Metal-ligand Coordination Interactions Research Articles

Facile preparation of SAN/NBR TPV with balanced stiffness-toughness via metal-ligand coordination-induced dynamic vulcanization and in situ interfacial compatibilization

In this work, metal-ligand coordination interaction was utilized to induce the dynamic vulcanization (DV) of styrene-acrylonitrile copolymer (SAN)/butadiene acrylonitrile rubber (NBR)/cupric sulfate (CuSO4) TPVs. The TPVs exhibited co-continuous structure, in which the CuSO4 particles distributed in continuous NBR network to cross-link NBR phase through interaction between Cu2+ and nitrile groups (-CN), enhancing the mechanical strength and thickness of NBR network. CuSO4 particles were refined to nanoparticles during DV, and then migrated to SAN/NBR interface and interacted with SAN and NBR simultaneously to realize in-situ compatibilization, resulting in efficient toughening of SAN without sacrificing its stiffness. With 20 phr CuSO4, the TPVs showed excellent impact toughness of 104.51 kJ/m2, which was 58 times that of the neat SAN. Meanwhile, the TPVs exhibited improved tensile strength, elongation at break, tensile toughness and Young's modulus, revealing the balanced stiffness-toughness properties of TPVs. We propose a feasible approach to fabricate high-performance TPVs, and it may expand the research scope of dynamic vulcanization.

Fabrication of Highly Thermally Resistant and Self-Healing Polysiloxane Elastomers by Constructing Covalent and Reversible Networks.

The fabrication of self-healing elastomers with high thermal stability for use in extreme thermal conditions such as aerospace remains a major challenge. A strategy for preparing self-healing elastomers with stable covalent bonds and dynamic metal-ligand coordination interactions as crosslinking sites in polydimethylsiloxane (PDMS) is proposed. The added Fe (III) not only serves as the dynamic crosslinking point at room temperature which is crucial for self-healing performance, but also plays a role as free radical scavenging agent at high temperatures. The results show that the PDMS elastomers possessed an initial thermal degradation temperature over 380°C and a room temperature self-healing efficiency as high as 65.7%. Moreover, the char residue at 800°C of PDMS elastomer reaches 7.19% in nitrogen atmosphere, and up to 14.02% in air atmosphere by doping a small amount (i.e., 0.3 wt%) of Fe (III), which is remarkable for the self-healing elastomers that contain weak and dynamic bonds with relatively poor thermal stability. This study provides an insight into designing self-healing PDMS-based materials that can be targeted for use as high-temperature thermal protection coatings.

A multi-stimuli-responsive metallosupramolecular gel based on pillararene hierarchical assembly

A metallosupramolecular polymer network is constructed by hierarchical self-assembly of a double-armed pillar[5]arene, a ditopic guest, and zinc ions, where host-guest recognition and metal-ligand coordination interactions play a crucial role.

Introducing metal-ligand coordination interaction for self-healing and recyclable nitrile–butadiene rubber: A facile strategy

Introducing metal-ligand coordination interaction for self-healing and recyclable nitrile–butadiene rubber: A facile strategy

Synthetic approaches to metal-coordination-directed macrocyclic complexes.

Metal-coordination-directed macrocyclic complexes, in which macrocyclic architectures are formed by metal-ligand coordination interactions, have emerged as attractive supramolecular scaffolds for the creation of materials for applications in biosensing and therapeutics. Despite recent progress, uncontrolled multicyclic cages and linear oligomers/polymers is the most likely outcome from metal-ligands assembly, representing a challenge to current synthetic methods. Herein we outlined the state-of-art synthetic approaches to the metal-coordination-directed macrocyclic complexes by using foldable ligands or through assembly of amphiphilic ligands. This mini-review offers a guideline for the efficient preparation of metal-coordination-directed macrocyclic complexes with predictable and controllable structures, which may find applications in many biology-related areas.

Preparation of Supramolecular Miktoarm Star Copolymers with a Zinc Phthalocyanine Core through ATRP and RAFT Polymerization.

Topological polymers have attracted considerable attention owing to their unique chemical and physical properties. This study demonstrates the formation of novel supramolecular miktoarm star copolymers with a zinc phthalocyanine (ZnPc) core using metal-ligand coordination interactions. Various linear polymers with pyridyl end groups, poly(methyl methacrylate), poly(vinyl acetate) and poly(N-vinyl carbazole), are prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. This facilitates coordination to the ZnPc core of 4-armed star-shaped polystyrene prepared via atom-transfer radical polymerization (ATRP). Furthermore, the formation of a 1:1 complex of a ZnPc molecule and pyridyl group of the chain-transfer agent for RAFT is confirmed by absorption spectral studies and 1 H NMR spectroscopic analyses. The concept of supramolecular complexation can be extended to the preparation of AB4 -type supramolecular miktoarm star-shaped copolymers with functional cores.

