Imidazole Complexes Research Articles

Synthesis, Crystal Structure, Spectroscopic and Antimicrobial Properties of Ruthenium Complexes of Vinyl Imidazole and 4-Ethylaminomethyl Pyridine Ligands

Ruthenium complexes of vinylimidazole (VIMD) and 4-ethylaminomethyl pyridine (EMP) ligands were synthesized and characterized by XRD and spectroscopic methods. The binding of these Ru(IIII) complexes with calf thymus-DNA has been studied by UV-visible spectroscopic and electrochemical studies. A prominent increase in the intensity of fluorescence spectra of these complexes with CT-DNA was observed and a distinct UV-visible spectral shift in presence of CT-DNA is probably due to an interaction of these complexes with CT-DNA. The evidence of DNA binding has been found from the change in the intensity of fluorescence and UV visible spectra. Also, the electron transfer ability of these complexes is very important in order to rationalize their activity towards the biological system therefore, we have studied the electrochemical studies of these complexes by using cyclic voltammetry. From this study, it is possible to draw some ideas on electrochemical potentials of the complexes relevant to biological reduction possibly Ru(III)/Ru(II). Both complexes were also tested for antimicrobial activity against bacterial strain and responses well as antimicrobial agent.

A Cu-bis(imidazole) Substrate Intermediate Is the Catalytically Competent Center for Catechol Oxidase Activity of Copper Amyloid-β.

Interaction of copper ions with Aβ peptides alters the redox activity of the metal ion and can be associated with neurodegeneration. Many studies deal with the characterization of the copper binding mode responsible for the reactivity. Oxidation experiments of dopamine and related catechols by copper(II) complexes with the N-terminal amyloid-β peptides Aβ16 and Aβ9, and the Aβ16[H6A] and Aβ16[H13A] mutant forms, both in their free amine and N-acetylated forms show that efficient reactivity requires the oxygenation of a CuI-bis(imidazole) complex with a bound substrate. Therefore, the active intermediate for catechol oxidation differs from the proposed “in-between state” for the catalytic oxidation of ascorbate. During the catechol oxidation process, hydrogen peroxide and superoxide anion are formed but give only a minor contribution to the reaction.

Detailed Insight into the Interaction of Bicyclic Somatostatin Analogue with Cu(II) Ions.

Somatostatin analogues are useful pharmaceuticals in peptide receptor radionuclide therapy. In previous studies, we analyzed a new bicyclic somatostatin analogue (BCS) in connection with Cu(II) ions. Two characteristic sites were present in the peptide chain: the receptor- and the metal-binding site. We have already shown that this ligand can form very stable imidazole complexes with the metal ion. In this work, our aim was to characterize the intramolecular interaction that occurs in the peptide molecule. Therefore, we analyzed the coordination abilities of two cyclic ligands, i.e., P1 only with the metal binding site and P2 with both sites, but without the disulfide bond. Furthermore, we used magnetic circular dichroism (MCD) spectroscopy to better understand the coordination process. We applied this method to analyze spectra of P1, P2, and BCS, which we have described previously. Additionally, we analyzed the MCD spectra of P3 ligand, which has only the receptor binding site in its structure. We have unequivocally shown that the presence of the Phe-Trp-Lys-Thr motif and the disulfide bond significantly increases the metal binding efficiency.

Molecular Scylla and Charybdis: Maneuvering between pH Sensitivity and Excited-State Localization in Ruthenium Bi(benz)imidazole Complexes.

