A novel multi-permselective mixed matrix membrane (MP-MMM) is developed by incorporating versatile fillers functionalized with ethylene oxide (EO) groups and an amine carrier into a polymer matrix. The as-prepared MP-MMMs can separate CO2 efficiently because of the simultaneous enhancement of diffusivity selectivity, solubility selectivity, and reactivity selectivity. To be specific, MP-MMMs were fabricated by incorporating polyethylene glycol- and polyethylenimine-functionalized graphene oxide nanosheets (PEG-PEI-GO) into a commercial low-cost Pebax matrix. The PEG-PEI-GO plays multiple roles in enhancing membrane performance. First, the high-aspect ratio GO nanosheets in a polymer matrix increase the length of the tortuous path of gas diffusion and generate a rigidified interface between the polymer matrix and fillers, enhancing the diffusivity selectivity. Second, PEG consisting of EO groups has excellent affinity for CO2 to enhance the solubility selectivity. Third, PEI with abundant primary, secondary, and tertiary amine groups reacts reversibly with CO2 to enhance reactivity selectivity. Thus, the as-prepared MP-MMMs exhibit excellent CO2 permeability and CO2/gas selectivity. The MP-MMM doped with 10 wt % PEG-PEI-GO displays optimal gas separation performance with a CO2 permeability of 1330 Barrer, a CO2/CH4 selectivity of 45, and a CO2/N2 selectivity of 120, surpassing the upper bound lines of the Robeson study of 2008 (1 Barrer = 10(-10) cm(3) (STP) cm(-2) s(-1) cm(-1) Hg).

Thermodynamic and kinetic properties are of critical importance for the applicability of computational models to biomolecules such as proteins. Here we present an extensive evaluation of the Amber ff99SB-ILDN force field for modeling of hydration and diffusion of amino acids with three-site (SPC, SPC/E, SPC/E, and TIP3P), four-site (TIP4P, TIP4P-Ew, and TIP4P/2005), and five-site (TIP5P and TIP5P-Ew) water models. Hydration free energies (HFEs) of neutral amino acid side chain analogues have little dependence on the water model, with a root-mean-square error (RMSE) of ∼1 kcal/mol from experimental observations. On the basis of the number of interacting sites in the water model, HFEs of charged side chains can be putatively classified into three groups, of which the group of three-site models lies between those of four- and five-site water models; for each group, the water model dependence is greatly eliminated when the solvent Galvani potential is considered. Some discrepancies in the location of the first hydration peak ( R) in the ion-water radial distribution function between experimental and calculated observations were detected, such as a systematic underestimation of the acetate (Asp side chain) ion. The RMSE of calculated diffusion coefficients of amino acids from experiment increases linearly with the increasing diffusion coefficients of the solvent water models at infinite dilution. TIP3P has the fastest diffusivity, in line with literature findings, while the "FB" and "OPC" water model families as well as TIP4P/2005 perform well, within a relative error of 5%, and TIP4P/2005 yields the most accurate estimate for the water diffusion coefficient. All of the tested water models overestimate amino acid diffusion coefficients by approximately 40% (TIP4P/2005) to 200% (TIP3P). Scaling of protein-water interactions with TIP4P/2005 in the Amber ff99SBws and ff03ws force fields leads to more negative HFEs but has little influence on the diffusion of amino acids. The most recent FF/water combinations of ff14SB/OPC3, ff15ipq/SPC/E, and fb15/TIP3P-FB do not show obvious improvements in accuracy for the tested quantities. These findings here establish a benchmark that may aid in the development and improvement of classical force fields to accurately model protein dynamics and thermodynamics.

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A nonbonded dummy model for metal ions is highly imperative for the computation of complex biological systems with for instance multiple metal centers. Here we present nonbonded dummy parameters of 11 divalent metallic cations, namely, Mg(2+), V(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Sn(2+), and Hg(2+), that are optimized to be compatible with three widely used water models (TIP3P, SPC/E, and TIP4P-EW). The three sets of metal parameters reproduce simultaneously the solvation free energies (ΔGsol), the ion-oxygen distance in the first solvation shell (IOD), and coordination numbers (CN) in explicit water with a relative error less than 1%. The main sources of errors to ΔGsol that arise from the boundary conditions and treatment of electrostatic interactions are corrected rationally, which ensures the independence of the proposed parameters on the methodology used in the calculation. This work will be of great value for the computational study of metal-containing biological systems.

