Academic literature on the topic 'Imidazole-based donors'

Six tetranuclear rectangular metallacycles were synthesized via the [2+2] coordination-driven self-assembly of imidazole-based ditopic donor 1,4-bis(imidazole-1-yl)benzene and 1,3-bis(imidazol-1-yl)benzene, with dinuclear half-sandwichp-cymene ruthenium(II) acceptors [Ru2(µ-η4-oxalato)(η6-p-cymene)2](SO3CF3)2, [Ru2(µ-η4-2,5-dioxido-1,4-benzoquinonato)(η6-p-cymene)2](SO3CF3)2and [Ru2(µ-η4-5,8-dioxido-1,4-naphtoquinonato)(η6-p-cymene)2](SO3CF3)2, respectively. Likewise, three hexanuclear trigonal prismatic metallacages were prepared via the [2+3] self-assembly of tritopic donor of 1,3,5-tri(1H-imidazol-1-yl)benzene with these ruthenium(II) acceptors respectively. Self-selection of the single symmetrical and stable metallacycle and cage was observed although there is the possibility of forming different conformational isomeric products due to different binding modes of these imidazole-based donors. The self-assembled macrocycles and cage containing the 5,8-dioxido-1,4-naphtoquinonato (donq) spacer exhibited good anticancer activity on all tested cancer cell lines (HCT-116, MDA-MB-231, MCF-7, HeLa, A549, and HepG-2), and showed decreased cytotoxicities in HBE and THLE-2 normal cells. The effect of Ru and imidazole moiety of these assemblies on the anticancer activity was discussed. The study of binding ability of these donq-based Ru assemblies with ctDNA indicated that the complex 9 with 180° linear 1 ligand has the highest bonding constantKbto ctDNA.

"The synthesis, structural characterization, as well as the chemical activity studies of a Cu(II) ""bowl complex", based on the resorcin[4]arene scaffold with three imidazole-containing coordinating arms grafted at the large rim, is presented. This complex is a biomimetic model of a metalloenzyme active site where a cofacial triade of amino-acid residues holds the metal ion in the active site [1]. The trisimidazole ligand reacts with a stoichiometric amount of copper(II) perchlorate to produce a Cu(II) diperchloratocomplex 1. Spectroscopic studies revealed a 5-coordinate SBP environment for the Cu(II) center provided by three imidazole arms, and two extra donors, one embedded in the resorcinarene cavity, the other exposed to the solvent, in exo position. These two labile sites are occupied by either coordinating solvent molecules or residual water, and are readily displaced by carboxylate donors, the position of which (endo or exo) is under tight control of the bowl-cavity. The reaction of 1 with CH3COONa led to a formation of the Cu(II) acetatocomplex 2. Molecular structure of 2 features a rigidified resorcinarene bowl, which was constructed by the addition of the four methylene bridges between the eight hydroxyl groups of the octol precursor [2]. The isolated resorcinarene basket reveals an approximate, non-crystallographic, 4mm point symmetry, and can easily host small guest molecules. Three methylimidazole-containing coordination arms at the large rim coordinate the Cu (II) ion. Its coordination sphere is completed by two O atoms from the intra-cavity bound acetate. The electron donors form a distorted square pyramide, where one of the nitrogens is at the appical position. The endo-coordination of the acetate is supported by an extensive network of intramolecular C-H···O and C-H···π interactions. Complex 2 crystallizes in P21/c space group; a=32.3310 (4)Å, b=11.5490 (1)Å, c=21.6020 (2)Å, beta=102.281(3)0."

