Imidazole Nitrogen Atoms Research Articles

Silver(I) and gold(III) complexes with miconazole: The influence of the metal ion on the antimicrobial activity of the coordinated azole

To develop a new antimicrobial agent, we used the clinically approved antifungal azole, miconazole (mcz), as a ligand for the synthesis of silver(I) and gold(III) complexes. The new complexes [Ag(NO3-O)(mcz-N)2] (1) and [AuCl3(mcz-N)] (2) were synthesized and characterized by 1H NMR, IR and UV–Vis spectroscopy and mass spectrometry, while the crystal structure of 1 was determined by single-crystal X-ray diffraction analysis. From the results obtained, it can be concluded that in both complexes, mcz is monodentately coordinated to the silver(I) and gold(III) ions through the imidazole nitrogen atom N3. In the solid state, complex 1 contains two mcz ligands and monodentately coordinated nitrate in the third position, while in the case of 2 gold(III) ion is coordinated by one mcz and three chlorido ligands, resulting in the expected square-planar arrangement around the metal center. DFT and TDDFT calculations were employed to elucidate the electronic structures and thermodynamic stability of the synthesized complexes in solution to complement the experimental findings. The coordination of mcz to silver(I) and gold(III) ions leads to an enhancement of its activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa strains, while against the panel of Staphylococcus aureus and Candida species, only 2 shows improved activity compared to mcz. Both complexes 1 and 2 were tested in vitro for their antimycobacterial activity against the strain Mycobacterium tuberculosis H37Rv and showed good growth inhibition with minimum inhibitory concentration (MIC) values of 3.12 and 8.69 μM, respectively, with complex 1 being twice effective as mcz (MIC = 7.50 μM). Complex 2 significantly reduced the production of pyocyanin, a virulence factor in P. aeruginosa controlled by quorum sensing, while this effect was not observed for 1.

Using dopants in the atmospheric pressure chemical ionization ion source to determine the site of protonation by ion mobility spectrometry.

Compounds like caffeine metabolites with more than one proton acceptor site can produce a mixture of isomeric protonated ions (protomers) in electrospray ionization and atmospheric pressure chemical ionization (APCI) ion sources. Discrimination between the protomers is of interest as the charge location influences ion structure and chemical and physical properties. Protonation of caffeine in an APCI ion source was studied using ion mobility spectrometry. The hydronium ions, H3O+(H2O)n, are the main reactant ions in the APCI ion source. Different dopant gases including NO2, NH3, and CH3NH2 were used to produce new reactant ions NO+, NH4 +, and CH3NH3 +, respectively. Density functional theory was employed to explain the experimental results and calculate the energies of the ionization reactions. The ion mobility spectrum of caffeine showed three peaks. In the presence of NO2 dopant and NO+ reactant ion, caffeine was ionized via charge transfer and formation of M+ ion. As NH3 and CH3NH2 are stronger bases than H2O, the reactant ions NH4 + and CH3NH3 + selectively protonated the more basic site of caffeine, that is, the imidazole nitrogen. Using these dopants, we could attribute the first ion mobility peak to M+ ion, the second peak to the protonation of caffeine at the carbonyl oxygen atom, and the third peak to the protonation of the imidazole nitrogen atom. The calculated collisional cross-sections of M+ and the protomers of caffeine confirmed the peaks' assignment. The criterion for the selection of an appropriate dopant is that its proton affinity (PA) should be between those of the proton acceptor sites of the molecule studied.

Silver(I) complexes containing antifungal azoles: significant improvement of the anti-Candida potential of the azole drug after its coordination to the silver(I) ion.

