Number Of Hydrogen Bonds Research Articles

Investigating the properties of the water−vapor and water−graphite interfaces by PC-SAFT based density functional theory: A comparative study of different association functionals and PC-SAFT water parameter sets

In this work, we apply the perturbed-chain statistical associating fluid theory (PC-SAFT) based classical density functional theory to investigate the thermodynamics and structures of the water−vapor and water−graphite interfaces. For the water−vapor interface, we examine the surface tension as well as structural characteristics such as density profiles and hydrogen bonding distributions along the interface. For the water−graphite interface, we investigate these same structural features at a contact angle of 90° at 300 K. Specifically, we focus on comparing the results obtained from the three association functionals and six PC-SAFT water parameter sets from literature with experimental data and molecular simulation results. We find that the three association functionals exhibit qualitatively similar behavior in the calculation of surface tension, and it is more influenced by the parameter set rather than the association functional. The optimal functional or parameter set for the calculation of density profile of the vapor − liquid interface remains inconclusive, whereas preferable parameter sets and functionals have been identified for the water−graphite interface. Furthermore, the three functionals demonstrate a remarkably similar and qualitatively accurate depiction of the hydrogen bonding structures at both interfaces when compared with molecular simulation results. The level of quantitative accuracy, however, relies on whether the parameter set accurately reproduces the average number of hydrogen bonds of bulk water as observed in this particular set of molecular simulation results. The results of the present work offer valuable guidance for further investigation into the adsorption and wetting behavior of water on graphite-like surface, as well as the properties of water confined at the nanoscale.

Nanoscale Insights into CO2 Enhanced Shale Gas Recovery in Gas-Water Coexisting Kerogen Nanopores.

The presence of water clusters in kerogen nanopores reduces the occurrence and migration of methane (CH4) and thus affects shale gas extraction. CO2 injection, as an effective approach to enhance shale gas recovery, still presents challenges in its ability to mitigate the impact of immobile water clusters within the kerogen. In this work, molecular dynamics simulations were employed to investigate the microscopic transport process of water clusters and CH4 following CO2 injection in the gas-water coexisting kerogen nanopores. The results demonstrate that CO2 can desorb irreducible water clusters to dredge the pores while extracting CH4, enhancing gas-water mobility, and shale gas recovery by transitioning the wettability of the kerogen nanopore surface from weakly water-wet to CO2-wet. The impact of CO2 on the wettability of kerogen surfaces is primarily manifested in two aspects: CO2 can intrude the interface between water clusters and kerogen to reduce the number of hydrogen bonds between them, resulting in the detachment of water clusters; and the surface of kerogen nanopores can form a layer of CO2 gas film, which prevents desorbed water clusters and CH4 from readsorbing onto the wall surface. This study provides important insights in enhancing the understanding of the microscopic mechanisms in nanoscale flow, as well as for the development of an unconventional gas reservoir.

Elucidation of temperature-induced water structuring on cellulose surfaces for environmental and energy sustainability

Optimizing drying energy in the forest products industry is critical for integrating lignocellulosic feedstocks across all manufacturing sectors. Despite substantial efforts to reduce thermal energy consumption during drying, further enhancements are possible. Cellulose, the main component of forest products, is Earth's most abundant biopolymer and a promising renewable feedstock. This study employs all-atom molecular dynamics (MD) simulations to explore the structural dynamics of a small Iβ-cellulose microcrystallite and surrounding water layers during drying. Molecular and atomistic profiles revealed localized water near the cellulose surface, with water structuring extending beyond 8 Å into the water bulk, influencing solvent-accessible surface area and solvation energy. With increasing temperature, there was a ∼20 % reduction in the cellulose surface available for interaction with water molecules, and a ∼22 % reduction in solvation energy. The number of hydrogen bonds increased with thicker water layers, facilitated by a “bridging” effect. Electrostatic interactions dominated the intermolecular interactions at all temperatures, creating an energetic barrier that hinders water removal, slowing the drying processes. Understanding temperature-dependent cellulose-water interactions at the molecular level will help in designing novel strategies to address drying energy consumption, advancing the adoption of lignocellulosics as viable manufacturing feedstocks.

