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In this work, Monte Carlo simulation of CO2, N2, and CH4adsorption on zeolite 13X is carried out in grand canonical ensemble. FAU framework was used to reproduce the structure of zeolite 13X. Universal force field was used to calculate the interactions between adsorbates and 13X. Metropolis method was used for calculating adsorption isotherm. Volumetric measurements were carried out to confirm the simulation results. The simulation results using Universal force field showed good agreement with experimental results. Highest CO2uptake for this zeolite was found as 5.67 mol/kg from GCMC. Isosteric heat of adsorption was investigated to find the heat released during adsorption of each gas. The simulation result of isosteric heat of adsorption for CO2, N2, and CH4was utmost 17.00, 4.37, and 6.14 kcal/mole, respectively. Radial distribution graphs were used to find affinity of constituents of zeolite for CO2. Henry’s constant evaluation was also performed at low pressure to find the selectivity of the structure. Henry’s constant of CO2in an equimolar mixture of N2and CH4was calculated 3.49 and 1.49 mol/kg.kPa, respectively. Finally, simulation results were fitted to Toth and dual-site Langmuir isotherms to find the best fit that belongs to dual-site Langmuir. [ABSTRACT FROM PUBLISHER]

A generalized methodology for statistical analogues of derivatives of the fundamental equation of state in the microcanonical and canonical ensembles is suggested. Those analogues include rigorous measuring prescriptions for any thermodynamic property in molecular NVE and NVT simulation. In particular, optimal data sets for exhaustive thermodynamic data correlation become rigorously accessible. [ABSTRACT FROM PUBLISHER]

Inhibiting angiotensin-converting enzyme 1 (ACE1) is a key strategy for managing hypertension as it prevents the formation of angiotensin II, a potent vasoconstrictor. Given the adverse effects associated with synthetic inhibitors, there is an increasing focus on exploring natural bioactive peptides as potential ACE1 inhibitors. Hemopressins (Hp) are peptides derived from hemoglobin. The present study investigated the ACE1 inhibitory activity of two Hp variants, Hp bearing phenylalaine (Hp-F) and Hp bearing leucine (Hp-L), using a combination of in vitro and in silico methodologies. In enzyme inhibition assays, Hp-L variants exhibited better inhibition when compared to Hp-F variants. Furthermore, in molecular docking and molecular dynamics simulations, Hp-L variants displayed favorable binding characteristics, in terms of binding energy and interactions, supporting their potential to be effective ACE1 inhibitors. The peptides were observed to interact with key residues involved in binding widely used ACE1 inhibitors. Notably, peptide RVD-Hp-L (RVDPVNFKLLSH) showed the lowest IC50 value, higher binding affinity and sustained interactions while binding to the catalytic site of ACE1. Finally, the substitution of phenylalanine with leucine in hemopressins significantly enhances their binding affinity and inhibitory potency. [ABSTRACT FROM AUTHOR]

Interest in the phase behavior of hydrocarbons in shale reservoirs has grown in recent years. Petroleum fluid phase behavior has been observed to differ significantly between conventional reservoirs and shale reservoirs. Within shale reservoirs, notable surface-fluid interactions can lead to non-uniform molecule distribution and an alteration in fluid phase behavior, primarily caused by the existence of nano-scale porous materials. In this work, we study the phase behavior of methane in single cylindrical pore models. We apply the gauge Gibbs ensemble Monte Carlo (gauge-GEMC) simulation technique to investigate the phase behavior of methane in 4–10 nm single nanopores and calculate the saturation pressures at various temperatures using the grand canonical Monte Carlo (GCMC) simulation technique. A shift in the phase diagram has been found for methane in nanopores. As pore size decreases, the shift becomes more significant. [ABSTRACT FROM AUTHOR]

