic dyes. The amido bonds or sulfamide bonds and π–π conjugation endow the resulted membrane with strong performance stability. Furthermore, by precisely selecting the size and charge the assembled dye, the prepared LBL GO membranes can efficiently separate mixed dyes in aqueous solution via charge repulsion or/and size sieving mechanism. For example, the separation selectivity of 39.2 for the mixed Rhodamine B/Ethyl Violet (RB/EV) dyes can be achieved with the LBL MV-0.25-2-2 membrane (it was assembled by 2 mmol L−1 Methyl violet solution for two S-GO layers with the Nylon-6 substrate modified with 0.25 wt % PEI aqueous solution). Simultaneously, the introduced cationic dyes endow these membranes with extra antibacterial capacity to both E. coli and S. aureus.

Adsorption of flexible proteins in the ‘wrong side’ of the isoelectric point: Casein macropeptide as a model system

We analyze the conditions of the adsorption of a flexible peptide onto a charged substrate in the ‘wrong side’ of the isoelectric point (WSIP), i.e. when surface and peptide charges have the same sign. As a model system, we focus on the casein macropeptide (CMP), both in the aglycosylated (aCMP) and fully glycosydated (gCMP) forms. We model the substrate as a uniformly charged plane while CMP is treated as a bead-and-spring model including electrostatic interactions, excluded volume effects and acid/base equilibria. Adsorption coverage, aminoacid charges and concentration profiles are computed by means of Monte Carlo simulations at fixed pH and salt concentration. We conclude that for different reasons the CMP can be adsorbed to both positively and negatively charged surfaces in the WSIP. For negatively charged surfaces, WSIP adsorption is due to the patchy distribution of charges: the peptide is attached to the surface by the positively charged end of the chain, while the repulsion of the surface for the negatively charged tail is screened by the small ions of the added salt. This effect increases with salt concentration. Conversely, a positively charged substrate induces strong charge regulation of the peptide: the acidic groups are deprotonated, and the peptide becomes negatively charged. This effect is stronger at low salt concentrations and it is more intense for gCMP than for aCMP, due to the presence of the additional sialic groups in gCMP.

Electrostatic Adsorption Behaviors of Charged Polymer-Tethered Nanoparticles on Oppositely Charged Surfaces.

Polymer-grafted hairy nanoparticles (HNPs) that combine the unique properties of inorganic nanoparticles (NPs) and polymers are attractive building blocks for the layer-by-layer assembly of functional hybrid materials, but the adsorption behaviors of HNPs on substrates remain unclear. This article describes a systematic study on the adsorption behaviors of charged polymer-grafted HNPs on oppositely charged substrates in different solvent media via a combination of experiments and simulations. It is shown in simulations that the adsorption process of HNPs is associated with the release of counterions around charged polymers on HNPs, thus resulting in a higher energy barrier of NP adsorption than bare NPs without charged polymer tethers. This energy barrier decreases with decreasing the dielectricity of solvents or ionization degree of grafted polymers or increasing ionic strength of the solution. Furthermore, the theoretical prediction is confirmed in experiments by using a model system of poly(acrylic acid)-grafted silica NPs and poly(diallyldimethylammonium chloride)-modified wafers. The work provides guidance for the electrostatic assembly of HNPs into functional hybrid composites with applications in membranes, optical devices, and biomedicines.

Charge density waves in monolayer and few-layer NbS2 and phase modulation by doping, thickness, and temperature