Solubilizer reconstructs the influences of the hydrogen-bond network of nonaqueous biphasic solvent on the absorption, phase splitting and desorption

Nonaqueous biphasic solvent has remarkable energy-saving potential. The weak force between N, N, N′, N″, N‴-pentamethyldiethylenetriamine (PMDETA) and Dimethyl sulfoxide (DMSO) contributes to facilitating the separation between DMSO and PMDETA, thereby enabling efficient liquid–liquid phase separation. Nevertheless, the weak interactions of PMDETA with other solvent molecules pose considerable challenges in the formulation of fresh homogeneous phase solutions. This study proposes a strategy to enhance PMDETA dissolution by introducing a solubilizer into a hybrid phase splitter, thereby increasing the concentration of PMDETA in the solvent. With the addition of a small quantity of solubilizer, the absorption, regeneration, and phase separation performance among the absorbents are comparable. The phase separation performance is influenced by the number of hydrogen bonds formed by the solubilizer, and the concentration of solubilizer in the lower phase is dependent on its hydrophobicity. Characterization using 13C NMR and FT-IR indicates that CO2 products primarily exist in the form of MEACOO−/MEAH+. Through DFT and molecular dynamics simulations, the impact of the solvent environment surrounding Ethanolamine (MEA) on the MEA+COO− deprotonation reaction is analyzed. While PMDETA offers a more favorable proton acceptance energy compared to MEA, the limited opportunities for PMDETA to come into contact with MEA molecules may be the primary hindrance to its participation in the reaction. Significantly lower corrosivity and regeneration energy requirements for non-aqueous biphasic solvents compared to 30 wt% MEA make them ideal candidates for energy-efficient, low-corrosivity CO2 capture.

Density functional theory and molecular dynamics simulation of water molecules confined between parallel graphene oxide surfaces using new interaction potentials

In this study, the interaction potential of water molecule with a graphene oxide (GO) plate containing OH and O groups has been calculated using the M06-2X/6-31g(d,p) level of theory at different orientations and intermolecular distances and fitted to the Born-Huggins-Meyer (BHM) model. There are good agreements between the calculated and the OPLS-AA and Dreiding models, especially for the GO(O)-H2O interactions. To examine the new computed models, we have used the closer potentials to the OPLS-AA and Dreiding models in the molecular dynamics (MD) simulations. We have calculated several properties using the different obtained interaction potentials including average number of hydrogen bonds per water molecule (〈HB〉) between confined water molecules and between water and GO-surfaces, radial distribution function (RDF), self-diffusion coefficient, and angle distribution function of the confined water molecules between the GO plates. Our results showed good agreements between the OPLS-AA and Dreiding models and some calculated potentials. However, some calculated models showed completely different behavior which discussed in details. According to the results, we concluded that the OH-2 and O1-OH2 models show totally better agreement with the famous force fields than the other calculated potentials. This work provides a simple method for the development of new force fields specifically for these types of systems which are in good agreement with the well-known force fields.

Molecular Dynamics Simulations on Spike Protein Mutants Binding with Human β Defensin Type 2.

Human β defensin type 2 (hBD-2), a cationic cysteine-rich peptide secreted from the human innate immune system, can bind Spike-RBD at the same site as receptor ACE2, thus blocking viral entry into ACE2-expressing cells. In order to find out the impact of CoV-2 mutations on hBD-2's antiviral activity, it is important to investigate the binding and interaction of hBD-2 with RBD mutants. All-atom molecular dynamics simulations were conducted on typical RBD mutants, including N501Y, E484K, P479S, T478I, S477N, N439K, K417N, and N501Y-E484K-K417N, binding with hBD-2. Starting from the stable binding structure of hBD-2 and wt-RBD and ClusPro and HADDOCK docking-predicted initial structures, the RBD variants bound with hBD-2 simulations were set up, and NAMD simulations were conducted. Based on the structure and dynamics analysis, it was found that most RBD variants can still form a similar number of hydrogen bonds with hBD-2, in addition to having a similar-sized buried surface area (BSA) and a similar binding interface to the RBD wildtype. However, the RBD triple mutant formed a less stable binding structure with hBD-2 than other variants. Additionally, the free energy perturbation (FEP) method was applied to calculate the contribution of key mutant residues to the binding and the free energy change caused by the mutations. The result shows that N439K, K417N, and the trimutation increase the binding free energy of RBD with hBD-2; thus, RBD should bind less stably with hBD-2. E484K decreases the binding free energy, thus it should bind more stably with hBD-2, while N501Y, S477N, T478I, and P479S almost do not change the binding free energy with hBD-2. The MM-GBSA method predicted the binding interaction energy which shows that the trimutant should be able to escape the binding with hBD-2 but N501Y should not. The result can provide insight into understanding the functional mechanism of hBD-2 combating SARS-CoV-2 mutants.