The adsorption characteristics of CH4 have an important influence on gas content prediction, gas extraction, and hazard prevention. Therefore, we explored the mechanism of CH4 adsorption under the action of water and temperature to grasp the influence of water and temperature on the adsorption characteristics of CH4. In this paper, a giant, regular-system Monte Carlo method is used to simulate the CH4 adsorption behavior at the molecular level under different temperatures, water contents, and the coupling of both. The results indicate that an empirical formula for the coupling effect of temperature and water content on CH4 adsorption was obtained. The impact of different effects on CH4 adsorption is as follows: coupling effect > single temperature effect > single water content effect. The optimal combination is at a temperature of 363 K and a water content of 8.31%. Compared with the CH4 adsorption capacity without water at room temperature, the CH4 adsorption capacity is reduced by 68.04% under the coupling effect of the optimal combination. Temperature has a negative effect on the adsorption of CH4, and temperature changes the adsorption capacity by changing the average molecular kinetic energy of CH4. The reason why the increase in H2O reduces the adsorption capacity of CH4 is that the interaction between H2O and the oxygen-containing functional groups of coal is stronger than that of CH4. As the water content increases, the adsorption heat decreases, thereby inhibiting the adsorption of CH4. In addition, H2O has a smaller molecular dynamics radius as compared to CH4; the larger the free volume and surface area in the pore structure, the more adsorption pores it occupies, resulting in a more significant reduction in the adsorption of CH4. [ABSTRACT FROM AUTHOR]

Generalized-ensemble algorithms are powerful techniques for investigating biomolecules such as protein, DNA, lipid membrane, and glycan. The generalized-ensemble algorithms were originally developed in the canonical ensemble. On the other hand, not only temperature but also pressure is controlled in experiments. Additionally, pressure is used as perturbation to study relationship between function and structure of biomolecules. For this reason, it is important to perform efficient conformation sampling based on the isothermal–isobaric ensemble. In this article, we review a series of the generalized-ensemble algorithms in the isothermal–isobaric ensemble: multibaric–multithermal, pressure- and temperature-simulated tempering, replica-exchange, and replica-permutation methods. These methods achieve more efficient simulation than the conventional isothermal–isobaric simulation. Furthermore, the isothermal–isobaric generalized-ensemble simulation samples conformations of biomolecules from wider range of temperature and pressure. Thus, we can estimate physical quantities more accurately at any temperature and pressure values. The applications to the biomolecular system are also presented. [ABSTRACT FROM AUTHOR]

This review provides a critical assessment of the current state of affairs regarding the solvation thermodynamics involving mixed-solvent systems. It focuses specifically on (i) its rigorous molecular-based foundations, (ii) the underlying connections between the microstructural behavior of the mixed-solvent environment and its thermodynamic responses, (iii) the microstructural characterization of the behavior of the mixed-solvent environment around the dilute solute via unique fundamental structure-making/-breaking functions and the universal preferential solvation function, (iv) the discussion of potential drawbacks associated with the molecular simulation-based determination of thermodynamic preferential interaction parameters, and (v) the forensic examination of frequent modeling pitfalls behind the interpretation of preferential solvation from experimental data of Gibbs free energy of solute transfer. [ABSTRACT FROM AUTHOR]

Low salinity water containing sulfate ions can significantly alter the surface wettability of carbonate rocks. Nevertheless, the impact of sulfate concentration on the desorption of oil film on the surface of carbonate rock is still unknown. This study examines the variations in the wettability of the surface of carbonate rocks in solutions containing varying amounts of sodium sulfate and pure water. The problem is addressed in the framework of molecular dynamics simulation (Material Studio software) and experiments. The experiment's findings demonstrate that sodium sulfate can increase the rate at which oil moisture is turned into water moisture. The final contact angle is smaller than that of pure water. The results of the simulations show that many water molecules travel down the water channel under the influence of several powerful forces, including the electrostatic force, the van der Waals force and hydrogen bond, crowding out the oil molecules on the calcite's surface and causing the oil film to separate. The relative concentration curve of water and oil molecules indicates that the separation rate of the oil film on the surface of calcite increases with the number of sulfate ions. Graphic Abstract [ABSTRACT FROM AUTHOR]

