Ag Nanoparticle-Induced Surface Chloride Immobilization Strategy Enables Stable Seawater Electrolysis.

Although hydrogen gas (H2 ) storage might enable offshore renewable energy to be stored at scale, the commercialization of technology for H2 generation by seawater electrolysis depends upon the development of methods that avoid the severe corrosion of anodes by chloride (Cl- ) ions. Here, it is revealed that the stability of an anode used for seawater splitting can be increased by more than an order of magnitude by loading Ag nanoparticles on the catalyst surface. In experiments, an optimized NiFe-layered double hydroxide (LDH)@Ag electrode displays stable operation at 400 mA cm-2 in alkaline saline electrolyte and seawater for over 5000 and 2500 h, respectively. The impressive long-term durability is more than 20 times that of an unmodified NiFe-LDH anode. Meticulous characterization and simulation reveals that in the presence of an applied electric field, free Cl- ions react with oxidized Ag nanoparticles to form stable AgCl species, giving rise to the formation of a Cl- -free layer near the anode surface. Because of its simplicity and effectiveness, it is anticipated that the proposed strategy to immobilize chloride ions on the surface of an anode has the potential to become a crucial technology to control corrosion during large-scale electrolysis of seawater to produce hydrogen.

A novel very small granular starch from Chlorella sp. MBFJNU-17.

Novel resources of very small granular starch are of great interests to food scientists. We previously found Chlorella sp. MBFJNU-17 contained small granular starch but whether the MBFJNU-17 was a novel resource of very small granular starch remained unresolved. This study isolated and characterized the starch from MBFJNU-17 in comparison with quinoa starch (a typical very small granular starch), and discussed whether the MBFJNU-17 could be a resource of very small granular starch. Results showed that chlorella starch displayed a smaller size (1024 nm) than quinoa starch did (1107 nm), suggesting MBFJNU-17 was a good resource of very small granular starch. Additionally, chlorella starch had less amylose, higher proportion of long amylopectin branches, more ordered structures, thinner amorphous lamellae, better paste thermostability, and slower enzymatic digestion than quinoa starch did. These findings indicated that Chlorella sp. MBFJNU-17 was a novel resource of very small granular starch with desirable thermostability and nutritional attributes.

Dialytic Synthesis of Two-Dimensional Cu-Based Metal-Organic Frameworks for Gas Separation: Designable MOF-Polymer Interface.

We demonstrate a dialytic strategy for the synthesis of congeneric two-dimensional metal-organic framework (2D MOF) nanosheets with a dialysis membrane using 1,4-benzenedicarboxylic acid (BDC), 1,4-naphthalenedicarboxylic acid (NDC), and 9,10-anthracenedicarboxylic acid (ADC) as organic linkers and copper(II) as a metal precursor, respectively. Polyimide (PI) membranes containing these empty 2D MOF nanosheets exhibit distinct molecular sieve effects. Molecular dynamic simulation results reveal that the structures of MOF-polymer interfaces are designable by modifying the MOF interlayer distance and aperture size, which has significant influences on gas permeability and selectivity. As a result, Cu-NDC/PI with the moderate composite interface structure shows superior performance toward H2/CH4 and CO2/CH4 separations with a selectivity of 199 and 63 over Cu-BDC (121 and 53) and Cu-ADC (135 and 54), respectively.

Rational Design of Smart Metal-Organic Frameworks for Light-Modulated Gas Transport.

Smart metal-organic frameworks (MOFs) are constructed by introducing stimuli-responsive functional groups into MOF platforms. Through membrane systems containing smart MOFs, external field-modulated gas transport can be achieved, which finds potential applications in chemical engineering. In this work, we design a series of Mg-MOF-74-III-based frameworks functionalized by arylazopyrazole groups. Methyleneamine chains with various lengths are attached to the photoresponsive azopyrazole moiety. Molecular dynamics simulations show that CO2 diffusion can be remarkably changed by controlling the cis-to-trans isomerization of the functional unit due to the tunable adsorbate-adsorbent and adsorbate-adsorbate interactions of the two states. With the optimal length of the functional chain, the spatial hindrance and adsorbate-adsorbent interaction exhibit a synergetic effect to maximize the stimuli-responsive kinetic separation of N2 over CO2. This work provides a promising strategy for elevating smart MOFs' potential in gas separation.

Sacrificial Synthesis of Supported Ru Single Atoms and Clusters on N-doped Carbon Derived from Covalent Triazine Frameworks: A Charge Modulation Approach.

