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Same Ligand (same + ligand)
Selected AbstractsStructure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H8OHECEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004Ulrike A. Böttger Abstract The solid-state structures of two new homodinuclear chelate complexes with the late lanthanide(III) ions Yb and Lu, [Na2(Yb2OHEC)].14.5H2O (1), and [Na2(Lu2OHEC)].14.5H2O (2) (H8OHEC = 1,4,7,10,14,17,20,23-octaazacyclohexacosane- 1,4,7,10,14,17,20,23-octaacetic acid), have been determined by X-ray crystal structure analysis. Each lanthanide(III) ion is coordinated by eight donor atoms of the ligand and the geometry of the coordination polyhedron approaches a bicapped trigonal prism. These structures are compared with those of the homodinuclear chelate complexes with the same ligand and the mid to early lanthanide(III) ions Gd, Eu, La and also Y. A distinctive structural change occurs across the lanthanide series. The centrosymmetric mid to early lanthanide(III) complexes are all ninefold-coordinated in a capped square antiprismatic arrangement with a water molecule coordinated in a prismatic position. This structure is maintained in aqueous solution, together with an asymmetric minor isomer. The late lanthanide(III) OHEC complexes not only lack the inner-sphere water, but the change of coordination sphere also results in a loss of symmetry of the whole complex molecule. The observed change of coordination mode and number of the lanthanide ion may offer a geometric model for the isomerization process in eight- and ninefold-coordinated complex species that are isomers in a possible coordination equilibrium observed by NMR in aqueous solution. This model may also explain the intramolecular rearrangements necessary during water exchange in the inner coordination sphere of the complex [(Gd2OHEC)(H2O)2]2, through a slow dissociative mechanism. Protonation constants of the H8OHEC ligand and complex formation constants of this ligand with GdIII, CaII, CuII and ZnII have been determined by solution thermodynamic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Comparison of the inward- and outward-open homology models and ligand binding of human P-glycoproteinFEBS JOURNAL, Issue 23 2009Ilza K. Pajeva An homology model of human P-glycoprotein, based on the X-ray structure of the recently resolved mouse P-glycoprotein, is presented. The model corresponds to the inward-facing conformation competent for drug binding. From the model, the residues involved in the protein-binding cavity are identified and compared with those in the outward-facing conformation of human P-glycoprotein developed previously based on the Sav1866 structure. A detailed analysis of the interactions of the cyclic peptides QZ59- RRR and QZ59- SSS is presented in both the X-ray structures of mouse P-glycoprotein and the human P-glycoprotein model generated by ligand docking. The results confirm the functional role of transmembrane domains TM4, TM6, TM10 and TM12 as entrance gates to the protein cavity, and also imply differences in their functions. The analysis of the cavities in both models suggests that the ligands remain bound to the same residues during the transition from the inward- to the outward-facing conformations. The analysis of the ligand,protein interactions in the X-ray complexes shows differences in the residues involved, as well as in the specific interactions performed by the same ligand within the same protein. This observation is supported by docking of the QZ59 ligands into human P-glycoprotein, thus aiding in the understanding of the complex behavior of P-glycoprotein substrates and inhibitors. The results confirm the possibility for multispecific drug interactions of the protein, and are important for elucidating the P-glycoprotein function and ligand interactions. [source] Cooperativity and allostery in haemoglobin functionIUBMB LIFE, Issue 2 2008Chiara Ciaccio Abstract Tetrameric haemoglobins display a cooperative ligand binding behaviour, which has been attributed to the functional interrelationship between multiple ligand binding sites. The quantitative description of this feature was initially carried out with a phenomenological approach, which was limited to the functional effect of the occupancy by a ligand molecule of a binding site on further binding steps. However, subsequent development of structural,functional models for the description of the cooperativity in haemoglobin brought about a much deeper information on the interrelationships between ligand binding at the heme and structural variations occurring in the surrounding free subunits. This approach opened the way to the evolution of the concept of allostery, which is intended as the structural,functional effect exerted by the presence of a ligand in a binding site on other binding sites present in the same molecule. This concept can be applied to either sites for the same ligand (homotropic allostery) and for sites of different ligands (heterotropic allostery). Several models trying to take into account the continuous building up of structural and functional information on the physicochemical properties of haemoglobin have been developed along this line. © 2008 IUBMB IUBMB Life, 60(2): 112,123, 2008 [source] Kinetic studies of biological interactions by affinity chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2009John E. Schiel Abstract The rates at which biological interactions occur can provide important information on the mechanism and behavior of such processes in living systems. This paper will discuss how affinity chromatography can be used as a tool to examine the kinetics of biological interactions. This approach, referred to here as biointeraction chromatography, uses a column with an immobilized binding agent to examine the association or dissociation of this agent with other compounds. The use of HPLC-based affinity columns in kinetic studies has received particular attention in recent years. Advantages of using HPLC with affinity chromatography for this purpose include the ability to reuse the same ligand within a column for a large number of experiments, and the good precision and accuracy of this approach. A number of techniques are available for kinetic studies through the use of affinity columns and biointeraction chromatography. These approaches include plate height measurements, peak profiling, peak fitting, split-peak measurements, and peak decay analysis. The general principles for each of these methods are discussed in this paper and some recent applications of these techniques are presented. The advantages and potential limitations of each approach are also considered. [source] A novel bridged asymmetric binuclear manganese(II) complex with DTPB [DTPB is 1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2004Xu-Xiu Yan The crystal structure of the title compound, tetrachloro[,-1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane]dimanganese(II) methanol pentasolvate tetrahydrate, [Mn2Cl4(C44H43N13)]·5CH4O·4H2O, contains an asymmetric dinuclear MnII,DTPB [DTPB is 1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane] complex with an intra-ligand bridging group (,NCH2CH2N,), as well as several solvate molecules (methanol and water). Both MnII cations have similar distorted octahedral coordination geometries. One MnII cation is coordinated by a Cl, anion and five N atoms from the ligand, and the other is coordinated by three Cl, anions and three N atoms of the same ligand. The Mn,Mn distance is 7.94,Å. A Cl,H,O,H,O,H,N hydrogen-bond chain is also observed, connecting the two parts of the complex. [source] Tris(tert -butyl isocyanide)bis[tris(4-methoxyphenyl)phosphine]cobalt(I) perchlorate dichloromethane disolvate and tris(tert -butyl isocyanide)bis[tris(4-methoxyphenyl)phosphine]cobalt(II) bis(perchlorate) dichloromethane disolvate: modification of a trigonal,bipyramidal structure with change of metal oxidation stateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2010Clifford A. L. Becker The title complexes, [Co(C5H9N)3(C21H21O3P)2]ClO4·2CH2Cl2, (I), and [Co(C5H9N)3(C21H21O3P)2](ClO4)2·2CH2Cl2, (II), respectively, crystallize in the hexagonal space group P63/m and the monoclinic space group P21/n, respectively. The cation of complex (I) has D3h site symmetry around the Co atom and the overall symmetry is C3h. Complex (II) is best described as having a distorted trigonal,bipyramidal coordination, with a Co site symmetry of Cs. Compounds (I) and (II) form an analogous pair of five-coordinate CoI and CoII complexes with the same ligands, making it possible to establish (i) if the Co site coordination for both complexes is indeed trigonal,bipyramidal, as initially assumed, and (ii) if significant structural differences occur when the oxidation state of the metal is changed. [source] | ||||||||||