In a world made of atoms, computer simulations of molecular systems such as proteins in water play an enormous role in science. Software packages for molecular simulation have been developed for decades. They all discretize Hamilton's equations of motion and treat long-range potentials through cutoffs or discretization of reciprocal space. This introduces severe approximations and artifacts that must be controlled algorithmically. Here, we bring to fruition a paradigm for molecular simulation that relies on modern concepts in statistics to explore the thermodynamic equilibrium with an exact and efficient non-reversible Markov process. It is free of all discretizations, approximations, and cutoffs. We explicitly demonstrate that this approach reaches a break-even point with traditional molecular simulation performed at high precision, but without any of its approximations. We stress the potential of our paradigm for crucial applications in biophysics and other fields, and as a practical approach to molecular simulation. We set out a strategy to reach our goal of rigorous molecular simulation. [ABSTRACT FROM AUTHOR]

• Compares simplified slit and realistic atomic models for gas adsorption on activated carbons. • Employs Grand Canonical Ensemble Monte Carlo and Gibbs Ensemble Monte Carlo methods. • Optimal pore widths: 0.65, 0.95 nm for CO 2 ; 0.65, 1.0 nm for H₂S selectivity. • –COOH doped cs1000a attains optimal CO 2 selectivity (67.3) and adsorption (12 mmol/g) • Emphasizes the need for materials with low density and optimized pore size distribution. We conducted a comparative analysis of the adsorption and separation of H 2 -CO 2 and CH 4 -H 2 S systems in simplified slit pore models and realistic atomic models. At 77 K and 4 MPa, cs1000a activated carbon demonstrates excess hydrogen adsorption with gravimetric and volumetric values of 3.2 wt% and 23 kg/m3, respectively. Considering the bulk density of cs1000a, the corresponding values in 0.9 nm slit pores are 7.75 wt% and 56 kg/m3. The adsorption isotherms indicates that the interaction between the walls of the slit pores and the adsorbed fluid molecules is stronger than in the realistic model from Hybrid Reverse Monte Carlo (HRMC) simulation, making adsorption more likely to saturate at low pressures. At 303 K and 4 MPa, cs1000a has the highest CO 2 adsorption (7.45 mmol/g) but the lowest selectivity (14.28). In a CH₄-H₂S mixture, it shows selectivity and adsorption capacity for H₂S of 12.1 mmol/g and 7.96, respectively. The slit with a 0.9 nm pore width shows a CO 2 selectivity of 127 and an 18.26 mmol/g adsorption capacity, and 14.46 and 15.54 mmol/g for H₂S, respectively. The CO 2 selectivity within slit pores peaks at 421 (0.65 nm) and 144 (0.95 nm), while H₂S selectivity follows a similar trend, reaching 40 (0.65 nm) and 28 (1.0 nm). Optimal widths show both single and double-layer adsorption, aligning with the molecular configurations. The HRMC model, with its non-optimal pores, exhibits reduced adsorption and separation capabilities owing to pronounced geometric and energy heterogeneity. By correlating material density, pore volume, and adsorption behavior, we found that cs1000a_24cooh material, doped with –COOH functional group, achieves an optimal balance in CO 2 selectivity and adsorption capacity, reaching 67.3 and 12 mmol/g. This underscores cs1000a's superior decarburization and desulfurization capabilities. In summary, the varying adsorption capacities, heats, and selectivities of fluids on the materials suggest that the simplistic slit pore model is inadequate for characterizing the amorphous nature of activated carbon. This emphasizes the importance of designing materials with low density and a concentrated pore width distribution at optimal values. [ABSTRACT FROM AUTHOR]