Application of temperature-dependent and steered molecular dynamics simulation to screen anti-dengue compounds against Marburg virus

Marburg virus infections are extremely fatal with a fatality range of 23% to 90%, therefore there is an urgent requirement to design and develop efficient therapeutic molecules. Here, a comprehensive temperature-dependent molecular dynamics (MD) simulation method was implemented to identify the potential molecule from the anti-dengue compound library that can inhibit the function of the VP24 protein of Marburg. Virtual high throughput screening identified five effective binders of VP24 after screening 484 anti-dengue compounds. These compounds were treated in MD simulation at four different temperatures: 300, 340, 380, and 420 K. Higher temperatures showed dissociation of hit compounds from the protein. Further, triplicates of 100 ns MD simulation were conducted which showed that compounds ID = 118717693, and ID = 5361 showed strong stability with the protein molecule. These compounds were further validated using Δ G binding free energies and they showed: −30.38 kcal/mol, and −67.83 kcal/mol binding free energies, respectively. Later, these two compounds were used in steered MD simulation to detect its dissociation. Compound ID = 5361 showed the maximum pulling force of 199.02 kcal/mol/nm to dissociate the protein-ligand complex while ID = 118717693 had a pulling force of 101.11 kcal/mol/nm, respectively. This ligand highest number of hydrogen bonds with varying occupancies at 89.93%, 69.80%, 57.93%, 52.33%, and 50.63%. This study showed that ID = 5361 can bind with the VP24 strongly and has the potential to inhibit its function which can be validated in the in-vitro experiment. Communicated by Ramaswamy H. Sarma

Silver nanoparticles coated cellulose-based flexible membrane with excellent UV resistance, high infrared reflection and water resistance for personal thermal management

Designing of a green and multifunctionally integrated cellulose-based flexible wearable material with personal thermoregulation, water and ultraviolet (UV) resistance is essential for the development of personal thermal management and smart textiles. Herein, a hydrophobic silver nanoparticles cellulose-based membrane (H-AgNPs/CEPCM) was prepared through simple solution blending, spin-coating process and chemical vapor modification. The prepared membrane exhibited excellent UV resistance due to the synergistic effect of carbon quantum dots (CQDs) as well as UV-absorbing functional groups. The spin-coated AgNPs layer with high infrared reflectivity has great radiant insulation, and temperature was reduced by 3.4 °C compared with H-CEPCM in indoor environment. Furthermore, the mechanical properties of H-AgNPs/CEPCM were significantly improved by the introduction of amide and ether bonds, as well as a large number of hydrogen bonds. This led to a tensile strength of 23.21 MPa and an elongation at break of 16.57 %, while also providing water resistance. Additionally, the H-AgNPs/CEPCM exhibited outstanding thermal stability and hydrophobicity. This work may provide a feasible and promising strategy for the construction of multifunctional integrated cellulose membrane materials for radiant insulation, outdoor textiles and novel UV protection applications.