Bi(benz)imidazoles (b(b)im) acting as N,N-chelates in ruthenium complexes represent a unique class of ligands. They do not harbor metal-to-ligand charge-transfer (MLCT) excited states in ruthenium polypyridyl complexes upon visible-light excitation provided that no substitution is introduced at the N atoms. Hence, they can be used to steer light-driven electron-transfer pathways in a desired direction. Nonetheless, the free N atoms are susceptible to protonation and, hence, introduce highly pH-dependent properties into the complexes. Previous results for ruthenium complexes containing R2bbim ligands with alkylic or arylic N,N'-substitution indicated that, although pH insensitivity was accomplished, unexpected losses of spectator ligand features incurred simultaneously. Here, we report the synthesis and photophysical characterization of a series of differently N,N'-alkylated b(b)im ligands along with their corresponding [(tbbpy)2Ru(R2b(b)im)](PF6)2 complexes (tbbpy = 4,4'-tert-butyl-2,2'-bipyridine). The data reveal that elongation of a rigid ethylene bridge by just one methylene group drastically increases the emission quantum yield, emission lifetime, and photostability of the resultant complexes. Quantum-chemical calculations support these findings and allow us to rationalize the observed effects based on the energetic positions of the respective excited states. We suggest that N,N'-propylene-protected 1H,1'H-2,2'-biimidazole (prbim) is a suitable spectator ligand because it stabilizes sufficiently long-lived MLCT excited states exclusively localized at auxiliary bipyridine ligands. This ligand represents, therefore, a vital building block for next-generation photochemical molecular devices in artificial photosynthesis.

Role of MLCT States in the Franck-Condon Region of Neutral, Heteroleptic Cu(I)-4H-imidazolate Complexes: A Spectroscopic and Theoretical Study.

The impact of the electronic structure of a series of 4H-imidazolate ligands in neutral, heteroleptic Cu(I) complexes is investigated. Remarkable broad and strong ligand-dependent absorption in the visible range of the electromagnetic spectrum renders the studied complexes promising photosensitizers for photocatalytic applications. The electronic structure of the Cu(I) complexes and the localization of photoexcited states in the Franck-Condon region are unraveled by means of UV-vis absorption and resonance Raman (rR) spectroscopy supported by time-dependent density functional theory (TD-DFT) calculations. The visible absorption bands stem from a superposition of bright metal-to-ligand charge-transfer (MLCT) and π-π* as well as weakly absorbing MLCT states. Additionally, the analysis of involved molecular orbitals and rR spectra upon excitation of MLCT and π-π* states highlights the impact of the electronic structure of the 4H-imidazolate ligands on the properties of the corresponding Cu(I) complexes to avail a toolbox for predictive studies and efficient complex design.

Rhodium(III) complexes of 1-Alkyl-2-{(o-thioalkyl) phenylazo}imidazoles: synthesis, structure, spectral characterization, DNA binding study and DFT calculation

The Rh(III) complexes of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SRaaiNR′, 1; R = R′= Me (a); R = Me, R′= Et (b); R = Et, R′= Me (c); R = R′= Et (d)), [Rh(SRaaiNR′)(PPh3)Cl2](ClO4) (2) have been synthesized. The complexes have been characterized by physicochemical and spectroscopic methods. The single-crystal X-ray diffraction study authenticates the structure of [Rh(SMeaaiNEt)(PPh3)Cl2](ClO4) (2b). The DNA binding ability of the complexes has been investigated by electronic absorption and fluorescence spectroscopic methods. Density functional theory computation technique has been used to enlighten the electronic structures and their spectral properties. 1-Alkyl-2-{(o-thioalkyl)phenylazo}imidazole complexes of Rh(III), [Rh(SRaaiNR′)(PPh3)Cl2](ClO4)](2) are synthesized and characterized. [Rh(SMeaaiNEt)(PPh3)Cl2](ClO4) (2b) is characterized by single-crystal X-ray diffraction study. Ligand acts as tridentate N(imidazole), N(azo) and S(thioether) donor centers. The DNA binding ability of the complexes is investigated by electronic absorption and fluorescence spectroscopic methods. The electronic structure and observed electronic transitions are interpreted by DFT and TDDFT computation.

