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41.
Geraldo L. Crossetti Carlos A. L. Filgueiras R. Alan Howie James L. Wardell Claudio M. Ziglio 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(11):1279-1281
In the title compound, [NiBr2(C31H32NP)], (I), the second reported example of a nickel–iminophosphine N,P-chelate in which the Ni atom has tetrahedral coordination, the Ni coordination is distorted as a consequence of the N—Ni—P chelate bite angle of 91.07 (6)° compensated by the Br—Ni—Br angle of 126.385 (18)°. In (I) and its analogue, viz. dichloro{[2-(4-isobutyloxazol-2-yl)phenyl]diphenylphosphine-N,P}nickel(II), the Ni—N and Ni—P distances are greater and the N—Ni—P ligand bite angles smaller than those observed in a series of related complexes with square-planar nickel. 相似文献
42.
Griselda Barrera Galland Luciana P. Da Silva Marcos L. Dias Geraldo L. Crossetti Cludio M. Ziglio Carlos A. L. Filgueiras 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2171-2178
A complete 13C NMR characterization of a polymer synthesized with a new Ni‐diimine complex [DADNi(NCS)2, where DAD = 2,6‐iPr? C6H3? N?C(Me)? C(Me)? N? 2,6‐iPr? C6H3] activated by methylaluminoxane by homopolymerization of propylene is presented. The amorphous material was made up mainly of blocks of syndiotactic polypropylene and ethylene–propylene copolymer. Some degree of propylene inversion (<1.2 mol %) and of long isobutyl and 2‐methyl hexyl branching (<1 mol %) were assigned and quantified. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2171–2178, 2004 相似文献
43.
Nery JG Bolbach G Weissbuch I Lahav M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):3039-3048
The formation of diastereoisomeric libraries of oligopeptides through the heterogeneous polymerization of racemic crystals of phenylalanine N-carboxyanhydride (PheNCA) is reported. The diastereoisomeric compositions of the oligopeptides formed on polymerization of (R,S) crystals incorporating the deuterium-tagged S enantiomer were determined by MALDI-TOF mass spectrometry. The racemic mixtures of the oligopeptides longer than pentamers are represented primarily by diastereoisomers of homochiral sequence and with peptides containing only one heterochiral repeating unit. A mechanism comprising the following three sequential steps to account for this unusual observation is proposed: 1) formation of dimers and trimers at a partially damaged liquid/solid interface, 2) chain propagation that takes place within the bulk of the crystal through a lattice-controlled "zipper-like" mechanism between homochiral molecules arranged in a head-to-tail motif to yield crystalline antiparallel beta-sheets of alternating oligopeptide chains of homochiral sequence of opposite handedness, and 3) enantiomeric cross-inhibition that results in chain termination. Induced desymmetrization of the racemic mixtures of the formed peptides was achieved by the polymerization of the mixed quasi-racemic crystals of (R)-PheNCA, ((S)-PheNCA), and (S)-ThieNCA (3-(2-thienyl)-alanine N-carboxyanhydride) of various compositions. These experiments resulted in the formation of nonracemic libraries of oligopeptides composed of homochiral chains of (R)-Phe and copolymers of randomly distributed (S)-Phe and (S)-Thie sequences. From these findings, we propose a stochastic model for the generation of libraries of nonracemic mixtures of oligopeptides from the polymerization of host (R,S)-PheNCA with racemic mixtures of other guest NCA amino acids dissolved in limited quantities in the crystal. 相似文献
44.
Daghastanli KR Ferreira RB Thedei G Maggio B Ciancaglini P 《Colloids and surfaces. B, Biointerfaces》2004,36(3-4):127-137
Membrane proteins from bacteria Pasteurella multocida were used as a model for studying its incorporation into liposomes. An important step to achieve efficient high yield protein incorporation in proteoliposomes is the study of the more suitable lipid composition. To this end, we compared the amount of total protein, reconstituted by co-solubilization methods, into liposomes of phospholipids with different polar head groups and acyl chain lengths. The liposomes and proteoliposomes were characterised by isopycnic centrifugation in sucrose gradient and by dynamic light scattering. Experimental and theoretical results were compared considering the effects exerted through the hydrocarbon chain length, volume, and optimal cross-sectional area of the phospholipid (combined in the geometrical critical packing parameter, lipid–protein matching), critical spontaneous radius of curvature of the bilayer vesicle, phase transition temperature of the lipid and ratio of lipid–protein molecules present in the vesicles. The highest incorporation of multiple proteins was found with dipalmitoylphosphatidylcholine (DPPC), reaching a yield of 93% compared to the lower relative amounts incorporated in proteoliposomes of the other lipids. The incorporation of multiple proteins induces a proportional enhancement of vesicular dimension, since DPPC–proteoliposomes have an average diameter of 1850 Å, compared to the 1430 Å for pure DPPC vesicles. 相似文献
45.