Inspired by the emergence of resistance to currently available antifungal therapy and by the great potential of metal complexes for the treatment of various diseases, we synthesized three new silver(I) complexes containing clinically used antifungal azoles as ligands, [Ag(ecz)2]SbF6 (1, ecz is econazole), {[Ag(vcz)2]SbF6}n (2, vcz is voriconazole), and [Ag(ctz)2]SbF6 (3, ctz is clotrimazole), and investigated their antimicrobial properties. The synthesized complexes were characterized by mass spectrometry, IR, UV-vis and 1H NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In the mononuclear complexes 1 and 3 with ecz and ctz, respectively, the silver(I) ion has the expected linear geometry, in which the azoles are monodentately coordinated to this metal center through the N3 imidazole nitrogen atom. In contrast, the vcz-containing complex 2 has a polymeric structure in the solid state in which the silver(I) ions are coordinated by four nitrogen atoms in a distorted tetrahedral geometry. DFT calculations were done to predict the most favorable structures of the studied complexes in DMSO solution. All the studied silver(I) complexes have shown excellent antifungal and good to moderate antibacterial activities with minimal inhibitory concentration (MIC) values in the ranges of 0.01-27.1 and 2.61-47.9 μM on the selected panel of fungi and bacteria, respectively. Importantly, the complexes 1-3 have exhibited a significantly improved antifungal activity compared to the free azoles, with the most pronounced effect observed in the case of complex 2 compared to the parent vcz against Candida glabrata with an increase of activity by five orders of magnitude. Moreover, the silver(I)-azole complexes 2 and 3 significantly inhibited the formation of C. albicans hyphae and biofilms at the subinhibitory concentration of 50% MIC. To investigate the impact of the complex 3 more thoroughly on Candida pathogenesis, its effect on the adherence of C. albicans to A549 cells (human adenocarcinoma alveolar basal epithelial cells), as an initial step of the invasion of host cells, was studied.

Synthesis and Characterization Some Complexes of Mixed Ligand and Study Its Effects as Antioxidant and Anticancer

A series of mixed ligand complexes of Co(II), Ni(II), Cu(II), Zn (II),Cd(II), Fe (III ) andAu(III) were prepared and characterized. A new azo ligand derived from 4-methylimidazole with sulfadiazine and Schiff base derived from 4-(dimethylamino)-2-hydroxobenzaldehyde and 4-amino-3-hydroxy benzene sulfonamide. Ligands structures and their transitional metal mix-ligand complexes were characterized using various analytical techniques, including molar conductance, elemental analysis (C.H.N), electronic spectral, magnetic measurements, 1HNMR, IR spectral studies and mass spectra. The data shows that these complexes have composition of [ML1L2H2O] where M = Co(II), Ni(II), Cu(II), Zn(II) ,Cd(II) and Hg(II). [ML1L2Cl] where M=Fe(III). [ML1L2]Cl2 where M=Au(III). The magnetic susceptibility and electronic spectral data of the complexes indicate that the octahedral geometry of all complexes, except the complex of Au(III) indicates a square plane geometry. The IR results demonstrate that the co-ordination sites are imidazole nitrogen atom and the farthest azo nitrogen atom of L1 as natural bidentate with nitrogen the azomethine and oxygen atoms of Schiff base L4. Azo ligand and Schiff base behave as tridentate manner. All the compounds showed DPPH radical scavenging activity. In general, the results indicated that the complexes have potential and promising anti-oxidant activities.

Polymerized methyl imidazole silver bromide (CH3C6H5AgBr)6: Synthesis, crystal structures, and catalytic activity