High-temperature pyrolysis of nitrogen (N)-rich, crystalline porous organic architectures in the presence of a metal precursor is an important chemical process in heterogeneous catalysis for the fabrication of highly porous N-carbon-supported metal catalysts. Herein, covalent triazine framework (CTF) and CTF-I (that is, CTF after charge modulation with iodomethane) are presented as sacrificial templates, for the synthesis of carbon-supported Ru catalysts-Ru-CTF-900 and Ru-CTF-I-900 respectively, following high-temperature pyrolysis at 900 °C under N2 atmosphere. Predictably, the dispersed Ru on pristine CTF carrier suffered severe sintering of the Ru nanoparticles (NPs) during heat treatment at 900 °C. However, the Ru-CTF-I-900 catalyst is composed of ultra-small Ru NPs and abundant Ru single atoms which may have resulted from much stronger Ru-N interactions. Through modification of the micro-environment within the CTF architecture, Ru precursor interacted on charged-modulated CTF framework shows electrostatic repulsion and steric hindrance, thus contributing toward the high density of single Ru atoms and even smaller Ru NPs after pyrolysis. A Ru-Ru coordination number of only 1.3 is observed in the novel Ru-CTF-I-900 catalyst, which exhibits significantly higher catalytic activity than Ru-CTF-900 for transfer hydrogenation of acetophenone.

Fabricating Single-Atom Catalysts from Chelating Metal in Open Frameworks.

In the present study, a highly efficient strategy is reported using open framework platforms with abundant chelating ligands to fabricate a series of stable metal single-atom catalysts (SACs). Here, the metal ions are initially anchored onto the active bipyridine sites through postsynthetic modification, followed by pyrolysis and acid leaching. The resulting single metal atoms are uniformly distributed on a nitrogen-doped carbon (N-C) matrix. Interestingly, each metal atom is found to be coordinated with five N atoms, in contrast to the average coordination number of four as previously reported. The as-prepared Fe SAC/N-C catalyst exhibits excellent oxygen reduction reaction (ORR) activity (with a half-wave potential of 0.89 V), outstanding stability, and good methanol tolerance. The density functional calculations reveal that the coordinated pyridine can favorably modulate the interaction strength of oxygen on the Fe ion and thus improve the ORR activity. More importantly, it is demonstrated that this strategy can be successfully extended to the preparation of other transition metal SACs, simply by altering the metal precursors used in the metalation step.

Atomic Substitution Enabled Synthesis of Vacancy-Rich Two-Dimensional Black TiO2- x Nanoflakes for High-Performance Rechargeable Magnesium Batteries.

Rechargeable magnesium (Mg) batteries assembled with dendrite-free, safe, and earth-abundant metal Mg anodes potentially have the advantages of high theoretical specific capacity and energy density. Nevertheless, owing to the large polarity of divalent Mg2+ ions, the insertion of Mg2+ into electrode materials suffers from sluggish kinetics, which seriously limit the performance of Mg batteries. Herein, we demonstrate an atomic substitution strategy for the controlled preparation of ultrathin black TiO2- x (B-TiO2- x) nanoflakes with rich oxygen vacancies (OVs) and porosity by utilizing ultrathin 2D TiS2 nanoflakes as precursors. We find out that the presence of OVs in B-TiO2- x electrode material can greatly improve the electrochemical performances of rechargeable Mg batteries. Both experimental results and density functional theory simulations confirm that the introduction of OVs can remarkably enhance the electrical conductivity and increase the number of active sites for Mg2+ ion storage. The vacancy-rich B-TiO2- x nanoflakes exhibit high reversible capacity and good capacity retention after long-term cycling at large current densities. It is hoped that this work can provide valuable insights and inspirations on the defect engineering of electrode materials for rechargeable magnesium batteries.

Surface modification of porous PLGA scaffolds with plasma for preventing dimensional shrinkage and promoting scaffold-cell/tissue interactions.

Due to numerous merits, polyesters have been widely used for the preparation of porous scaffolds for biomedical applications. However, insufficient dimensional stability and weak cell interaction are two critical challenges to highly porous polyester scaffolds fulfilling their roles during applications. Here, we report the surface modification of PLGA scaffolds with air plasma for simultaneously tackling the dimensional shrinkage of PLGA scaffolds and improving scaffold-tissue integration. Highly porous PLGA scaffolds with interconnected pore structures and well orientated microtubules were prepared through lyophilization, and an air plasma process with varied duration was applied to the porous scaffolds. Water contact angle measurements indicated that moderate treatment (120 seconds) can significantly increase the wettability without distorting the morphology of and damaging the PLGA scaffolds. Further characterization (SEM, XPS, µ-CT, and theoretical computations) revealed that the plasma treatment enabled the generation of carboxyl groups on the surface of the PLGA scaffold, and the hydrophilic PLGA chain tends to extend under aqueous conditions in comparison to the hydrophobic pristine PLGA chain. Consequently, this could eliminate the hydrophobic-scaffold/water interface and weaken the driving force behind the distortion of the scaffolds in aqueous conditions, and finally inhibit overall shrinkage and maintain the microstructures of the porous scaffolds. Similar results were observed with porous PLA scaffolds, indicating the generality of air plasma treatment in inhibiting the shrinkage of polyester scaffolds. In the meantime, in vitro cell attachment experiments and in vivo subcutaneous implantation results consistently indicated that better maintaining the microstructure could significantly enhance the short-term cell attachment/proliferation on the scaffold and the long-term scaffold-tissue integration. These findings may inspire many creative and efficient strategies for the surface modification of polyester scaffolds to improve their performance for biomedical applications.

