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11.
Thermogravimetric (t.g.) and differential scanning calorimetric (d.s.c.) data have been used to study metal–amino acid interactions in adducts of general formula MnCl2 · ngly (gly = glycine, n = 0.7, 2.0, 4.0 and 5.0). All the prepared adducts exhibit only a one step mass loss associated with the release of glycine molecules, except for the 0.7gly adduct, which exhibits two glycine mass loss steps. From d.s.c. data, the enthalpy values associated with the glycine mass loss can be calculated: MnCl2 · 0.7gly = 409 and 399 kJ mol–1, MnCl2 · 2.0gly = 216 kJ mol–1, MnCl2 · 4.0gly = 326 kJ mol–1 and MnCl2 · 5.0gly = 423 kJ mol–1, respectively. The enthalpy associated with the ligand loss, plotted as function of the number of ligands for the n = 2.0, 4.0 and 5.0 adducts, gave a linear correlation, fitting the equation: H (ligand loss)/kJ mol–1 = 67 × (number of ligands, n) + 76. A similar result was achieved when the enthalpy associated with the ligand loss was plotted as a function of the
a(COO–) bands associated with the coordination through the carboxylate group, 1571, 1575 and 1577 cm–1, respectively, for the n = 2.0, 4.0 and 5.0 adducts, giving the equation H (ligand loss) /kJ mol–1 = 33.5 ×
a(COO–) /cm–1 – 52418.5. This simple equation provides evidence for the enthalpy associated with the ligand loss being very closely related to the electronic density associated with the metal–amino acid bonds. 相似文献
12.
An automatic procedure for the determination of ethanol in wines using a flow system based on multicommutation and enzymatic reaction is described. Alcohol oxidase was immobilized on aminopropyl glass beads and packed in an acrylic column. The peroxide due to enzymatic reaction with ethanol reacted with luminol and generated the chemiluminescence radiation that was monitored by using a laboratory-made detector based on photodiodes. The system manifold comprised a set of 3-way solenoid valves controlled by a microcomputer furnished with electronic interfaces, which ran on software written in Quick BASIC 4.5 to provide facilities to perform on-line sample dilution, reagent addition, and data acquisition. After system parameters optimization, ethanol samples were processed without prior pretreatment. The following suitable features were achieved: linear response ranging from 2.5 to 25% (v/v) ethanol, relative standard deviation of 1.8% (n = 10), detection limit of 0.3% (v/v) ethanol, sampling rate of 23 determinations per hour, and low reagent consumption of 0.23 mg luminol and 7 mg hexacyanoferrate (III) per determination. When the results were compared with those obtained using the AOAC Official Method, no significant difference at the 90% confidence level was observed. 相似文献
13.
G. L. Morgans S. M. Scalzullo M. A. Fernandes J. P. Michael W. A. L. van Otterlo 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(5):o309-o311
The title compound, C20H19NO5S2, crystallizes as an almost 2:1 mixture of two molecular orientations (described as Orient‐A and Orient‐B). The consequences of these two orientations is the formation of three types of N—H...O hydrogen‐bonded dimers in which the (Orient‐A + Orient‐A) dimers are likely to be the most stable, while the mixed (Orient‐A + Orient‐B) dimers are more frequent. Extra interactions in the form of C—H...O and C—H...π interactions act to further stabilize these dimers and probably allow the less energetically favourable (Orient‐A + Orient‐B) and (Orient‐B + Orient‐B) hydrogen‐bonded dimers to exist by preventing their conversion to (Orient‐A + Orient‐A)‐only hydrogen‐bonded dimers during the crystal‐growth process. 相似文献
14.
de Farias Robson Fernandes Martínez Leandro Airoldi Claudio 《Transition Metal Chemistry》2002,27(7):748-750
This paper describes the synthesis, characterization and a thermogravimetric (t.g.) study of 11 adducts of general formula MCl2·nL (M = Cu, Co and Sn; n = 1 and 2 for Sn, and 2 for Cu and Co; L = ethyleneurea eu, ethylenethiourea etu, and propyleneurea pu). The i.r. results shows that the eu and pu adducts are coordinated through oxygen, whereas for etu nitrogen is the coordination site. The (C=O) or (C=S) trend is: Cu > Co > Sn. The t.g. curves show that the adducts release ligand molecules in a single mass loss step. As regards considering adducts with the same stoichiometry, the observed thermal stability trend is: etu > pu > eu. 相似文献
15.
