Molecular dynamics (MD) and dissipative particle dynamics (DPD) simulations are integrated to investigate the loading/releasing of anti-cancer drug camptothecin (CPT) in pH-sensitive amphiphilic ...copolymer, composed of hydrophobic poly(β-amino ester) (PAE) and hydrophilic methyl ether-capped poly(ethylene glycol) (PEG). MD simulation is used to estimate the Flory–Huggins interaction parameters and miscibility of binary components. On this basis, DPD simulation is applied to examine the micellization of PAE–PEG, CPT loading in PAE–PEG, and CPT releasing in PAEH–PEG. With increasing concentration, PAE–PEG forms spherical then disk-like micelles and finally vesicles, as a competitive counterbalance of free energies for the formation of shell, interface and core. CPT loading in PAE–PEG micelles/vesicles is governed by adsorption-growth-micellization mechanism, and CPT is loaded into both hydrophobic core and interface of hydrophobic core/hydrophilic shell. The predicted loading efficiency is close to experimental value. Similar to literature reports, the loading of high concentration of CPT is observed to cause morphology transition from micelles to vesicles. Upon protonation, CPT is released from micelles/vesicles by swelling-demicellization-releasing mechanism. This multi-scale simulation study provides microscopic insight into the mechanisms of drug loading and releasing, and might be useful for the design of new materials for high-efficacy drug delivery.
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We report a computational study to screen 4764 computation-ready experimental metal-organic frameworks (CoRE-MOF) for the membrane separation of a ternary gas mixture (CO2/N2/CH4) at 298K and 10bar. ...Combining Monte Carlo and molecular dynamics simulations, the adsorption, diffusion and permeation of the gas mixture are predicted. The structure-performance relationships are established between the geometrical descriptors of MOFs (pore liming diameter, density, void fraction and volumetric surface area) and the evaluation criteria of membrane performance (permeability and permselectivity). Furthermore, principal component analysis is used to assess the interrelationships among the descriptors, then multiple linear regression is applied to quantitatively determine the respective effects of descriptors on performance. In addition, decision tree modeling is adopted to define a clear effective path for screening. Finally, seven best MOF membranes are identified for the single-step separation of both CO2 and N2 from CH4. The microscopic insights and structure-performance relationships from this computational study can facilitate the development of new MOF membranes for the upgrading of natural gas.
A computational study is reported to screen 4764 computation-ready experimental MOFs for membrane separation of CH4 from a ternary CO2/N2/CH4 mixture. Display omitted
•A single-step separation of both CO2 and N2 from a three-component CO2/N2/CH4 mixture.•Integration of computational techniques including geometry analysis, Monte Carlo and molecular dynamics simulations.•Structure-performance relationships between the geometrical descriptors of MOFs and membrane performance.•Multivariate statistical tools including principal component analysis, multiple linear regression and decision tree modeling.
It is highly desirable to reduce the membrane thickness in order to maximize the throughput and break the trade-off limitation for membrane-based gas separation. Two-dimensional membranes composed of ...atomic-thick graphene or graphene oxide nanosheets have gas transport pathways that are at least three orders of magnitude higher than the membrane thickness, leading to reduced gas permeation flux and impaired separation throughput. Here we present nm-thick molecular sieving membranes composed of porous two-dimensional metal-organic nanosheets. These membranes possess pore openings parallel to gas concentration gradient allowing high gas permeation flux and high selectivity, which are proven by both experiment and molecular dynamics simulation. Furthermore, the gas transport pathways of these membranes exhibit a reversed thermo-switchable feature, which is attributed to the molecular flexibility of the building metal-organic nanosheets.
The miscibility of poly(ethylene oxide) (PEO)/poly(vinyl chloride) (PVC) blends are investigated by atomistic molecular dynamics and mesoscale dissipative dynamics simulations. The specific volumes ...of three PEO/PVC blends (with weight ratio at 70/30, 50/50 and 30/70) as well as pure PEO and PVC are examined as a function of temperature. The glass transition temperatures are estimated to be 251, 268, 280, 313 and 350K for pure PEO, PEO/PVC 70/30, 50/50, 30/70 and pure PVC. Among different energy contributions, the torsion and van der Waals energies exhibit pronounced kinks versus temperature. The Flory–Huggins parameters determined from the cohesive energy densities and the radial distribution functions of the inter-molecular atoms suggest that PEO/PVC 70/30 and 30/70 blends are more miscible than 50/50 blend. This is further supported by the morphologies of PEO/PVC blends, in which the 50/50 blend exhibits segregated domains implying a weak phase separation. Hydrogen bonds are found to form between O atoms of PEO and H atoms of PVC, with a larger degree in PEO/PVC 70/30 and 30/70 blends than in 50/50 blend. The addition of PVC into PEO suppresses the mobility of PEO chains, which is consistent with the experiment observation of decreased crystallization rate as well as crystallization temperature of PEO.
