Imidazole Coordination Research Articles

Room‐temperature self‐healing polyurethanes with high mechanical strength and superior toughness for sensor application

AbstractIt remains enormous challenges to balance the conflict between high strength and toughness mechanical properties and excellent room‐temperature self‐healing abilities of polyurethane elastomers. In this work, we report a recyclable room‐temperature self‐healing polyurethane elastomer with excellent mechanical properties. The prepared polyurethane elastomer (PU‐DA‐Zn0.50) exhibits high tensile strength of 15.33 MPa, high toughness of 76.77 MJ m−3, and high elongation at break of 1604.46% by introducing isophorone diamine (IPDA), 1‐(3‐aminopropyl) imidazole (IMZ) and zinc ions into polymer system to form a dynamic double‐cross‐linked structure (hydrogen bonds and Zn2+‐imidazole coordination bonds). In addition, the tensile strength of fractured polyurethane can reach more than 80% of the original sample after 48 h of self‐healing at room temperature without external stimuli, which is attributed to the kinetics of rapid exchange of Zn2+‐imidazole coordination bonds at room temperature. It is worth noting that the balance between excellent mechanical properties and outstanding room‐temperature self‐healing ability can be optimized by adjusting the Zn2+‐imidazole coordination bond density in the system. Moreover, the dynamic nature of the double‐cross‐linking network endows polyurethane with favorable recyclability. The above remarkable comprehensive performances reveal a great potential of PU‐DA‐Znx elastomer in the fields of wearable flexible electronic devices such as bionic skin, human motion monitoring, and soft robots.

Highly Stable Luminescent Metal–Organic Frameworks for Ultrasensitive Detection of Nitroaniline Isomers: Application in In Situ Imaging of Toxic Pesticides

A powerful and promising route for developing chemically stable luminescent sensors for visible sensing of toxic pesticides in water and actual food samples is presented. Herein, a novel twofold interpenetrated luminescent metal–organic framework (MOF), Cd-TM, is prepared by incorporating 2-methyl-1H-imidazole-5-carbaldehyde as the imidazole-containing tridentate coordination linker and the luminescent organic bridging linker 4,4′,4″-tricarboxyltriphenylamine (H3tca) into a framework. Thanks to the imidazole coordination and structurally interpenetrated nature, the MOF exhibits high fluorescence stability and water stability up to 6 months. Fluorescence titration experiments reveal that Cd-TM shows rapid and ultrasensitive fluorescence response to p-nitroaniline compared with other nitroanilines with the limit of detection of about 8 nM. In particular, the Cd-TM material also shows high sensitivity to detect dicloran (DCN, 2,6-dichloro-4-nitroaniline) pesticides with the structure similar to that of p-NA. The detection limit is 7.6 nM, which is found to be superior to those of the recently reported MOF-based sensors. In addition, the detection mechanism of DCN is studied by FT-IR analysis, SEM/EDX elemental mapping, XPS, and theoretical calculations. Practically, the recoveries of spiked environmental samples were found to be satisfactory (95.8–106.4%). Further, Cd-TM is also used for the rapid in situ nondestructive imaging detection of pesticide residues in simulated fresh agricultural products. These results indicate that Cd-TM has the potential to detect organophosphorus pesticide contamination with rapid in situ imaging via easy-to-read visual signals.

Chelator PBT2 Forms a Ternary Cu2+ Complex with β-Amyloid That Has High Stability but Low Specificity.