Abstract One-pot synthesis of polymerized methyl imidazole silver bromide (CH3C6H5AgBr)6 Compound 1 was carried out by the reaction of methylimidazole, 1,2-dibromoethane, and Ag2O in tetrahydrofuran at 60°C for 2 h. Compound 1 was characterized by elemental analysis, 1 H nuclear magnetic resonance, and single crystal X-ray diffraction. The crystal cell parameters of Compound 1 are as follows: a = 8.916(4) Å, b = 17.655(9) Å, c = 9.024(4) Å, α = 90°, β = 103.621(7)°, γ = 90°, V = 1380.6(12) Å3, and Z = 4. The silver atoms in Compound 1 are pentacoordinated with three bromine atoms, one silver atom, and one nitrogen atom of methyl imidazole, and polymeric methyl imidazole silver bromide was formed based on this structure. The catalytic effects under optimized conditions were investigated in this study, and the results showed that Compound 1 possesses a strong catalytic effect on the oxidation of 2-methylnaphthalene with a conversion rate of 77.15% by using hydrogen peroxide as the oxidant at 80°C for 3 h. The catalytic mechanism was explored simultaneously.

Ligand-Structure Effects on N-Heterocyclic Carbene Rhenium Photo- and Electrocatalysts of CO2 Reduction.

Three novel rhenium N-heterocyclic carbene complexes, [Re]-NHC-1-3 ([Re] = fac-Re(CO)3Br), were synthesized and characterized using a range of spectroscopic techniques. Photophysical, electrochemical and spectroelectrochemical studies were carried out to probe the properties of these organometallic compounds. Re-NHC-1 and Re-NHC-2 bear a phenanthrene backbone on an imidazole (NHC) ring, coordinating to Re by both the carbene C and a pyridyl group attached to one of the imidazole nitrogen atoms. Re-NHC-2 differs from Re-NHC-1 by replacing N-H with an N-benzyl group as the second substituent on imidazole. The replacement of the phenanthrene backbone in Re-NHC-2 with the larger pyrene gives Re-NHC-3. The two-electron electrochemical reductions of Re-NHC-2 and Re-NHC-3 result in the formation of the five-coordinate anions that are capable of electrocatalytic CO2 reduction. These catalysts are formed first at the initial cathodic wave R1, and then, ultimately, via the reduction of Re-Re bound dimer intermediates at the second cathodic wave R2. All three Re-NHC-1-3 complexes are active photocatalysts for the transformation of CO2 to CO, with the most photostable complex, Re-NHC-3, being the most effective for this conversion. Re-NHC-1 and Re-NHC-2 afforded modest CO turnover numbers (TONs), following irradiation at 355 nm, but were inactive at the longer irradiation wavelength of 470 nm. In contrast, Re-NHC-3, when photoexcited at 470 nm, yielded the highest TON in this study, but remained inactive at 355 nm. The luminescence spectrum of Re-NHC-3 is red-shifted compared to those of Re-NHC-1 and Re-NHC-2, and previously reported similar [Re]-NHC complexes. This observation, together with TD-DFT calculations, suggests that the nature of the lowest-energy optical excitation for Re-NHC-3 has π→π*(NHC-pyrene) and dπ(Re)→π*(pyridine) (IL/MLCT) character. The stability and superior photocatalytic performance of Re-NHC-3 are attributed to the extended conjugation of the π-electron system, leading to the beneficial modulation of the strongly electron-donating tendency of the NHC group.

Benzimidazole-based covalent organic polymer nanosheets incorporated in mesoporous organosilica nanoparticles with excitation-dependent fluorescence for sensing of Cu2+

A novel type of small-sized nanosheets (TD-Si) was prepared by chemical exfoliating stacked bulk materials of benzimidazole-based covalent organic polymer (TpDAB). Then TD-Si was used as organosiloxane precursor to incorporate into silica frameworks of mesoporous organosilica nanoparticles (TD-MONs) using CTAB as structural-directing agents. The obtained TD-MONs show a clearly hexagonal mesoporous structure with high surface area. Moreover, the optical properties of TD-MONs were measured with fluorescence and Ultraviolet–visible (UV–vis) spectroscopies. The results showed that TD-MONs possessed excitation wavelength dependent fluorescence and had better fluorescence properties due to the reduction of π-π stacking between nano-layers of TpDAB polymer. The emission peaks of TD-MONs were red-shifted as the excitation wavelength increases and TD-MONs exhibited the optimal fluorescence emission at 525 nm when excited at 400 nm. TD-MONs showed high selectivity, sensitivity and recyclability toward copper ions and could be used for the detection of Cu2+ with a low limit of detection (LOD) as low as 3.77 × 10−7 M. In addition, the coordination interaction between TD-MONs and copper ions was demonstrated by FT-IR spectra and high-resolution X-ray photoelectron spectra, and further proved that the binding sites were carbonyl oxygen atoms and imidazole nitrogen atoms in TD-MONs. Therefore, TD-MONs is expected to be a high-sensitive chemical sensor for detecting Cu2+.