ABO blood types and postpartum depression among Chinese women: A prospective cohort study in Tianjin, China.

Postpartum depression is associated with adverse consequences for mother and offspring. The heritable ABO blood group has been associated with multiple diseases, including mental illness and diabetes. We explored the association of ABO blood group and postpartum depressive symptoms (PPDS) in a population-based cohort of pregnant Chinese women. From 2010 to August 2012, we recruited 8842 pregnant women with a mean age of 28.5 years (SD: 2.94) and mean body mass index of 22.4kg/m2 (SD: 3.45) in Tianjin, China. We used the Mainland Chinese version of the Edinburgh Postnatal Depression Scale after delivery with a cutoff score of 10 to define PPDS. Odds ratios (ORs) and 95% confidence intervals (CIs) for PPDS were obtained using binary logistic regression. Of 8842 women, 8.5% (n = 747) developed PPDS. Compared to those with blood group B, women with blood groups A, AB or O had a higher odds of PPDS (adjusted ORs: 1.23 (95% CI: 1.13-1.40), 1.31 (95% CI: 0.98-1.74), and 1.30(95% CI:1.03-1.60), respectively). Blood group B was associated with reduced odds of PPDS in pregnant Chinese women. If replicated in other studies, non-blood group B may be a useful risk factors for PPDS in Chinese pregnant women.

Unconventional O-H···C Hydrogen Bonding and Effects of Conformational Changes on Infrared Spectroscopy of o-Cresol in Solutions.

The unconventional O-H···C intramolecular hydrogen bonding and the effect of conformational changes on IR spectra of o-cresol in aqueous solutions were investigated by using molecular dynamics (MD) simulations, density functional theory (DFT), and experiments. A facial rotational isomerization between global minimum with trans conformation and the cis isomer is predicted to take place in gas phase with a low barrier of about 3.7 kcal/mol through a vertical-like transition state. Upon solvation in aqueous solution, the contents of energetically high-lying vertical and cis conformations of neutral o-cresol are increased to 19% and 57%, respectively, in comparison with those (vertical, 0%; cis, 27%) in vacuum. The IR spectra of aqueous solution are closely related to the relative population of the different conformations, especially for the cis conformation with hydroxyl group facing to alkyl group. The appearance of cis conformations and unconventional O-H···C intramolecular hydrogen bond (HB) caused the low-frequency shift in OH stretching vibration of the IR spectra, which was also correlated with cation-like charge distribution and the decrease in s-component of oxygen hybridization orbital. However, the intermolecular HB between the o-cresol and surrounding water (o-cresol) molecules gave rise to more evident shifts in IR spectra than that caused by the intramolecular HB contributions in cis isomer. Further identification of intramolecular HB effect is performed through the comparison of spectrum changes that occurs on passing from aqueous solution to less interacting (carbon tetrachloride and cyclohexane) solvents. The absence of the intermolecular HB interaction between o-cresol and carbon tetrachloride (and cyclohexane) solvents leads to the weaker intensity and narrower width of OH stretching vibration region (around 3407 cm-1) in the IR spectra than that in aqueous solution.

Structural Analysis of the Hg(II)-Regulatory Protein Tn501 MerR from Pseudomonas aeruginosa.

The metalloprotein MerR is a mercury(II)-dependent transcriptional repressor-activator that responds to mercury(II) with extraordinary sensitivity and selectivity. It's widely distributed in both Gram-negative and Gram-positive bacteria but with barely detectable sequence identities between the two sources. To provide structural basis for the considerable biochemical and biophysical experiments previously performed on Tn501 and Tn21 MerR from Gram-negative bacteria, we analyzed the crystal structure of mercury(II)-bound Tn501 MerR. The structure in the metal-binding domain provides Tn501 MerR with a high affinity for mercury(II) and the ability to distinguish mercury(II) from other metals with its unique planar trigonal coordination geometry, which is adopted by both Gram-negative and Gram-positive bacteria. The mercury(II) coordination state in the C-terminal metal-binding domain is transmitted through the allosteric network across the dimer interface to the N-terminal DNA-binding domain. Together with the previous mutagenesis analyses, the present data indicate that the residues in the allosteric pathway have a central role in maintaining the functions of Tn501 MerR. In addition, the complex structure exhibits significant differences in tertiary and quaternary structural arrangements compared to those of Bacillus MerR from Gram-positive bacteria, which probably enable them to function with specific promoter DNA with different spacers between -35 and -10 elements.