The metal chelator PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) acts as a terdentate ligand capable of forming binary and ternary Cu2+ complexes. It was clinically trialed as an Alzheimer's disease (AD) therapy but failed to progress beyond phase II. The β-amyloid (Aβ) peptide associated with AD was recently concluded to form a unique Cu(Aβ) complex that is inaccessible to PBT2. Herein, it is shown that the species ascribed to this binary Cu(Aβ) complex in fact corresponds to ternary Cu(PBT2)NImAβ complexes formed by the anchoring of Cu(PBT2) on imine nitrogen (NIm) donors of His side chains. The primary site of ternary complex formation is His6, with a conditional stepwise formation constant at pH 7.4 (Kc [M-1]) of logKc = 6.4 ± 0.1, and a second site is supplied by His13 or His14 (logKc = 4.4 ± 0.1). The stability of Cu(PBT2)NImH13/14 is comparable with that of the simplest Cu(PBT2)NIm complexes involving the NIm coordination of free imidazole (logKc = 4.22 ± 0.09) and histamine (logKc = 4.00 ± 0.05). The 100-fold larger formation constant for Cu(PBT2)NImH6 indicates that outer-sphere ligand-peptide interactions strongly stabilize its structure. Despite the relatively high stability of Cu(PBT2)NImH6, PBT2 is a promiscuous chelator capable of forming a ternary Cu(PBT2)NIm complex with any ligand containing an NIm donor. These ligands include histamine, L-His, and ubiquitous His side chains of peptides and proteins in the extracellular milieu, whose combined effect should outweigh that of a single Cu(PBT2)NImH6 complex regardless of its stability. We therefore conclude that PBT2 is capable of accessing Cu(Aβ) complexes with high stability but low specificity. The results have implications for future AD therapeutic strategies and understanding the role of PBT2 in the bulk transport of transition metal ions. Given the repurposing of PBT2 as a drug for breaking antibiotic resistance, ternary Cu(PBT2)NIm and analogous Zn(PBT2)NIm complexes may be relevant to its antimicrobial properties.

F‐Doped Co−N−C Catalysts for Enhancing the Oxygen Reduction Reaction in Zn‐Air Batteries

AbstractZn‐air battery is a promising next‐generation energy storage device. Its performance, however, is limited by a high overpotential resulted from the slow kinetics of the cathodic oxygen reduction reaction (ORR). This study reports a simple strategy for preparation of a fluorine‐doped Co−N−C composite as highly efficient electrocatalyst for ORR. The C@PVI‐(TPFC)Co‐800 catalyst was prepared by pyrolysis of F‐containing Co‐corrole that was assembled on PVI‐functionalized carbon black through the axial imidazole coordination (PVI=polyvinylimidazole, TPFC=5,10,15‐triperfluorophenyl‐21H, 22H‐corrole). The C@PVI‐(TPFC)Co‐800 catalyst exhibited much more positive ORR half‐wave potential (E1/2=0.88 V vs. RHE) than its counterpart C@PVI‐(TPC)Co‐800 (E1/2=0.82 V, TPC=5,10,15‐triphenyl‐21H, 22H‐corrole) without F‐doping in 0.1 M KOH electrolyte. C@PVI‐(TPFC)Co‐800 also achieved a greater kinetic current density and enhanced durability in alkaline media. In addition, a Zn‐air battery with C@PVI‐(TPFC)Co‐800 loaded at the cathode delivered much higher peak power density (Pmax=141 mW/cm2) and open‐circuit voltage (OCV=1.45 V) over the C@PVI‐(TPC)Co‐800 counterpart (Pmax=110 mW/cm2, OCV=1.39 V) and the commercial 20 % Pt/C (Pmax=119 mW/cm2, OCV=1.42 V) as well. The promoted catalyst performance for ORR was attributed to the increased specific surface area, more defects generated, and reduced electron density distribution around the Co metal center after F‐doping.