Stereochemistry of low-spin cobalt porphyrins. 9. Molecular stereochemistry of two picket fence cobalt(II) derivatives

The preparation and molecular structures of two five-coordinate cobalt(II) picket fence porphyrinates with imidazole ligands are described, [Co(TpivPP)(L)] (TpivPP, dianion of picket fence porphyrin). The ligands are the unhindered imidazole, 1-ethylimidazole, and the sterically hindered imidazole, 1,2-dimethylimidazole. Although the equatorial aspects of the geometry are quite equivalent, the axial coordination group geometry strongly reflects the differing steric requirements of the axial ligand. The hindering methyl group in 1,2-dimethylimidazole, adjacent to the coordinated imidazole nitrogen atom, leads to an increased CoNIm bond distance, a tilt of the CoN bond and unequal CoNCIm bond angles, all of which serve to reduce the steric strain when compared with the unhindered derivative.

A Rare Structural Motif for a Luminescent Cu(I) Coordination Polymer with 3-(Pyridin-2-yl)triimidazotriazine

The coordination ability of the pyridine derivative of cyclic triimidazole, namely 3-(pyridin-2-yl)triimidazotriazine (TT-Py) towards Cu(I) was explored. TT-Py is an appealing nitrogen-rich ligand characterized by the presence of three imidazole nitrogen atoms with trigonal symmetry and a pyridine moiety, available for coordination to metal ions. The multidentate nature of TT-Py allows to isolate, by reaction with CuI at room temperature, the one-dimensional coordination network [Cu2I2(TT-Py)]n (1). 1 is characterized by a rare structural network built-up by the combination in a 1:2 ratio of two common motifs for Cu(I) halides coordination polymers, which are the double-stranded stair and the zig-zag chain. 1 displays one broad long-lived emission in the solid state, which has been associated, by the support of DFT and TDDFT calculation, with low-energy transitions of MLCT or XMLCT character.

Histamine-bound magnesium porphyrins: diverse coordination modes, inhibitory role in photodegradation of chlorophyll a and antioxidant activity.

The neurotransmitter histamine exists in two isomeric forms and could be an interesting ligand due to three nitrogen atoms with the possibility of binding to metals in different ways besides its crucial role in biological systems. However, no metal-histamine interaction is known in the literature. Therefore, two histamine-bound magnesium porphyrins [MgT(4-Cl)PP(hist)2] 1 and [MgT(4-Br)PP(hist)] 2 have been synthesized and structurally characterized. Interestingly, 1 is a hexa-coordinated magnesium porphyrin due to the axial coordination of two histamine molecules via the nitrogen of the aliphatic amino group with the Mg-Nhistamine distance of 2.300 Å, while 2 is penta-coordinated due to the axial coordination of one histamine molecule through the imidazole nitrogen atom with the Mg-Nhistamine distance of 2.145 Å. The diverse coordination modes of this unique ligand are explored for the first time. Theoretical studies at the level of DFT supported the binding of histamine via imidazole nitrogen atoms for complex 2. Histamine-bound magnesium porphyrins are found to be stable against the photodegradation of magnesium porphyrin in the presence of light and oxygen. Freshly isolated chlorophyll a from spinach showed similar resistivity against photodegradation. Moreover, the histamine-bound complexes showed higher antioxidant activity for 1 (92.45%) compared to the free base porphyrin (73.11%) and MgT(4-Cl)PP (75.89%).

