Metal-hydrogen Bond Research Articles

Self-healable and redox active hydrogel obtained via incorporation of ferric ion for supercapacitor applications

Poly (vinyl alcohol)/phytic acid (PVA/PA) hydrogels have been identified as self-healable electrolytes. In this work, a novel redox active and self-healable PVA/PA/Fe3+ (PPFe) hydrogel containing dual cross-linking network through the formation of both metal coordination bonds and hydrogen bonds was fabricated via a freezing-thawing method. For the first time to our best knowledge, it was found that the introduction of dynamic Fe3+ coordination bonds into the PPFe hydrogel not only improved its mechanical properties and self-healing ability via re-configuration of various bonds, but also afforded the hydrogel high electrochemical redox activity. Compared with plain PVA/PA hydrogels, the as-fabricated PPFe gel delivered greatly improved mechanical properties, including a tensile stress of 0.618 MPa and tensile strain of 924 %, as well as a strain self-healing efficiency of 72 %. The self-healable and redox active PPFe hydrogel was further utilized to fabricate supercapacitors, where the redox reaction of Fe3+ occurred on polyaniline/carbon nanotubes (PANI/CNTs) electro-active material, resulting in an ultra-high 1526 mF/cm2 at 0.5 mA/cm2, and a remarkable energy density of 0.212 mWh/cm2 at 0.25 mW/cm2, as wells as an excellent cycling stability. Moreover, it could recover its electrochemical performance after the cutting-healing, which would greatly improve the reliability and safety of the energy storage device.

Self-Healing, Anti-Fatigue, antimicrobial ionic conductive hydrogels based on Choline-Amino acid polyionic liquids for Multi-Functional sensors

Conductive hydrogels have recently attracted extensive attention due to their broad application prospects in flexible electronic devices and artificial intelligence. However, it is still a great challenge to develop integrated conductive hydrogels with excellent mechanical properties, efficient self-healing ability and high sensitivity. Moreover, most conductive hydrogels have no antimicrobial activity, which may lead to microbial infection during their applications. Herein, a series of versatile ionic conductive hydrogels based on choline-amino acid polyionic liquids(Cho-AA PILs) were designed by double network (DN) methodology. Owing to the reversible nature of dynamic coordination interaction, including metal coordination bonds, hydrogen bonds and electrostatic interactions, the resultant PIL hydrogels exhibited efficient self-healing ability, high energy dissipation capacity and outstanding fatigue resistance. The incorporation of Cho-AA PILs endowed hydrogels with not only high antimicrobial activity but also sensitive, rapid and stable strain sensing ability. The gauge factor(GF) and response time of PIL flexible sensors were 2.65 and 100 ms, respectively. During 1000 cycles, the electrical response signal of the strain sensor still remained stable. Significantly, PIL flexible sensors were able to monitor and distinguish large human body motions and subtle physiological activities and show sensitivity to pressure and handwriting. In addition, PIL hydrogels exhibited excellent biocompatibility. These results predicted that the prepared PIL hydrogels possess promising application prospects in the fields of artificial intelligence and biomedical engineering.

Study on the Highly Efficient Reduction of CO2 to Formate Using Zinc under Mild Hydrothermal Conditions

In this study, the reaction mechanism of CO2 reduction by using Zn under mild hydrothermal condition was investigated by DFT calculation method. Based on the calculation of the transition state, as well as the IRC and HOMO/LUMO, the Zn-H was considered as a key intermediate for the high formate production from CO2. This study provides information on the reaction pathway of metal reduction with the metal hydrogen bond under hydrothermal conditions. The energy diagram showed that the Zn-H has high reducing activity, which induced that the formate was easily produced through hydrothermal reactions. From the viewpoint of energy, in the CO2 reaction system, the HCOO- was easily produced than that in the HCO3 - reaction system. This process provides new concept for the high efficient production of value-added chemicals in the carbon dioxide utilization research area.

Chemical Templates That Assemble the Metal Superhydrides

The recent discoveries of many metal superhydrides provide a new route to room-temperature superconductors. However, their stability and structure trends and the large chemical driving force needed to dissociate H2 molecules and form H covalent network cannot be explained by direct metal-hydrogen bonds and volume effect. Here, we demonstrate that the understanding of superhydrides formation needs a perspective beyond traditional chemical bond theory. Using high-throughput calculations, we show that, after removing H atoms, the remaining metal lattices exhibit large electron localization at the interstitial regions, which matches excellently to the H lattice like a template. Furthermore, H lattices consist of 3D aromatic building units that are greatly stabilized by chemical templates of metals close to s-d border. The chemical template theory can naturally explain the stability and structure trends of superhydrides and help to predict new materials such as two-metal superhydrides.