Nanoelectrochemical devices have become a promising candidate technology across various applications, including sensing and energy storage, and provide new platforms for studying fundamental properties of electrode/electrolyte interfaces. In this work, we employ constant-potential molecular dynamics simulations to investigate the impedance of gold-aqueous electrolyte nanocapacitors, exploiting a recently introduced fluctuation--dissipation relation. In particular, we relate the frequency-dependent impedance of these nanocapacitors to the complex conductivity of the bulk electrolyte in different regimes, and use this connection to design simple but accurate equivalent circuit models. We show that the electrode/electrolyte interfacial contribution is essentially capacitive and that the electrolyte response is bulk-like even when the interelectrode distance is only a few nanometers, provided that the latter is sufficiently large compared to the Debye screening length. We extensively compare our simulation results with spectroscopy experiments and predictions from analytical theories. In contrast to experiments, direct access in simulations to the ionic and solvent contributions to the polarization allows us to highlight their significant and persistent anticorrelation and to investigate the microscopic origin of the timescales observed in the impedance spectrum. This work opens avenues for the molecular interpretation of impedance measurements, and offers valuable contributions for future developments of accurate coarse-grained representations of confined electrolytes. [ABSTRACT FROM AUTHOR]

We report a coarse-grained molecular dynamics simulation study of a bundle of parallel actin filaments under supercritical conditions pressing against a loaded mobile wall using a particle-based approach where each particle represents an actin unit. The filaments are grafted to a fixed wall at one end and are reactive at the other end, where they can perform single monomer (de)polymerization steps and push on a mobile obstacle. We simulate a reactive grand canonical ensemble in a box of fixed transverse area A, with a fixed number of grafted filaments Nf, at temperature T and monomer chemical potential μ1. For a single filament case (Nf = 1) and for a bundle of Nf = 8 filaments, we analyze the structural and dynamical properties at equilibrium where the external load compensates the average force exerted by the bundle. The dynamics of the bundle-moving-wall unit are characteristic of an over-damped Brownian oscillator in agreement with recent in vitro experiments by an optical trap setup. We analyze the influence of the pressing wall on the kinetic rates of (de)polymerization events for the filaments. Both static and dynamic results compare reasonably well with recent theoretical treatments of the same system. Thus, we consider the proposed model as a good tool to investigate the properties of a bundle of living filaments. [ABSTRACT FROM AUTHOR]

An empirical equation of state correlation is proposed for the Lennard-Jones model fluid. The equation in terms of the Helmholtz energy is based on a large molecular simulation data set and thermal virial coefficients. The underlying data set consists of directly simulated residual Helmholtz energy derivatives with respect to temperature and density in the canonical ensemble. Using these data introduces a new methodology for developing equations of state from molecular simulation. The correlation is valid for temperatures 0.5 < T/Tc < 7 and pressures up to p/pc = 500. Extensive comparisons to simulation data from the literature are made. The accuracy and extrapolation behavior are better than for existing equations of state. [ABSTRACT FROM AUTHOR]