Atomically precise binding conformations of adenine and its variants on gold using single molecule conductance signatures.

We demonstrate single molecule conductance as a sensitive and atomically precise probe of binding configurations of adenine and its biologically relevant variants on gold. By combining experimental measurements and density functional theory (DFT) calculations of single molecule-metal junction structures in aqueous conditions, we determine for the first time that robust binding of adenine occurs in neutral or basic pH when the molecule is deprotonated at the imidazole moiety. The molecule binds through the donation of the electron lone pairs from the imidazole nitrogen atoms, N7 and N9, to the gold electrodes. In addition, the pyrimidine ring nitrogen, N3, can bind concurrently and strengthen the overall metal-molecule interaction. The amine does not participate in binding to gold in contrast to most other amine-terminated molecular wires due to the planar geometry of the nucleobase. DFT calculations reveal the importance of interface charge transfer in stabilizing the experimentally observed binding configurations. We demonstrate that biologically relevant variants of adenine, 6-methyladenine and 2'-deoxyadenosine, have distinct conductance signatures. These results lay the foundation for biosensing on gold using single molecule conductance readout.

Bis(1-methyl-imidazole)[meso-α,α,α,α-tetra-kis(o-nicotinamido-phen-yl)porphinato]iron(II)-1-methyl-imidazole-tetra-hydro-furan (1/1/1.5).

In the title compound, [FeII(C68H44N12O4)(C4H6N2)2]·C4H6N2·1.5C4H8O, the central FeII ion is coordinated by four pyrrole N atoms of the porphyrin core and two N atoms of the 1-methyl-imidazole ligands in the axial sites. One 1-methyl-imidazole and one and a half tetra-hydro-furan solvent mol-ecules are also present in the asymmetric unit. The complex exhibits a near planar porphyrin core conformation, in which the iron centre is slightly displaced towards the hindered porphyrin side (0.01 Å). The average Fe-Np (Np refers to the pyrrole nitro-gen atoms in the porphyrin) bond length is 1.990 (9) Å, and the axial Fe-NIm (NIm refers to the imidazole nitro-gen atoms) bond lengths are 1.993 (3) and 2.004 (3) Å. The dihedral angle between the two coordinated 1-methyl-imidazole planes is 56.6 (2)°. The dihedral angles between the 1-methyl-imidazole planes and the planes of the closest Fe-Np vector are 16.8 (2) and 39.8 (2)°. N-H⋯N and N-H⋯O inter-actions are observed in the crystal structure.

Synthesis, structural and DFT investigation of Zn(nba)2(meim)2 for adsorptive removal of eosin yellow dye from aqueous solution

AbstractA novel Zn(II) mixed‐ligand complex, Zn(nba)2(meim)2 (1), synthesized from Zn(NO3)2.6H2O, nitrobenzoic acid (Hnba) and 1‐methylimidazole (meim) is reported. The complex was characterized by elemental analysis, FT‐IR, powder and single crystal X‐ray crystallography and TGA/DSC. 1 exhibits a tetrahedral geometry for Zn(II), which is coordinated to two carboxylate oxygen atoms from two nba anions and two imidazole nitrogen atoms from two meim molecules. Thermal analysis shows the stability of 1 up to 260 °C. The adsorption of eosin yellow (EY) dye on 1 was investigated. The adsorption capacity of 1 for EY amounted to 65.32 mg/g, fitting best into Langmuir isotherm and pseudo second order kinetic models. From DFT studies, it was determined that adsorption is predominantly due to electrostatic, hydrogen bonding and π‐π interactions.