Synergistic Multiple Bonds Induced Dynamic Self-Assembly of Silver Nanoclusters into Lamellar Frameworks with Tailored Luminescence

Incorporating atomically precise metal nanoclusters (NCs) into ordered self-assemblies endows them with advanced photophysical properties; however, their ordered arrangement in space is difficult to achieve with only noncovalent bonds between individual clusters. Herein, we illustrate the hierarchical self-assembly of atomically precise silver NCs (NH4)6[Ag6(mna)6] (Ag6-NCs) into hexagonal two-dimensional lamellas by intercluster π···π and C-H···π interactions, which then pack into three-dimensional metal–organic frameworks (MOFs) by the metal–ligand coordination interaction. Synergistic multiple bond-induced dynamic coassembly greatly enhanced the quantum yields and lifetimes, achieving the transformation of weak fluorescence to strong thermally activated delayed fluorescence (TADF). The structure and luminescence transformation could be reversibly switched by tuning the pH values. The Ag6-NCs/Ca2+ coassemblies behaved as efficient yellow phosphors to afford white light emitting diode devices. This work demonstrates a synergistic multiple bond-induced hierarchical self-assembly to realize ordered layer-by-layer MOFs from NCs-based secondary building units with advanced TADF emission in a pH-tailored manner for potential applications in luminescent devices and sensors.

Balancing Microthrombosis and Inflammation via Injectable Protein Hydrogel for Inflammatory Bowel Disease.

Emerging evidence indicates that a vicious cycle between inflammation and microthrombosis catalyzes the pathogenesis of inflammatory bowel disease (IBD). Over‐stimulated inflammation triggers a coagulation cascade and leads to microthrombosis, which further complicates the injury through tissue hypoxia and ischemia. Herein, an injectable protein hydrogel with anti‐thrombosis and anti‐inflammation competency is developed to impede this cycle, cross‐linked by silver ion mediated metal‐ligand coordination and electronic interaction with sulfhydryl functionalized bovine serum albumin and heparin, respectively. The ex vivo experiments show that the hydrogel, HEP‐Ag‐BSA, exhibits excellent self‐healing ability, injectability, biocompatibility, and sustained drug release. HEP‐Ag‐BSA also demonstrates anti‐coagulation and anti‐inflammation abilities via coagulation analysis and lipopolysaccharide stimulation assay. The in vivo imaging confirms the longer retention time of HEP‐Ag‐BSA at inflammatory sites than in normal mucosa owing to electrostatic interactions. The in vivo study applying a mouse model with colitis also reveals that HEP‐Ag‐BSA can robustly inhibit inflammatory microthrombosis with reduced bleeding risk. This versatile protein hydrogel platform can definitively hinder the “inflammation and microthrombosis” cycle, providing a novel integrated approach against IBD.

Synthesis of orange-emissive silicon nanoparticles as “off-on” fluorescence probe for sensitive and selective detection of l-methionine and copper

Fluorescent silicon nanoparticles (Si NPs) are of great interest as they are free of heavy ions. However, most of Si NPs exhibit blue or green emission, while orange or red-emitting Si NPs are required for an extensive range of applications. Copper ion (Cu2+) and l-methionine (L-Met) detection is critically valuable point since their abnormal level is an indicator of various diseases. In this work, we illustrate an “off-on” method for sensitively and selectively determination of Cu2+ and L-Met using Si NPs as fluorescent probe. The Si NPs emitting orange fluorescence with the quantum yield of 2.23% were prepared via one and easy step of hydrothermal treatment of 3(2-aminoethylamino) propyl (dimethoxymethylsilane) (AEAPDMMS) and 2–aminophenol as precursors. The fluorescence of Si NPs was quenched in the presence of Cu2+ due to the strong metal-ligand coordination and electrostatic interactions between the large amount of amino and hydroxyl groups on the surface of Si NPs and Cu2+. Surprisingly, the resulted non-fluorescent Si NPs-Cu2+ complex displayed a fluorescence “turn-on” toward L-Met, due to the competitive coordination of Cu2+ between L-Met and Si NPs which leads to the unique “off-on” response to L-Met after the release of free Si NPs. The as-proposed approach is fast, simple, low cost and environmental-friendly. More importantly, it has been applied in the determination of Cu2+ and L-Met in water and urine samples, respectively with satisfactory recoveries. Furthermore, the approach could detect Cu2+ and L-Met with detection limit of 0.012 μM and 0.07 μM, which are lower than the level of Cu2+ in drinking water and of L-Met in human urine sample (maximum ~20 μM and ~5.9 μM, respectively).