Mixed complexes of Co(III) with 2-oximinopropionic (H2A) or 2-oximino-3-phenylpropionic (H2B) acid and different amine (imidazole, benzimidazole, pyridine, β-picoline, γ-picoline) are reported. Characterization of the complexes was based upon elemental analysis, conductivity and JR, 1H NMR, and electronic absorption spectra, and X-ray diffraction analysis. The organic ligands behave as O,N donors via the carboxyl oxygen and the oxime nitrogen atoms. A trans-octahedral structure has been assigned to the bis(2-oximinocarboxylato)bis(amine)cobalt(III) on the basis of 1H NMR data.The crystal and molecular structures of the complexes trans-[bis(2-oximinopropionato)bis-(imidazole)]- (I) and trans-[bis(2-oximinopropionato)bis(pyridine)]cobalt(III) (II) were determined. I crystallizes in space group P2/n with a = 14.1 67(2), b = 8.774(1), c = 14.785(2) Å,β = 113.37(1)°, Z = 4, Dcalc = 1.568 g · cm-3. II crystallizes in space group P1̄ with a = 9.122(2), b = 10.038(2), c = 11.759(2) Å, α = 69.95(1)°, β = 67.47(2)°, γ = 69.49(2)°, Ζ = 2, Dcalc = 1.547 g cm-3. The structures were refined to unweighted R factors of 0.036 and 0.028, respectively. The coordination sphere around Co is pseudo-octahedral with the 2-oximinopropionato ligands occupying four equatorial positions, and the amines in axial positions.

Human carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the hydration and dehydration of CO2 and HCO3-, respectively. The reaction follows a ping-pong mechanism, where the rate limiting step is the transfer of a proton from the zinc-bound solvent out of the active site, via His64 which is widely believed to be the proton shuttling residue. Being involved in a number of physiological processes such as respiration, pH regulation, ureagenesis etc., CAs are therapeutic targets for inhibition to treat various diseases. However, the physiologically dominant isoform is CA II, which is catalytically highly efficient and is easily crystallizable. Thus, most of our knowledge in the design of CA inhibitors with pharmacological applications is based on detailed CA II crystallographic studies. The catalytic activity of a variant of CA II in which His64 is replaced with Ala (H64A CA II) can be enhanced by exogenous proton donors/acceptors, usually derivatives of imidazoles and pyridines. This article examines the mechanism through which this activity enhancement might occur. X-ray crystal structures of H64A CA II in complex with four imidazole derivatives have been determined and reveal multiple binding sites. We have identified two molecules of imidazoles that bind in region that is otherwise occupied by the "in" and "out" dual conformation of the side chain of His64 in wild-type CA II. The data presented here not only corroborates the importance of imidazole side chain of His64 in proton transfer during CA catalysis, but also provides a complete structural understanding of the mechanism by which imidazoles enhance (and inhibit when used in higher concentrations) the activity of H64A CA II. In addition to inhibition of CA by these imidazoles, the presence of a large number of binding sites also gives insights and preliminary data required to fragment addition approach of drug design against CA.

Elucidation of the structure and function of biomolecules provides us knowledge that can be transferred into the generation of new materials and eventually applications in e.g., catalysis or bioassays. The main problems, however, concern the complexity of the natural systems and their limited availability, which necessitates utilization of simple biomimetic analogues that are, to a certain degree, similar in terms of structure and thus behaviour. We have, therefore, devised a small library of six tridentate N-heterocyclic coordinating agents (L1–L6), which, upon complexation, form two groups of artificial, monometallic non-heme iron species. Utilization of iron(III) chloride leads to the formation of the 1:1 (Fe:Ln) ‘open’ complexes, whereas iron(II) trifluoromethanosulfonate allows for the synthesis of 1:2 (M:Ln) ‘closed’ systems. The structural differences between the individual complexes are a result of the information encoded within the metallic centre and the chosen counterion, whereas the organic scaffold influences the observed properties. Indeed, the number and nature of the external hydrogen bond donors coming from the presence of (benz)imidazole moieties in the ligand framework are responsible for the observed biological behaviour in terms of mimicking phenoxazinone synthase activity and interaction with DNA.