Investigating the effects of four medicinal plants against dengue virus through QSAR modeling and molecular dynamics studies

The Dengue virus (DENV) has been increasingly recognized as a prevalent viral pathogen responsible for global transmission of infection. It has been established that DENV's NS5 methyltransferase (MTase) controls viral replication. As a result, NS5 MTase is considered a potentially useful drug target for DENV. In this study, the two phases of virtual screening were conducted using the ML-based QSAR model and molecular docking to identify potential compounds against NS5 of DENV. Four medicinal plants [Aloe vera, Cannabis sativa (Hemp), Ocimum sanctum (Holy Basil; Tulsi), and Zingiber officinale (Ginger)] that showed anti-viral properties were selected for sourcing the phytochemicals and screening them against NS5. Additionally, re-docking at higher exhaustiveness and interaction analysis were performed which resulted in the identification of the top four hits (135398658, 5281675, 119394, and 969516) which showed comparable results with the control Sinefungin (SFG). Post molecular dynamics simulation, 135398658 showed the lowest RMSD (0.4–0.5 nm) and the maximum number of hydrogen bonds (eight hydrogen bonds) after the control while 5281675 and 969516 showed comparable hydrogen bonds to the control. These compounds showed direct interactions with the catalytic site residues GLU111 and ASP131, in addition to this these compounds showed stable complex formation as depicted by principal component analysis and free energy landscape. 135398658 showed lower total binding free energy (ΔG Total = −36.56 kcal/mol) than the control, while 5281675 had comparable values to the control (ΔG Total = −34.1 kcal/mol). Overall, the purpose of this study was to identify phytochemicals that inhibit NS5 function, that could be further tested experimentally to treat dengue virus (DENV). Communicated by Ramaswamy H. Sarma

In silico approaches for predicting natural compounds with therapeutic potential and vaccine candidates against Streptococcus equi

Equine strangles is a prevalent disease that affects the upper respiratory in horses and is caused by the Gram-positive bacterium Streptococcus equi. In addition to strangles, other clinical conditions are caused by the two S. equi subspecies, equi and zooepidemicus, which present relevant zoonotic potential. Treatment of infections caused by S. equi has become challenging due to the worldwide spreading of infected horses and the unavailability of effective therapeutics and vaccines. Penicillin treatment is often recommended, but multidrug resistance issues arised. We explored the whole genome sequence of 18 S. equi isolates to identify candidate proteins to be targeted by natural drug-like compounds or explored as immunogens. We considered only proteins shared among the sequenced strains of subspecies equi and zooepidemicus, absent in the equine host and predicted to be essential and involved in virulence. Of these, 4 proteins with cytoplasmic subcellular location were selected for molecular docking with a library of 5008 compounds, while 6 proteins were proposed as prominent immunogens against S. equi due to their probabilities of behaving as adhesins. The molecular docking analyses revealed the best ten ligands for each of the 4 drug target candidates, and they were ranked according to their binding affinities and the number of hydrogen bonds for complex stability. Finally, the natural 5-ring compound C25H20F3N5O3 excelled in molecular dynamics simulations for the increased stability in the interaction with UDP-N-acetylenolpyruvoylglucosamine reductase (MurB). This research paves the way to developing new therapeutics to minimize the impacts caused by S. equi infections. Communicated by Ramaswamy H. Sarma

Impact of the number of hydrogen bonds on proton conductivity in metallo-hydrogen-bonded organic frameworks: the more the number of hydrogen bonds, the better the proton conductivity at the maximum relative humidity

Proton conductivities in two metallo-hydrogen-bonded organic frameworks are mainly affected by the number of hydrogen bonds at ∼97% relative humidity.

Graph-based analysis of H-bond networks and unsupervised learning reveal conformational coupling in prion peptide segments.

In this study, we employed a comprehensive computational approach to investigate the physical chemistry of the water networks surrounding hydrated peptide segments, as derived from molecular dynamics simulations. Our analysis uncovers a complex interplay of direct and water-mediated hydrogen bonds that intricately weave through the peptides. We demonstrate that these hydrogen bond networks encode critical information about the peptides' conformational behavior, with the dimensionality of these networks showing sensitivity to the peptides' conformations. Additionally, we estimated the free-energy landscape of the peptides across various conformations, revealing that their structures are predominantly characterized by unfolded, partially folded, and folded configurations, resulting in broad and rugged free-energy surfaces due to the numerous degrees of freedom contributed by the surrounding solvent. Importantly, the structured nature of this free-energy landscape becomes obscured when conventional collective variables, such as the number of hydrogen bonds, are used. Our findings provide new insights into the molecular mechanisms that couple protein and solvent degrees of freedom, highlighting their significance in the functioning of biological systems.

