Imidazole Ligands Research Articles

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Solvent-Switchable Remote C-H Activation via 1,4-Palladium Migration Enables Site-Selective C-P Bond Formation: A Tool for the Synthesis of P-Chiral Phosphinyl Imidazoles.

Solvent-switchable and site-selective phosphorylation of imidazoles at the C2 or C5 position of the imidazole ring was achieved via 1,4-palladium migration. P-Chiral tert-butyl(aryl)phosphine oxides were cross-coupled to 1-(2-bromophenyl)-1H-imidazoles with high enantiospecificity, thereby leading to a novel class of chiral imidazole-based phosphine oxides. As proof of concept, reduction of an analogue yielded the corresponding P-chiral 2-phosphinyl imidazole ligand, which was shown to induce high enantioselectivity in the formation of axially chiral molecules synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling.

Synthesis, structural characterization and cytoprotective activity of a new mixed oxidovanadium(IV) compound with nitrilotriacetate and imidazole ligands

Herein, we have shown that the water molecule in [VO(nta)(H2O)]- can be replaced by an imidazole moiety which is a versatile binding site in various biological systems. These findings offer a new approach for synthesizing mixed ligand complexes with desired physicochemical and biological properties. In this study, a new hetero-ligand oxidovanadium(IV) monohydrate salt was successfully synthesized and structurally characterized. The compound consists of a mononuclear [VO(nta)(im)]- entity, where nitrilotriacetato–(nta) and imidazole (im) ligands are incorporated, along with an imidazolinium counterion, [im(H)][VO(nta)(im)]H2O. To characterize the complex in a solid state, various techniques were employed including elemental analysis, thermogravimetric analysis (TG-FTIR), single-crystal X-ray diffraction method and IR spectroscopy. In addition, the investigation included a study of the speciation of the complex ion [VO(nta)(im)]- in an aqueous solution. Furthermore, the influence of imidazole as an auxiliary ligand (im) in the coordination sphere of V(IV) is investigated in terms of its effects on ABTS+• radical scavenging activity and cytoprotective properties against oxidative damage in the hippocampal neuronal HT22 cell line. Finally, this study compares and discusses the physicochemical properties and biological activities of the newly synthesised compound and those containing [VO(nta)(H2O)]- complex anions.

Electrochemical aptasensors based on porous carbon derived from graphene oxide/ZIF-8 composites for the detection of Erwinia cypripedii

In this research, self-screening aptamer and MOFs-derived nanomaterial have been combined to construct electrochemical aptasensor for environmental detection. By utilizing the large specific surface area of reduced graphene oxide (rGO), ZIF-8 was grown in situ on surface of rGO, and the composites was pyrolyzed to obtain MOFs-derived porous carbon materials (rGO-NCZIF). Thanks to the synergistic effect between rGO and NCZIF, the complex exhibits remarkable characteristics, including a high electron transfer rate and electrocatalytic activity. In addition, the orderly arrangement of imidazole ligands within ZIF-8 facilitated the uniform doping of nitrogen elements into the porous carbon, thereby significantly enhancing its electrochemical performance. After carboxylation, rGO-NCZIF was functionalized with self-screening aptamer for fabricating electrochemical aptasensor, which can be used to detect Erwinia cypripedii, a kind of quarantine plant bacteria, with detection limit of 4.92 × 103 cfu/mL. Due to the simplicity and speed, the aptasensor is suitable for rapid customs inspection and quarantine. Additionally, the universality of this sensing strategy was verified through exosomes detection by changing the aptamer. The results indicated that the rGO-NCZIF-based electrochemical aptasensor had practical value in the environmental and medical fields.

Improved Mechanical Strength without Sacrificing Li-Ion Transport in Polymer Electrolytes.

Next-generation batteries demand solid polymer electrolytes (SPEs) with rapid ion transport and robust mechanical properties. However, many SPEs with liquid-like Li+ transport mechanisms suffer a fundamental trade-off between conductivity and strength. Dynamic polymer networks can improve bulk mechanics with minimal impact to segmental relaxation or ionic conductivity. This study demonstrates a system where a single polymer-bound ligand simultaneously dissociates Li+ and forms long-lived Ni2+ networks. The polymer comprises an ethylene oxide backbone and imidazole (Im) ligands, blended with Li+ and Ni2+ salts. Ni2+-Im dynamic cross-links result in the formation of a rubbery plateau resulting in, consequently, storage modulus improvement by a factor of 133× with the introduction of Ni2+ at rNi = 0.08, from 0.014 to 1.907 MPa. Even with Ni2+ loading, the high Li+ conductivity of 3.7 × 10-6 S/cm is retained at 90 °C. This work demonstrates that decoupling of ion transport and bulk mechanics can be readily achieved by the addition of multivalent metal cations to polymers with chelating ligands.