Metal–organic frameworks (MOFs) based on multidentate N-heterocyclic ligands involving imidazole, triazole, tetrazole, benzimidazole, benzotriazole or pyridine present intriguing molecular topologies and have potential applications in ion exchange, magnetism, gas sorption and storage, catalysis, optics and biomedicine. The 2-[(1H-1,2,4-triazol-1-yl)methyl]-1H-benzimidazole (tmb) ligand has four potential N-atom donors and can act in monodentate, chelating, bridging and tridentate coordination modes in the construction of complexes, and can also act as both a hydrogen-bond donor and acceptor. In addition, the tmb ligand can adopt different coordination conformations, resulting in complexes with helical structures due to the presence of the flexible methylene spacer. A new three-dimensional coordination polymer, poly[[bis(μ2-benzene-1,4-dicarboxylato)-κ4O1,O1′:O4,O4′;κ2O1:O4-bis{μ2-2-[(1H-1,2,4-triazol-1-yl)methyl-κN4]-1H-benzimidazole-κN3}dizinc(II)] trihydrate], {[Zn(C8H4O4)(C10H9N5)]·1.5H2O}n, has been synthesized by the reaction of ZnCl2with tmb and benzene-1,4-dicarboxylic acid (H2bdic) under solvothermal conditions. There are two crystallographically distinct bdic2−ligands [bdic2−(A) and bdic2−(B)] in the structure which adopt different coordination modes. The ZnIIions are bridged by tmb ligands, leading to one-dimensional helical chains with different handedness, and adjacent helices are linked by bdic2−(A) ligands, forming a two-dimensional network structure. The two-dimensional layers are further connected by bdic2−(B) ligands, resulting in a three-dimensional framework with the topological notation 66. The IR spectra and thermogravimetric curves are consistent with the results of the X-ray crystal structure analysis and the title polymer exhibits good fluorescence in the solid state at room temperature.

Abstract Glyphosate, the active ingredient in Roundup® agricultural herbicides, is used on crops that are commonly grown for animal feed. Even though there has not been empirical data to suggest that animal productivity and health are affected when glyphosate-based products are used as labeled, accusations based on hazard identification alone have circulated widely. One of these accusations originates regarding a patent that was never held by Monsanto (now part of the Bayer Group) that did not include glyphosate. This claim hypothesizes that glyphosate could chelate minerals in the gut and prevent absorption. Formation constants measure the strength of complexation between metal ions and ligands and can be used to model the speciation in mixtures of minerals, amino acids, VFAs, and glyphosate as they exist in the rumen. The amines and carboxylic acids of all amino acids and functional side chains such as the imidazole group of histidine are potential donors for binding minerals. Likewise, carboxylic acid groups from VFAs are prevalent sources for binding of minerals. Literature references of concentrations of minerals and amino acids were used along with a measurement of glyphosate, and speciation calculations were performed at three pH’s commonly encountered in the rumen (5.8, 6.3 and 6.8). This calculation identified all species present at ≥0.01%. Using pH=6.3 as an example, 55.1% of cobalt is present as free Co2+, 28.6% is bound to a VFA (acetate, propionate or butyrate), and 13.1% is bound to histidine. The remaining 1.6% is distributed among Ala, Asp, Cys, Glu, Gly, Lys, Met, Ser, Thr, NH3 and OH. Similar results by ligand will be presented for Fe, Zn, Cu, Mn, Ca, His, Cys, and Glu. Data from these models confirm that glyphosate is a relatively weak chelator that should not have deleterious effects in the rumen.