Neuroprotective Potential of Polydatin in Combating Parkinson’s Disease through the Inhibition of Monoamine Oxidase-B and Catechol-o-Methyl Transferase

Aims: This study aims to deduce the plausible contribution of polydatin in dopamine replenishment and dopaminergic neuroprotection to unveil its potential as a drug candidate for PD. Background: Available therapies for the management of dopaminergic degradation in Parkinson’s disease (PD) provide only symptomatic relief and are associated with various adverse effects. Levodopa (L-DOPA) is an age-old therapy in the treatment paradigm of PD, either used as mono-therapy or in combination with the inhibitors of the dopamine catabolising enzymes monoamine oxidase-B (MAO-B) and catechol O-methyltransferase (COMT) for replenishing the levels of the neurotransmitter. The discovery of plant-based novel drug therapies would help to target multiple pathways underlying the disease pathogenesis and are associated with minimal side effects. Polydatin, the precursor of resveratrol, has been explored recently to possess neuroprotective efficacy, however, the molecular mechanisms that underlie the Parkinsonism-associated neurobehavioral recovery as well as the neurorescue potential of polydatin has not been illustrated yet. Objective: The present study aimed to unveil the role of polydatin in dopamine upregulation in PD, by determining its dual inhibitory potential on the enzymes responsible for its breakdown, MAO-B and COMT. The study further aimed to elucidate the role of this molecule in regulating the enzymatic activity of Cytosolic Phospholipase A2 (cPLA2), the crucial enzyme underlying several pathogenic pathways leading to neurodegeneration. Methods: Molecular docking simulation of polydatin with the dopamine catabolizing enzymes MAO-B and COMT, as well as cPLA2, along with their respective known inhibitors was performed using the Molegro Virtual Docker (MVD) 2.1 package. Results: In-silico analyses revealed that polydatin could significantly inhibit the activities of this dopamine catabolizing enzyme, MAO-B, and COMT with comparable docking scores and more numbers of hydrogen bonds, and weaker interactions as that of their respective available synthetic inhibitors. Moreover, it was found that polydatin could regulate the activity of cPLA2 comparable to its known inhibitors. Conclusion: Polydatin exhibited efficacy as a potent dopamine replenishing agent by inhibiting its metabolizing enzymes as well as found to have efficacy against neuroinflammation, thereby highlighting the significance of designing novel phyto drugs for combating dopamine deficiency in PD.

Molecular insights into the nanoconfinement effect on the structure and dynamics of ionic liquids in carbon nanotubes.

The properties and applications of ionic liquids (ILs) have been widely investigated when they are confined within nanochannels such as carbon nanotubes (CNTs). The confined ILs exhibit very different properties from their bulk state due to a nanoconfinement effect, which plays an important role in the performances of devices with ILs. In this work, we studied the effect of the charge carried by CNTs on confined ILs inside CNTs using molecular dynamics simulations. In charged CNTs, cations and anions are distributed separately along the radial directions, and the transition of orientations of the cations between parallel and vertical to CNTs occurs by changing the charge state of CNTs. The number of hydrogen bonds (HBs) formed by the confined ILs can be reduced by switching the surface charge of CNTs from positive to negative due to the contact modes between cations and anions as well as the distributions of cations in CNTs. The diffusivities along and vertical to the axial direction of CNTs were found to be non-monotonic owing to the "trade-off" effect from both ion pair interlocking and anchoring ILs on the CNT walls. Additionally, the region-dependent dynamics of ILs were also related to the intermolecular interactions in different regions of CNTs. Furthermore, the vibrational modes of ILs were obviously influenced in highly charged CNTs as determined by calculating the density of vibrational states, which demonstrated the transitions in the structure and interactions. The density distributions changed from single layer to double layers when increasing the pore size of neutral CNTs while the hydrogen bonds exhibited a non-monotonic tendency versus the pore sizes. Our results might help to understand the structure and dynamics of confined ILs as well as aid optimizing the performance of devices with ILs.