A Strategy of Thiolactone Chemistry to Construct Strong and Tough Self-Healing Supramolecular Polyurethane Elastomers via Hierarchical Hydrogen Bonds and Coordination Bonds

Self-healing elastomers with extended service life and enhanced reliability have attracted extensive attention in recent years due to their broad application in fields such as protective coatings, wearable electronics, shape memory materials, and health-care monitoring. However, it is challenging to simultaneously optimize the mechanical properties (strength and toughness) and self-healing capacity of the elastomers. Herein, thiolactone chemistry was delicately used as a bridge to address this conundrum by incorporating 2-ureido-4[1H]-pyrimidinone (UPy) motifs and imidazole ligands into the side chains of linear polyurethane. The synergistic cross-linking of UPy H-bonds and Zn2+-imidazole coordination afforded a robust supramolecular network to significantly improve the strength. Meanwhile, these dynamic cross-linking points acted as sacrificial bonds for energy dissipation under external stress, which played a dominant role in toughening. Therefore, the resultant elastomer (PU-Im-UPy-Zn) exhibited a tensile strength of 9.1 MPa, a breaking elongation of 989%, and toughness up to 62.1 MJ m–3. In addition, the reversible exchange of hierarchical hydrogen bonds (single H-bonds between the carbamate groups and quadruple H-bonds of the UPy dimers) and coordination bonds as well as the high mobility of side chains were conducive to repairing under mild conditions. The superficial scratches completely disappeared at 60 °C, and a satisfactory healing efficiency of 78% was observed after 24 h. This work provides some insights into future design of self-healable supramolecular polyurethane elastomers integrated with conspicuous strength and toughness.

Highly Coupled Heterobicycle-Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C60.

Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole-fused porphyrin dimers and their mono- and bis-zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady-state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free-base and zinc porphyrin) reveals the occurrence of efficient singlet-singlet energy transfer (>95 % efficiency and rate constant >1012 s-1 ) within the dyad. Further, donor-acceptor conjugates were formed by metal-ligand axial coordination of phenyl imidazole functionalized C60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge-separated state was in the 30-40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π-spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Coordination Polymer Electrocatalysts Enable Efficient CO-to-Acetate Conversion.

Upgrading carbon dioxide/monoxide to multi-carbon C2+ products using renewable electricity offers one route to more sustainable fuel and chemical production. One of the most appealing products is acetate, the profitable electrosynthesis of which demands a catalyst with higher efficiency. Here, a coordination polymer (CP) catalyst is reported that consists of Cu(I) and benzimidazole units linked via Cu(I)-imidazole coordination bonds, which enables selective reduction of CO to acetate with a 61% Faradaic efficiency at -0.59 volts versus the reversible hydrogen electrode at a current density of 400mA cm-2 in flow cells. The catalyst is integrated in a cation exchange membrane-based membrane electrode assembly that enables stable acetate electrosynthesis for 190h, while achieving direct collection of concentrated acetate (3.3 molar) from the cathodic liquid stream, an average single-pass utilization of 50% toward CO-to-acetate conversion, and an average acetate full-cell energy efficiency of 15% at a current density of 250mAcm-2 .

Double Modification of Poly(urethane-urea): Toward Healable, Tear-Resistant, and Mechanically Robust Elastomers for Strain Sensors.

Polyurethane elastomers with mechanical robustness, tear resistance, and healing efficiency hold great potential in wearable sensors and soft robots. However, achieving excellent mechanical properties and healable capability simultaneously remains highly desirable but exclusive. Herein, we propose a straightforward procedure for double modification of poly(urethane-urea) (PUU) via thiolactone chemistry, and two different dynamic cross-linking bonds (disulfide linkages and Zn2+/imidazole coordination) are successively incorporated into the side chain of PUU, producing double cross-linking elastomers (PUU-I/Zn-S). The synergy between disulfide linkages and Zn2+/imidazole coordination forms a robust and dynamic network, endowing PUU-I/Zn-S with excellent mechanical and healing properties. The tensile stress, elongation at break, and toughness of the resultant elastomer can reach 44.06 MPa, 1000%, and 181.93 MJ m-3, respectively. Meanwhile, PUU-I/Zn-S exhibits outstanding tearing resistance with a tearing energy of 42.1 kJ m-2. The PUU-I/Zn-S can restore its mechanical robustness after self-healing at room temperature (25 ± 2 °C) or 60 °C and even maintain 91% of its original tensile strength after reprocessing two times. Additionally, PUU-I/Zn-S-based strain sensors are fabricated by introducing conductive nanofillers and demonstrate remarkable sensing capability to diverse human body motions. This work demonstrates a simple and feasible method for the postfunctionalization and enhancement of polyurethane and provides some insights into reconciling the traditional contradictory properties of mechanical robustness and healing efficiency.