The application of bidentate N,N'-donor ligands, such as 2,2'-biimidazole (BIIMH2) and 2,2'-pyridylimidazole (PIMH) and (1H-benzimidazol-2yl)-N-methylmethanamine (BIMAH), in the solvent extraction of base metal ions from an acidic sulfate/sulfonate medium was investigated. PIMH and BIMAH showed selectivity for Ni(II) with the only interfering ion being Cu(II) in the pH range 1.2-1.8 but BIIMH2 lacked selectivity. The extraction patterns observed were influenced by stereochemical aspects, and this agreed well with the envisaged design of nickel(II)-specific extractants through stereochemical “tailor-making” which is proposed in this study. The extraction patterns were explained from a coordination chemistry point of view using spectroscopic analysis and single crystal X-ray analysis to diagnose the geometry of the complexes formed from the interaction of the base metal ions with the ligands. The formation of the trigonal bipyrimidal [Cu(PIM)2(H2O)](SO4) complex, with a water molecule coordinated, while nickel(II) forms a square planar bisPIMH was put forward as the reason for extraction pattern observed with this ligand. Cobalt(II) also forms a bisPIMH complex but has two water molecules coordinated in the formation of a distorted octahedral complex, and this results in less extractable species. A similar observation as for PIMH was noticed in BIMAH complexation reactions. The BIIMH2 complexes were found to be distorted octahedral, through the bis-coordination of BIIMH2 and two sulfonate ions, resulting in lack of pH-metric separation of the later 3d metal ions. The stability constants data was in agreement with what was observed in the solvent extraction and coordination chemistry studies for the three ligand systems.

The nature of ligands coordinated to the metal ion mostly determines the properties of the inorganic, organometallic or bioinorganic model compounds. The pyrazole is one of the most studied heterocyclic aromatic compounds in coordination chemistry as single ligand or incorporated in polidentate ligands, such as in poly(pyrazolyl)borates (‘scorpionates'), poly(pyrazolyl)alkanes, etc. The great versatility of the pyrazole allows the formation of several ligands with different functionalizations, which mainly influence the geometry and nuclearity of the diverse coordination complexes afforded by the reaction of the pyrazole-based chelating ligands and a metal ion. Another of the most studied heterocyclic aromatic compounds in coordination chemistry is an analogue of pyrazole with two non-adjacent nitrogen atoms, the imidazole, which represents the main structure of the most common and studied N-Heterocyclic carbenes (NHCs), in particular the imidazol‐2‐ylidenes. These general informations arouse curiosity in main features and reactivity, synthesis and coordination modes, potential and ensured applications of various N-donor ligands, such as poly(pyrazolyl)borates or scorpionates, their isoelectronic and isosteric neutral analogues poly(pyrazolyl)alkanes and N-heterocyclic carbenes, presented, thus, in detail, in Chapter 1. The focus on the electronic and steric properties, the coordinating behaviour and several applications of scorpionates metal complexes, the state-of-art on coordination chemistry and reactivity of the poly(pyrazolyl)alkanes derivatives, the advantages of NHCs over phosphines, including ease of handling, minimal toxicity and powerful electron-donating properties, as enhanced stability of their transition metal complexes, which lead to the synthesis of highly active derivatives in homogeneous catalysis, anticipate the research work of this thesis on the nitrogen pyrazole- and imidazole-based ligands and their organometallic compounds. Beginning from Chapter 2, which describes the aims of the research work, all the chapters are divided in four sub-chapters. In the first sub-chapter differently halogen substituted bis- and tris-(pyrazolyl)borate ligands (BpBr3, TpBr3 and TpiPr,4Br) are compared in terms of electron-donor character through their interactions with various ruthenium(II) arene dimers, as also through electrochemical studies. Interestingly, an unexpected dinuclear ionic compound accounted for by its low thermodynamic stability, confirmed by theoretical calculations at the DFT level, due to steric reasons. The second sub-chapter is centered on the synthesis, characterization and crystal structure of the complexes of the second-lowest steric hindrance scorpionate ligand, TpTn, towards CuI, CuII, ZnII and CdII acceptors. A remarkable coordinative aspect of this ligand is pointed out, as well as the thermal and air stability of the relative complexes, confirmed by thermogravimetric and differential thermal analysis (TGA-DTA). By contrast, the interaction between TpTn and PtI2 proceeded through ligand decomposition, affording a monomeric complex. In the third sub-chapter, the varying, different stoichiometries and the N,N-chelating coordination modes of the bis(pyrazolyl)methanes, in particular of the two indazolyl-based regio-isomeric ligands, L1, bis(1H-indazol-1-yl)methane, and L2, bis(2H-indazol-2-yl)methane, toward XI group metal centers are studied. The synthesis and full characterization of analogous adducts of both regio-isomers allow a systematic comparison of their structural and spectral features, depending on the regio-isomeric ligand and counter-ion used, and the reaction conditions employed. The synthesis and characterization of a new series of stable, cationic gold(I/III) NHC complexes, as well as their catalytic activity in five well-established organic gold-mediated transformations, performed at the University of Strasbourg, under guidance of Director of Research Pierre Braunstein and coworkers (Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Universita'© de Strasbourg, France) is described in the fourth sub-chapter. Interestingly, various attempts to synthesize gold(III) NHC bis- or tris-pyridine complexes, as also the comparative behaviour of NHCs respect to phosphine ligands, are presented. Going further on the thesis structure, all the general procedures and experimental data are reported in Chapter 3, while the discussion and elaboration of the results are described in Chapter 4. Concluding remarks and future perspectives are discussed in Chapter 5, whereas all the references and some notes are given in Chapter 6. In Annexes section, the Curriculum Vitae, the List of Pubblications and the Contributions to Congresses are presented.