Design of [2]rotaxane through image threshold segmentation of electrostatic potential image.

An electrostatic potential (ESP)-based image segmentation method has been used to estimate the ability of proton donation and acceptance involved in ring-rod recognition. The relative binding strength of [2]rotaxane has also been further estimated from the difference of the characteristic image-segmentation derived ESP between proton donor and proton acceptor. The size and electrostatic compatibility criteria are introduced to guide the design of interlocked [2]rotaxane. A library of 75 thermodynamically stable [2]rotaxane candidates has been generated, including 16 experimentally known systems. The theoretical results for 16 experimentally known [2]rotaxanes are in good agreement with both the experimental association constants and density functional theory-calculated binding energies. Our ESP-based image segmentation model is also applicable to the tristable [2]rotaxane molecular shuttle as well as [1]rotaxane with self-inclusion function, indicating this simple method is generic in the field of constructing other supramolecular architectures formed with donor/acceptor molecular recognition. © 2016 Wiley Periodicals, Inc.

Factor Analysis of Conformations and NMR Signals of Rotaxanes: AIMD and Polarizable MD Simulations.

The interlocked ⟨rod | ring⟩ structures of pseudorotaxanes and [2]rotaxanes are usually maintained by the complex hydrogen-bonding (H-bonding) network between the rod and ring. Ab initio molecular dynamics (AIMD) using generalized energy-based fragmentation approach and polarizable force field (polar FF)-based molecular dynamics (MD) simulations were performed to investigate the conformational changes of mechanically interlocked systems and to obtain the ensemble-averaged NMR chemical shifts. Factor analysis (FA) demonstrates that the ring H-donor (2,6 pyridinedicarboxamide group) plays an important role in the ring-rod recognition. In comparison to the conventional fixed-charge force field, the polarization effect is crucial to account for the H-bonding interactions in supramolecular systems. In the hybrid scheme, the polar FF-based MD simulations are used to generate different initial states for the AIMD simulations, which are able to give better prediction of ensemble-averaged NMR signals for chemically equivalent amide protons. The magnitude of the deshielding shift of NMR signal is correlated with the length of hydrogen bond. The polar FF model with variable charges shows that the dipole-dipole interactions between the flexible diethylene glycol chain of ring and polar solvents induce the upfield shifts of NMR signals of rod H-donors and the directional distribution of the neighboring CH3CN solvents.

Theoretical study on conformation dynamics of three-station molecular shuttle in different environments and its influence on NMR chemical shifts and binding interactions.

Microscopic information on conformational flexibility and macrocycle-thread binding interactions is helpful in rational design of novel multistation molecular shuttles with interesting topology and functions. Molecular dynamics (MD) was applied to simulate conformational changes of thread and macrocycle of a three-station molecular shuttle in different chemical environments (vacuum, CD3CN-CDCl3 solution, and crystal). In contrast with the highly distorted thread conformation in the gas phase and nonpolar CDCl3 solution, the solvated thread in CD3CN-CDCl3 (1:1) mix solvents exhibited a relatively rigid structure. Experimental observations of preferential binding at the protonated dibenzylammonium group (station I) were rationalized by quantum chemical calculations of macrocycle-thread binding energies at three different stations. The orthogonality of site-specific binding interactions at three different stations was also revealed by the nearly constant binding energy obtained at each specific recognition center with the replacement of different neighboring groups and terminal stoppers on the thread. Conformational flexibility has little effect on NMR signals of binding sites, but for some protons that are close to the solvent molecules in the first solvent shell, their chemical shifts are sensitive to the local electrostatic environment caused by nearby solvents. In crystal, π stacking induced evident upfield shifts of NMR signals in comparison with the isolated monomer.

Dynamic self-inclusion behavior of pillar[5]arene-based pseudo[1]rotaxanes.

It was found that spontaneous isomerization takes place between three isomers of a pillar[5]arene (P5)-based pseudo[1]rotaxane. The isomerization process could be monitored by (1)H NMR spectra in polar solvent and the geometric configurations of the three isomers were further evaluated by theoretical calculations. In the threaded forms, the alkyl side chain might be preorganized by intramolecular N-HO bonds between the urea group of the side chain and the methoxy group of the P5 and further stabilized by multiple interactions, including H-bonding, C-H∙∙∙π interactions, and the steric effect of the N-Boc moiety. These cooperative interactions greatly enhance the stability of the threaded form in polar solvent, and endow it with very special self-inclusion behavior.