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Imidazole Ligands (imidazole + ligand)
Selected AbstractsChemInform Abstract: Synthesis of Dendritic Iron(II) Porphyrins with a Tethered Axial Imidazole Ligand Designed as New Model Compounds for Globins.CHEMINFORM, Issue 18 2001Philipp Weyermann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Orientation- and Temperature-Dependent Rotational Behavior of Imidazole Ligands (L) in ,-[Ru(azpy)2(L)2](PF6)2 ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2003Aldrik H. Velders Abstract The synthesis and characterization of the cis bifunctional coordinated ruthenium(II) complexes ,-[Ru(azpy)2(MeIm)2](PF6)2 (,-MeIm) and ,-[Ru(azpy)2(MeBim)2](PF6)2 (,-MeBim) (azpy = 2-phenylazopyridine, MeIm = 1-methylimidazole and MeBim = 1-methylbenzimidazole) is reported. In ,-MeIm the two MeIm ligands can both freely rotate around the Ru,N axes on the NMR timescale. In ,-MeBim the two MeBim ligands appear restricted in their rotation around the Ru,N axes, which becomes slow on the NMR timescale at low temperatures. In contrast to the analogous complexes ,-[Ru(azpy)2(MeBim)2](PF6)2 and cis -[Ru(bpy)2(MeBim)2](PF6)2, only one atropisomer is observed for the two MeBim ligands in ,-MeBim. The orientation of the MeBim ligands appears to correspond to an HT isomer which is similar to the orientation of the MeBim ligands in the most abundant atropisomer found in the related ,-[Ru(azpy)2(MeBim)2](PF6)2. A stacking interaction between the phenyl ring of one azpy and one MeBim ligand is likely to stabilize the observed atropisomer of ,-MeBim, and is such that the rotation of the phenyl ring of one of the two azpy ligands is restricted. At very low temperatures this rotation, or flipping of the phenyl ring between two identical positions, is in the slow-exchange range on the NMR timescale. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003) [source] A CSOV study of the difference between HF and DFT intermolecular interaction energy values: The importance of the charge transfer contributionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005Jean-Philip Piquemal Abstract Intermolecular interaction energy decompositions using the Constrained Space Orbital Variation (CSOV) method are carried out at the Hartree,Fock level on the one hand and using DFT with usual GGA functionals on the other for a number of model complexes to analyze the role of electron correlation in the intermolecular stabilization energy. In addition to the overall stabilization, the results provide information on the variation, with respect to the computational level, of the different contributions to the interaction energy. The complexes studied are the water linear dimer, the N -methylformamide dimer, the nucleic acid base pairs, the benzene,methane and benzene-N2 van der Waals complexes, [Cu+ -(ImH)3]2, where "ImH" stands for the Imidazole ligand, and ImH-Zn++. The variation of the frozen core energy (the sum of the intermolecular electrostatic energy and the Pauli repulsion energy) calculated from the unperturbed orbitals of the interacting entities indicates that the intramolecular correlation contributions can be stabilizing as well as destabilizing, and that general trends can be derived from the results obtained using usual density functionals. The most important difference between the values obtained from HF and DFT computations concerns the charge transfer contribution, which, in most cases, undergoes the largest increase. The physical meaning of these results is discussed. The present work gives reference calculations that might be used to parametrize new correlated molecular mechanics potentials. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1052,1062, 2005 [source] Coordination chemistry of iron(III),porphyrin,antibody complexesFEBS JOURNAL, Issue 2 2002Influence on the peroxidase activity of the axial coordination of an imidazole on the iron atom An artificial peroxidase-like hemoprotein has been obtained by associating a monoclonal antibody, 13G10, and its iron(III),,,,,,,,- meso -tetrakis(ortho -carboxyphenyl)porphyrin [Fe(ToCPP)] hapten. In this antibody, about two-thirds of the porphyrin moiety is inserted in the binding site, its ortho -COOH substituents being recognized by amino-acids of the protein, and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O,O bond of H2O2, but no amino-acid residue is acting as an axial ligand of the iron. We here show that the iron of 13G10,Fe(ToCPP) is able to bind, like that of free Fe(ToCPP), two small ligands such as CN,, but only one imidazole ligand, in contrast to to the iron(III) of,Fe(ToCPP) that binds two. This phenomenon is general for a series of monosubstituted imidazoles, the 2- and 4-alkyl-substituted imidazoles being the best ligands, in agreement with the hydrophobic character of the antibody binding site. Complexes of antibody 13G10 with less hindered iron(III),tetraarylporphyrins bearing only one [Fe(MoCPP)] or two meso-[ortho -carboxyphenyl] substituents [Fe(DoCPP)] also bind only one imidazole. Finally, peroxidase activity studies show that imidazole inhibits the peroxidase activity of 13G10,Fe(ToCPP) whereas it increases that of 13G10,Fe(DoCPP). This could be interpreted by the binding of the imidazole ligand on the iron atom which probably occurs in the case of 13G10,Fe(ToCPP) on the less hindered face of the porphyrin, close to the catalytic COOH residue, whereas in the case of 13G10,Fe(DoCPP) it can occur on the other face of the porphyrin. The 13G10,Fe(DoCPP),imidazole complex thus constitutes a nice artificial peroxidase-like hemoprotein, with the axial imidazole ligand of the iron mimicking the proximal histidine of peroxidases and a COOH side chain of the antibody acting as a general acid-base catalyst like the distal histidine of peroxidases does. [source] Effect of the Nature of the Substituent in N -Alkylimidazole Ligands on the Outcome of Deprotonation: Ring Opening versus the Formation of N-Heterocyclic Carbene ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Miguel Abstract Complexes [Re(CO)3(N -RIm)3]OTf (N -RIm=N -alkylimidazole, OTf=trifluoromethanesulfonate; 1,a,d) have been straightforwardly synthesised from [Re(OTf)(CO)5] and the appropriate N -alkylimidazole. The reaction of compounds 1,a,d with the strong base KN(SiMe3)2 led to deprotonation of a central CH group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1,a contains three N -MeIm ligands, and its product 2,a features a C-bound imidazol-2-yl ligand. When 2,a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3,a or 4,a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2,a with [AuCl(PPh3)] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1,b,d, with at least one N -arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2H group of an imidazole ligand attacks a central CH group of a neighbouring N -RIm ligand, thus affording the product of CC coupling and ring-opening of the imidazole moiety that has been attacked (2,c,,d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3,c,,d or 4,c,,d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N -RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product. [source] Six-coordinate Co2+ with imidazole, NH3, and H2O ligands: Approaching spin crossoverINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007Ann M. Schmiedekamp Abstract Octahedral, six-coordinate Co2+ can exist in two spin states: S = 3/2 and S = 1/2. The difference in energy between high spin (S = 3/2) and low spin (S = 1/2) is dependent on both the ligand mix and coordination stereochemistry. B3LYP calculations on combinations of neutral imidazole, NH3, and H2O ligands show that low-spin isomers are stabilized by axial H2O ligands and in structures that also include trans pairs of equatorial NH3 and protonated imidazole ligands, spin crossover structures are predicted from spin state energy differences. Occupied Co d orbitals from the DFT calculations provide a means of estimating effective ligand strength for homoleptic and mixed ligand combinations. These calculations suggest that in a labile biological system, a spin crossover environment can be created. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Diaquadichloridobis(1H -imidazole)manganese(II) at 100 KACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2009Barbara Hachu The mononuclear title complex, [MnCl2(C3H4N2)2(H2O)2], is located on a crystallographic inversion center. The MnII ion is coordinated by two imidazole ligands [Mn,N = 2.2080,(9),Å], two Cl atoms [Mn,Cl = 2.5747,(3),Å] and two water molecules [Mn,O = 2.2064,(8),Å]. These six monodentate ligands define an octahedron with almost ideal angles: the adjacent N,Mn,O, N,Mn,Cl and O,Mn,Cl angles are 90.56,(3), 92.04,(2) and 90.21,(2)°, respectively. Hydrogen bonds between the coordinated water molecules and Cl atoms form a two-dimensional network parallel to (100) involving R42(8) rings. The two-dimensional networks link into a three-dimensional framework through weaker N,H...Cl interactions. Thermogravimetric analysis results are in accordance with the water-coordinated character of the substance and its dehydration in two successive steps. [source] A novel cobalt(II) coordination polymer with an unusual four-connected 42.63.8 topologyACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Guo-Hua Wei In the cobalt(II) coordination polymer poly[[(,2 -benzene-1,3-dicarboxylato){,2 -1,1,-[2,2,-oxybis(ethane-2,1-diyl)]di-1H -imidazole}cobalt(II)] monohydrate], {[Co(C10H14N4O)(C8H4O4)]·H2O}n, two crystallographically distinct CoII cations are four-coordinated by N2O2 donor sets in distorted tetrahedral geometries. The CoII centers are connected by benzene-1,3-dicarboxylate (m -BDC) anions, giving two types of linear chains, which are further joined via meso -helical 1,1,-[2,2,-oxybis(ethane-2,1-diyl)]di-1H -imidazole ligands to yield a thick two-dimensional slab. The compound displays a two-dimensional four-connected 42.63.8 topology, which is unprecedented in coordination polymers. [source] X-ray structure of azide-bound fully oxidized cytochrome c oxidase from bovine heart at 2.9,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2000Ming Jie Fei Two azide ions were identified, one between the Fe and Cu atoms in the O2 -reduction site and the other at the transmembrane surface of the enzyme, in the crystal structure of the azide-bound form of bovine heart cytochrome c oxidase at 2.9,Å resolution. Two geometries, a ,-1,3 type geometry between the Fe and Cu atoms and a terminal geometry on the Fe atom, are equally possible for an azide ion in the O2 -reduction site. The other azide molecule was hydrogen bonded to an amide group of an asparagine and a hydroxyl group of tyrosine in a ,-1,1 type geometry. The antisymmetric infrared bands arising from these azide ions, which show essentially identical intensity [Yoshikawa & Caughey (1992), J. Biol. Chem.267, 9757,9766], strongly suggest terminal binding of the azide to Fe. The electron density of all three imidazole ligands to CuB was clearly seen in the electron-density map of the azide-bound form of bovine heart enzyme, in contrast to the crystal structure of the azide-bound form of the bacterial enzyme [Iwata et al. (1995), Nature (London), 376, 660,669], which lacks one of the three imidazole ligands to CuB. [source] Effect of the Nature of the Substituent in N -Alkylimidazole Ligands on the Outcome of Deprotonation: Ring Opening versus the Formation of N-Heterocyclic Carbene ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Miguel Abstract Complexes [Re(CO)3(N -RIm)3]OTf (N -RIm=N -alkylimidazole, OTf=trifluoromethanesulfonate; 1,a,d) have been straightforwardly synthesised from [Re(OTf)(CO)5] and the appropriate N -alkylimidazole. The reaction of compounds 1,a,d with the strong base KN(SiMe3)2 led to deprotonation of a central CH group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1,a contains three N -MeIm ligands, and its product 2,a features a C-bound imidazol-2-yl ligand. When 2,a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3,a or 4,a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2,a with [AuCl(PPh3)] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1,b,d, with at least one N -arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2H group of an imidazole ligand attacks a central CH group of a neighbouring N -RIm ligand, thus affording the product of CC coupling and ring-opening of the imidazole moiety that has been attacked (2,c,,d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3,c,,d or 4,c,,d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N -RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product. [source] | ||||||||||