Van Der Waals Interaction Energy Research Articles

Exploring the mutation landscape of SARS-CoV-2 Variant JN.1

Although Covid-19 is no longer a global pandemic, the spread of SARS-CoV-2 variants, currently led by Omicron and its subvariant, remains prevalent worldwide and causes health issues. In mid-2023, a descendant of BA.2, BA.2.86, carries more than 30 mutations in the Receptor Binding Domain (RBD), helping this variant transmit to create thousands of new COVID-19 cases in many countries worldwide. JN.1 was determined as a descendant of BA.2.86 by WHO because of the mutation profile in spike protein. JN.1 transmission is currently in Europe, the United States and other countries. Therefore, examining unique mutations in RBD of JN.1 to bind with hACE2 plays an important role in discovering the infectious efficiency of this variant. Our study shows that JN.1 has a lower affinity for hACE2 than the ancestral variant BA.2.86. In particular, L455S mutation reduces binding free energy by decreasing Van der Waals interaction energy. We also provide new insights into the significance of E484K in the RBD of JN.1, helping to bind stable with hACE2. Collectively, we suggest that residues positively charged in the RBD of JN.1 play the most important role in the interaction mechanism with hACE2. Future new variants should emphasize positively charged amino acid substitutions in the RBD.

Evaluation and improvement of Gay-Berne interaction potential to simulate 3D DLVO interaction of clay particles

This paper first presents a set of DLVO-based energy-separation functions for a pair of finite uniformly charged square platelets of infinitesimal thickness in three elementary configurations: face-to-face, edge-to-edge, and edge-to-face. The novel dataset was generated by summing the electrostatic interaction energy computed numerically by solving the non-linear 3D Poisson-Boltzmann equation and the van der Waals interaction energy calculated analytically. The dataset aims to inform qualitatively and quantitatively the energy/force separation functions used in the Discrete Element Method (DEM) and Coarse-Grained Molecular Dynamics (CGMD) modelling of clays. The same dataset was then used to calibrate and evaluate two Gay-Berne (GB)-type potentials: i) a DLVO-adapted Gay-Berne potential, where the Born-van der Waals branches of the underlying Lennard-Jones (LJ) potential are replaced with van der Waals-Columbic branches to represent DLVO interactions; ii) the Mie potential, where the exponents of the two energy terms are ‘unlocked’ instead of being set equal to 12 and 6 as per the original LJ potential. It is shown that the orientation parameter, µ, and the anisotropy parameter, ν, need to be different from µ = 2 and ν = 1 as adopted in CGMD clay modelling to capture the progression of the shape of the pair energy-separation function from face-to-face to edge-to-face and edge-to-edge configuration. It is also shown that the MIE potential (with exponents m = 3 and n = 1.5) better captures the slow decay of the electrostatic repulsive energy component of the DLVO potential energy Coulombic branch of the interaction potential compared to the DLVO-adapted GB potential, which embeds the Lennard-Jones (LJ) exponents m = 12 and n = 6.

Theoretical study on symmetric and asymmetric stacking in the self-assembly of bola-amphiphilic peptides into membranes with mixtures of EF4E and KF4K

In this work, we conducted a study on peptide membranes formed by the amino acid sequences EF4E and KF4K with the aim of obtaining energetic and structural results for asymmetric and symmetric membrane nanostructures. The results show that the lifetime of hydrogen bonds (HBs) for peptides in the symmetric membrane is ∼12 % higher than that observed for the asymmetric structure, providing greater rigidity to the former. These findings are consistent with those obtained for Coulomb and van der Waals interaction energies and demonstrate that the Symmetric model exhibits better stability compared to the Asymmetric model. The average thickness of the membranes is ∼1.72 ± 0.06 nm and ∼2.27 ± 0.02 nm for the asymmetric and symmetric models, respectively. Our results show that the symmetric model stands out due to greater structural organization and consequently a less hydrated appearance in the membrane region, which could be crucial for applications. From an electrical perspective, both membranes display clear differences, underscoring the influence of peptide arrangement on the membrane structure.