Effect of Boron-Doping on Gate-Opening CO2 Adsorption in Zinc-Benzimidazolate Coordination Networks.

Flexible metal-organic frameworks (MOFs) have attracted much attention as selective gas adsorption and storage. This report describes boron doping in zeolitic imidazolate framework-7 (B-ZIF-7), which exhibits reversible phase transition during CO2 adsorption/desorption. We have successfully prepared B-ZIF-7 coordination networks using boron-bridged benzimidazolate (B(bim)4-) as organic ligands. Powder X-ray diffraction (PXRD) measurements and infrared spectroscopy revealed that B-ZIF-7 has a crystal structure similar to that of ZIF-7 while containing boron bridging in the coordination network. Since B-ZIF-7 forms a cationic coordination network, the guest anions are encapsulated within the pore. CO2 adsorption/desorption measurements at 300 K showed that B-ZIF-7(NO3), which contains nitrate ions (NO3-) as guest anions in its pores, exhibits a S-shaped CO2 adsorption/desorption isotherm, which is characteristic of gate-opening type MOFs. Compared with ZIF-7, B-ZIF-7(NO3) has superior CO2 adsorption capacity in the low-pressure and superior CO2 storage capacity. The CO2 adsorption and desorption behavior of B-ZIF-7(NO3) was analyzed by in situ temperature-controlled PXRD measurements and thermogravimetric analysis under a CO2 atmosphere, and a reversible phase transition was observed. We have also successfully prepared B-ZIF-7(Cl) and B-ZIF-7(OTf) (OTf = CF3SO3-) with different guest anions. The CO2 adsorption/desorption behaviors of B-ZIF-7(Cl) and B-ZIF-7(OTf) were significantly different from those of B-ZIF-7(NO3) and ZIF-7. B-ZIF-7(Cl) showed gate opening at a higher pressure than ZIF-7, and B-ZIF-7(OTf) did not show S-shaped CO2 adsorption isotherm and showed adsorption behavior in micropores. These results indicate that the CO2 adsorption behavior of B-ZIF-7 depends on the interaction between the guest anions and CO2 molecules or the cationic framework and the bulkiness of the guest anions. Boron doping in a coordination network with boron-bridged imidazolate ligands is a promising strategy to increase the gas adsorption capability of porous materials.

Synthesize and Characterization of Pt-supported Co-ZIF for Catalytic Hydrocracking and Hydroisomerization of n-Hexadecane

Zeolitic Imidazole Frameworks (ZIFs) are prospective porous materials as catalyst support due to their relatively large surface area, and tunability in size, structure, and porosity. Recent studies have also shown that ZIF is the best candidate for various catalytic redox reactions such as the oxidation of benzyl aromatic hydrocarbons. In this study, the synthesized Pt catalyst supported on Co-ZIF was varied by the organic ligands: imidazole, benzimidazole, and 1-(3-aminopropyl) imidazole, then followed by impregnation of Pt precursor. The catalysts were characterized its physical and chemicals properties such as Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Brunauer Emmet Teller (BET), Temperature-Programmed Desorption (NH3-TPD and CO2-TPD). The prepared catalysts were evaluated for catalytic hydrocracking and hydroisomerization of n-hexadecane in a 100 ml-batch reactor. GC-MS analysis presented that the Pt/ZIF catalyst with imidazole ligands has better performance than others. Hence, the optimization of n-Hexadecane conversion was carried out by the Pt/ZIF-imidazole catalyst varying the amount of metal loading, time and temperature reaction. The results showed that the reaction temperature of 350 ºC using 20 bar H2 for 4 h and the addition of 15 wt% Pt successfully achieved 90.77% conversion and produced the highest yield of isomers and alkanes, 4.04% and 35.75%, respectively. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Zn(II)-Coordination Polymers Constructed from Isomeric Bis(Imidazole) Derivative Ligands and Tetracarboxylic Acid for the Detection of Iron Ions