NMR Chemical Shift and Methylation of 4-Nitroimidazole: Experiment and Theory

Nitroimidazoles and derivatives are a class of active pharmaceutical ingredients (APIs) first introduced sixty years ago. As anti-infection agents, the structure–activity relationships of nitroimidazole compounds have been particularly difficult to study due to their low reduction potentials and unique electronic structures. In this study, we combine dynamic nuclear polarization (DNP)-enhanced solid-state (100K), solid-state (298K), and 1H-13C heteronuclear single quantum coherence (HSQC) solution-state NMR techniques (303K) with density functional theory (DFT) to study the 1H, 13C, and 15N chemical shifts of 4-nitroimidazole (4-NI) and 1-methyl-4-nitroimidazole (CH3-4NI). The 4-NI chemical shifts were observed at 119.4, 136.4, and 144.7ppm for 13C, and at 181.5, 237.4, and 363.0ppm for 15N. The measurements revealed that methylation (deprotonation) of the amino nitrogen N(1) of 4-NI had less effect (Δδ=−4.8ppm) on the N(1) chemical shift but was compensated by shielding of the N(3) (Δδ=11.6ppm) in CH3-4NI. The calculated chemical shifts using DFT for 4-NI and CH3-4NI agreed well with the experimental values (within 2%) for the imidazole carbons. However, larger discrepancies (up to 13%) were observed between the calculated and measured 15N NMR chemical shifts for the imidazole nitrogen atoms of both molecules, which indicate that effects such as imidazole ring resonant structures and molecular dynamics may also contribute to the nitrogen chemical environment.

Highly selective and sensitive detection towards cationic Cu2+ and Fe3+ contaminants via an In-MOF based dual-responsive fluorescence probe

Effective recognition and detection of heavy metal Cu2+ and Fe3+ ions from water are highly desirable because of their serious harms to human health and environmental safety. However, the existing detection techniques are still high cost, time-consuming and highly demanding for operators. As an alternative approach to address this issue, an indium-based MOF labeled as In-MOF of 1 with high water stability and opposite charges to Cu2+ and Fe3+ ions was successfully prepared and deployed as optical sensor to sense target analytes, according to our previous work. Prominently, this anionic framework exhibits high photoluminescence property and excellent fluorescence quenching response to target analytes with high selectivity, sensitivity and detection limits of 3.88 ppb for Cu2+, 4.2 ppb for Fe3+ ions, respectively, both of which have been confirmed to be ultro-low values among all reported MOFs-based photochemical sensors. Furthermore, the quick and accurate probing capability of 1 also has been proved even under the interference of dozens of anions or cations. The possible photoluminescence and fluorescence quenching mechanisms were studied in detail, revealing that rapid coordination reactions between free imidazole nitrogen and carboxyl oxygen atoms of the framework (Lewis basic sites) and the metal ions of Cu2+/Fe3+ (Lewis acid sites) should be proposed to be the key reason for high efficiency fluorescence quenching.

Microsolvation of Histidine—A Theoretical Study of Intermolecular Interactions Based on AIM and SAPT Approaches

Histidine is unique among amino acids because of its rich tautomeric properties. It participates in essential enzymatic centers, such as catalytic triads. The main aim of the study is the modeling of the change of molecular properties between the gas phase and solution using microsolvation models. We investigate histidine in its three protonation states, microsolvated with 1:6 water molecules. These clusters are studied computationally, in the gas phase and with water as a solvent (Polarizable Continuum Model, PCM) within the Density Functional Theory (DFT) framework. The structural analysis reveals the presence of intra- and intermolecular hydrogen bonds. The Atoms-in-Molecules (AIM) theory is employed to determine the impact of solvation on the charge flow within the histidine, with emphasis on the similarity of the two imidazole nitrogen atoms—topologically not equivalent, they are revealed as electronically similar due to the heterocyclic ring aromaticity. Finally, the Symmetry-Adapted Perturbation Theory (SAPT) is used to examine the stability of the microsolvation clusters. While electrostatic and exchange terms dominate in magnitude over polarization and dispersion, the sum of electrostatic and exchange term is close to zero. This makes polarization the factor governing the actual interaction energy. The most important finding of this study is that even with microsolvation, the polarization induced by the presence of implicit solvent is still significant. Therefore, we recommend combined approaches, mixing explicit water molecules with implicit models.