Solvent-free synthesis of self-regenerative superhydrophobic film from silicone waste with drag-reduction and selective oil absorption behaviour

In the present work, we devised an ecological solution for recycling silicone waste into functionalized films possessing superhydrophobicity with low drag and oil adsorption characteristics. We used two ecological approaches to transform silicone waste into nanoparticles with inherently distinct surface characteristics. These spheroidal silica nanoparticles, with an average size of 150 nm, showed hydrophilic and hydrophobic characteristics. The detailed characterization confirmed hydrophobic silica being grafted with –CH3 oligomers compared to hydrophilic counterparts. These silica nanoparticles were used to fabricate flexible superhydrophobic films through a solvent-free approach. Films synthesized using hydrophilic particles showed better de-wetting characteristics with advancing angle > 150°, low hysteresis (<5°) and sliding angle (<5°) at an optimum volumetric concentration. High de-wetting stability and low adhesion of ∼ 20 μN with water droplet were noticed for these films due to homogenous particle distribution, leading to significant protrusions and favourable line tension. High van der Waals interaction energy aided better mixing of hydrophilic particles in the matrix than the hydrophobic counterpart. This also resulted in high mechanical strength ∼ 7 MPa (matrix strength ∼ 3 MPa) and better robustness under different harsh conditions, sustaining more than ten months of weathering and one month of immersion. Films showed real-time self-regeneration capability, retaining high de-wetting due to surface chemistry and morphology rejuvenation. The film also displayed extremely low drag, promoting water droplet mobility at ∼ 0.5 m/s wind velocity and oil–water separation capability. The fluorine-free flexible superhydrophobic films synthesized using silicone waste exhibited multi-dimensional characteristics for wide-range applications.

Contact-line bending energy controls phospholipid vesicle adhesion

Phospholipid bilayer bending energy is often discarded in the analysis of vesicle adhesion on the basis of a dimensionless parameter w = − Δ U R 0 2 / κ b ≫ 1 (interaction energy Δ U , spherical radius R 0 , bending rigidity κ b ), considered a regime of strong adhesion. In this study, we propose a model by which bending energy in a singular proximity of the contact line balances the adhesion energy. This is developed for a regime in which the membrane correlation length ξ is small compared with the vesicle radius R 0 , so a spherical cap with circular footprint presents an effective contact angle θ . Experiments are conducted in which the adhesion of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) vesicles to hyaluronic acid hydrogel substrates is controlled by tuning the van der Waals attraction with systematic change in the hydrogel concentration. Theoretical interpretation of the data furnishes a dimensionless model parameter α ≈ 2 – 10 for contact angles θ ≈ 20 – 80 ∘ , beyond which vesicles collapse into discs. We show that the van der Waals interaction energy varies in the range − Δ U ≈ 0.14 – 0.68 μ J m − 2 in response to varying the hydrogel concentration in a range c ha ≈ 2 – 10 %. The analysis provides a foundation for exploring vesicle–hydrogel interactions with electro-steric influences; these are poorly understood but pertinent in a wide variety of biological and technological applications.

Adhesion properties of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2 &lt;/sub&gt;interface: Size and temperature effects

The interface adhesion properties are crucial for designing and fabricating two-dimensional materials and related nanoelectronic and nanomechanical devices. Although some progress of the interface adhesion properties of two-dimensional materials has been made, the underlying mechanism behind the size and temperature dependence of interface adhesion energy and related physical properties from the perspective of atomistic origin remain unclear. In this work, we investigate the effects of size and temperature on the thermal expansion coefficient and Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; as well as interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; based on the atomic-bond-relaxation approach and continuum medium mechanics. It is found that the thermal expansion coefficient of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; is significantly larger than that of its few-layer and bulk counterparts under the condition of ambient temperature due to size effect and its influence on Debye temperature, whereas the thermal expansion coefficient increases with temperature going up and almost tends to a constant as the temperature approaches the Debye temperature. Moreover, the variations of bond identity induced by size effect and temperature effect will change the mechanical properties of MoS&lt;sub&gt;2&lt;/sub&gt;. When the temperature is fixed, the Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; increases with size decreasing. However, the thermal strain induces the volume expansion, resulting in the Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; decreasing. Furthermore, the size and temperature dependence of lattice strain, mismatch strain of interface, and Young’s modulus will lead the van der Waals interaction energy and elastic strain energy to change, resulting in the change of interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt;. Noticeably, the interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; gradually increases with MoS&lt;sub&gt;2&lt;/sub&gt; size decreasing, while the thermal strain induced by temperature causes interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; to decrease with temperature increasing. In addition, we predict the conditions of the interface separation of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; under different sizes and temperatures. Our results demonstrate that increasing both size and temperature can significantly reduce the interface adhesion energy, which is of great benefit in detaching MoS&lt;sub&gt;2&lt;/sub&gt; film from the substrate. Therefore, the proposed theory not only clarifies the physical mechanism regarding the interface adhesion properties of transition metal dichalcogenides (TMDs) membranes, but also provides an effective way to design TMDs-based nanodevices for desirable applications.