Molecular dynamics simulation of effect of non-condensable gases on heat transfer of water molecule flow in nanochannels

With the development of higher performance and miniaturization of electronic components, the flow heat transfer of working fluids in nanochannels has received more attention. To elucidate this phenomenon, molecular dynamics simulations are used to simulate the behaviors of fluids within nanochannels at temperatures of 300 K, 325 K, and 350 K. Water serves as a flow medium, with argon substituted for any non-condensable gases. In the flow process, argon atoms aggregate into clusters that are characterized by high potential energy. As the temperature rises, the concomitant increases in the fluid’s potential energy, which leads to the gradual diminution or complete dissipation of these clusters. A minor presence of gas atoms can facilitate fluid movement; however, an excess of argon promotes the formation of larger gaseous clusters in the central region of the channel, thereby impeding fluid flow. Concurrently, the application of heat to the fluid appreciably diminishes the coefficient of flow resistance. The temperature of the fluid in the near-wall region exceeds that of the central area. In the clusters, the atoms exhibit heightened activity, leading to an increase in the average molecular kinetic energy and a concomitant rise in temperature. The inherent hydrogen-bonding structure of water enhances heat transfer within the nanochannels. Argon atoms exert an influence on the number of hydrogen bonds, and rising temperatures disrupts the hydrogen-bond network established by water molecules, ultimately leading to a decrease of the Nusselt number. This investigation offers insights into the heat transfer dynamics of water molecular flow within microchannels under the perturbation of non-condensable gases, thereby furnishing theoretical guidance for enhancing heat transfer within electronic devices.

Terahertz electric field induced melting and transport of monolayer water confined in double-walled carbon nanotubes.

Understanding the structures and dynamics of confined water in nanochannels holds great promise for various applications, ranging from membrane separation to blue energy collection. A setting of particular interest is the confined monolayer water within double-walled carbon nanotubes (DWCNTs), which demonstrates rich ice morphologies; however, the dynamics of this peculiar system are still unexplored. In this work, a series of molecular dynamics (MD) simulations reveal that the two-dimensional ice in DWCNTs can be effectively melted by terahertz electric fields but not by static electric fields, exhibiting an interesting ice to vapor-like transition along with extraordinary dynamical behaviors. Specifically, under appropriate field frequency, the water flow presents a sharp increase with the increase in field strength, indicating an excellent gating behavior. These remarkable findings are attributed to the resonance effect between the terahertz electric field and inherent vibration of water hydrogen bonds, causing the water molecules to change from the frozen to super permeation states. The amount of confined water exhibits a sudden reduction, confirming the breakdown of the hydrogen bond network. The distributions of density profiles, hydrogen bond number and dipole orientation demonstrate more details of the water structural change. Furthermore, under a certain field strength, the water flow shows a peculiar maximum behavior with the increase in field frequency, implying frequency optimization for water transport. These findings not only enhance our understanding of the phase transition behavior of water molecules confined within DWCNTs under the influence of a terahertz electric field but also provide a promising avenue for designing innovative nanofluidic devices.

Comparative analysis of tropomyosin allergenicity in three different species of molluscs: insights into the role of amino acid composition in IgE epitopes.