A refractory wound healing hydrogel with integrated functions of photothermal anti-infection, superoxide dismutase mimicking activity, and intelligent infection management

Promoting refractory wound healing remains a challenging issue. Currently, dressings with intelligent infection management functions built on infection eradication and reactive oxygen species (ROS) scavenging abilities are lacking. In this study, an approach based on Cu2+-imidazole coordination cross-linked histidine grafted chitosan (CS-His) and carbon quantum dots (CQDs) was developed to engineer superoxide dismutase (SOD) mimicking centers with photothermal anti-infection and intelligent anti-infection abilities, beyond typical ROS scavenging activity. The cross-linked coordination network was further promoted with tanshinol-encapsulated ZIF-8 frameworks (ZIF-8@Ts) to achieve intelligent infection management behaviors. These designs generate a refractory wound-healing hydrogel with integrated functions of photothermal anti-infection, SOD mimicking activity, and intelligent infection management. In response to infection exacerbation, the SOD mimicking centers and ZIF-8@Ts nanoparticles could release CQDs for anti-infection and Ts for antioxidation, respectively. In vitro results revealed photothermal anti-infection, ROS scavenging, and intelligent infection management capacities of the hydrogel. These abilities promoted the M2 transformation of macrophages and rescued the inhibitory effect of infection on fibroblast proliferation and migration. The hydrogel exhibited high regenerative efficacy in a rat model of chronically infected diabetic wounds. These results demonstrated the immense potential of the intelligent hydrogel integrated with multifunctions for refractory wound healing.

Unexpected Imidazole Coordination to the Dirhodium Center in a Protein Environment: Insights from X-ray Crystallography and Quantum Chemistry.

X-ray diffraction data demonstrate that the adduct formed upon the reaction of dirhodium(II,II) tetraacetate with RNase A reacts with imidazole, leading to the formation of an unexpected product with the imidazole that binds the dirhodium center at an equatorial site rather than an axial site. The origin of this result has been dissected using quantum-chemical calculations.

Activation of Cadmium–Imidazole Buffering Coordination Polymer by Sulfur-Doping for the Enhancement of Photocatalytic Degradation of Cationic and Anionic Dyes Under Visible Light

The buffering Cadmium–Imidazole Coordination Polymer (Cd–Im-CP) was synthesized hydrothermally from cadmium chloride and imidazole at 70 °C and then was subjected to doping- by the non-metal sulfur using Na2S solution as a novel modification strategy to produce S–Cd–Im CPs. To investigate doping nature and its effects, Cd–Im CP and S–Cd–Im CPs were characterized applying different analyses techniques, FTIR, Raman, PXRD, SEM/EDX, TGA, and UV–Vis DRS analyses. Characterizations showed the successful chemical doping of sulfur. The inclusion of sulfur within chemical CP structure caused narrowing of material’s bandgap from 4.55 and 3.4 eV to 4.25 and 2.35 eV for S–Cd–Im CPs allowing it for photoresponse towards Visible-light. Both Cd–Im CP and S–Cd–Im CPs were applied for photocatalytic degradation of the selected dyes methylene blue (MB),and methyl orange (MO) employing visible and UV irradiations considering three different initial pH levels to investigate the consequence of sulfur doping. After eliminating the photolysis effect, the best degradation by S–Cd–Im CPs was recorded for MB at initial pH 4 being 13 fold that is for Cd–Im CP. The highest apparent turnover frequencies are 1.2 × 10−3 h−1 for MB at initial pH 10 and 1.03 × 10−4 h−1 for MO at initial pH 4 are given by 10S–Cd–IM CP under Visible-light. Generally, S–Cd–Im CPs remarkably improved photocatalysis degradation of both the dyes for all initial pH levels under Visible-light.