Ternary Mg-Nb-H polyhydrides under high pressure

Magnesium based alloys are promising solid materials for hydrogen storage. However, it is a real challenge to synthesise hydrogen storage materials with high hydrogen storage capacity and low dehydrogenation temperature. Here, we have performed extensively structural searches for ternary magnesium-based hydrogen storage compounds of ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{n}$ with n ranging from 16 to 25 by calypso method and first-principles calculations. We readily identified the experimentally observed ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ hydride and uncovered a stable stoichiometry of ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{19}$ with high hydrogen storage capacity of 6.7 wt% and low dehydrogenation temperature of 273 K. The remarkable decrease of the hydrogen release temperature is attributed to the atomic rearrangements in ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{19}$, which forms H-H pairs and has weakened metal-hydrogen chemical bonds compared to the stable ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ and $\mathrm{Mg}{\mathrm{H}}_{2}$ compounds. Our calculations show that ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ undergoes a structural phase transition from its $P\overline{4}2m$ phase to a $Fm\overline{3}m$ phase at 75 GPa, and the $Fm\overline{3}m$ phase is a potential polyhydride superconductor. The present findings offer insights for understanding the hydrogen storage and release of Mg-Nb-H ternary magnesium-based hydrogen storage compounds, which open avenues for the design and synthesis of magnesium-based hydrogen storage material.

Solvent-responsive strong hydrogel with programmable deformation and reversible shape memory for load-carrying soft robot

The development of shape deformation hydrogels has aroused interests of their immense applications in diverse fields such as actuators, soft robotics, and artificial muscles. However, the existing deformable hydrogels can hardly meet the requirements of facile preparation, excellent mechanical properties and reversible shape memory, which greatly limits their further applications. In this work, a new type of fully physically cross-linked deformable hydrogel with mechanically strong, tough, stretchable, and solvent-responsive property is fabricated via free radical polymerization at room temperature, followed by immersed in a Fe3+ aqueous solution. The strong physical interactions of polyacrylic acid (PAA)-Fe3+ metal complexation and hydrogen bond endowed this hydrogel with high tensile strength (~5.14 MPa), high stretchability (~1000%), high toughness (~20.36 MJ/m3) and excellent flexibility (~0.53 MPa). In addition, programmable shape deformation hydrogel is achieved by selective coating of Fe3+ on surface, the hydrogel strips can be deformed into arbitrary shapes such as the letter “o”, “d”, “s”, and “w”. More impressively, reversible shape recovery of hydrogel has been achieved via two methods: the elimination of coated Fe3+ with the reaction of NaOH and the dehydration of the glycerin. Taking advantage of this property, we simulate the closure and opening of hydrogel flower by soaking it into water and NaOH/glycerin alternately. Moreover, the soft robotic gripper has been fabricated based on the mechanically strong and solvent-triggered hydrogel, capable of grabbing about 1.56 times its own weight, which indicating the potential application as load-carrying soft robots.

Synthesis of some metal nanoparticles using the effective media of choline chloride based deep eutectic solvents

Nanoparticles are potential candidates for numerous biological as well as chemical applications due to their exotic properties 1 - 3. Low lattice energy ions are found in deep eutectic solvents (DES). A quaternary ammonium salt is frequently complexed with a metal salt or hydrogen bond donor to produce these compounds (HBD) 4 - 6. The green synthesis of nanoparticles using DESs is always eco-friendly and attractive. The current study focuses on the synthesis of mercuric sulphide, Zirconium oxide, Manganese oxide and Copper oxide nanoparticles using the Choline Chloride - Ethylene Glycol DES as the solvent in presence of a reducing agent, hydrazine hydrate. The UV-Visible, FTIR spectra, XRD, SEM and EDAX analysis were carried out on these metal nanoparticles. The average sizes of these metal nanoparticles were found to be 50 to 150 nm. Hence the green synthesis of metal nanoparticles using Ch. Cl – EG can be considered as an alternative route in chemical synthesis of metal nanoparticles.

Chiral Bipyridine Ligand with Flexible Molecular Recognition Site: Development and Application to Copper‐Catalyzed Asymmetric Borylation of α,β‐Unsaturated Ketones

AbstractA novel chiral bipyridine ligand bearing a flexible side chain with a molecular recognition site enables precise stereocontrol through the cooperative action of metal center and hydrogen bonds. This new chiral ligand was applied to the copper‐catalyzed asymmetric borylation of α,β‐unsaturated carbonyl compounds. The reaction afforded the corresponding borylated products in good yields with high enantioselectivities. Preliminary studies of the functional group‐selective transformation revealed that the newly designed chiral bipyridine ligand has the potential to control chemo‐ and site selectivity in addition to stereoselectivity.