Our researches are based on the fact that the systems composed of polyacrylamide and montmorillonite under a kind of shear state often appear in some important practical processes like drilling well etc. The viscosity of polyacrylamide is usually the most important one among the characteristics to decide if the practical processes succeed or not. Therefore, we studied the effect of hydrated montmorillonite on the viscosities of polyacrylamide with temperature and shear rate varying under confined shear by molecular simulation method. Adopting the condition of confined shear in the research could make our simulations and the practical processes as similar as possible. First, the model of one polyacrylamide polymer chain with 20 monomers linearly linking surrounded by water molecules between two of montmorillonite layers was constructed. Then canonical ensemble (NVT) MD simulations were carried out for the built model at different temperatures and shear rates. From the gained simulation results, we calculated the polymer's structural property-radius of gyration, which was directly related to the viscosity property of polyacrylamide polymer. It was found that the viscosity of the polyacrylamide polymer between hydrated clay layers decreased with the temperature increasing from 298 to 343 K under the condition of confined shear. The variation trend of viscosity from simulation results was also confirmed by our experiments. Besides, the viscosity of the polyacrylamide between hydrated clay layers decreased with the shear rate increasing within the range of higher shear rates. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the confinement effect of nanopores, the fluid-phase behavior of shale oil reservoirs is much different from that of conventional reservoirs. The accurate description of the phase change characteristics of fluid in nanopores is the basis to design development plan, production system, and EOR methods of shale oil reservoirs. In this study, molecular dynamics simulation was employed to analyze the phase behavior of single-component system and hydrocarbon–CO2 mixture system in organic nanopores. The results show that the confinement effect on the phase change pressure of the single-component system is influenced by the distribution of the electron cloud. The phase change pressure of hydrocarbons with even distribution of the electron cloud would be increased, while that of CO2 would be decreased due to the instantaneous dipole moment. In addition, as the length of carbon chains increases, the confinement effect on hydrocarbons becomes stronger. When the temperature increases, the confinement effect becomes weaker. In the hydrocarbon–CO2 mixture system, when the occurrence condition changes from bulk to the nanopore of 5 nm, the bubble point pressure decreases by 39.21–68.85%, and the critical temperature and pressure decrease by 75.98% and 7.13%, respectively. On the whole, the P–T phase envelope is shrunken under the confinement effect. CO2 is much easier to be miscible with shale oil in nanopores. Moreover, full mixing and keeping in single liquid phase of CO2–hydrocarbons mixture system can reduce the adsorption of hydrocarbons on organic pore walls. Therefore, CO2 injection could be a feasible method to enhance oil recovery in the matrix of shale oil reservoirs. [ABSTRACT FROM AUTHOR]

Dry modified Styrene-Butadiene-Styrene block copolymer (SBS) is an innovative method of modifying asphalt mixture that has gained attention due to its convenience, low carbon footprint, and high efficiency. To understand the diffusion behavior and micromechanism of dry modified SBS at the asphalt-aggregate interface, molecular dynamic simulation technology was employed to investigate its behavior at various temperatures. The mean square displacement, diffusion coefficient, statistical relative concentration distribution, and interfacial energy were used to calculate the diffusion and migration mechanism of dry modified SBS at the asphalt-aggregate interface. Additionally, the water-boiling test and Fourier transform infrared spectroscopy (FTIR) test were conducted to analyze the interfacial stripping form and SBS dispersion in the asphalt film. The results indicated that at high temperatures, dry modified SBS exhibited the highest mean square displacement and diffusion coefficient, suggesting that higher temperatures promoted its diffusion toward the asphalt layer. Dry modified SBS clusters and asphalt displayed opposite migration diffusion tendencies, with the migration of dry modified SBS toward the asphalt film becoming more pronounced over time. The introduction of SBS altered the distribution of asphalt components on the aggregate surface, increasing the interfacial energy and adhesion strength between asphalt and aggregate. Laboratory experiments supported these findings, confirming that dry modified SBS enhanced diffusion distribution and interfacial strength. The diffusion distribution of dry modification was found to be similar to that of wet-process SBS modified asphalt under sufficient temperature and time. Therefore, in engineering applications, raising the mixing temperature can improve the diffusion distribution of dry modified SBS, further enhancing its modification efficiency and effectiveness. [ABSTRACT FROM AUTHOR]