By carrying out first-principles calculations, we studied the charge density waves (CDWs) in monolayer/few-layer $H\text{\ensuremath{-}}{\mathrm{NbS}}_{2}$. For monolayer ${\mathrm{NbS}}_{2}$, unstable phonon modes are found to develop at the $2/3\mathrm{\ensuremath{\Gamma}}\mathrm{M}$ point and its symmetric points in the whole Brillouin zone. By displacing the atoms along the unstable mode, a new dynamically stable $3\ifmmode\times\else\texttimes\fi{}3$ structure with lower total energy is obtained, which corresponds well to the experimentally observed $3\ifmmode\times\else\texttimes\fi{}3$ CDW phase. The symmetries are broken in the $3\ifmmode\times\else\texttimes\fi{}3$ CDW phase, leading to gap opening and anisotropic properties. The $3\ifmmode\times\else\texttimes\fi{}3$ CDW phase of ${\mathrm{NbS}}_{2}$ is found to be stable with respect to small strains. In comparison with ${\mathrm{NbSe}}_{2}$, it is found that the Se atoms are much more active in vibration than the S atoms, resulting in the different CDW behaviors in these two very similar materials. We explored the CDW phase tuning by electron doping, and a sequence of CDW phase transitions from $3\ifmmode\times\else\texttimes\fi{}3$ to $2\ifmmode\times\else\texttimes\fi{}2$ and to $4\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}4\ensuremath{\surd}3$ is found. The doping-dependent CDW phase provides insight into the inconsistent observation of CDW phases in ${\mathrm{NbS}}_{2}$/graphene and ${\mathrm{NbS}}_{2}$/Au(111) based on the difference in substrate charge doping. We further investigated the CDW phases of the bilayer and trilayer ${\mathrm{NbS}}_{2}$. With the decrease of the temperature, a series of instabilities occur in the phonon spectrum of bilayer ${\mathrm{NbS}}_{2}$, which correspond to $2\ifmmode\times\else\texttimes\fi{}2, 3\ifmmode\times\else\texttimes\fi{}3$, and $4\ifmmode\times\else\texttimes\fi{}4$ CDW phases. For trilayer ${\mathrm{NbS}}_{2}$, in contrast, only a $2\ifmmode\times\else\texttimes\fi{}2$ CDW phase is found, whereas the $3\ifmmode\times\else\texttimes\fi{}3$ CDW phase, which exists in monolayer and bilayer, is not manifested even at ultralow temperature. The layer-dependent CDW phases indicate significant effects of interlayer interactions.

The Role of Benzotriazole in Electrodeposition of Cu1−xNix Alloys (0.05 < x < 0.15) on Cu and Ni Substrates

We investigated the benzotriazole enabled growth of low Ni content (5–15 at.%) CuNi alloy deposits by characterisation of its morphology and elemental composition as a function of substrate metal (Cu and Ni), charge density, current density, and potential-time response measured during electrodeposition. Alloy deposition starts in favor of Cu, forming a Cu-rich layer on a Ni substrate and Cu-rich islands on a Cu substrate after which aggregates only form on a Cu substrate, due to the ability of benzotriazole (BTAH) to chemically bond to Cu but not to a Ni surface. Furthermore, Ni deposits preferably on grain boundaries, BTAH gets incorporated in the deposit and forms a thin layer between the Cu substrate and the alloy deposit. Based on our findings a growth model for BTAH enabled CuNi growth is proposed which describes that the BTAH working mechanism is twofold. First, the additive shifts the onset potential of Cu2+ reduction closer to the Ni2+ reduction potential by forming a chemisorbed BTAH layer, thereby enabling Cu and Ni co-deposition and, secondly, during deposition it specifically interacts with Cu, thus inhibiting Cu dendrite formation.

Dopamine-intercalated polyelectrolyte multilayered nanofiltration membranes: Toward high permselectivity and ion-ion selectivity