Co(II)-porphyrin complexes with nitrogen monoxide and imidazole: synthesis, optimized structures, electrochemical behavior and photochemical stability

UV-vis and 1H-NMR spectroscopy were applied to study axial coordination of imidazole (L1) and nitrogen monoxide (L2) with CoII-porphyrins (CoIIP) containing halogen substituents in the pyrrole and meso-phenyl positions of the macrocycle. The number and positions of bromine and chlorine atoms cause considerable deformation of the tetrapyrrole macrocycle. Cyclic voltammetry was used to determine the oxidation potentials of CoII/CoIII (Е1 ох) in the compounds. Both mono-axial complexes (CoII(L)) and diaxial complexes (CoIIIP(L)2) or CoIIP-π cation radicals could be the products of CoIIP interaction with L1 and L2, depending on the porphyrinate structure. The interconnection between halogen substitution in the porphyrin macrocycle and its ability to reversibly bind NO was established. The photochemical activity of the synthesized complexes in the presence of active oxygen forming (tert-butylperoxide) was investigated. The results extend our understanding of the valence state of cobalt cations in porphyrin molecules depending on the macrocycle structure and surrounding conditions (solvent, temperature, organic and inorganic impurities), and demonstrate the possibility of reversible binding of both the NO molecules and various imidazole-containing biomolecules and drug compounds based on them.

Donor-acceptor conjugates derived from cobalt porphyrin and fullerene via metal-ligand axial coordination: Formation and excited state charge separation

Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA)4P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC[Formula: see text] to form a new series of donor–acceptor constructs. A 1:2 complex formation with ImC[Formula: see text] was established in the case of (TTP)Co while for [(TPA)4P]Co only a 1:1 complex was possible to positively identify. The binding constants [Formula: see text] and [Formula: see text] for step-wise addition of ImC[Formula: see text] to (TTP)Co were found to be 1.07 × 105 and 3.20 × 104 M[Formula: see text], respectively. For [(TPA)4P]Co:ImC[Formula: see text], the measured [Formula: see text] values was found to be 6.48 × 104 M[Formula: see text], slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluorescence of ImC[Formula: see text] indicating occurrence of excited state events in the supramolecular donor-acceptor complexes. Electrochemistry coupled with spectroelectrochemistry, revealed the formation of cobalt(III) porphyrin cation instead of a cobalt(II) porphyrin radical cation, as the main product, during oxidation of phenyl imidazole coordinated cobalt porphyrin. With the help of computational and electrochemical results, an energy level diagram was constructed to witness excited state photo-events. Competitive energy and electron transfer from excited CoP to coordinated ImC[Formula: see text], and electron transfer from Im1C[Formula: see text]* to cobalt(II) porphyrin resulting into the formation of PCo[Formula: see text]:ImC[Formula: see text] charge separated state was possible to envision from the energy diagram. Finally, using femtosecond transient absorption spectroscopy and data analysis by Glotaran, it was possible to establish sequential occurrence of energy transfer and charge separation processes. The lifetime of the final charge separated state was [Formula: see text] 2 ns. A slightly better charge stabilization was observed in the case of [(TPA)4P]Co:ImC[Formula: see text] due to the presence of electron rich, peripheral triphenylamine substituents on the cobalt porphyrin.

Zn2+-Imidazole Coordination Crosslinks for Elastic Polymeric Binders in High-Capacity Silicon Electrodes.

Recent research has built a consensus that the binder plays a key role in the performance of high‐capacity silicon anodes in lithium‐ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+–imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+–imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long‐term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full‐cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion‐ligand coordination chemistries for binders intended for high capacity alloying‐based electrodes.