Limited research has been conducted on the differences in allergenicity among Alectryonella plicatula tropomyosin (ATM), Haliotis discus hannai tropomyosin (HTM), and Mimachlamys nobilis tropomyosin (MTM) in molluscs. Our study aimed to comprehensively analyze and compare their immunoreactivity, sensitization, and allergenicity while simultaneously elucidating the underlying molecular mechanisms involved. We assessed the immune binding activity of TM utilizing 86 sera from allergic patients and evaluated sensitization and allergenicity through two different types of mouse models. The dot-blot and basophil activation test assays revealed strong immunoreactivity for HTM, ATM, and MTM, with HTM exhibiting significantly lower levels compared to ATM. In the BALB/c mouse sensitization model, all TM groups stimulated the production of specific antibodies, elicited IgE-mediated immediate hypersensitivity responses, and caused an imbalance in the IL-4/IFN-γ ratio. Similarly, in the BALB/c mouse model of food allergy, all TM variants induced IgE-mediated type I hypersensitivity responses, leading to the development of food allergies characterized by clinical symptoms and an imbalance in the IL-4/IFN-γ ratio. The stimulation ability of sensitization and the severity of food allergies consistently ranked as ATM > MTM > HTM. Through an in-depth analysis of non-polar amino acid frequency and polar hydrogen bonds, HTM exhibited higher frequencies of non-polar amino acids in its amino acid sequence and IgE epitopes, in comparison with ATM and MTM. Furthermore, HTM demonstrated a lower number of polar hydrogen bonds in IgE epitopes. Overall, HTM exhibited the lowest allergenic potential in both allergic patients and mouse models, likely due to its lower polarity in the amino acid sequence and IgE epitopes.

Strength, number, and kinetics of hydrogen bonds for water confined inside boron nitride nanotubes

Reactive force-field based molecular simulations reveal that extreme confinement drives significant changes in the characteristics, strength, and kinetics of water–water hydrogen bonds.

Stability and structure of the aqueous LiTFSI-LiCl interface.

It has recently been demonstrated that aqueous lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium chloride (LiCl) solutions can form stable liquid-liquid biphasic systems when both electrolyte phases have sufficiently high concentrations. In this work, we combine molecular dynamics simulations and experimental analysis to investigate what drives the formation of the interface and how the interfacial molecular structure correlates with its thermodynamic stability. We observe that at the liquid-vapour interface, TFSI- anions exhibit surfactant-like properties, leading to a reduction in surface tension and an increase in interfacial thickness. In contrast, the interfacial stability of the LiTFSI-LiCl biphasic systems increases with the concentration of both salts, as evidenced by the increasing surface tension and decreasing interfacial thickness. The opposing effects that the ionic concentration has on the thermodynamic stability of the different interfaces are linked to the anions' interfacial adsorption/desorption, which in turn affects the number and strength of water-water hydrogen bonds, the interfacial molecular structure and the diffusion of cations across the interface. Finally, calculations and experiments indicate that the liquid-liquid separation is driven primarily by the concentration of LiCl, and is the result of a 'salting out' effect.

Constructing hydrophobic microenvironment in the separation layer by a small molecule for improving reverse osmosis membrane performance

The development of reverse osmosis (RO) membranes with both high permeability and selectivity is a key goal for RO technology, the leading water treatment technology. This work presents a simple and cost-effective method for improving RO membrane performance obviously via introducing a hydrophobic small molecule, benzoic acid (BA), in the polyamide (PA) separation layer. The introduction of BA is achieved by adding it in the oil phase of the interfacial polymerization technology because of its oil solubility, which is pretty simple. The hydrophobicity and self-assembly characteristic of BA could establish hydrophobic microenvironments within the PA separation layer. The hydrophobicity of this microenvironment can reduce the number of hydrogen bonds between water molecules, accelerating the rapid transport of water and thereby enhancing membrane performance. Concurrently, BA as a small molecule could moderately increase the space between PA chains and thus enlarge the free volume of hydrophobic microenvironment region, which is also in favour of the improvement of membrane flux. The as-developed RO membrane possessed both high rejection rate (with a NaCl rejection rate of 98.9 %) and high flux (91.7 L m−2 h−1) under the brackish water testing condition, surpassing the performance of many previously reported membranes, and noticeably, a flux increase of 113 % was achieved by utilizing BA. Besides, the performance showed a good long-term stability. It is worth mentioning that small molecules are generally purchasable and cheap, which is beneficial to the large-scale production. This work showcased the great potential of hydrophobic small molecules in improving PA water treatment membrane performance, paving the way for diverse small molecules to develop PA water treatment membrane with both high permeability and selectivity.