Self-assembly and noncovalent interactions play a pivotal role in the design of complex, and intricate functional structures. Among several design approaches, metal-ligand coordinationdriven self-assembly has emerged as one of the most efficient methodology for constructing complex 2D and 3D architectures. This approach is favored due to its relatively simple design principle, predictable directionality, and high bond enthalpy. Over the years, a vast range of topologically intricate structures was designed using this approach. However, reports on the construction of complex 2D, and 3D architectures using highly symmetric and rigid square planner Pd(II)/Pt(II)-based metal acceptor in combination with rigid polypyridyl donor building blocks dominate the literature so far. In this context, imidazole-based donors and flexible donors remained less explored than conventional pyridyl donors. It is envisioned that the use of imidazole-based donors as well as flexible donors might provide interesting results in terms of the structure of the final assembly. The rotational degree of freedom in these cases can offer different bite angles to the rigid pyridyl donor and may affect the structure of the final assembly. On the other hand, supramolecular coordination polymers (SCPs) that are made up of an ordered arrangement of repeating monomeric units have gained significant attention as they offer high surface area, ordered porosity, and better stability compared to discrete supramolecular coordination complexes. The objective of the thesis is to synthesize various functional supramolecular architectures (both discrete and coordination polymers) using imidazole-based donors and flexible donors via the metal-ligand coordination approach. And to explore these self-assembled architectures for fluorescence modulation, visible-light-driven photocatalysis, and light harvesting.

碩士
國立彰化師範大學
化學系
105
A series of imidazolium chlorides for the formation of tridentate C^N^O-donor palladium(II) complexes featuring N-heterocyclic carbene moieties have been developed from cheap and readily available starting materials with high yields. Their palladium complexes were prepared by reactions between the ligand precursors and PdCl2 using K2CO3 as base in pyridine with reasonable yields. These air-stable metal complexes have been characterized by 1H and 13C{1H} NMR spectroscopy and elemental analyses. HMBC experiments were performed to identify key NMR signals of these compounds. The structures of two of the complexes have also been established by single-crystal X-ray diffraction analysis. One of these complexes was successfully applied in the direct C—H functionalization reactions between heterocyclic compounds and aryl bromides, producing excellent yields of coupled products. The coupling reactions were scalable, allowing grams of coupled products to be obtained with a mere 2 mol% of Pd loading. The catalyst system developed allowed a large-scale preparation of several push-pull dyes straightforwardly. Photophysical properties based on UV/Vis and fluorescence spectroscopy for these dyes were investigated. Deep blue photoluminescence with moderate quantum efficiency and twisted ICT excited state were observed for these dyes. DFT and TDDFT calculations were performed to support the experimental results