Very Stable Two Mega Dalton High-Molecular-Mass Multiprotein Complex from Sea Cucumber Eupentacta fraudatrix.

In contrast to many human organs, only the human liver can self-regenerate, to some degree. Some marine echinoderms are convenient objects for studying the processes of regenerations of organs and tissues. For example, sea cucumbers Eupentacta fraudatrix can completely restore within several weeks, the internal organs and the whole body after their division into two or three parts. Therefore, these cucumbers are a very convenient model for studying the general mechanisms of regeneration. However, there is no literature data yet on which biomolecules of these cucumbers can stimulate the regeneration of organs and the whole-body processes. Studying the mechanisms of restoration is very important for modern biology and medicine, since it can help researchers to understand which proteins, enzymes, hormones, or possible complexes can play an essential role in regeneration. This work is the first to analyze the possible content of very stable protein complexes in sea cucumbers Eupentacta fraudatrix. It has been shown that their organisms contain a very stable multiprotein complex of about 2000 kDa. This complex contains 15 proteins with molecular masses (MMs) >10 kDa and 21 small proteins and peptides with MMs 2.0–8.6 kDa. It is effectively destroyed only in the presence of 3.0 M MgCl2 and, to a lesser extent, 3.0 M NaCl, while the best dissociation occurs in the presence of 8.0 M urea + 0.1 M EDTA. Our data indicate that forming a very stable proteins complex occurs due to the combination of bridges formed by metal ions, electrostatic contacts, and hydrogen bonds.

Soil organic matter stabilization at molecular scale: The role of metal cations and hydrogen bonds

Do humic substances exist naturally? Recently, this question has taken relevance in light of new evidence that supports the theory that soil organic matter (SOM) is an assembly of molecular species. Depending on the conditions, this assembly behaves as a macromolecular specie of high-weight or as a collection of low-weight molecular species. Nevertheless, it is an undeniable fact that some fractions of soil organic matter can be more resistant to ongoing physical and (bio)chemical degradation processes than others. This can be attributed to several factors ranging from molecular properties to the preference for digesting other molecular species by microorganisms. In this work, we explain the influence of cations and hydrogen bonds in SOM stabilization at the molecular level. By using molecular dynamics simulations and analyzing volumetric and structural properties, we elucidate the possible mechanisms of the formation of stable SOM aggregates, hardly accessible from the experimental point of view due to the molecular complexity of soil. Our results show that organic matter tends to form aggregates of big molecular size due to the presence of metal cations commonly found in soils, in agreement with other works and experimental observations. For the first time, the different complex structures of cation-SOM and their distribution are reported in models highly concentrated in organic matter. We conclude that cations serve as seeds to agglomerate organic matter and thus give rise to aggregates. The organic matter exhibits more stable aggregates with Ca2+ than with Na+ cations at different pH conditions; whereas, the absence of cations leads to the SOM destabilization and potentially also to the dispersion of the organic matter components, mainly due to electrostatic repulsion among them.

Multifunctional hydrogel prepared via polymerization initiated by mechanically induced heat of coordination

Multifunctional materials that simulate biological tissues have promising applications as next-generation ionic skin and soft robot equipment. Such materials feature self-healing, stretchability, outstanding electrochemical performance, and lubrication. The mechanical performance and self-healing properties are essential for the material application. To date, however, few reports have combined these properties in one matrix, which requires a complex process. This paper presents a gelation strategy based on heat generated during the mechanical coordination process. The hydrogel was polymerized using two kinds of monomers: acrylic acid and acrylamide, in which the interactions between metal coordination bond and hydrogen bond equipped the hydrogel with high stretch strength, mechanical strength, prominent tensile strain, and healing time.

Antityrosinase Mechanism and Antimelanogenic Effect of Arbutin Esters Synthesis Catalyzed by Whole-Cell Biocatalyst.

Tyrosinase is a key enzyme responsible for enzymatic browning of fruits and vegetables and skin disorders due to overproduction of melanin. Arbutin is an inhibitor of tyrosinase; however, its high polarity and weak transdermal absorption capacity limit its applications. In this paper, a green solvent system was developed to successfully synthesize arbutin esters with improved liposolubilities (Clog P values = 0.27-5.03). Among the obtained esters, arbutin undecenoate (AU) showed the strongest tyrosinase-inhibiting activity (15.6%), which was 9.0 times higher than that of arbutin. An enzyme kinetics study indicated that AU was a competitive inhibitor with reversible inhibition. The esters inhibited tyrosinase by making the secondary structure of tyrosinase looser and less stable; moreover, the interactions between tyrosinase and AU driven by metal interactions and hydrogen bonds also offered a mechanism for inhibition of AU on tyrosinase. In addition, AU (100 μM) reduced the melanin content of B16 mouse melanoma cells to 61.3% of the control group.