Polycyclic aromatic hydrocarbons dissolution in supercritical carbon dioxide by molecular dynamics simulation

With the rapid development of industry, the problem of soil contamination has grown increasingly serious, posing a serious threat to the wellness of people. Polycyclic aromatic hydrocarbons (PAHs) are among the most common soil contaminants. Supercritical CO2 extraction has been widely used to treat PAHs in soils. Solute solubility in supercritical fluids is a fundamental thermophysical parameter that must be investigated and modeled. In this work, we employed molecular dynamics simulation to investigate the microscopic dissolution process in supercritical CO2 of four PAHs: naphthalene, anthracene, pyrene, and benzo(α)pyrene. We also looked into the implications of changing the ring number of PAHs on the ability of supercritical CO2 to dissolve PAHs by calculating the interaction energy, radial distribution function, and the coordination number between PAHs and supercritical CO2. The results indicated that the PAHs’ capacity to dissolve in supercritical CO2 decreased gradually with the increase of ring number. The interaction energy between PAHs and supercritical CO2 decreases as the number of PAHs rings increases. Among them, the van der Waals interaction energy plays a decisive role in the dissolution of PAHs in supercritical CO2. As the number of PAHs rings increased, the positions of the first peak and valley of the radial distribution function remained the same, which appeared at about 4.3 Å and 6.1 Å, respectively. However, the magnitudes of the peaks and valleys decreased. As the number of PAHs rings increased, the coordination number of the C atoms of supercritical CO2 around the C atoms of PAHs decreased.

Study on the mechanism of the influence of surfactant alkyl chain length on the wettability of anthracite dust based on EDLVO theory and inverse gas chromatography

The dispersion of coal dust on roadways adversely affects the productivity of coal mines and threatens the lives of mine workers. Accordingly, it is crucial to enhance the wettability of coal dust to improve its suppression efficiency. Herein, the mechanism of the influence of the surfactant alkyl chain length on the wettability of anthracite was investigated by systematically analyzing the degree of modification of anthracite with sodium dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates using the “macroscopic + mesoscopic + microscopic + theoretical calculation” method. First, the differences in the macroscopic effects of different surfactants on modified anthracite were investigated via contact angle, settling time, and water retention rate experiments. It was concluded that surfactants with shorter alkyl chains exhibit a stronger ability to enhance the wettability of anthracite. Second, the mesoscopic characterization of different coal samples via laser particle size distribution, zeta potential, X-ray photoelectron spectroscopy, and inverse gas chromatography surface energy analyses revealed that the adsorption amount and intensity of surfactants on the anthracite surface increased with shortening surfactant alkyl chains owing to the spatial site resistance effect. Furthermore, molecular dynamic simulations of the microscopic molecular mechanism of adding different surfactants to enhance the wettability of anthracite showed that the interaction energy between coal dust and water molecules as well as the number of hydrogen bonds formed in the system rapidly increased with the shortening of the alkyl chains of anionic surfactants, which had a stronger binding ability to water molecules. Finally, the extended Derjaguin, Landau, Verwey, and Overbeek theory was employed to explain the relationship between the variation in electrostatic interaction, van der Waals, hydrophobic interaction, and total interaction energies and confirm that the wettability of anthracite particles increases with their dispersion in water. The ability of the surfactants to improve the wettability of anthracite increased at different degrees with the shortening surfactant alkyl chains. This study can provide breakthrough inspiration for the fields of coal flotation and haze control.