Zeolite additional layers coating on metal oxide surfaces to improve the selectivity and response values of the sensors are effective and widely used. The specific adsorption and diffusion of gas molecules in the zeolite are recognised to play an important role in gas sensing improvement. In this work, the adsorption and diffusion behaviours of formaldehyde and acetone in H-Y and H-A zeolites were calculated by Monte Carlo and molecular dynamics simulations. The loading of acetone is greater than formaldehyde in these two kinds of zeolites under the same temperature and pressure, and the water load is lower. The simulation results show that the effects of the nature of the guest molecule and steric hindrance of the diffusing molecule on diffusivity are significant. The diffusivity in H-A zeolite decreases by several orders of magnitude than that in H-Y zeolite However, in H-A zeolite, the internal diffusion dominates, and only the smaller diameter formaldehyde can diffuse between the pores, which is beneficial to improving the sensing properties of formaldehyde. In addition, in the competition diffusion with water molecules, formaldehyde dominates than acetone. The H-Y/SnO2 and H-A/SnO2 sensors were prepared to verify the reliability of the molecular simulations. Research highlights The adsorption and diffusion behaviour of formaldehyde and acetone in H-Y and H-A zeolites were investigated using molecular simulation. Molecular diameter mainly influences the kinetic behaviour. The sensitisation mechanism of H-Y/SnO2 sensor to acetone and H-A/SnO2 sensor to formaldehyde was proved. Focuses on the relationship between gas-sensing the performance of zeolite-covered SnO2 sensors and the adsorption. [ABSTRACT FROM AUTHOR]

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Dyna is the property of Universidad Nacional de Colombia, Medellin, Facultad de Minas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The adsorption of pure methane in activated carbon Ecosorb was studied by combining grand canonical ensemble Monte Carlo molecular simulations and an experimental approach based on a gravimetric device. Experimental and calculated adsorption isotherms of methane were determined in supercritical conditions at 303.15 and 353.15 K and pressures up to 10 MPa. The comparison between both experimental and estimated data proves the consistency of the methodology used in this work, starting from the characterization of the porous media in terms of pore size distribution, the determination of the experimental adsorption isotherms, and the final estimation of computational results through estimated isotherms determination. Moreover, additional differential enthalpy of adsorption calculations were compared with experimental values obtained by means of a manometric/calorimetric technique. The good agreement shows the strength and the originality of this paper by combining experimental and computational homemade results allowing a complete characterization of the activated carbon substrate and its methane storage capacity. [ABSTRACT FROM AUTHOR]

Using the framework of Wertheim's thermodynamic perturbation theory, a new polyatomic density functional theory is developed to account for the intermolecular association of cyclic molecules in interfacial systems. To test the theory, Monte Carlo simulations in the canonical ensemble were performed for the specific case of an associating triatomic ring with one association site next to a hard wall. The theory and simulation results were found to be in good agreement. [ABSTRACT FROM AUTHOR]

Molecular simulations of interactions between urea molecules and lignin polymer have been carried out with the aim of understanding the mechanism of urea slow-release behaviours in lignin–urea materials. It has been found, by docking technology and natural bond orbital analysis, that H-bonds and π-electronic conjugation effect are the main driving forces to keep urea molecules adsorbed on the lignin. In the NPT (isothermal–isobaric ensemble) simulations, mean-squared displacement results show that water molecules can promote the urea molecules gradually away from the lignin. Furthermore, in NVT (canonical ensemble) molecular dynamic simulations, results on diffusion constants of urea molecules in lignin–urea system show that diffusion constant of urea molecules in a urea–water–lignin system increases with an increase in the water content. Conclusions gained from two different kinds of simulation are in agreement with each other and are consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

This article presents a methodology for checking the existence of the azeotrope and computing its composition, density, and pressure at a given temperature by integrating chemical engineering insights with molecular simulation principles. Liquid-vapor equilibrium points are computed by molecular simulations using the Gibbs ensemble Monte Carlo (GEMC) method at constant volume. The appearance of the azeotropic point is marked by a shift of the equilibrium constant from one side of the unity to the other. After each GEMC simulation, an identity change move is derived in the grand canonical ensemble to progress towards the azeotrope along the equilibrium curve. The effectiveness of the proposed methodology is successfully tested for several binary Lennard-Jones mixtures reported in the literature. [ABSTRACT FROM AUTHOR]