Manganese (II)-imidazole complexes of the non-steroidal anti-inflammatory drug mefenamic acid: Synthesis, and structural studies

Two new complexes of Mn(II) have been synthesized with a non-steroidal anti-inflammatory drug, mefenamic acid, 2-[(2,3-dimethylphenyl)amino]benzoic acid (mef) and the nitrogen donor ligands; imidazole (imi) and 2-methylimidazole (mei), viz. [Mn(mef)2(imi)2(EtOH)2]; M−1 and [Mn(mef)2(mei)2(EtOH)2]; M−2. Also, when mefenamic acid interacted with MnCl2·4H2O in the presence of 2-aminopyridine (apy), a salt of ((mef)(apy)(H2O)); M−3 was isolated. The complexes were characterized using elemental analysis, FTIR, UV–Visible (M−1 and M−2), and single-crystal X-ray diffraction studies. Monodentate coordination of the mefenamate ligand in M−1 and M−2 was confirmed from the FTIR studies. The X-ray structural analysis shows that the two Mn(II) complexes and one salt crystallize in the triclinic space group P-1. M−1 consists of monomeric Mn(II) in hexacoordination with two monodentate mefenamate, two imidazoles, and two ethanol solvent ligands. M−2 consists of monomeric Mn(II) complex in octahedral geometry and coordinated to two each of monodentate mefenamate, 2-methylimidazole, and two ethanol solvent ligands. M−3 consists of salt of mefenamate anion linked to an aminopyridinium cation, with a hydrogen-bonded water molecule present in the crystal lattice which connects the cation and anion via intermolecular OH···O and NH···O interactions.

Imidazole and Benzimidazole Modified Half-Sandwich IridiumIII N-Heterocyclic Carbene Complexes: Synthesis, Anticancer Application, and Organelle Targeting.

Herein, we report the synthesis, characterization and anticancer activity of a series of half-sandwich iridiumIII imidazole and benzimidazole N-heterocyclic carbene (NHC) anticancer complexes, and the general formula of which can be expressed as [(η5-Cpx)Ir(C∧N)Cl]Cl (Cpx: pentamethylcyclopentadienyl (Cp*) or biphenyl derivatives (Cpxbiph); C∧N: imidazole and benzimidazole NHC chelating ligands). Compared with cis-platin, these complexes showed interesting antitumor activity against A549 cells. Complexes could bind to bovine serum albumin (BSA) by means of static quenching mode, catalyze the oxidation of nicotinamide adenine dinucleotide (NADH) and increase the levels of reactive oxygen species (ROS). Meanwhile, these complexes could arrest the cell cycles of A549 cells and influence the mitochondrial membrane potential significantly. Due to the inherent luminescence property, laser confocal test show that complexes could enter cells followed an energy-dependent mechanism and effectively accumulate in lysosome (the value of Pearson's co-localization coefficient is 0.70 after 1 h), further destroy lysosome integrity and induce apoptosis.

Development of a fluorescent chemosensor for chloride ion detection in sweat using Ag+-benzimidazole complexes

The level of chloride ions (Cl⁻) in sweat is a recognized biomarker for the genetic disorder cystic fibrosis (CF). The accurate quantitation of chloride ions in sweat is therefore a vital diagnostic tool for this life-threatening disease. In this work, a fluorescent, chloride ion chemosensor was developed by exploiting the strong interaction between silver (Ag+) and chloride ions. Using the concept of ligand displacement, six Ag+-benzimidazole complexes were prepared as candidate chloride ion chemosensors. The Ag+-2-(Furan-2-yl)-1H-benzo[d]imidazole (Ag+-FBI) complex was identified as the optimal sensor owing to its Ag+-FBI high sensitivity (limit of detection = 19 μM), short response time (<3 min), and remarkable fluorescence turn-on response across a broad pH range (pH 6–9). The Ag+-FBI complex exhibited high selectivity for Cl⁻ ions and was successfully used to quantify chloride ions in artificial sweat samples containing multiple ions and other biological constituents. This unique, simple, and effective probe thus shows great potential for clinical diagnostic applications.