The layer-by-layer (LbL) self-assembly is a common method for fabricating nanofiltration (NF) membranes. However, most multilayers are usually too thick and lack the necessary attributes to endow NF membranes with good permselectivity. In this study, we present a polyelectrolyte multilayered method by integrating dopamine as a “bio-glue”. A three-step deposition was applied to the negatively charged PES substrate surface, following an alternate sequence of poly(allylamine hydrochloride) (PAH), dopamine (DA) and poly(sodium 4-styrenesulfonate) (PSS). The dopamine molecules were intercalated between the PAH and PSS layers to achieve a thinner thickness, higher hydrophilicity, smaller surface roughness and narrower pore size distribution. The resultant flat sheet (PAH/DA/PSS)4 polyelectrolyte multilayered (PEM) membranes exhibited enhanced water permeability (more than 60% increment from 13.5 to 21.9 LMH/bar) and higher rejection toward divalent ions (increasing MgCl 2 rejection from 91.0% to 94.8%) as compared with the control (PAH/PSS)4 NF membrane. Furthermore, the developed LbL method was applied on hollow fiber membrane modules and was able to achieve a higher Li + /Mg 2+ selectivity from 15.6 to 37.8 and Na + /Mg 2+ selectivity from 11.0 to 19.1 using different simulated brines as feed solutions. On the whole, this polyelectrolyte multilayered method shows great potential for practical applications, including groundwater softening, seawater pretreatment and lithium extraction. • A novel three-step LbL self-assembly method was proposed by integrating dopamine. • Dopamine intercalated selective layer exhibited a thinner and smoother surface. • The NF (PAH/DA/PSS)4 membrane showed better water permeability and higher divalent ion rejection. • Higher Na + /Mg 2+ and Li + /Mg 2+ selectivity was achieved due to the smaller pore size distribution.

Metal-insulator transition in monolayer MoS2 via contactless chemical doping

Much effort has been made to modify the properties of transition metal dichalcogenide layers via their environment as a route to new functionalization. However, it remains a challenge to induce large electronic changes without chemically altering the layer or compromising its two-dimensionality. Here, a non-invasive technique is used to shift the chemical potential of monolayer MoS2 through p- and n-type doping of graphene (Gr), which remains a well-decoupled 2D substrate. With the intercalation of oxygen (O) under Gr, a nearly rigid Fermi level shift of 0.45 eV in MoS2 is demonstrated, whereas the intercalation of europium (Eu) induces a metal–insulator transition in MoS2, accompanied by a giant band gap reduction of 0.67 eV. Additionally, the effect of the substrate charge on 1D states within MoS2 mirror-twin boundaries (MTBs) is explored. It is found that the 1D nature of the MTB states is not compromised, even when MoS2 is made metallic. Furthermore, with the periodicity of the 1D states dependent on substrate-induced charging and depletion, the boundaries serve as chemical potential sensors functional up to room temperature.

Constructing bifunctional metal–organic framework based nanozymes with fluorescence and oxidase activity for the dual-channel detection of butyrylcholinesterase

Herein, we reported a novel strategy for the fabrication of bifunctional metal–organic framework based nanozymes (oxidized UiO-66-NH2@Ce), which displayed excellent oxidase mimic activity as well as fluorescence property. The bifunctional oxidized UiO-66-NH2@Ce possess excellent oxidase activity due to oxidase-like active Ce4+/Ce3+ sites, which makes the nanozymes have strong positive charge, resulting in a stronger affinity for the negatively charged chromogenic substrate 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Utilizing the bifunctional oxidized UiO-66-NH2@Ce, a sensitive fluorometric and colorimetric dual-channel detection strategy for butyrylcholinesterase (BChE) was fabricated for the first time. The oxidized UiO-66-NH2@Ce could catalyze the oxidation of colorless ABTS to green oxABTS, which in turn quench the fluorescence of oxidized UiO-66-NH2@Ce. Butyrylcholinesterase (BChE) can catalyze the hydrolysis of S-butyrylthiocholine iodide (BTCh) to produce thiocholine, which could prevent the oxidation of ABTS, resulting in the fluorescence of oxidized UiO-66-NH2@Ce recovered. Both the colorimetric and fluorometric dual-channel sensing platform displayed a sensitive response to BChE, and the limits of detection (LOD) for BChE could achieve as low as 0.056 and 0.050U/L, respectively. The dual-output assay for BChE detection displayed excellent application prospects.

Structure and Optical Properties of Opal Films Made by an Out-of-Plane Electric Field-Assisted Capillary Deposition Method.

Self-assembled opals that are considered as a promising candidate for three-dimensional photonic crystals often suffer from the existence of internal defects. Defects influence optical properties and limit the applicability of opal films. Directed assembly using external fields may offer a certain degree of tunability in the opal formation process. We investigate the effect of an out-of-plane electric field on the formation and optical properties of opal films deposited using the capillary deposition method. The application of an electric field of intermediate strength (20–30 V/cm) can improve opal quality. The quality of opal films was found to depend on the polarity of the bottom substrate resulting from the beneficial influence of an asymmetry between the growths and the interplay with gravity. The negatively charged bottom substrate results in slightly better opal quality. This finding shows the potential of electric fields to tune opal formation in order to reduce the defect content.