Crystal and electronic structure manipulation of Laves intermetallics for boosting hydrogen evolution reaction.

Since the 1970s, Laves intermetallics (AB2) have been widely used in hydrogen storage technology (e.g., nickel-metal hydride batteries) due to the abundant interstitial sites and moderate metal-hydrogen bond strength (EM-H). They, however, have been rarely used in the hydrogen evolution reaction (HER) because of the same reason (i.e. moderate EM-H), which results in poor HER efficiency. In this study, by applying lanthanide contraction and ligand effect, we have successfully lowered the EM-H and substantially boosted the HER activity of Laves intermetallics (RECo2 and RERu0.5Co1.5 (RE = Pr, Tb, Y and Er)) to outperform those of commercial Pt/C catalyst. Hydrogen overpotential decreases from ErCo2 (η10 = 169 mV) to PrCo2 (η10 = 113 mV) and then to PrRu0.5Co1.5 (η10 = 29 mV). The expansion of lattice constants for PrCo2 may alleviate the obstacle of H atom diffusing through interstitial sites, while the inclusion of Ru element can raise the antibonding population of Co-Co/Ru bonds, which consequently lowers EM-H and thus elevates HER activity according to the Sabatier principle. This outcome indicates that the manipulation of the crystal structure and electronic structure factor is an efficient strategy to boost the HER activity of Laves intermetallics.

Structural properties of Mg - x wt% Co (x = 0, 5, 10 & 20) nanocomposites for hydrogen storage applications

Abstract This work represents the hydrogen storage possibilities in Magnesium (Mg)-based nanocomposites. Mg materials are abundant in nature and are of interest as hydrogen storage material due to their cost effectiveness and better hydrogen storage capacity. But, in Mg hydrides strong metal-hydrogen bond results very slow dehydrogenation process, that hinder its application for onboard storage. Effect of the cobalt on ball-milled Mg with different wt% is studied in atmospheric condition. Pristine Mg was ball milled for 12 h and after addition of Co the mixture was ball milled for further 2 h. X‐ray Diffraction (XRD) technique was employed for structural analysis. Field Emission Scanning Electron Microscope and energy-dispersive X-ray spectroscopy (EDXS) were employed to analyze the particle morphology, distribution and elemental analysis of the Mg - x wt% Co (x = 0, 5,10 & 20) nanocomposites respectively.

Combining Coordination and Hydrogen Bonds to Develop Discrete Supramolecular Metalla-Assemblies

In Nature, metal ions play critical roles at different levels, and they are often found in proteins. Therefore, metal ions are naturally incorporated in hydrogen-bonded systems. In addition, the combination of metal coordination and hydrogen bonds have been used extensively to develop supramolecular materials. However, despite this win-win combination between coordination and hydrogen bonds in many supramolecular systems, the same combination remains scarce in the field of coordination-driven self-assemblies. Indeed, as illustrated in this mini-review, only a few discrete supramolecular metalla-assemblies combining coordination and hydrogen bonds can be found in the literature, but that figure might change rapidly.

Stereoselectivity and nonmigratory insertion mechanism of dimethylacetylene dicarboxylate into metallocene‐hydride of Cp2M(L)H [Cp = η5‐C5H5; M = Nb, V; L = CO, P (OMe)3]: A DFT study

The insertion of an alkyne into transition metal–hydrogen bonds is a key elementary step in catalytic polymerization and hydrogenation processes. It was found that a (Z)‐ or (E)‐type alkyenyl complex can be formed through trans/cis stereospecific processes. In this work, the reaction mechanism of Cp2M(L)H [Cp = η5‐C5H5; M = Nb, V; L = CO, P (OMe)3] with dimethylacetylene dicarboxylate (DMAD), and the factors influencing the stereoselectivity have been investigated based on density functional theory calculations. The calculated results show that all of the reactions are exothermic. For L = CO, the Z‐isomer product forms first even at low temperatures because of the low Gibbs free energy barrier (ΔG#). Then the Z‐pro converts to E‐pro, while for L = P (OMe)3, the exclusive product is the E‐isomer. For different metal centers, the reaction mechanisms of the Cp2M(CO)H + DMAD (M = Nb and V) reaction are similar, while their products are different at room temperature. For M = Nb, because the energy barrier of the isomerization from Z‐pro to E‐pro is low and the relative free energies of Z‐pro and E‐pro are almost equal, both Z‐pro and E‐pro can be obtained. While for the Cp2V(CO)H + DMAD reaction, only the Z‐pro can be obtained under mild conditions, E‐pro can be obtained only at high temperatures. For the Cp2M(CO)H+DMAD(M=V and Nb) reactions, the formation of E‐isomer products proceeds via two five‐membered ring transition states. The calculated results provide an reasonable explanation for the experimental results and predict a new insertion reaction.