Thermodynamic, spectroscopic and biological investigation of interaction of anionic surfactants with [Cu(im)6]F2·4H2O complex in aqueous solution

Present study describes the physicochemical behavior of the coordination complex of copper i.e. [Cu(im)6]F2.4H2O (Hexakis(imidazole)copper(II) fluoride tetrahydrate) and its solubilization by anionic surfactants sodium dodecyl sulphate (SDS) and sodium stearate (SS). The detailed investigation was accomplished by electrical conductivity measurements and UV–visible spectroscopy in aqueous solutions of anionic surfactants in the sub micellar and micellar concentration ranges. Furthermore, thermodynamic parameters of complex-surfactant interaction and CMC of both surfactants in the presence of copper imidazole complex were evaluated by electrical conductivity and experimental results revealed an increase in CMC of both surfactants in the presence of complex. CMC increases with rise in temperature and the trend of variation in thermodynamic parameters indicates that the solubilization of copper imidazole complex in micelles of both surfactants is spontaneous and enthalpy as well as entropy driven. Spectroscopic investigation indicates high degree of solubilization and strong interaction in case of complex and SDS than for SS.

A new approach to the synthesis of trinuclear gold(i) imidazolate complexes and their silver(i)-induced photoluminescence behavior.

New trinuclear gold(i) N-arylimidazolate cluster complexes have been synthesized from cationic [Au(CNR)2]+ isocyanide complexes and their structure and photoluminescence behavior have been compared with those of their 1-methylimidazolate counterpart. A drastic change in their photophysical properties was observed upon coordination of the Ag+ cation.

Inhibition of 3D colon cancer stem cell spheroids by cytotoxic RuII-p-cymene complexes of mesalazine derivatives.

The Ru(ii) complex of an imidazole-mesalazine Schiff base is a unique example showing growth inhibition of 3D-colon cancer stem cell spheroids and bulk colon cancer cells at lower dosage than salinomycin or oxaliplatin. Unlike oxaliplatin which increases the expression of stemness genes (SOX2, KLF4, HES1 and Oct4), these complexes maintain a tight regulation.

Synthesis, X-ray crystallography, spectroscopic and in vitro antimicrobial studies of a new Cu(II) complex of trichloroacetic acid and imidazole

Cu(II) complex with trichloroacetic acid and imidazole have been synthesized and characterized by elemental analysis, Uv–Vis, FTIR and single crystal X-ray crystallographic analysis. The compound was synthesized through green synthetic route by simply grinding and dissolving the homogenous mixture of the three components in distilled water at room temperature. The newly synthesized Cu(II) complex crystallized in monoclinic crystal system with C2/c space group. The Cu is in a square planar milieu formed by oxygen atoms from four trichloroacetato ligands. The chlorine atoms are disordered. The imidazole molecules are not directly bonded to the Cu but hydrogen bonding exist between the imidazole and the Cu(II) tetratrichloroacetato complex. The Cu(II) complex shows a significant activity when tested against selected bacteria and fungi compared to its parent ligands.

Cucurbit[8]uril-Mediated Polypseudorotaxane for Enhanced Lanthanide Luminescence Behavior in Water.

A novel supramolecular polypseudorotaxane was successfully constructed with pseudo[3]rotaxanes between pyridine-2,6-dicarboxylic acid imidazolium (G1) and cucurbit[8]uril (CB[8]) and the subsequent coordination with lanthanide ions. Significantly, compared with the pyridine-2,6-dicarboxylic acid imidazolium complex G1@Tb3+, CB[8]-mediated polypseudorotaxane CB[8]@G12@Tb3+ not only displayed enhanced lanthanide luminescence behavior with a 29.1-fold time enhancement (from 45.76 μs to 1.33 ms) of the excited-state lifetime (τ) and a 8.7-fold increase (from 0.89% to 7.81%) in the quantum yield (Φ) but also exhibited a specific fluorescence response to antibiotics in an aqueous solution and a solid film.