Ion-induced white-light-emitting polymeric hydrogels with high mechanical strength and reversible stimuli-responsive properties

We have developed a facile strategy to fabricate model multicolor hydrogels via a straightforward mixing process of poly acrylonitrile-grafted methacrylamide (PANMAM), polymethacrylic acid (PMAA) and doped lanthanide (Eu/Tb) and zinc ions to form the interpenetrating dual-polymer gel networks. The hydrogels exhibit excellent tunability of multi-spectrum emission colors (including white light) by simply varying the stoichiometry of metal ions. Furthermore, taking the advantage of different metal ion response mechanisms, we have demonstrated the reversible acidity/alkalinity stimuli-responsive behaviors of white-light-emitting hydrogel (WLE gel). Meanwhile, the unique cross-linked network formed through hydrogen-bonding, metal-ligand coordination and ionic interaction is introduced to achieve favorable mechanical strength of hydrogels. These properties enable the possibility in obtaining fluorescent patterns on hydrogels, which are promising candidate for encrypted information with improved security.

Photoresponsive supramolecular coordination polyelectrolyte as smart anticounterfeiting inks

While photoluminescence printing is a widely applied anticounterfeiting technique, there are still challenges in developing new generation anticounterfeiting materials with high security. Here we report the construction of a photoresponsive supramolecular coordination polyelectrolyte (SCP) through hierarchical self-assembly of lanthanide ion, bis-ligand and diarylethene unit, driven by metal-ligand coordination and ionic interaction. Owing to the conformation-dependent photochromic fluorescence resonance energy transfer between the lanthanide donor and diarylethene acceptor, the ring-closure/ring-opening isomerization of the diarylethene unit leads to a photoreversible luminescence on/off switch in the SCP. The SCP is then utilized as security ink to print various patterns, through which photoreversible multiple information patterns with visible/invisible transformations are realized by simply alternating the irradiation with UV and visible light. This work demonstrates the possibility of developing a new class of smart anticounterfeiting materials, which could be operated in a noninvasive manner with a higher level of security.

Conjugated Polymer Nanoparticles Based on Copper Coordination for Real-Time Monitoring of pH-Responsive Drug Delivery.

Metal coordination-driven composite systems have excellent stability and pH-responsive ability, making them suitable for specific drug delivery in physiological conditions. In this study, an anionic conjugated polymer PPEIDA with a poly(p-phenylene ethynylene) backbone and iminodiacetic acid (IDA) side chains is used as a drug carrier to construct a class of pH-responsive nanoparticles, PPEIDA-Cu-DOX conjugated polymer nanoparticles (CPNs), by taking advantage of the metal coordination interaction of Cu2+ with PPEIDA and the drug doxorubicin (DOX). PPEIDA-Cu-DOX CPNs have high drug loading and encapsulation efficiency (EE), calculated to be 54.30 ± 1.10 and 95.80 ± 0.84%, respectively. Due to the good spectral overlap, Förster resonance energy transfer (FRET) takes place between PPEIDA and the drug DOX, which enables the observation of the loading and the release of DOX from CPNs in an acidic environment by monitoring fluorescence emission changes. Therefore, PPEIDA-Cu-DOX CPNs can also be used in real-time cell imaging to monitor drug release in addition to delivering DOX targeting tumor cells. Compared with free DOX, PPEIDA-Cu-DOX CPNs show a similar inhibition to tumor cells and lower toxicity to normal cells. Our results demonstrate the feasibility and potential of constructing pH-responsive CPNs via metal-ligand coordination interactions for cancer treatment.

Orthogonal Self-Assembly of a Two-Step Fluorescence-Resonance Energy Transfer System with Improved Photosensitization Efficiency and Photooxidation Activity.