Three Zn(II)-coordination polymers, namely, {[Zn2(µ4-L)(µ-obix)2]·4DMF}n (1), {[Zn2(µ4-L)(µ-mbix)2]·6H2O}n (2) and {[Zn2(µ4-L)(µ-pbix)2]·5H2O}n (3), (L4−: 5,5’-(terephthaloylbis(azanediyl))diisophthalate and obix (y = 2), mbix (y = 3), pbix (y = 4): 1,y-bis((1H-imidazol-1-yl)methyl)benzene) were prepared with a tetracarboxylic acid and flexible isomeric bis(imidazole) linkers and characterized. The compounds displayed structural diversity depending on the rotation of imidazole rings around the –CH2- groups on bis(imidazole) ligands. Compounds 1–3 showed 2-fold interpenetrated 3D framework, 2D structure and 3D framework, respectively. The compounds showed high emissions in solid-state and solutions. Luminescence experiments showed that compounds 1–3 displayed sensitive detection towards Fe3+ ions with detection limits of 2.31 ppm, 5.17 ppm and 2.61 ppm, respectively. Moreover, the compounds could selectively detect Fe3+ ions over the other interfering metal ions via luminescence quenching. The detection mechanism could be ascribed to the competitive light absorption between Fe3+ ions and the compounds.

Pore size regulation of ZIFs for adsorptive separation of branched chain and aromatic amino acids

AbstractThis research endeavour aims to investigate the adsorptive separation of the branched chain (BCAA) and aromatic amino acids (AAA). Based on the different molecular sizes of BCAA and AAA, zeolitic imidazolate frameworks (ZIFs) with different pore structures were prepared by regulating the size of imidazole ligands. The structure and pore shape were characterized by Fourier transform infrared spectroscopy (FT‐IR), x‐ray diffraction (XRD), scanning electron microscope (SEM), and BET surface area (BET). The results indicated the successful synthesis of ZIF‐[Co(mIm)2], ZIF‐[Co(eIm)2], and ZIF‐[Co(pIm)2] with pore size distribution of 7.821, 6.943, and 9.394 Å, and particle size of these ZIFs was approximately 4 μm. ZIF‐[Co(eIm)2] was chosen as the optimal ZIFs for the separation of BCAA and AAA. The adsorption experiment was evaluated in the respective single and binary systems. The corresponding data in a single system demonstrated that ZIF‐[Co(eIm)2] showed good adsorption performance for BCAA and poor for AAA. Furthermore, the adsorption behaviour under experimental conditions conformed well to the pseudo‐second‐order kinetic model and Langmuir isotherm. ZIF‐[Co(eIm)2] had great separation ability for BCAA/AAA in their binary system. Finally, regeneration studies further manifested that ZIF‐[Co(eIm)2] exhibited fine reusability performance with adsorption efficiencies still higher than 70% after five cycles. This study exhibits a novel path for the design of adsorbents for efficient separation of BCAA/AAA.

Structure of the five-coordinate CoII complex (1H-imidazole){tris-[(1-benzyl-triazol-4-yl-κN3)meth-yl]amine-κN}cobalt(II) bis-(tetra-fluoro-borate).

The title compound, [Co(C3H4N2)(C30H30N10)](BF4)2, is a five-coordinate CoII complex based on the neutral ligands tris-[(1-benzyl-triazol-4-yl)meth-yl]amine (tbta) and imidazole. It exhibits a distorted trigonal bipyramidal geometry in which the equatorial positions are occupied by the three N-atom donors from the triazole rings of the tripodal tbta ligand. The apical amine N-atom donor of tbta and the N-atom donor of the imidazole ligand occupy the axial positions of the coordination sphere. Two tetra-fluoro-borate anions provide charge balance in the crystal.

Design, synthesize, physicochemical characterization, nonlinear optical properties structural elucidation, biomedical studies, and DNA interaction of some new mixed ligand complexes incorporating 4,6‐dimethylpyrimidine derivative and imidazole ligand