Preparation, Charecterazation of new nitro-chalcone azo ligands and their divalent ionic complexes

In this study two of nitro-chalcone azo ligands were synthesized via the reaction of the diazonium salt of amino p-nitro chalcone (pNAC) with the coupling components (4,5-diphenylimidazole &2-naphthol) respectively.The new ligands were charecterized with many identificational tools such (H1NMR,FTIR and UV-Visible) spectroscopies, in addation to (CHNO)analysis for ensurance of the preparation of these ligands.A UV-Visible study for the aqueous mixtures of three divalent metal ions (Co,Ni and Cu) were perfomed to determination of the (λmax) of their colored mixtures, also to confirm the solid complexes structures via the determination of the suitable mole ratio (M:L), that all complexes mole ratios were (1:2, M:L). The solid complexes were synthesized and characterized by the obvious techniques, indeed, to the complementary techniques such (electrical conductivity, magnetic susceptibility) for determination of the complex formula and suggested their geometries, from the whole results, octahedral geometry can conculded for nitro chalcone azo imidazole complexes with the observation of the ionic characteristic of its, while the second ligand complexes differ from tetrahedral for (Co & Cu) complexes and square planer for nickel complex.

Modeling Solid State Stability for Speciation: A Ten-Year Long Study.

Speciation studies are based on fundamental models that relate the properties of biomimetic coordination compounds to the stability of the complexes. In addition to the classic approach based on solution studies, solid state properties have been recently proposed as supporting tools to understand the bioavailability of the involved metal. A ten-year long systematic study of several different complexes of imidazole substituted ligands with transition metal ions led our group to the definition of a model based on experimental evidences. This model revealed to be a useful tool to predict the stability of such coordination complexes and is based on the induced behavior under thermal stress. Several different solid state complexes were characterized by Thermally Induced Evolved Gas Analysis by Mass Spectrometry (TI-EGA-MS). This hyphenated technique provides fundamental information to determine the solid state properties and to create a model that relates stability to coordination. In this research, the model resulting from our ten-year long systematic study of complexes of transition metal ions with imidazole substituted ligands is described. In view of a systematic addition of information, new complexes of Cu(II), Zn(II), or Cd(II) with 2-propyl-4,5-imidazoledicarboxylic acid were precipitated, characterized, and studied by means of Thermally Induced Evolved Gas Analysis performed by mass spectrometry (TI-EGA-MS). The hyphenated approach was applied to enrich the information related to thermally induced steps, to confirm the supposed decomposition mechanism, and to determine the thermal stability of the studied complexes. Results, again, allowed supporting the theory that only two main characteristic and common thermally induced decomposition behaviors join the imidazole substituted complexes studied by our group. These two behaviors could be considered as typical trends and the model allowed to predict coordination behavior and to provide speciation information.

Electronic structure and spectral characteristics of alkyl substituted imidazolium based dication-X2 (X = Br, BF4, PF6 and CF3SO3) complexes from theory

Electronic structure, cation-anion binding and spectral characteristics of the alkyl substituted imidazolium dication and Br−, BF4−, PF6− or CF3SO3− anion complexes have been obtained employing the M06-2X based density functional theory. The dication-anion complexes serve as model systems for describing dicationic ionic liquids and are facilitated by electrostatic, bifurcated hydrogen bonding (C-H⋯O) and anion---π interactions. The lowest energy conformer possesses relatively strong interactions from reactive vinylic protons on the imidazolium cation whereas the largely destabilized conformers reveal increasing contributions to binding from the interactions arising from by ethyl/butyl substituents at the expense of strong hydrogen bonding from vinylic protons on the imidazolium moiety. Underlying dication-anion binding has been probed through quantum theory of atoms in molecules (QTAIM) approach and the natural bond orbital analyses. It has been predicted that binding energies in the lowest energy complexes of the methyl substituted imidazolium complex emerge with a hierarchy: Br− > BF4− > CF3SO3− > PF6−, which is qualitatively different from that of butyl substituted complexes; the latter revealing stronger binding with CF3SO3− anion. The reactive vinylic proton engenders largely downfield δH signals (beyond 8.8 ppm) in their 1H NMR spectra. It has been further shown that hydrogen bond energies of the reactive proton (H1) estimated from the QTAIM theory correlate well with the 1H NMR chemical shifts measured from the experiments. The ramifications of dication-anion binding to vibrational spectra are also presented.