During the past few decades, fabrication of multistep fluorescence-resonance energy transfer (FRET) systems has become one of the most attractive topics within supramolecular chemistry, chemical biology, and materials science. However, it is challenging to efficiently prepare multistep FRET systems with precise control of the distances between locations and the numbers of fluorophores. Herein we present the successful fabrication of a two-step FRET system bearing specific numbers of anthracene, coumarin, and BODIPY moieties at precise distances and locations through an efficient and controllable orthogonal self-assembly approach based on metal-ligand coordination and host-guest interactions. Notably, the photosensitization efficiency and photooxidation activity of the two-step FRET system gradually increased with the number of energy transfer steps. For example, the two-step FRET system exhibited 1.5-fold higher 1O2 generation efficiency and 1.2-fold higher photooxidation activity than that of its corresponding one-step FRET system. This research not only provides the first successful example of the efficient preparation of multistep FRET systems through orthogonal self-assembly involving coordination and host-guest interactions but also pushes multistep FRET systems toward the application of photosensitized oxidation of a sulfur mustard simulant.

Selective Metal-Ligand Bond-Breaking Driven by Weak Intermolecular Interactions: From Metamagnetic Mn(III)-Monomer to Hexacyanoferrate(II)-Bridged Metamagnetic Mn2Fe Trimer.

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn2Fe complex {[Mn(L)(H2O)]2Fe(CN)6},2- starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H2O)Cl] (1) and [Fe(CN)6]4- anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H2O)Cl] (1) and of compound (H3O)[Mn(L)(H2O)2]{[Mn(L)(H2O)]2Fe(CN)6}·4H2O (2) (H2L = 2,2'-((1E,1'E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1 is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H2O molecule and a Cl- ion at the axial sites and the monomeric units are assembled by π-π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)6]4- with complex 1 leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two trans cyano groups of the [Fe(CN)6]4- anion replace the labile chloride from the coordination sphere of two [Mn(L)(H2O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H2O)]2Fe(CN)6}2- trimer. This Mn2Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H2O)2]+ cation, closely related to the precursor neutral complex [Mn(L)(H2O)Cl]. In compound 2, the Mn2Fe trimers are assembled by several hydrogen-bonding and π-π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (-29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (-30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1 and 2, respectively. The magnetic properties of compound 1 have been fit with a simple S = 2 monomer with g = 1.959, a weak zero-field splitting (|D| = 1.23 cm-1), and a very weak intermolecular interaction (zJ = -0.03 cm-1). For compound 2, we have used a model with an S = 2 monomer with ZFS plus an S = 2 antiferromagnetically coupled dimer with g = 2.009, |D| = 1.21 cm-1, and J = -0.42 cm-1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π-π and hydrogen-bonding interactions.

Fabrication of Janus graphene oxide hybrid nanosheets by Pickering emulsion template for self-healing nanocomposite hydrogels

Janus nanomaterials can be highlighted to design a series of smart materials with the remarkable characteristic of two different properties or constituents. In this manuscript, functional Janus graphene oxide-type (GO-type) nanomaterials were fabricated by Pickering emulsion template and successfully applied to develop of dual self-healing nanocomposite hydrogels. Asymmetric functionalization of Janus nanosheets were achieved in typical oil-in-water Pickering emulsion by atom transfer radical polymerization (ATRP) and mussel-inspired chemistry. Poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PMAEFc) and polydopamine (PDA) were unsymmetrically grafted on the two sides of GO (Janus GO-PMAEF/PDA (JGNs)), which successfully applied in self-healing nanocomposite hydrogels. The collaborative effect of metal-ligand coordination and host-guest interaction make the dual self-healing hydrogels have excellent self-healing properties (self-healing efficiency can reach to 93.4% within 1 h) and mechanical strength (tensile strength of 0.94 MPa and strain of 508.5%). Therefore, these chemical asymmetric JGNs have outstandingly application prospect in the development of smart materials.

Continuous liquid interface production of alginate/polyacrylamide hydrogels with supramolecular shape memory properties

A recently developed three-dimensional (3D) gel-printing technology, namely continuous liquid interface production (CLIP), was utilized to fabricate supramolecular shape memory hydrogels with high resolutions and complex 3D geometries. The UV-curable ink for CLIP was composed of hydrogel precursors (alginate and acrylamide) and a photo-initiator (ammonium persulfate). As expected, the double network formed from ionically crosslinked alginate and covalently crosslinked polyacrylamide endowed the printed hydrogels with excellent mechanical properties. Meanwhile, due to the reversible metal-ligand coordination interaction, the hydrogel could be temporarily immobilized into an optional shape after introducing calcium ions and return to its original shapes upon ion removal, exhibiting ion-triggered shape memory effect. Moreover, the presence of ions greatly improved the conductivity of the resultant hydrogels. Such 3D printed versatile hydrogels with complex geometries demonstrated the potential for selected applications, particularly in load-bearing materials and flexible electronic devices.