Exploring binding modes of the selected inhibitors to SND1 by all-atom molecular dynamics simulations

Breast cancer is the leading cause of cancer-related deaths in women. Previous studies have indicated that disrupting the interaction between Metadherin (MTDH) and Staphylococcal nuclease domain containing 1 (SND1) can inhibit breast cancer development. Understanding the binding mode of small molecule inhibitors with SND1 is of great significance for designing drugs targeting the MTDH-SND1 complex. In this study, we conducted all-atom molecular dynamics (MD) simulations in solution and performed binding energy calculations to gain insights into the binding mechanism of small molecules to SND1. The binding site of SND1 for small molecules is relatively rigid, and the binding of the small molecule and the mutation of key residues have little effect on the conformation of the binding site. SND1 binds more tightly to C26-A6 than to C26-A2, as C26-A2 undergoes a 180° directional change during the simulation process. The key residue mutations have a direct effect on the position and orientation of small molecule in the binding site. The key residues make primary contributions to the binding energy through van der Waals interaction and nonpolar solvation energy, although the contribution from nonpolar solvation is relatively minor. The key residue mutations also affect the formation of hydrogen bonds and ultimately the stability of the small molecule-SND1 complex. Communicated by Ramaswamy H. Sarma

The Role of Cosolvent-Water Interactions in Effects of the Media on Functionality of Enzymes: A Case Study of Photobacterium leiognathi Luciferase.

A complex heterogeneous intracellular environment seems to affect enzymatic catalysis by changing the mobility of biomolecules, their stability, and their conformational states, as well as by facilitating or hindering continuously occurring interactions. The evaluation and description of the influence of the cytoplasmic matrix components on enzymatic activity are problems that remain unsolved. In this work, we aimed to determine the mechanisms of action of two-component media with cosolvents of various molecular sizes on the complex multi-stage bioluminescent reaction catalyzed by bacterial luciferase. Kinetic and structural effects of ethylene glycol, glycerol, sorbitol, glucose, sucrose, dextran, and polyethylene glycol on bacterial luciferase were studied using stopped-flow and fluorescence spectroscopy techniques and molecular dynamics simulations. We have found that diffusion limitations in the presence of cosolvents promote the stabilization of flavin substrate and peroxyflavin intermediate of the reaction, but do not provide any advantages in bioluminescence quantum yield, because substrate binding is slowed down as well. The catalytic constant of bacterial luciferase has been found to be viscosity-independent and correlated with parameters of water-cosolvent interactions (Norrish constant, van der Waals interaction energies). Crowding agents, in contrast to low-molecular-weight cosolvents, had little effect on peroxyflavin intermediate decay and enzyme catalytic constant. We attributed specific kinetic effects to the preferential interaction of the cosolvents with enzyme surface and their penetration into the active site.

Van der Waals interaction energies for ferric ion sensors using prismatic and cylindrical pore approximations for a MOF pore.

Using the Lennard-Jones potential, we determine analytical expressions for van der Waals interaction energies between a point and a rectangular prism-shaped pore, writing them in terms of standard elementary functions. The parameter values for a new ferric ion sensor are used to compare these calculations with the cylindrical pore approximation for the interactions between an ion and a metal organic framework (MOF) pore. The results using the prismatic pore approximation predict the same qualitative outcomes as a cylindrical pore approximation. However, the prismatic approximation predicts lower magnitudes for both the interaction potential energy minimum and the force maximum, since the average distance from the centre-line to the surface of the prism is greater. We suggest that in some circumstances it is sufficient to use the simpler cylindrical approximation, provided that the cylinder radius is chosen so that the cross-sectional area is equal to the area of the prism pore opening. However, atoms at the nodes should remain approximated by semi-infinite lines. We also determine the interaction between a second ferric ion and a blocked MOF pore; as expected, the second ferric ion experiences a force away from the pore, implying that approaching ferric ions can only occupy vacant MOF pores.

A nanoscroll robustly formed by self-folding a γ-graphyne ribbon on a CNT

Graphynes are one-atom-thick carbon allotropes that are similar to graphene. Direct synthesis of the nanoscrolls from graphynes still faces challenges. This study introduces a physical approach for producing a γ-graphyne nanoscroll (GNS) from a graphyne ribbon. The molecular dynamics method is used to verify the feasibility and the robustness of the physical method by simulating the process of fabricating γ-GNSs from γ-graph-n-yne (acetylenic repeats n = 1–4 in this study) ribbons on a carbon nanotube (CNT). The competition between the bending energy required by the ribbon and the local van der Waals (vdW) interaction energy dominates the self-folding process. Both energies decrease with an increase in n and the ambient temperature. Only when the vdW interaction energy is higher than the bending energy, the self-folding process can be triggered. Hence, either the radius or the length of CNT has a minimum, over which the ribbon can fold into a scroll. The minima are higher at a relatively low temperature between 100 K and 300 K. The initial relative locations of the CNT to the free edge of the ribbon influences the successful formation of the nanoscrolls. The conclusions obtained are helpful for fabricating high-quality γ-GNSs.