Coordinated Molecule-Modulated Magnetic Phase with Metamagnetism in Metal–Organic Frameworks

Metal Organic Frameworks (MOFs) are a very prominent research topic because of their potential uses in applications such as molecular devices, gas storage systems, and especially single chain magnet (SCM) materials. Among these MOFs, those that feature open metal sites (Ni2+) inherently possess spin states that are tunable via organic molecular coordination. They have demonstrated the potential of SCM materials, exhibiting the possibilities for the spin-canting, magnetic phase transition, and field-induced spin slow dynamics behavior.In this paper, we experimentally and theoretically investigated the magnetic properties of a MOF possessing an open metal site, and its derivatives. It exhibits a magnetic ordered state at low temperatures, which can be altered by altering its imidazole (IM) coordination. Our results show that coordinated IM clearly influences the spin state of Ni(II) ions with orbital geometries, resulting in shifts in critical temperature and field. These obtained results imply that the magnetic behavior in MOFs with IM reveals the coexistence of spin-canting, metamagnetism, magnetic phase transitions, and field-induced spin slow dynamics.To the best of our knowledge, this is the first example of a MOF exhibiting the influence of the spin state of Ni(II) ions with orbital geometries via organic molecular coordination, which shows the coexistence of spin-canting, metamagnetism, magnetic phase transition, and field-induced spin slow dynamics.

Reversible switching of arylazopyrazole within a metal-organic cage.

Arylazopyrazoles represent a new family of molecular photoswitches characterized by a near-quantitative conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd–imidazole coordination. Owing to its high water solubility, the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not soluble in water. NMR spectroscopy and X-ray crystallography have independently demonstrated that each cage can encapsulate two molecules of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calculations suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage.

Controlling Charge-Transport in Metal-Organic Frameworks: Contribution of Topological and Spin-State Variation on the Iron-Porphyrin Centered Redox Hopping Rate.

Metal-organic frameworks (MOFs) are an emerging class of compositions for electro- and photoelectrocatalytic energy conversion processes. Understanding and improving the charge-transport processes within these high surface area molecular redox catalyst assemblies are critical since the charge carrier conductivity is inherently limited in MOFs. Here, we examine a series of four chemically identical but structurally different hydrolytically robust ZrIV-MOFs constructed from tetrakis(4-carboxyphenyl)porphyrinato iron(III), TCPP(FeIII) to understand how their topological construction affects redox hopping conductivity. While a structural variation fixes center-to-center distances to define the hopping rate, we probe that altering the central metal spin-state can further tune the TCPP(FeIII/II) reorganization energy of the self-exchange process. Significant increase in the hopping rate was observed upon axial coordination of 1-methyl imidazole (MIM), which converts a weakly halide bound high-spin (HS) TCPP(FeIII/II) to the six-coordinated low-spin (LS) complex. Our electrochemical and resonance Raman data reveal that pore geometry that defines the Fe-Fe distance in these frameworks dictate the steric demand to accommodate two MIM-molecules, and thus, the population of LS vs HS species is a function of topology in the presence of an excess ligand.

Self-healing polymers with tunable mechanical strengths via combined hydrogen bonding and zinc-imidazole interactions

The development of self-healing polymers with tunable mechanical performances is an enormous challenge. Herein, self-healing polymers with tunable mechanical strengths via combined hydrogen bonding and Zn(II)-imidazole interactions were successfully synthesized. This synthesis was accomplished by introducing urea hydrogen bonding and Zn(II)-imidazole interactions into self-healing polymers polymerized from a new bifunctional monomer of 2-(3-(3-imidazolylpropyl)ureido)ethyl acrylate (IUA). The dual dynamic effects of urea hydrogen bonding and Zn(II)-imidazole interactions can simultaneously endow polymers with better self-healing capacities and mechanical properties. The synthesized polymers with urea hydrogen bonding and Zn(II)-imidazole interactions motifs exhibited over 90% self-healing efficiency under mild conditions. The mechanical strengths of the polymers can be flexibly tuned from 35.0 kPa to 4.41 MPa by varying the molar ratio of imidazole/Zn(II). When the polymers are damaged, the urea hydrogen bonds and Zn(II)-imidazole coordination can contribute to the reconstruction of the broken polymer networks and thus provide self-healing abilities. The interactions of hydrogen bonding and Zn(II)-imidazole coordination were confirmed by in-situ FT-IR spectra of the self-healing polymers at different temperatures.