Atomically dispersed Eu(III) sites in natural deep eutectic solvents based fluorescent probe efficient identification of Fe3+ and Cu2+ in wastewater.

Heavy metal ions in wastewater have brought serious environmental pollution. To improve the detection efficiency, it is important to find useful fluorescent probes. The emerging green natural deep eutectic solvents (NADESs) offer attractive option for "green" detection for its good biocompatibility, easy preparation, and high sensitivity. In this study, a multi-functionalized fluorescent probe with atomically dispersed EuCl3·6H2O in amino acid-based NADESs (l-Glutamic acid/Glycerol, l-Glu/Gly) was synthesized by metal-ligand coordination interactions with a mass ratio of 15:1. Combined with the NADESs and rare earth metal, the l-Glu/Gly/EuCl3·6H2O could form the amino site and Eu2+ site fluorescent centers. Under the excitation wavelength of 370nm, it had dual emission peaks at 425nm and 470nm with efficient resonance energy transfer. The stable optoelectronic properties of l-Glu/Gly/EuCl3·6H2O under external factors, such as mass ratio (13,1 to 18:1), temperature (30-50°C), pH (1 to 14) and storage time ( >42days), approved l-Glu/Gly/EuCl3·6H2O an excellent fluorescence probe. In the application of water-quality monitoring, Fe3+ and Cu2+ could react with l-Glu/Gly/EuCl3·6H2O in different reactive patterns. The blue fluorescence was quenched by Fe3+ and enhanced by Cu2+, thus metal ions could be distinguished with high sensitivity. The detective process was determined and the fluorescent mechanism was also proposed. l-Glu/Gly/EuCl3·6H2O fluorescent probe was demonstrated to be an efficient fluorescent probe for metal detection avoiding the hydrothermal process, and the cumbersome of ilter, dialysis, freeze drying.

A carbon dots-based fluorescent probe for turn-on sensing of ampicillin

Carbon dots (CDs) with blue fluorescence were synthesized through hydrothermal treatment of p-dihydroxybenzene and hydrazine hydrate. The fluorescence of the investigated CDs could be selectively quenched by iron ions (Fe3+) because of the strong metal-ligand coordination and electrostatic interactions between the large amount of hydroxyl, amino, and carboxyl groups on CDs’ surface and Fe3+. Interestingly, this non-fluorescent CDs + Fe3+ complex displayed a sensitive and selective turn-on fluorescence toward ampicillin with a limit of detection of 0.70 μM. The sensing process could be observed by naked eyes under the 365 nm UV light irradiation. Importantly, CDs + Fe3+ complex had been successfully applied in the detection of ampicillin in river water.

Self-Assembled Amphiphilic Janus Double Metallacycle.

A double metallacycle was prepared via the size-selective integrative self-sorting of four different building blocks driven by a reversible metal-ligand coordination interaction. A hydrophobic dendron was placed on a metallacycle and a hydrophilic dendron was attached to the other metallacycle, producing a two-faced Janus-type supramolecule with two distinct functionalities. In aqueous media, hierarchical self-assembly of the supramolecular system was induced by the combination of coordination interactions and hydrophobic-hydrophilic interactions resulting in the formation of micrometer-sized fiber-like structures, a morphology distinct from metallacycles bearing only one type of functionality. This study provides a versatile approach for the construction of Janus-type molecules and demonstrates that integrative self-sorting of a supramolecular coordination system can be utilized for the preparation of complex supramolecular systems with predesigned functionalities and morphologies.

Development of supramolecular shape-memory polyurethanes based on Cu(II)–pyridine coordination interactions

Shape-memory polymers with supramolecular switch have received increasing attention. This study reports the synthesis and characterization of supramolecular shape-memory polyurethane based on Cu(II)–pyridine coordination, obtained by mixing pyridine containing polyurethane with CuCl2. The results show that there are strong metal–ligand coordination interactions formed between Cu(II) and the pyridine ring in a series of CuCl2-doped polyurethane samples. The Cu(II)–pyridine coordination plays a crucial role in the enhanced physical netpoints for outstanding shape-memory properties. Indeed, the so-synthesized CuCl2-doped polyurethane exhibits not only a rapid tensile shape recovery but also excellent crimp shape recovery. The CuCl2-doped polyurethane containing suitable metal–ligand coordination interactions shows more than 99% shape fixation and more than 95% shape recovery. Our findings promote further applications of shape-memory polymers in multiple engineering fields.