Photochromic Evaluation of 3(5)-Arylazo-1H-pyrazoles.

The desire to photocontrol molecular properties ranging from materials to pharmacology using light as an external trigger with high spatiotemporal resolution led to the development of a broad range of photochromic scaffolds. Among them, azobenzenes are synthetically well accessible and show excellent fatigue resistance. Their photochromic properties vary with the substitution pattern and for different heteroarenes. However, the photochromism of 3(5)-substituted-1H-pryazoles has not yet been investigated, although this compound class offers interesting possibilities of metal ion coordination and hydrogen bond formation via its NH moiety. Herein, we present the results of an experimental and computational investigation of arylazo-3(5)-arylazo-1H-pyrazoles. To elucidate their properties, solvent and substitution effects on their light absorption, thermal half-lives, photostationary states, fatigue, and quantum yields were determined.

Influence of Hydrogen Bond Donating Sites in UiO‐66 Metal‐Organic Framework for Highly Regioselective Methanolysis of Epoxides

AbstractA Zr(IV)‐based UiO‐66 metal‐organic framework (MOF) (named 1) was synthesized by employing 1‐(aminomethyl)naphthalene‐2‐ol appended terephthalate linker and Zr(IV) salt via solvothermal method and subsequently characterized. Furthermore, the potential efficiency of activated (named 1′) form of as‐synthesized MOF was investigated as an organocatalyst for the ring‐opening of epoxide by methanol. The catalytic performance of 1 and 1′ was studied in the methanolysis of styrene oxide as a model substrate and the activity of 1′ was also examined with various alcohols. Under the optimized reaction conditions, the catalytic performance of 1′ reached 96 % conversion of styrene oxide to its corresponding product with 98 % regioselectivity. The reusability and stability of the catalyst were proved by recycling up to four runs in the methanolysis of styrene oxide. The Lewis acidity originating from metal nodes and hydrogen bond donating (HBD) sites in the linker is distributed homogeneously throughout the framework, thus playing crucial role in the activation of epoxide with easy accessibility.

Insight into the catalytic performance of HER catalysis of noble metal/3D-G nanocomposites

Development of multifunctional materials has shown a great interest in recent years. Herein, we report the simple, cost-effective, one step, and surfactant-free synthesis of three-dimensional graphenes (3D-G) nanocomposites with Pt, Pd, Au and Ag and explore their catalytic activity and investigated the dynamics for the hydrogen evolution reaction (HER). Field emission scanning electron microscopy (FEG-SEM) and high resolution transmission electron microscopy (HRTEM) study reveals the uniform incorporation of noble metal on the 3D-G. The 3D-G with Pt composite (Pt/3D-G) has shown significantly enhanced catalytic performance over the commercially available Pt/C for HER, suggesting significant improvements in catalytic performance on the incorporation of 3D-G. The Temperature dependent HER investigation has been performed and the apparent activation energy (Eaapp) for Pt/3D-G. Pd/3D-G, Au/3D-G, and Ag/3D-G catalysts are obtained as 25.37, 32.36, 16.14, and 24.82 kJ/mol, respectively. Eaapp of Pt/3D-G and Pd/3D-G are found to decrease with increase in the overpotential, and the Eaapp of Au/3D-G and Ag/3D-G is found to increase with overpotential. This variation of Eaapp with the applied potential is correlated with the metal-hydrogen bond energy with respect to the potential of zero charges (PZC). The kinetics of HER on catalysts is explained in terms of temperature variation of the Tafel slope. The Tafel slopes of Pt/3D-G and Pd/3D-G are increased with increase in temperature, and for Au/3D-G and Ag/3D-G, the Tafel slopes are decreased with increase in temperature, which suggests the enthalpy driven process for Pt/3D-G and Pd/3D-G and entropy driven process for Au/3D-G and Ag/3D-G.

Correction to “Formation of Giant and Small Cyclic Complexes from a Flexible Tripeptide Ligand Controlled by Metal Coordination and Hydrogen Bonds”

Correction to “Formation of Giant and Small Cyclic Complexes from a Flexible Tripeptide Ligand Controlled by Metal Coordination and Hydrogen Bonds”