An Undergraduate Experiment To Explore Cu(II) Coordination Environment in Multihistidine Compounds through Electron Spin Resonance Spectroscopy

Electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy is an incisive technique for the characterization of paramagnetic centers in inorganic, bioinorganic, and organic molecules and materials. These measurements are enabled with the help of paramagnetic species, such as organic free radicals and ions, electronically excited states, and metal–ligand compounds, some of which with biological importance. In this experiment, analogues of histidine–copper coordination compounds are investigated to show students how ESR line shapes depend on the complexed copper ion electronic structure as well as how the spectral features elucidate the coordination environment of copper. These coordinated compounds play an important role in metal ion coordination in proteins and peptides. The experiment has two parts. First, three copper–imidazole complexes that mimic copper–histidine compounds in the human body are synthesized. Second, the ESR spectrum of each complex is obtained at 77 K from frozen chloroform/methanol and acetonitrile/methanol matrixes and used to elucidate the ligand arrangement of the Cu2+ ion and the effect on the unpaired electron density.

A fascinating multifunctional bis(2-(4,5-diphenyl-1H-imidazol-2-yl)phenoxy)nickel complex: An excellent electrode material for supercapacitor and uric acid sensor

In the present work, nickel-trisubstituted imidazole complex, bis(2-(4,5-diphenyl-1H-imidazol-2-yl)phenoxy)nickel complex, abbreviated as NDIP was prepared by chemical method and its application as an electrode for supercapacitor was demonstrated. The structure and composition of the as-synthesized NDIP was confirmed by various spectral and analytical tools and further it was examined for its sensing and supercapacitor applications. NDIP coated working electrode delivered the specific capacitance of 712 F/g at the current density of 1 A/g and capacitance retention of 87% upto 2000 GCD cycles. The developed sensor was explored to detect Uric Acid. The response for amperometric detection of UA on NDIP displayed a wide linear range (0.1 nm – 1031 μM) with low detection limit (0.412 μM). Furthermore, NDIP@GCE electrode showed a high selectivity and good responsiveness towards UA detection.

Synthesis of copper(II)–imidazole complex modified sandwich-type polyoxometalates for enhancing the power conversion efficiency in dye-sensitized solar cells

A inorganic–organic hybrids based on copper(II)–imidazole complex modified sandwich-type tungstoantimonite H6[Cu(im)4][Na2Cu3(H2O)3Cu(H2O)2(SbW9O33)2]·36H2O (1) (im = imidazole) was hydrothermally synthesized and characterized structurally by single crystal X-ray diffraction analysis. Its central band is composed of four Cu2+ and two Na+ forming a rare plane hexagon, and the sandwich-type anions [Na2Cu3(H2O)3Cu(H2O)2(SbW9O33)2]8- are further joined into a one-dimensional chain by a [Cu(im)4]2+ cation. The Kubelka-Munk function F and electrochemical cyclic voltammetry (CV) indicate that the energy level of 1 match well with the conduction band of TiO2, and compound 1 can act as an electron acceptor to accelerate the transfer of electrons. The UV–vis absorption Spectra of 1 has a wide range, and the absorption range of TiO2 can be extended to the visible region to improve the light absorption of TiO2 after doping with TiO2. The incorporation of 1 into TiO2 as the photoelectrodes of Dye-sensitized Solar Cells (DSSCs) improves the Jsc (the short circuit current density) and PCE (the power conversion efficiency) of DSSC, the DSSC assembled with 5%1@TiO2/P25 photoelectrodes has the best performance and its Jsc and PCE is 17.54 mA cm−2 and 7.71% respectively, the improvement of the efficiency is 26.8% compared with pure P25 (6.08%). In addition, electrochemical impedance spectroscopy and open circuit voltage decay show that 1 can promote electronic transfer, suppress charge recombination, and extend electronic lifetime.