Moura Edmilson M. Terra Vilma R. Siebald Helmuth G. L. de Lima Geraldo M. Paim Lilian A. Dias Fabrícia M. 《Transition Metal Chemistry》2003,28(4):437-442
A series of heterobimetallic complexes containing Ru–Sn bonds, of general formula [RuCp(L)2SnX2Y] [L = PPh3, 1/2 dppe = 1,2-bis(diphenylphosphino)ethane; X, Y = F, Cl and Br], was prepared and studied by elemental analysis, 119Sn-Mössbauer spectroscopy, i.r. and 1H-, 13C-, 19F-, 31P- and 119Sn-n.m.r. spectroscopy. 119Sn-Mössbauer studies allowed determination of the coordination number of the SnII center as well as the group electronegativity of the organometallic fragment [RuCp(L)2]+. These results, supported by multinuclear n.m.r. data suggested that the electronic charge distribution between the RuII and SnII centers are strongly dependant upon the nature of L and the electronegativity of X and Y. 相似文献
46.
Cristian?Linares Daniela?Geraldo Maritza?Paez José?H.?ZagalEmail author 《Journal of Solid State Electrochemistry》2003,7(9):626-631
The activity of the different iron phthalocyanines was examined using the complexes adsorbed on graphite electrodes. The effect of the Fe(II)/(I) formal potential of iron phthalocyanines on the their catalytic activity for the electro-oxidation of hydrazine was investigated. A plot of log k (rate constant at constant potential) versus the Fe(II)/(I) formal potential gives a volcano curve. The rate of the reaction increases with the driving force of the catalyst (measured as its formal potential) and then decreases for higher driving forces. A similar graph is obtained with a plot of log k versus the sum of the Hammett parameters of the substituents on the periphery of the phthalocyanine ligand. A maximum activity is obtained for a complexes having an M(II)/(I) redox potential close to –0.6 V which agrees with previous studies conducted with phthalocyanines of different metals and with cobalt phthalocyanines bearing different substituents.Dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry. 相似文献
47.
48.
Effects of different water storage procedures on the dissolved Fe concentration and isotopic composition of chemically contrasted waters from the Amazon River Basin 下载免费PDF全文
49.
Geraldo Alfonso Ivonne Chvez Vernica Arancibia Juan Manuel Manríquez María Teresa Garland Anna Roig Elies Molins Ricardo Fortunato Baggio 《Journal of organometallic chemistry》2001,620(1-2):32-38
[Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*]n+ (Cp*=pentamethylciclopentadiene, n=0, 1), respectively named complexes V and VI, were synthesized and characterized. The X-ray structure has been solved and 1H-, 13C-NMR and elemental analysis were performed for the n=0 complex. Cyclic voltammetry showed a potential difference of 360 mV within the two redox peaks. An absorption band at 850 nm was assigned to an intervalence band. The Mössbauer investigations show a uniform Fe2+ environment for the neutral compound and two sites, assigned to Fe2+ and Fe3+ for the monoxidized compound. The information gathered by all the previously mentioned techniques indicates that the studied binuclear compound belongs to the mixed valence class II using Robin and Day classification. 相似文献
50.
A series of organotin(IV) derivatives of 2,6-pyridinedicarboxylate has been investigated by Mössbauer spectroscopy in order to elucidate aspects concerning bonding and structural features in the solid state. A geometrical pattern of five-fold coordination at the metal centre has been revealed for SnCl3Bu and SnClBu3 derivatives. Trans stereochemistry for the butyl and vinyl groups of SnCl2Bu2 and SnCl2(Vin)2 derivatives has also been identified by this method. The isomer shift for the divinyl derivative is concurrent to a 7-coordinate metal centre contrasting to that for the dibutyl one. Although there is a discrepancy in isomer shift between these compounds, both have seven-fold coordination at the Sn(IV) nucleus. The resulting data has given evidence that 2,6-pyridinedicarboxylate is acting as a tridentate ligand through pyridil and carbolxylate moiety to all derivatives except for SnClBu3. For the latter, the coordination mode occurs via carboxylate groups. The overall data support distorted geometrical pattern to all complexes in solid state. 相似文献