This study was planned to prepare new mixed ligand chelates derived from N‐(4,6‐dimethylpyrimidin‐2‐yl)‐3a,4,5,6,7,7a‐hexahydro‐1H‐benzimidazol‐2‐amine (BIP), and imidazole (I). They identified through CHN study, spectroscopic (NMR, FT‐IR, and UV–Vis), conductivity, magnetic susceptibility, mass analysis, and thermal analysis. Correlation between all results exposed that the BIP ligand performed as a bi‐dentate ligand through NN donation locations, where the co‐ligand shows as N–H monodentate. The optimization for the studied chelates led to the formation of distorted octahedral geometry for BIPICu and BIPIVO chelates, distorted (tetrahedral and square planar) geometry for BIPIAg and BIPIPd chelates, respectively, around the metal salt. The B3LYP level, B3LYP/6‐311G** level for the free ligand, and B3LYP/6–311G**‐LANL2DZ functional level for the solid chelates were used in density functional theory (DFT) calculations. The findings showed that DFT calculations produce conclusions that are consistent with those of the experiments. The resulting compounds' nonlinear optical properties were examined by calculating the hyperpolarizability (β) and molecular polarizability (α) parameters, which gave rise to several unexpected optical properties for the synthesized compounds. Using the agar well diffusion method, the antimicrobial activity of the produced compounds was experimentally confirmed against a subset of G+ and G− bacteria. To ascertain how these substances attach to the targeted protein binding sites, a molecular docking mechanism between the microbially resistant chelates and their suppressed microbial protein pocket receptors was investigated. Also, DNA binding estimated for studied structures was tested by electronic absorption spectrum, viscosity estimation, and gel electrophoresis. Data proposed that all tested compounds link with DNA using an intercalation, electrostatic, and covalent binding mechanism. Moreover, antioxidant performance for studied compounds was governed by radical scavenging techniques in vitro. In addition, an MTT assay has been worked out to explore in vitro cytotoxic impending. All the tested chelates assumed antimicrobial, antitumor, and antioxidant performances that cause them to suggest drugs.

Discovery of novel dihydronaphthalene—imidazole ligands as potential inhibitors of Staphylococcus aureus multidrug resistant NorA efflux pump: A combination of experimental and in silico molecular docking studies

Overexpression of the efflux pump is a predominant mechanism by which bacteria show antimicrobial resistance (AMR) and leads to the global emergence of multidrug resistance (MDR). In this work, the inhibitory potential of library of dihydronapthyl scaffold-based imidazole derivatives having structural resemblances with some known efflux pump inhibitors (EPI) were designed, synthesized and evaluated against efflux pump inhibitor against overexpressing bacterial strains to study the synergistic effect of compounds and antibiotics. Out of 15 compounds, four compounds (Dz-1, Dz-3, Dz-7, and Dz-8) were found to be highly active. DZ-3 modulated the MIC of ciprofloxacin, erythromycin, and tetracycline by 128-fold each against 1199B, XU212 and RN4220 strains of S. aureus respectively. DZ-3 also potentiated tetracycline by 64-fold in E. coli AG100 strain. DZ-7 modulated the MIC of both tetracycline and erythromycin 128-fold each in S. aureus XU212 and S. aureus RN4220 strains. DZ-1 and DZ-8 showed the moderate reduction in MIC of tetracycline in E. coli AG100 only by 16-fold and 8-fold, respectively. DZ-3 was found to be the potential inhibitor of NorA as determined by ethidium bromide efflux inhibition and accumulation studies employing NorA overexpressing strain SA-1199B. DZ-3 displayed EPI activity at non-cytotoxic concentration to human cells and did not possess any antibacterial activity. Furthermore, molecular docking studies of DZ-3 was carried out in order to understand the possible binding sites of DZ-3 with the active site of the protein. These studies indicate that dihydronaphthalene scaffolds could serve as valuable cores for the development of promising EPIs.

Can Iron-Porphyrins Behave as Single-Molecule Magnets?

The study of magnetic properties, especially the magnetic anisotropy of iron-porphyrin complexes employing multiconfigurational methods, is quite challenging due to many strongly correlated electrons in nearly degenerate orbitals. However, a prerequisite for observing the magnetic anisotropy and slow magnetization relaxation, the zero-field splitting parameter, D, was experimentally observed decades ago for halide-based axially ligated penta-coordinate Fe(III)-porphyrins. In these complexes, the signs of D were reported mostly as positive; in a few cases, inconclusive signs of the D parameter were also mentioned. However, no ab initio calculations have been reported to shed light on this. Deciphering the electronic structure of these penta-coordinated complexes employing the complete active space self-consistent field method and N-electron valence second-order perturbation theory, we confirm the positive D values. However, a negative D value is highly desired to observe the single-molecule magnet properties without an external magnetic field, which we observed in the Fe(II)-porphyrin complexes with axial imidazole ligands instead of halide ligands. The detailed analysis of the multireference wave functions unravels the role of axial ligands in determining the sign and magnitude of the D parameters.