Synthesis, structure, and BSA binding studies of a new Co(II) complex based on 2-(1H-tetrazol-1-methyl)-1H-imidazole-4,5-dicarboxylic acid

A new complex [Co(Htmidc)(H2O)2]n (1) based on 2-(1H-tetrazol-1-methyl)-1H-imidazole-4,5-dicarboxylic acid (H3tmidc) has been synthesized by reacting CoSO4·7H2O with H3tmidc. Its structure, chemical component and properties were determined by single-crystal X-ray diffraction, element analysis, XPS, UV Vis spectra and FS spectra. The results show that complex 1 exhibits one-dimensional structure in which Co(II) ions are bridged by tetradentate Htmidc2− ligands with two carboxylate oxygen atoms and two imidazole nitrogen atoms. The fluorescence spectrum reveals that complex 1 can significantly quench the fluorescence intensity of BSA, which indicates that it has good ability in binding with BSA. The interaction between complex 1 and BSA is a static quenching process with formation of one binding site. In addition, the synchronous fluorescence spectrum suggested that the conformations of both tryptophan and tyrosine residues in the BSA have changed during the interaction of complex 1 with BSA.

2-Amino- and 2-hydroxymethylbenzimidazolium bromides as protein tyrosine phosphatase 1В (PTP1В) inhibitors and other targets associated with diabetes mellitus

New 2-amino- and 2-hydroxymethylbenzimidazoles were synthesized and used to prepare the previously unknown 1,2,3-tri- and 1,2,3,5-tetrasubstituted benzimidazolium bromides with a biphenyl-containing substituent at the imidazole nitrogen atom. In some cases, these bromides exhibit activity against targets associated with diabetes mellitus. These compounds are strong protein tyrosine phosphatase 1B (PTP1B) inhibitors, exhibit chelating and antiglycation activity, but have no significant AT1 receptor antagonist activity. Hence, biphenyl-containing benzimidazolium derivatives can be considered as a basis for the development of new promising agents for the treatment of type 2 diabetes mellitus (DM2) and other diseases mediated by high phosphatase PTP1B activity.

Alkyl-substituted 1,1'-Dihydroxy-2,2'bimidazoles: Reactions with Methyl Iodide and Trimethyl Phosphite

The alkylation of alkyl-substituted 1,1'-dihydroxy-2,2'-biimidazoles with an equimolar amount of methyl iodide occurs exclusively at the imidazole nitrogen atom, while with a three-fold excess of methyl iodide, both the imidazole nitrogen atom and two hydroxy groups are involved in alkylation. The reaction of 1,1'-dihydroxy-2,2'-biimidazoles with P(OMe)3 forms the corresponding 2,2'-biimidazoles.

A cyclometalated trinuclear Ir(iii)/Pt(ii) complex as a luminescent probe for histidine-rich proteins.

Organometallic complexes have important application in the field of protein staining, with potential for use in proteomic analysis. The rational synthesis of a trinuclear luminescent organometallic complex with two platinum(ii) centres appended to the cyclometalated ligand of the iridium(iii) centre is reported here. Two di-2-picolylamine groups bonded to the cyclometalated phenyl pyridine moiety provide three coordinating sites to each platinum centre. The replacement of chloride in the fourth coordination site of two square planar platinum metal centres with the imidazole nitrogen or sulphur atom of histidine/cysteine is evident from the change in luminescence intensity upon binding these amino acids. The increase in luminescence emission intensity upon binding of histidine to the organometallic complex allowed it to be used as a protein staining agent. Reversibility of staining upon washing with imidazole enhances the possibility of its application in mass spectrometric analysis.