The state of art in the prediction of mechanism and modeling of the processes of surface functionalized carbon nanotubes into the membrane cell

Carbon nanotubes (CNTs), due to their unique properties, are attracting increasing attention in biomedicine applications. Chemically functionalized CNTs (fCNTs) are being developed for therapeutic and diagnostic applications, and it is important to understand how they penetrate living cells. By examining the behavior of CNT around the membrane cell, it is possible to find which types of interactions are involved in the insertion mechanism, as well as what kinds of functional groups the nanotube surface has to offer. Here, classical molecular dynamics (MD) simulations are used to investigate the interactions of CNT and fCNT with a cell membrane model. The MD simulation results showed that in all systems during the simulation, the nanotubes with a “nanoneedle” mechanism spontaneously move from the water bulk toward the membrane center. The type of functional group on the nanotube can strongly affect the “permeation” phase. The interaction of fCNTs with membrane head groups is enhanced due to the presence of functional groups on their surface. The van der Waals interaction energy for CNT, NH2-CNT, and COOH-CNT systems reached ∼−1059, −1180, and −1255 kJ/mol, respectively, which indicates the COOH-CNT has a stronger interaction with the lipid bilayer than the CNT and NH2-CNT. It is found that the location of functional groups can be affected the diffusion of CNT into the membrane.

Variant Plateau’s law in atomically thin transition metal dichalcogenide dome networks

Since its fundamental inception from soap bubbles, Plateau’s law has sparked extensive research in equilibrated states. However, most studies primarily relied on liquids, foams or cellular structures, whereas its applicability has yet to be explored in nano-scale solid films. Here, we observed a variant Plateau’s law in networks of atomically thin domes made of solid two-dimensional (2D) transition metal dichalcogenides (TMDs). Discrete layer-dependent van der Waals (vdWs) interaction energies were experimentally and theoretically obtained for domes protruding in different TMD layers. Significant surface tension differences from layer-dependent vdWs interaction energies manifest in a variant of this fundamental law. The equivalent surface tension ranges from 2.4 to 3.6 N/m, around two orders of magnitude greater than conventional liquid films, enabling domes to sustain high gas pressure and exist in a fundamentally variant nature for several years. Our findings pave the way towards exploring variant discretised states with applications in opto-electro-mechanical devices.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) adsorbed on microplastics in drinking water: Implications for female exposure, reproductive health risk and its mitigation strategies through in silico methods

In this paper, molecular dynamics (MD) simulations were used to analyze the effects of different additive combinations in microplastics (MPs) on the female reproductive toxicity of perfluoroalkyl and polyfluoroalkyl substances (PFAS). It was found that 59.38% of plastic additive combinations had synergistic toxicity effects. And the plastic additive combination scheme with 31.10% decrease of joint toxic action was selected. By simulating the PFAS adsorption by MPs in drinking water through MD, it was found that hydrophobic PFAS was more easily adsorbed by MPs, and the van der Waals interaction energy may have an influential role in MPs adsorbing PFAS. The degree of interference with PFAS adsorption by MPs is greater when the MP is supplemented with a more hydrophobic additive. During AC adsorbing PFAS and MPs, it was found that some of the PFAS was adsorbed by MPs, and improving the adsorption of MPs by AC could also improve the removal rate of PFAS from drinking water. The effect of hydrophobic natural organic matter (NOM) on AC adsorbing PFAS and MPs was more significant, and the higher the molecular weight, the greater the effect on the adsorption performance of the AC. Within a certain range, ACs show an increasing tendency to adsorb PFAS and MPs with decreasing pore size and increasing amine functionalization. Machine learning method was used to get the influence rule of molecular parameters on improving PFAS function and reducing female reproductive toxicity. This study aims to mitigate the toxic hazards to female reproductive from current exposure to PFAS through drinking water, and to provide theoretical guidance for designing PFAS alternatives with low female reproductive toxicity.

