1,720,992 research outputs found
2.Synthesis, crystal structure and magnetic properties of the mixed-ligand complex [Gd(F3CCO2)3(phen)2(H2O)]
No full textThe mononuclear gadolinium mixed-ligand complex [Gd(CF3CO2)3(phen)2(H2O)] has been prepared and structurally characterized by X-ray crystallography. Two complex molecules are doubly bridged by H bonds between carboxylate and aqua ligands with a Gd−Gd separation of 7.16(1) Å. Magnetic susceptibility and EPR measurements showed weak magnetic exchange coupling of the 3D type.Fil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Baggio, Ricardo Fortunato. Comisión Nacional de Energía Atómica; ArgentinaFil: Calvo, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Garland, Marías. Universidad de Chile; ChileFil: Peña, Octavio. Universite de Rennes I; FranciaFil: Perec, Mireille. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin
Overexpression, purification, and biochemical and spectroscopic characterization of copper-containing nitrite reductase from Sinorhizobium meliloti 2011. Study of the interaction of the catalytic copper center with nitrite and NO
Get PDFThe entire nirK gene coding for a putative copper-nitrite reductase (Nir) from Sinorhizobium meliloti 2011 (Sm) was cloned and overexpressed heterologously in Escherichia coli for the first time. The spectroscopic and molecular properties of the enzyme indicate that SmNir is a green Nir with homotrimeric structure (42.5 kDa/subunit) containing two copper atoms per monomer, one of type 1 and the other of type 2. SmNir follows a Michaelis-Menten mechanism and is inhibited by cyanide. EPR spectra of the as-purified enzyme exhibit two magnetically different components associated with type 1 and type 2 copper centers in a 1:1 ratio. EPR characterization of the copper species obtained upon interaction of SmNir with nitrite, and catalytically-generated and exogenous NO reveals the formation of a Cu-NO EPR active species not detected before in closely related Nirs.Fil: Ferroni, Felix Martín. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Guerrero, Sergio Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral; ArgentinaFil: Brondino, Carlos Dante. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin
Carboxylate-Bridged Copper(II)-Lanthanide(III) Complexes [{Cu3Ln2(oda)6(H2O)6}.12H2O]n (Ln = Dy, Ho, Er, Y; oda = oxydiacetate
Get PDFThe hydrothermal reaction of Ln2O3 (Ln = Dy and Ho), Cu(OAc)2·2H2O, and oxydiacetic acid in the approximate mole ratio of 1:3:8 resulted in the formation of two new members of the isostructural series of polymers formulated as [{Cu3Ln2(oda)6(H2O)6}·12H2O]n, crystallizing in the hexagonal crystal system, space group P6/mcc (No. 192). Temperature-dependent magnetic susceptibilities and EPR spectra are reported for the heterometallic compounds Cu−Dy 1, Cu−Ho 2, Cu−Er 3, and Cu−Y 4. The results are discussed in terms of the structure of the compounds, the electronic properties of the lanthanide ions, and the exchange interactions between the magnetic ions.Fil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Calvo, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baggio, Ricardo Fortunato. Comisión Nacional de Energía Atómica; ArgentinaFil: Garland, María Teresa. Universidad de Chile; ChileFil: Peña, Octavio. Universite de Rennes I; FranciaFil: Perec, Mireille. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin
EPR studies of the Mo-enzyme aldehyde oxidoreductase from Desulfovibrio gigas: An application of the Bloch–Wangsness–Redfield theory to a system containing weakly-coupled paramagnetic redox centers with different relaxation rates
Get PDFElectron transfer proteins and redox enzymes containing paramagnetic redox centers with different relaxation rates are widespread in nature. Despite both the long distances and chemical paths connecting these centers, they can present weak magnetic couplings produced by spin-spin interactions such as dipolar and isotropic exchange. We present here a theoretical model based on the Bloch-Wangsness-Redfield theory to analyze the dependence with temperature of EPR spectra of interacting pairs of spin 1/2 centers having different relaxation rates, as is the case of the molybdenum-containing enzyme aldehyde oxidoreductase from Desulfovibrio gigas. We analyze the changes of the EPR spectra of the slow relaxing center (Mo(V)) induced by the faster relaxing center (FeS center). At high temperatures, when the relaxation time T(1) of the fast relaxing center is very short, the magnetic coupling between centers is averaged to zero. Conversely, at low temperatures when T(1) is longer, no modulation of the coupling between metal centers can be detected.Fil: González, Pablo J.. Universidade Nova de Lisboa; PortugalFil: Barrera, Guillermo Ignacio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Moura, José J.G.. Universidade Nova de Lisboa; PortugalFil: Passeggi, Mario Cesar Genaro. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Brondino, Carlos Dante. Universidade Nova de Lisboa; Portuga
Electron transfer pathways and spin–spin interactions in Mo- and Cu-containing oxidoreductases
