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Ligand Bound (ligand + bound)
Selected AbstractsTripyrrinatocadmium Complexes: Enforcing Supramolecular Aggregation by a Large IonEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Martin Bröring Abstract A newly developed method for the preparation of free base tripyrrin ligands HTrpy by cyanide-promoted demetalation of nickel chelates TrpyNiNCO was used in order to explore the chemistry of cadmium tripyrrins TrpyCdX with a variety of anionic co-ligands X. The introduction of the large CdII ion into the tripyrrin N3 coordination site was accomplished by the use of cadmium acetate as the metal precursor. Ligand exchange experiments using sodium salts of different anions disclose a marked tendency for pentacoordination, which is achieved either by the formation of chelates or of 1D coordination polymers that form as a consequence of the size of the central metal. The attempted introduction of chlorido, iodido, or cyanato ligands thus leads mainly to decomposed material, while the use of 1,1,1-trifluoracetylacetonate, salicylate, and acetate ligands results in stable, pentacoordinate and monomeric complexes with the external ligand bound as a four- or six-membered O,O -chelate ring. With the pseudohalogenido ligands thiocyanate, selenocyanate, and azide as well as with the weakly coordinating trifluoroacetate 1D coordination polymers with a variety of chain structures were obtained and investigated by X-ray diffraction studies. Interestingly TrpyCdN3 is present in the crystal as a coordinatively and hydrogen-bonded methanol adduct with a dimeric repeating subunit. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Proximal ligand motions in H93G myoglobinFEBS JOURNAL, Issue 19 2002Stefan Franzen Resonance Raman spectroscopy has been used to observe changes in the iron,ligand stretching frequency in photoproduct spectra of the proximal cavity mutant of myoglobin H93G. The measurements compare the deoxy ferrous state of the heme iron in H93G(L), where L is an exogenous imidazole ligand bound in the proximal cavity, to the photolyzed intermediate of H93G(L)*CO at 8 ns. There are significant differences in the frequencies of the iron,ligand axial out-of-plane mode ,(Fe,L) in the photoproduct spectra depending on the nature of L for a series of methyl-substituted imidazoles. Further comparison was made with the proximal cavity mutant of myoglobin in the absence of exogenous ligand (H93G) and the photoproduct of the carbonmonoxy adduct of H93G (H93G-*CO). For this case, it has been shown that H2O is the axial (fifth) ligand to the heme iron in the deoxy form of H93G. The photoproduct of H93G-*CO is consistent with a transiently bound ligand proposed to be a histidine. The data presented here further substantiate the conclusion that a conformationally driven ligand switch exists in photolyzed H93G-*CO. The results suggest that ligand conformational changes in response to dynamic motions of the globin on the nanosecond and longer time scales are a general feature of the H93G proximal cavity mutant. [source] Video Microscopy for the Investigation of Gas Phase CopolymerizationMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2005Daniela Ferrari Abstract Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using 13C NMR analysis and single particle energy dispersive X-ray (EDX mapping). This allowed us to adapt the "polymer growth and particle expansion model" to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the 13C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration. Snapshot of the polymer particles taken after 165 min of ethylene-1-butene copolymerization with catalyst 1. [source] Structure determination of a Galectin-3,carbohydrate complex using paramagnetism-based NMR constraintsPROTEIN SCIENCE, Issue 7 2008Tiandi Zhuang Abstract The determination of the location and conformation of a natural ligand bound to a protein receptor is often a first step in the rational design of molecules that can modulate receptor function. NMR observables, including NOEs, often provide the basis for these determinations. However, when ligands are carbohydrates, interactions mediated by extensive hydrogen-bonding networks often reduce or eliminate NOEs between ligand and protein protons. In these cases, it is useful to look to other distance- and orientation-dependent observables that can constrain the geometry of ligand,protein complexes. Here we illustrate the use of paramagnetism-based NMR constraints, including pseudo-contact shifts (PCS) and field-induced residual dipolar couplings (RDCs). When a paramagnetic center can be attached to the protein, field-induced RDCs and PCS reflect only bound-state properties of the ligand, even when averages over small fractions of bound states and large fractions of free states are observed. The effects can also be observed over a long range, making it possible to attach a paramagnetic center to a remote part of the protein. The system studied here is a Galectin-3,lactose complex. A lanthanide-binding peptide showing minimal flexibility with respect to the protein was integrated into the C terminus of an expression construct for the Galectin-3,carbohydrate-binding domain. Dysprosium ion, which has a large magnetic susceptibility anisotropy, was complexed to the peptide, making it possible to observe both PCSs and field-induced RDCs for the protein and the ligand. The structure determined from these constraints shows agreement with a crystal structure of a Galectin-3,N -acetyllactosamine complex. [source] Dimeric (isoquinoline)(N -salicylidene- d,l -glutamato)copper(II) ethanol solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Vratislav Langer The title racemic complex, bis[,- N -(2-oxidobenzylidene)- d,l -glutamato(2,)]bis[(isoquinoline)copper(II)] ethanol disolvate, [Cu2(C12H11NO5)2(C9H7N)2]·2C2H6O, adopts a square-pyramidal CuII coordination mode with a tridentate N -salicylideneglutamato Schiff base dianion and an isoquinoline ligand bound in the basal plane. The apex of the pyramid is occupied by a phenolic O atom from the adjacent chelate molecule at an apical distance of 2.487,(3),Å, building a dimer located on the crystallographic inversion center. The Cu...Cu spacing within the dimers is 3.3264,(12),Å. The ethanol solvent molecules are hydrogen bonded to the dimeric complex molecules, forming infinite chains in the a direction. The biological activity of the title complex has been studied. [source] Ligand binding at the transthyretin dimer,dimer interface: structure of the transthyretin,T4Ac complex at 2.2,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2005Vivian Cody The crystal structure of the complex of human transthyretin (hTTR) with 3,3,,5,5,-tetraiodothyroacetic acid (T4Ac) has been determined to 2.2,Å resolution. The complex crystallizes in the orthorhombic space group P21212, with unit-cell parameters a = 43.46, b = 85.85, c = 65.44,Å. The structure was refined to R = 17.3% and Rfree = 21.9% for reflections without any ,-cutoff. T4Ac is bound in both the forward and the reverse mode in the two binding sites of hTTR. In the forward orientation, T4Ac binds in a position similar to that described for thyroxine (T4) in the orthorhombic hTTR,T4 complex. In this orientation, the iodine substituents of the phenolic ring are bound in the P3,/P2 halogen pockets. In the reverse orientation, which is the major binding mode of T4Ac, the ligand is bound deep in the TTR channel, with the carboxylic group bound in the P3, pocket and forming simultaneous polar interactions with the residues constituting the two hormone-binding sites. Such interactions of a thyroxine-analogue ligand bound in the reverse mode have never been observed in TTR complexes previously. [source] | ||||||||||