Structure and interaction between the novel graphene-like planar biphenylene network and DNA: Molecular dynamics simulations

The study of interactions between biomolecules and nanomaterial surfaces is of great significance for the development of nanomaterials for biomedical applications. Recently, Science reported a novel graphene-like planar biphenylene network, which has attracted the attention of many researchers. In this paper, molecular dynamics simulation of DNA adsorption on the surface of biphenylene network was used to study the biocompatibility of DNA and biphenylene network. It is found by calculation that π − π stacking is the main source of DNA adsorption on the biphenylene network surface. The single-stranded DNA segment will lie flat and adsorb on the biphenyl surface. The 9 bases in single-stranded DNA are completely adsorbed to produce strong van der Waals interaction energy, resulting in severe damage to the molecular structure of ssDNA. However, double-stranded DNA molecules will be adsorbed vertically on the biphenylene network surface, and only the terminal 2 bases will be adsorbed. Meanwhile, the configuration of double-stranded DNA did not change much. In conclusion, biphenylene network has good biocompatibility to double-stranded DNA and is toxic to single-stranded DNA. It can open up the possibility of using biphenylene network in biomedicine, promote its application in the field of biomedicine in the future, and facilitate the design of DNA/biphenylene network nanomaterials. • Molecular dynamics simulations were conducted to study the adsorption process and interaction of ssDNA and dsDNA on a novel graphene-like biphenylene network (BPN) surface. • π − π stacking was the main driving force of DNA adsorption on the surface of BPN. • The ssDNA will lie flat on the surface of the BPN, but dsDNA is perpendicular to the surface of the BPN. • Most of the bases in ssDNA are adsorbed to the surface of BPN, while only the terminal bases in dsDNA are adsorbed. • SsDNA configuration will be destroyed by BPN, while dsDNA configuration is relatively well preserved.

Interactions between β-cyclodextrin as a carrier for anti-cancer drug delivery: a molecular dynamics simulation study

A series of molecular dynamics simulations were performed on 5-fluorouracil (5-Fu), Alendronate (Ald), and Temozolomide (TMZ) anticancer drugs in the presence and absence of β-cyclodextrin (βCD) as a carrier. Thermodynamic investigations showed that the van der Waals interaction energy was dominant in loading all drugs inside the βCD cavity. The sum of the interaction energies illustrated that the highest affinity was related to Ald (−136.5 kJ/mol), which in turn was due to the presence of bulky and charged atoms of phosphorus and oxygen, although TMZ (−115.92 kJ/mol) showed a very high affinity as well. At the same time, the hydrogen bond analysis also represented that Ald had the most hydrogen bond (1.97) with the highest half-life (3.13 ps) with βCD. Investigation of the root mean fluctuation (RMSF) indicated that all the drugs had a relatively rigid structure and maintain this rigidity during loading in the βCD cavity, and in the meantime, Ald was slightly more flexible than 5-Fu and TMZ. The area of ​the primary hydroxyl rim decreased in all drug-containing systems, which in turn was caused by the attractive interaction of drugs with oxygens in the primary hydroxyl rim. Especially for those drugs that were able to penetrate to the end of the primary hydroxyl rim of the βCD, that means TMZ and 5-Fu. Meanwhile, due to the lack of Ald penetration to the end of the primary hydroxyl rim, the area change in the Ald-containing system was less than in the two others. Communicated by Ramaswamy H. Sarma

Interaction mechanisms of fouling and cleaning protocol for A/O-MBR treatment of coal⁃to⁃hydrogen wastewater

The anoxic/aerobic membrane bioreactor (A/O-MBR) was conducted to investigate pollutants removal in coal⁃to⁃hydrogen wastewater at the pilot experiment. Results showed that the system exhibited effective removal of chemical oxygen demand (∼90%), ammonia nitrogen (>95%), and total phenols (>95%). Moreover, the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach was used to predict the MBR system's membrane fouling and chemical cleaning mechanisms in the MBR system. The results indicated that the initial stage dominated membrane fouling by the acid-base (AB) interaction energy. With aggravated membrane fouling, the determinate role was the van der Waals (LW) interaction energy. Furthermore, the cleaning agent NaClO obtained the highest trans-membrane pressure recovery (104.7% of the virgin trans-membrane pressure) in CGW treatment, compared with HCl or NaOH cleaning. It was attributed to the higher LW interaction energy between foulants and the NaClO-cleaned membrane than those between foulants and the HCl-/NaOH-cleaned membrane. Meanwhile, it could effectively restrain AB interaction energy decline between them. The findings of this study confirmed successful development of A/O-MBR for bio-refractory CGW treatment with NaClO chemically enhanced backwash. It also provided an in-depth understanding on the fouling and cleaning mechanisms of the MBR system.