H. Oliveira E. A. N. Fernandes E. S. B. Ferraz 《Journal of Radioanalytical and Nuclear Chemistry》1997,217(1):125-129
The elemental composition of pine trees as a function of age was achieved by the tree-ring method. By using instrumental neutron activation analysis, trace elements were determined in individual rings ofPinus elliottii var.elliottii of 32, 14 and 9 years, from an implanted forest ofPinus sp., Buri, São Paulo, far away from industrial pollution. Different components of the system such as needles, pith, bark, soil and litter were also analyzed for 18 elements (As, Br, Ce, Co, Cs, Eu, Fe, Hf, K, La, Mn, Na, Rb, Sc, Sm, Yb, Zn, and Zr). Al, B, Ba, Ca, Fe, K, Mg, and P concentrations were determined by atomic absorption and/or emission spectrometry (AAS; ICP-AES). Some elements have showed similar radial distribution of the concentration for the three ages. Abrupt concentration changes in the pith and ring-bark boundary corresponding to the first and last growth rings were observed. 相似文献
16.
Manuel A. Fernandes Marcus Layh Bernard Omondi 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):o384-o385
The title compound, C10H11N, displays a crystallographic mirror plane that incorporates all the non‐H atoms, as well as the H atoms attached to the aromatic ring. The isocyano group is almost linear and shows an N[triple‐bond]C bond distance of 1.158 (3) Å. 相似文献
17.
Ramo Marceli Fernandes Gelson Manzoni de Oliveira Ernesto Schulz Lang Ezequiel M. Vzquez‐Lpez 《无机化学与普通化学杂志》2004,630(15):2687-2691
The reaction of tellurium(IV) tetrahalides with hydrochloric and hydrobromic acid leads to the formation of (H3O)2[TeX6], which reacts subsequently with (2‐Br‐C5NH5)+X‐ to afford (2‐Br‐C5NH5)2[TeCl6] ( 1 ) and (2‐Br‐C5NH5)2[TeBr6] ( 2 ). The structure of the complex salts were analysed by X‐ray diffractometry affording the centrosymmetric space groups P21/n (monoclinic, 1 ) and P1¯ (triclinic, 2 ). Interionic hydrogen bondings hold their lattices in bidimensional supramolecular arrays not yet described in the literature. The lone electron pair of the AX6E‐system of the hexahalotellurates [TeX6]2‐ (X = Cl, Br) seems to be fully delocalized since only small octahedral deviations were observed for the anionic species. The structures of the title compounds were refined with the Te atoms occupying sites with full point symmetry, approximately m3¯m. In both cases the Te atoms enclose centers of inversion and the octahedrally dynamic structures are enforced and stabilized along the supramolecular lattices by the crystal field of the 2‐Br‐pyridinium cations. 相似文献
18.
19.
Pedro J.?Silva Pedro A.?Fernandes Maria J.?RamosEmail author 《Theoretical chemistry accounts》2003,110(5):345-351
Prostaglandin H synthase catalyzes the oxygenation of arachidonic acid into the cyclic endoperoxide, prostaglandin G2 (PGG2), and the subsequent reduction of PGG2 to the corresponding alcohol, prostaglandin H2 (PGH2), the precursor of all prostaglandins and thromboxanes. Both radical abstraction by a neighboring tyrosyl radical and combined radical/carbocationic models have been proposed to explain the cyclooxygenase part of this reaction. We have used density functional theory calculations to study the mechanism of the formation of the cyclooxygenated product PGG2. We found an activation free energy for the initial hydrogen abstraction by the tyrosine radical of 15.6 kcal/mol, and of 14.5 kcal/mol for peroxo bridge formation, in remarkable agreement with the experimental value of 15.0 kcal/mol. Subsequent steps of the radical-based mechanism were found to happen with smaller barriers. A combined radical/carbocation mechanism proceeding through a sigmatropic hydrogen shift was ruled out, owing to its much larger activation free energy of 36.5 kcal/mol. Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00214-003-0476-9. Electronic Supplementary MaterialSupplementary material is available in the online version of this article at
Electronic Supplementary Material: Supplementary material is available in the online version of this article at 相似文献
20.
José A. Fernandes Susana S. Braga Rute A. Sá Ferreira Martyn Pillinger Luís D. Carlos Paulo Ribeiro-Claro Isabel S. Gonçalves 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):329-333
A 1:1 inclusion compound between octakis(2,3,6-tri-O-methyl)-γ-cyclodextrin (TRIMEG) and the chelate complex Eu(NTA)3·2H2O (NTA=1-(2-naphthoyl)-3,3,3-trifluoroacetonate) was prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and photoluminescence spectroscopy. The results were compared with those obtained for the corresponding native γ-CD adduct. Excitation and emission spectra were measured, and the lifetimes were determined for the Eu3+ first excited state (5D0). The results indicate the presence of only one low-symmetry environment for the Eu3+ cations in the inclusion compounds. Encapsulation of the Europium complex in the two CDs increases the quantum efficiency of the ligand-to-metal energy transfer pathway, but the efficiency of the Eu3+ sensitization was significantly higher with TRIMEG as the host molecule. This may be related with the observation that the two hosts appear to have different influences on the Eu3+ coordination environments for the guest molecule. 相似文献