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Accurate PGSE NMR measurements to identify the level of aggregation in solution of half-sandwich diamino Ru(II) salts
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An accurate methodology to identify the level of aggregation in solution by PGSE NMR measurements: The case of half-sandwich diamino ruthenium(II) salts
No full textThe utility of PGSE NMR measurements in determining hydrodynamic radii (r(H)) and volumes (V(H)) of small- and medium-size molecules (3 angstrom < r(H) < 6 angstrom) was evaluated by performing measurements for a variety of pure deuterated solvents and their solutions containing the internal standard TMSS [tetrakis(trimethylsilyl)silane] also in the presence of a variable concentration of 3BPh(4). It was found that accurate rH and VH values can be obtained by introducing in the Stokes-Einstein equation (D(t) = kT/c pi eta r(H)) not only the correct values for temperature (T) and viscosity (eta) but, particularly, that for the C factor. PGSE NMR measurements were then applied to an investigation of the aggregation tendency of complexes [Ru(eta(6)-cymene)(R(1)R(2)NCH(2)CH(2)NR(1)R(2))Cl]X (R(1) = R(2) = H, 1; R(1) = H, R(2) = H, 2; R(1) = R(2) = Me, 3; X(-) = PF(6)(-) or BPh(4)(-)) in both protic and aprotic solvents with a relative permittivity (epsilon(r)) ranging from 4.81 (chloroform-d) to 32.66 (methanol-d(4)). Compounds I and 2 exhibited a remarkable tendency to aggregate through intercationic N-H(...)Cl and cation/anion N-H(...)FPF(5)(-) hydrogen bonds. In addition to ion pairs, ion triples and ion quadruples were also observed in solution. Compound 3, having no N-H moiety, showed less tendency to aggregate than I and 2, even though it also afforded ion quadruples in apolar and aprotic solvents. Relative anion-cation orientations and arene conformations were investigated by means of (1)H-NOESY and (19)F,(1)H-HOESY NMR spectroscopy. The relative anion-cation position was well-defined, especially for compounds bearing the PF(6)(-) counterion, and was modulated by the nature of the N,N ligand. A progressive slackening of the contact aggregates was observed in the series 1-3 that led to a higher mobility of the anion, as indicated by the observation of less specific interionic NOEs
Aggregation in solution of neutral half-sandwich Ru(II) precatalysts for transfer hydrogenation
No full textDiffusion NMR measurements and ONIOM (B3PW91:UFF) calculations show that amino amidate and acidate half-sandwich Ru(II) precatalysts for transfer hydrogenation have a remarkable tendency to form dimers and even larger aggregates in several solvents, including isopropanol, that is, the solvent used in the catalysis reaction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Application of NOE and PGSE NMR methodologies to investigate non-covalent intimate inorganic adducts in solution
No full textNOE and PGSE NMR experiments provide crucial information for the structural characterization of non-covalent intimate adducts in solution. The possible presence and the favorite relative orientation of the interacting units can be deduced from NOE results, while the size of the non-covalent adducts can be estimated through PGSE measurements. The complementarity of the two methodologies has been successfully used to investigate transition metal complex ion pairs and, to a lesser extent, intermolecular adducts. The main results concerning the solution structures of non-covalent inorganic adducts are reported and compared with those in the solid state and those from theoretical calculations
A Multicationic Dab-Organo-Ruthenium Dendrimers: Synthesis and Intra e Intermolecular NMR Characterization
No full textLinear gold(I) complexes: A systematic NMR/DFT study on the ligand effect on the structure of the ion pair in solution
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