The conformational stability and activity of Candida antarctica lipase B (CALB) in the polar and nonpolar organic solvents were investigated by molecular dynamics and quantum mechanics/molecular mechanics simulations. The conformation change of CALB in the polar and nonpolar solvents was examined in two aspects: the overall conformation change of CALB and the conformation change of the active site. The simulation results show that the overall conformation of CALB is stable in the organic solvents. In the nonpolar solvents, the conformation of the active site keeps stable, whereas in the polar solvents, the solvent molecules reach into the active site and interact intensively with the active site. This interaction destroys the hydrogen bonding between Ser 105 and His 224 . In the solvents, the activation energy of CALB and that of the active site region were further simulated by quantum mechanics/molecular mechanics simulation. The results indicate that the conformation change in the region of active sites is the main factor that influences the activity of CALB.Because of its high enantioselectivity and catalytic activity, wide range of substrates, and thermal stability, Candida antarctica lipase B (CALB) 3 is widely used in many industrial applications and scientific researches (1). CALB is composed of 317 amino acid residues and has a molecular mass of 33 K (2). Similar to other serine hydrolyzes, a serine-histidine-asparate catalytic triad is responsible for the catalytic activity of CALB. The mechanism is outlined in Fig. 1. It is a two-step mechanism with an acylation step and a deacylation step separated by a covalent acyl-enzyme intermediate (3).The activity of the enzymes is strongly affected by the choice of solvent (4 -7). As a matter of fact, even reversal of substrate specificity (8, 9) and enantiopreference (10, 11) has been reported. A higher thermostability and altered stereoselectivity for CALB in organic solvents have also been observed (12, 13). Many researchers have put effort into elucidating the underlying mechanisms responsible for the observed solvent effects. The most widely accepted model was described by Laane (14), who summarized the influence of organic solvents on the enzymatic reactions and concluded that the enzyme activity is higher in the environment surrounded by nonpolar and midpolar solvents, whereas the lowest activity is expressed in polar solvents. The Laane model has been widely used in solvent selection in enzymatic reactions. However, the Laane model does not describe the mechanisms of solvent effect on a molecular level.Molecular dynamics simulations have been proven to be a useful tool in understanding protein structure and have been used to get insights into the structure and behavior of the enzymes (15-18). The effect of solvents on the activity of CALB might be the results of the conformational change around the activity site or some particular area. In this work, the overall conformational change of CALB and the local conformational change around the active site in ...

Computational free-energy correction strategies and the choice of experimental proton hydration free energy, ΔG(H), are analyzed to investigate the apparent controversy in experimental thermodynamics of ionic hydration. Without corrections, the hydration free-energy (ΔG) calculations match experiments with ΔG(H) = -1064 kJ/mol as reference. Using the Galvani surface potential the resulting (real) ΔG are consistent with ΔG(H) = -1098 kJ/mol. When applying, in an ad hoc manner, the discrete solvent correction, ΔG matching the "consensus" ΔG(H) of -1112 kJ/mol are obtained. This analysis rationalizes reports on ΔG calculations for ions using different experimental references. For neutral amino acid side chains ΔG are independent of the water model, whereas there are large differences in ΔG due to the water model for charged species, suggesting that long-range ordering of water around ions yields an important contribution to the ΔG. These differences are reduced significantly when applying consistent corrections, but to obtain the most accurate results it is recommended to use the water model belonging to the force field.

There are several researches on the preparation and application of hydrazone-linked covalent organic frameworks (COFs), and all of them generally necessitate rigid aromatic amines. Herein, we report a strategy for design and synthesis of COF with flexible alkyl amine as a building block and intramolecular hydrogen bonding as a knot in the network. The proof-of-concept design was demonstrated by exploring 1,3,5-triformylphloroglucinol and oxalyldihydrazide (ODH) as precursors to synthesize a novel COF material (TpODH), in which different organic building units are combined through hydrazone bonds to form twodimensional porous frameworks. It should be pointed that irreversible enol-to-keto tautomerism and intramolecular N−H•••OC hydrogen bonding of TpODH would enhance the crystallinity and chemical stability, leading to large specific surface area of 835 m 2 g −1 . However, another COF synthesized with 1,3,5-triformylbenzene and ODH exhibited less crystallinity and low special surface area (94 m 2 g −1 ). Representatively, the resulting TpODH afforded Cu(II) and Hg(II) capacities of 324 and 1692 mg g −1 , respectively, which exceeded that of most COFs previously reported. Moreover, the Fourier-transform infrared and X-ray photoelectron spectroscopy spectra analyses were taken to demonstrate the adsorption mechanism. These results suggested that the materials could be applied to the removal of metallic ions in the future.

Here we report one-pot synthesis of tetraphenylethene-based tetracationic dicyclophane (1) and its self-assembly behaviors with aggregation-induced emission (AIE) and light-harvesting function. Confirmed by X-ray crystal structure and high resolution transmission electron microscopy, this tetracationic dicyclophane can self-assemble into a 3D supramolecular framework to form crystalline nanospheres (2) finally, which exhibits a strong emission (ΦF = 97.7%) via AIE effect in aqueous solution. Interestingly, AIE-active 2 as a single-molecule-based fluorescent supramolecular platform can encapsulate an organic dye (e.g., Nile red) to form light-harvesting nanospheres (3) further with a large red-shift (Δλ = ∼70 nm), highly efficient energy-transfer ability (ΦET = 77.5%), and high antenna effect (14.3).