Adsorption Characteristics of Carbon Monoxide on Ag- and Au-Doped HfS2 Monolayers Based on Density Functional Theory

A large amount of power equipment works in closed or semi-closed environments for a long time. Carbon monoxide (CO) is the most prevalent discharge gas following a fault in the components. Based on the density functional theory of first principles, the adsorption behavior of CO gas molecules on intrinsic, Ag-doped and Au-doped hafnium disulfide (HfS2) monolayers was systematically studied at the atomic scale. Firstly, the intrinsic HfS2 monolayer, Ag-doped HfS2 (Ag-HfS2) monolayer and Au-doped HfS2 (Au-HfS2) monolayer, with different doping sites, were created. The structural stability, dopant charge transfer, substrate conductivity and energy band structure of different doping sites of the Ag-HfS2 and Au-HfS2 monolayer structures were calculated. The most stable doping structure was selected with which to obtain the best performance on the subsequent gas adsorption test. Then, the CO adsorption models of intrinsic HfS2, Ag-HfS2 and Au-HfS2 were constructed and geometrically optimized. The results show that the adsorption energy of the Ag-HfS2 monolayer for CO gas is −0.815 eV, which has good detection sensitivity and adsorption performance. The adsorption energy of CO on the Au-HfS2 monolayer is 2.142 eV, the adsorption cannot react spontaneously, and the detection sensitivity is low. The research content of this paper provides a theoretical basis for the design and research of gas sensing materials based on HfS2, promoting the development and application of HfS2 in gas sensing and other fields.

Tuning ceria catalysts in aqueous media at the nanoscale: how do surface charge and surface defects determine peroxidase- and haloperoxidase-like reactivity.

Designing the shape and size of catalyst particles, and their interfacial charge, at the nanometer scale can radically change their performance. We demonstrate this with ceria nanoparticles. In aqueous media, nanoceria is a functional mimic of haloperoxidases, a group of enzymes that oxidize organic substrates, or of peroxidases that can degrade reactive oxygen species (ROS) such as H2O2 by oxidizing an organic substrate. We show that the chemical activity of CeO2-x nanoparticles in haloperoxidase- and peroxidase-like reactions scales with their active surface area, their surface charge, given by the ζ-potential, and their surface defects (via the Ce3+/Ce4+ ratio). Haloperoxidase-like reactions are controlled through the ζ-potential as they involve the adsorption of charged halide anions to the CeO2 surface, whereas peroxidase-like reactions without charged substrates are controlled through the specific surface area SBET. Mesoporous CeO2-x particles, with large surface areas, were prepared via template-free hydrothermal reactions and characterized by small-angle X-ray scattering. Surface area, ζ-potential and the Ce3+/Ce4+ ratio are controlled in a simple and predictable manner by the synthesis time of the hydrothermal reaction as demonstrated by X-ray photoelectron spectroscopy, sorption and ζ-potential measurements. The surface area increased with synthesis time, whilst the Ce3+/Ce4+ ratio scales inversely with decreasing ζ-potential. In this way the catalytic activity of mesoporous CeO2-x particles could be tailored selectively for haloperoxidase- and peroxidase-like reactions. The ease of tuning the surface properties of mesoporous CeO2x particles by varying the synthesis time makes the synthesis a powerful general tool for the preparation of nanocatalysts according to individual needs.

Investigation on substrate specificity and catalytic activity of serine protease neuropsin.