Molecular dynamics simulations of the microscopic mechanism of thermal conductivity enhancement of ethylene Glycol–Water–Au nanofluids

With an increase of the heat load of internal combustion engines, the heat dissipation of the equipment increases accordingly. Traditional ethylene glycol (EG)–water coolants are unable to meet the heat dissipation demands of high heat load internal combustion engines. Nanofluids have better heat transfer performances than conventional fluids, suggesting they can be used to solve the problem of the insufficient heat dissipation capacity of internal combustion engines. In this paper, EG–water–Au nanofluids are formed by adding Au nanoparticles with a volume fraction of 1.5% to EG–water solutions. These are used to investigate the effect of the EG mass concentration on the thermal conductivity of the EG–water solutions and their nanofluids, and to analyze the microscopic mechanism of thermal conductivity enhancement of the nanofluids. It is found that the thermal conductivity of the EG–water solutions are positively correlated with the water content of the system, and the higher the water content of the system, the better the diffusion performance of the system components. The thermal conductivity of the EG–water solutions increase for all EG mass concentrations after the addition of Au nanoparticles, up to 17.20%. The presence of an adsorption layer of base liquid molecules on the surface of the nanoparticles is an important reason for the improved thermal conductivity of the nanofluids. According to the analysis of molecular radius of gyration, end-to-end distance and intermolecular interaction energy in the systems, it is found that the addition of the nanoparticles has no significant effect on the conformation of EG molecular chain, and the van der Waals interaction energy in the nanofluid systems is slightly enhanced. Through an analysis of the radial distribution function and density distribution of the nanofluid systems, it is found that the base liquid molecules that adsorb on the surface of the nanoparticles are stratified. The high-density interval of EG molecules is (0.65, 1.25) nm, while water molecules mostly gather in the form of clusters in the (1.15, 1.65) nm interval, and the arrangement of base liquid molecules in the adsorption layer is similar to the orderly arrangement of solids. The properties of some components in the nanofluids show a solid-like microstructure, which makes the thermal conductivity of the nanofluids higher than that of the base solution. These research results can provide an important reference for improving the heat transfer performance of traditional alcohol–water coolants.

Study of the inter-diffusion characteristics and cracking resistance of virgin-aged asphalt binders using molecular dynamics simulation

• Inter-diffusion behavior between virgin and aged asphalt binders were investigated. • The degree of blending between virgin and aged asphalt binders were determined at the molecular level. • The cracking patterns of partial blending and total blending were distinguished. • The relationship between degree of blending and cracking resistance of blended asphalt were explored. To investigate the inter-diffusion characteristics and cracking resistance of blended asphalt binders, the virgin-aged asphalt models were developed through the molecular dynamics (MD) simulation. Based on the mass density profiles of virgin and aged asphalt binders, the effect of temperature on the inter-diffusion coefficients was analyzed. According to the spatial distribution of atoms, different blending states including partial blending and total blending were distinguished. The cracking resistance of blended asphalt binders was characterized by the fracture energy obtained from the stress-displacement responses. Relationship between degree of blending and cracking resistance was explored. Results show that high temperatures can increase the inter-diffusion coefficients of virgin and aged asphalt binders by enhancing the intramolecular potential energy and Van der Waals (VdW) interaction energy. Compared to aged asphalt binder, the virgin asphalt binder may be more susceptible to temperature. Under tensile loading, the crack always initiates in the blending zone of partially blended asphalt binders. However, for the totally blended asphalt binder, the crack is more likely to occur at localized defect locations which is randomly distributed. The ability of blended asphalt binder to withstand deformations becomes better, but the maximum tensile strength decreases a lot as the temperature increases. There is a positive correlation between the degree of blending and fracture energy of blended asphalt binders, indicating that the asphalt binder with a higher degree of blending has better cracking resistance. The results of MD simulations can help determine how much aged binder can be mobilized to blend with virgin binder and help select appropriate virgin binders or other additives that can improve the blending between virgin and aged asphalt.