Reactions of Cyclometalated Platinum(II) [Pt(N∧C)(PR3)Cl] Complexes with Imidazole and Imidazole-Containing Biomolecules: Fine-Tuning of Reactivity and Photophysical Properties via Ligand Design.

This work describes interaction of a family of [Pt(N∧C)(PR3)Cl] complexes with imidazole (Im), possible application of this chemistry for regioselective labeling of proteins through imidazole rings of histidine residues and employment of the resulting phosphorescent products in bioimaging. It was found that the complexes containing aliphatic phosphines display reversible substitution of chloride ligand for imidazole function that required considerable excess of imidazole to obtain full conversion into the substituted [Pt(ppy)(PR3)(Im)] product, whereas the substitution in the complexes with aromatic phosphines readily proceeds in 1:1.5 mixture of reagents. Rapid, selective, and quantitative coordination of imidazole to the platinum complexes enabled regioselective labeling of ubiquitin. X-ray protein crystallography of the {[Pt(ppy)(PPh3)]/ubiquitin} conjugate revealed direct bonding of the platinum center to unique histidine-68 residue through the nitrogen atom of imidazole function, the coordination being also supported by noncovalent interaction of the ligands with the protein secondary structure. The variations of the cyclometalating N∧C ligands gave a series of [Pt(N∧C)(PPh3)Cl] complexes (N∧C = 2-phenylpyridine, 2-(benzofuran-3-yl)pyridine, 2-(benzo[b]thiophen-3-yl)pyridine, methyl-2-phenylquinoline-4-carboxylate), which were used to investigate the impact of N∧C-ligand onto photophysical properties of the imidazole complexes and conjugates with human serum albumin (HSA). The chloride ligand substitution for imidazole and formation of the conjugates results in ignition of the platinum chromophore luminescence with substantially higher quantum yield in the latter case. Variation of the metalating N∧C-ligand made possible the shift of the emission to the red region of visible spectrum for both types of the products. Cell-viability tests revealed low cytotoxicity of all {[Pt(N∧C)(PPh3)Cl]/HSA} conjugates, while PLIM experiments demonstrated their high potential for oxygen sensing.

Arylazoimidazole Coordinated and Naphthalene-Dicarboxylato Bridged Polymers of Co(II) and Photochromic Zn(II) Complexes

Naphtheledicarboxylato ((NDC2–) bridged coordination polymers (CPs) along with (E)-1-methyl-2-(p-chlorophenylazo)imidazole (ClPai-Me) coordination to Co(II), [Co(∝-NDC)0.5(∝4-NDC)0.5(ClPai-Me)]·0.5H2O (1), and to Zn(II), [Zn(∝-NDC)0.5(∝4-NDC)0.5(ClPai-Me)]·0.5H2O (2), have been characterized. In the single crystal X-ray structure of 1, ClPai-Me chelates to the Co(II) ion by N(azo) and N(imidazolyl), whereas in compound 2, it acts as a monodentate N(imidazolyl) donor to the Zn(II) ion. The coordination atmosphere around Co(II) in the 1 ion is distorted octahedral CoN2O4, whereas in the case of 2, it is distorted square pyramidal ZnNO4. Compounds 1 and 2 exhibit the right-handed (P) and left-handed (M) one-dimensional helical chain. NDC–2 is serving as a bridge between two M(II) ions to constitute μ-NDC and four M(II) ions to construct μ4-NDC to assemble three-dimensional polymers. Upon UV light (369 nm) irradiation, compound 2 shows trans-to-cis isomerization of -N═N–C6H4–Cl-p both in the solid and solutio...