Neuropsin is one of serine proteases mainly found at the hippocampus and the amygdala, where it contributes to the long-term potentiation and memory acquisition by rebuilding of synaptic connections. Despite of the importance of neuropsin, the substrate specificity and regulation mechanisms of neuropsin have been unclear. Thus, we investigated the substrate specificity and the catalytic activity of neuropsin by the protein-ligand docking and molecular dynamics (MD) simulations and succeeded to reproduce the trend of the experimental results. Our study revealed that the substrate specificity and the activity of neuropsin depended on multiple factors: the substrate charge, the substrate orientation, the hydrogen bond network within the catalytic triad and the substrate, and the formation of the oxyanion hole. The apo neuropsin was not reactive without proper alignment of catalytic triad. The substrate binding induced the reactive alignment of catalytic triad. Then the substrate-neuropsin interaction forms the oxyanion hole that stabilizes the transition state and reduces the free-energy barrier of the following scission reaction.

A review of graphene derivative enhancers for perovskite solar cells.

Due to the finite nature, health and environmental hazards currently associated with the use of fossil energy resources, there is a global drive to hasten the development and deployment of renewable energy technologies. One such area encompasses perovskite solar cells (PSCs) that have shown photoconversion efficiencies (PCE) comparable to silicon-based photovoltaics, but their commercialisation has been set back by short-term stability and toxicity issues, among others. A tremendous potential to overcome these drawbacks is presented by the emerging applications of graphene derivative-based materials in PSCs as substitutes or components, composites with other functional materials, and enhancers of charge transport, blocking action, exciton dissociation, substrate coverage, sensitisation and stabilisation. This review aims to illustrate how these highly capable carbon-based materials can advance PSCs by critically outlining and discussing their current applications and strategically identifying prospective research avenues. The reviewed works show that graphene derivatives have great potential in boosting the performance and stability of PSCs through morphological modifications and compositional engineering. This can drive the sustainability and commercial viability aspects of PSCs.

Single DNA Translocation and Electrical Characterization Based on Atomic Force Microscopy and Nanoelectrodes.

Precision DNA translocation control is critical for achieving high accuracy in single molecule-based DNA sequencing. In this report, we describe an atomic force microscopy (AFM) based method to linearize a double-stranded DNA strand during the translocation process and characterize the electrical properties of the moving DNA using a platinum (Pt) nanoelectrode gap. In this method, λDNAs were first deposited on a charged mica substrate surface and topographically scanned. A single DNA suitable for translocation was then identified and electrostatically attached to an AFM probe by pressing the probe tip down onto one end of the DNA strand without chemical functionalizations. Next, the DNA strand was lifted off the mica surface by the probe tip. The pulling force required to completely lift off the DNA agreed well with the theoretical DNA adhesion force to a charged mica surface. After liftoff, the captured DNA was translocated at varied speeds across the substrate and ultimately across the Pt nanoelectrode gap for electrical characterizations. Finally, finite element analysis of the effect of the translocating DNA on the conductivity of the nanoelectrode gap was conducted, validating the range of the gap current measured experimentally during the DNA translocation process.

Serine racemase interaction with N-methyl-D-aspartate receptors antagonist reveals potential alternative target of chronic pain treatment: Molecular docking study.

ABSTRACTSerine racemase (SR) catalyzes L-serine racemization to activate the N-methyl-D-aspartate receptor (NMDAR). NMDAR activation is associated with the progression of acute-to-chronic neuropathic pain. This study aimed to investigate NMDAR antagonist interactions with SR to obtain potential chronic pain target therapy. Several NMDAR antagonist drugs were obtained from the drug bank, and malonate was used as a control inhibitor. Ligands were prepared using the open babel feature on PyRx. The SR structure was obtained from Protein data bank (PDB) (3l6B) and then docked with ligands using the AutoDock Vina. Haloperidol had a lower binding affinity than malonate and other ligands. Ethanol had the highest binding affinity than other drugs but could bind to the Adenosine triphosphate (ATP)-binding domain. Haloperidol is bound to reface that function for reprotonation in racemization reaction to produce D-serine. Halothane bond with Arg135 residues aligned negatively charged substrates to be reprotonated properly by reface. Tramadol is bound to amino acid residues in the triple serine loop, which determines the direction of the SR reaction. Several NMDAR antagonists such as haloperidol, halothane, ethanol, and tramadol bind to SR in the specific binding site. It reveals that SR potentially becomes an alternative target for chronic pain treatment.