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A new force field and a hybrid Monte Carlo/molecular dynamics simulation method are developed to investigate the structural transition of zeolitic imidazolate framework-8 (ZIF-8) induced by N2 ...sorption. At a high loading (approximately 50 N2 molecules per unit cell), ZIF-8 shifts from low-loading (LL) to high-loading (HL) structure. A stepped sorption isotherm is predicted with three distinct regions, which agrees well with experimental data. The orientation of imidazolate rings and the motion of framework atoms exhibit sharp changes upon structural transition. Furthermore, pronounced changes are observed in various contributions to potential energies (including stretching, bending, torsional, van der Waals, and coulombic). The analysis of radial distribution functions between N2 and framework atoms suggests N2 interacts strongly with the imidazolate rings in ZIF-8. The simulation reveals that the structural transition of ZIF-8 is largely related to the reorientation of imidazolate rings, as attributed to the enhanced van der Waals interaction between N2 and imidazolate rings as well as the reduced torsional interaction of framework in the HL structure. This is the first molecular simulation study to describe the continuous structural transition of ZIF-8 and, it provides microscopic insight into the underlying mechanism.
To meet the increasing global energy demand and reduce the dependency on traditional fossil fuels, renewable biomass particularly cellulose has attracted considerable interest. Prior to processing ...and conversion into valuable products, cellulose needs to be pretreated (dissolved and then regenerated) via an environmentally benign route. Emerging as versatile solvents, ionic liquids (ILs) have been extensively examined for cellulose dissolution/regeneration. However, the underlying mechanisms of cellulose dissolution/regeneration in ILs remain elusive and the key governing factors are not fully understood at a microscopic level. This review summarizes the recent computational studies on cellulose pretreatment, including cellulose dissolution in neat ILs and IL/solvent mixtures, as well as cellulose regeneration by anti-solvents. Atom-resolution and time-resolved insights are provided to microscopically and fundamentally elucidate cellulose dissolution/regeneration, which are indispensable in the rational screening and design of new ILs for efficient cellulose pretreatment. Furthermore, the challenges for future computational exploration in this field are discussed.
•Computational studies for cellulose dissolution/regeneration in ILs are reviewed.•Hydrogen-bonding plays a paramount role in both dissolution and regeneration.•Cosolvents facilitate hydrogen-bonding of cellulose–IL and enhance dissolution.•Anti-solvents destruct hydrogen-bonding of cellulose–IL and cause regeneration.
Separation of p‐xylene (kinetic diameter ca. 0.58 nm) from its bulkier isomers (o‐xylene and m‐xylene, ca. 0.68 nm) is challenging, but important in the petrochemical industry. Herein, we developed a ...highly selective and stable metal–organic framework (MOF) MIL‐160 membrane for selective separation of p‐xylene from its isomers by pervaporation. The suitable pore size (0.5∼0.6 nm) of the MIL‐160 membrane selectively allows p‐xylene to pass through, while excluding the bulkier o‐xylene and m‐xylene. For the separation of equimolar binary p‐/o‐xylene mixtures at 75 °C, high p‐xylene flux of 467 g m−2 h−1 and p‐/o‐xylene selectivity of 38.5 could be achieved. The stability of MIL‐160, ensured the separation performance of the MIL‐160 membrane was unchanged over a 24 h measurement. The high separation performance combined with its high thermal and chemical stability makes the MIL‐160 membrane a promising candidate for the separation of xylene isomers.
Come on xylene: Through chemical modification of the Al2O3 support by bio‐inspired polydopamine, a highly selective and stable MIL‐160 membrane was developed for separation of p‐xylene from its isomers by pervaporation. Attributed to its suitable pore size (0.5≈0.6 nm), the MIL‐160 membrane selectively allows p‐xylene to pass through, while excluding the bulkier o‐xylene and m‐xylene.
The separation of racemic molecules is of substantial significance not only for basic science but also for technical applications, such as fine chemicals and drug development. Here we report two ...isostructural chiral metal-organic frameworks decorated with chiral dihydroxy or -methoxy auxiliares from enantiopure tetracarboxylate-bridging ligands of 1,1'-biphenol and a manganese carboxylate chain. The framework bearing dihydroxy groups functions as a solid-state host capable of adsorbing and separating mixtures of a range of chiral aromatic and aliphatic amines, with high enantioselectivity. The host material can be readily recycled and reused without any apparent loss of performance. The utility of the present adsorption separation is demonstrated in the large-scale resolution of racemic 1-phenylethylamine. Control experiments and molecular simulations suggest that the chiral recognition and separation are attributed to the different orientations and specific binding energies of the enantiomers in the microenvironment of the framework.
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