Application of lithium modified ZIF-90 in a hybrid absorption-adsorption method for carbon capture

Herein, a lithium modified Zeolitic Imidazolate Framework-90 (ZIF-90-OLi) was used in a slurry with its organic ligand Imidazole Carboxaldehyde (ICA) water, and glycol to improve the process conditions for the capture system and enhance the sorption ability. The performance of this slurry was compared to two other slurries, one based on the parent ZIF-90 nanoporous material with ICA/water/glycol and another based on ZIF-8, its organic ligand Methylimidazole (MIm) and water/glycol. The comparison to ZIF-8 was done because of its use as a ZIF of reference in carbon capture. The maximum sorption capacity for CO2 by the alkali containing slurry was 7.19 mol/L and the maximum CO2/N2 selectivity was 222.93 compared to 2.72 mol/L and 121.63 for the ZIF-8/water/glycol/mlm slurry.

Tailoring the adsorption properties of imidazole-based halogen bonded organic frameworks for anionic dye removal

A novel class of [N⋯I⋯N]+ halogen-bonded XOFs were synthesized using imidazole ligands. XOF-TIB showed strong adsorption capacity and selectivity for anionic dyes, with excellent stability and reusability for environmental remediation.

First-principles study of molecular hydrogen binding to heme in competition with O2, NO and CO.

Molecular hydrogen shows antioxidant activity and distinct efficacy towards vascular diseases, but the understanding of this is not yet satisfactory at the atomic level. In this work, we study the binding properties of H2 to the heme group in relation with other diatomic molecules (DMs), including O2, NO and CO, and their displacement reactions, using first-principles calculations. We carry out molecular modeling of the heme group, using iron-porphyrin with the imidazole ligand, i.e., FePIm, and smaller models of Fe(CnHn+2N2)2NH3 with n = 3 and 1, and of molecular complexes of heme-DM and -H. Through analysis of optimized geometries and energetics, it is found that the order of binding strength of DMs or H to the Fe of heme is NO > O2 > CO > H > H2 for FePIm-based systems, while it is H > O2 > NO > CO > H2 for model-based systems. We calculate the activation energies for displacement reactions of H2 and H by other DMs, revealing that the H2 displacements occur spontaneously while the H displacements require a large amount of energy. Finally, our calculations corroborate that the rate constants increase with increasing temperature according to the Arrhenius relation.

A copper(ii) metal–organic framework with 2,2-dimethylglutarate and imidazole ligands: synthesis, characterization and catalytic performance for cycloaddition of CO2 to epoxides

A new 3D framework with the general formula {[Cu(μ3-dmg)(im)2]·3H2O}n (1) was synthesized using an aliphatic dicarboxylic acid linker 2,2-dimethylglutarate (dmg2−) and nitrogen-containing imidazole ligand (im) under conventional methods.

Tuning the product selectivity of single-atom catalysts for CO2 reduction beyond CO formation by orbital engineering.

Electrochemical CO2 reduction (CO2R) is one of the promising strategies for developing sustainable energy resources. Single-atom catalysts (SACs) have emerged as efficient catalysts for CO2R. However, the efficiency of SACs for the formation of reduction products beyond two-step CO formation is low due to the lower binding strength of the CO intermediate. In this study, we present an orbital engineering strategy based on density functional theory calculations and the fragment molecular orbital approach to tune product selectivity for the CO2R reaction on macrocycle based molecular catalysts (porphyrin and phthalocyanine) and extended SACs (graphene and covalent organic frameworks) with Fe, Co, and Ni dopants. The introduction of neutral axial ligands such as imidazole, pyridine, and trimethyl phosphine to the metal dopants enhances the binding affinity of the CO intermediate. The stability of the catalysts is investigated through the thermodynamic binding energy of the axial ligands and ab initio molecular dynamics simulations (AIMD). The grand canonical potential method is used to determine the reaction free energy values. Using a unified activity volcano plot based on the reaction free energy values, we investigated the catalytic activity and product selectivity at an applied potential of -0.8 V vs. SHE and a pH of 6.8. We found that with the imidazole and pyridine axial ligands, the selectivity of Fe-doped SACs towards the formation of the methanol product is improved. The activity volcano plot for these SACs shows a similar activity to that of the Cu (211) surface. The catalytic activity is found to be directly proportional to the sigma-donating ability of the axial ligands.

Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands.

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

Copper(i) and cobalt(ii) frameworks with a tetraphenylethene–imidazole ligand for the electroreduction of CO2 to CH4

Two new MOFs with different metal centers were synthesized and applied to the electroreduction of CO2. Cu-MOF was found to show the capacity for the electrocatalytic conversion of CO2 to CH4, while Co-MOF is unsuitable due to its low stability.