No full textOxidoreductases containing transition metal ions are widespread in nature and are essential for living organisms. In these enzymes, transition metal ions are present either as mononuclear centers or organized into clusters, accomplishing two main roles. One is to be the core of active sites where the substrate is converted into product, and the other is to serve as electron transfer centers. Oxidoreductases containing multiple redox cofactors bind both the substrate and an external electron donor/acceptor at distant protein sites for them to exchange the electrons involved in the redox reaction. Intra-protein electron transfer occurs through specific pathways that link distant metal cofactors, which may additionally be magnetically coupled. Here we review the current understanding on the molecular properties of these long chemical pathways involved in metal coordination, intra − protein electron transfer processes, and transmitting magnetic interactions in Mo- and Cu-containing oxidoreductases.Fil: González, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Rivas, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Ferroni, Felix Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Brondino, Carlos Dante. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentin
Studying Electron Transfer Pathways in Oxidoreductases
Get PDFOxidoreductases containing transition metal ions are widespread in nature and are essential for living organisms. The copper-containing nitrite reductase (NirK) and the molybdenum-containing aldehyde oxidoreductase (Aor) are typical examples of oxidoreductases. Metal ions in these enzymes are present either as mononuclear centers or organized into clusters and accomplish two main roles. One of them is to be the active site where the substrate is converted into product, and the other one is to serve as electron transfer center. Both enzymes transiently bind the substrate and an external electron donor/acceptor in NirK/Aor, respectively, at distinct protein points for them to exchange the electrons involved in the redox reaction. Electron exchange occurs through a specific intra-protein chemical pathway that connects the different enzyme metal cofactors. Based on the two oxidoreductases presented here, we describe how the different actors involved in the intra-protein electron transfer process can be characterized and studied employing molecular biology, spectroscopic, electrochemical, and structural techniques.Fil: Rivas, Maria Gabriela. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: González, Pablo Javier. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Ferroni, Felix Martín. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Brondino, Carlos Dante. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentin
EPR as a Tool for Study of Isolated and Coupled Paramagnetic Centers in Coordination Compounds and Macromolecules of Biological Interest (Eur. J. Inorg. Chem. 2/2016)
No full textThe cover picture shows a painting by Nilda Marsili inspired by results obtained from single‐crystal EPR experiments performed on an extended lattice of CuII dimers (small squares in the painting), in which the metal centers are coupled by exchange interactions mediated by hydrophobic interactions. The red lines are the theoretical positions of the EPR resonances in the absence of exchange, whereas the red dots between the lines are the experimental positions. Details are presented in the Microreview by C. D. Brondino et al. on p. 192 ff. For more on the story behind the cover research, see the Cover Profile.Fil: Rizzi, Alberto Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Neuman, Nicolás Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: González, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Brondino, Carlos Dante. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentin
Structure and Magnetic Properties of Layered High-Spin Co(II)(L-threonine)2(H2O)2
Get PDFWe report the structure and the magnetic properties of a cobalt(II) compound with the amino acid L-threonine, Co(C4H8NO3)2(H2O)2. It crystallizes in the orthorhombic chiral space group C2221, with a = 5.843(5) Å, b = 10.120(10) Å, c = 22.36(3) Å, and Z =) 4. The Co(II) ion is in a deformed octahedral environment on a 2-fold symmetry axis parallel to the crystallographic axis b. It is bonded to two threonine molecules in a bidentate fashion, via one oxygen from the carboxylate end and the R-amino nitrogen. A water molecule occupies the third independent site.The Co(II) ions are arranged in layers with intralayer and interlayer distances of 5.84 and 11.18 Å, respectively. Magnetic measurements data reflect the molecular character of a compound with weak exchange interactions. EPR measurements in polycrystalline and single-crystal samples indicate a distorted axial symmetry around the Co(II) ion, as expected from the structural results. Eigenvalues and eigenvectors of the g tensor are determined. The measured principal g values (5.81, 4.56, and 2.23) reflect a high-spin Co(II) ion, as suggested by the type of ligands and the molecular symmetry. From the incomplete collapse of the hyperfine structure we estimate 0.25 |J| < 1.2 cm-1 between neighboring Co(II) ions within a layer, transmitted through H-bonds. A higher limit |J´| < 0.07 cm-1 is estimated for the exchange interactions between Co(II) ions in neighboring layers. From a global fit of a spin Hamiltonian with spin 3/2 to magnetization and EPR data we obtain a zero field splitting d ~ 231 cm-1 between the two lowest doublet states. The results are discussed in terms of the molecular and electronic structure of the compound.Fil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Brondino, Carlos Dante. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Calvo, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baggio, Ricardo Fortunato. Comisión Nacional de Energía Atómica; ArgentinaFil: Garland, M.T.. Universidad de Chile; ChileFil: Rapp, R.E.. Universidade Federal do Rio de Janeiro; Brasi
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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