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921.
György Bor Urs K. Dietler Pier Liugi Stanghellini Giuliana Gervasio Rosanna Rossetti Gino Sbrignadello Giovanni A. Battiston 《Journal of organometallic chemistry》1981,213(1):277-292
Co6C(CO)12S2 (I) has been isolated in crystalline form from the mixture of more than a dozen of carbonyl products formed when Co2(CO)8 reacts at room temperature with CS2. Crystals of I are monoclinic with space group Cc, and lattice constants a 16.250(5), b 9.413(4), c 16.036(5) Å, β 116.77(4)°. Structure refinement gave R 0.034 for 1974 reflections. The CCo6S2 core of the molecule possesses idealized D3h geometry. It is composed of a Co6 trigonal prism, enclosing a C atom in the centre, and the triangular faces are capped symmetrically by the two S atoms. The core contains two sorts od CoCo distances: short one (2.432 Å) along the triangular edges, and long ones (2.669 Å) along the lateral edges. The average CoC distance is 1.94 Å, and the average CoS distance 2.192 Å.13CO-enriched samples were prepared photochemically and their IR spectra used in the assignment of the CO stretching frequencies. The CO stretching force constant was calculated to be 1670(2) Nm-1.By the use of 13CS2, I has also been obtained in a selectively carbido-13C-labelled form. The vibrational frequencies of the carbide atom were observed, and that at 819 cm-1 (13C: 790 cm-1) assigned to the species , and that at 548 cm-1 (13C: 535.5 cm-1) to species E′. For the Co-C(carbide) force constant a value of 155 Nm-1 was calculated. The cobalt—sulphur stretching frequencies were found at 309 cm-1 () and 239 cm-1 (E′). The CoS stretching force constant, 78 Nm-1, is considerably lower than that obtained for SCo3-(CO)9, viz. 112 Nm-1. 相似文献
922.
Antonova AB Bruce MI Ellis BG Gaudio M Humphrey PA Jevric M Melino G Nicholson BK Perkins GJ Skelton BW Stapleton B White AH Zaitseva NN 《Chemical communications (Cambridge, England)》2004,(8):960-961
Elimination of AuX(PR3)(X = halogen, R = Ph, tol) occurs readily in reactions between compounds containing C(sp)- or C(sp2)-X bonds and alkynyl or polyynyl gold(I) complexes; this reaction has been applied to the syntheses of complexes containing a variety of metal centres linked by C(n) chains (n up to 16). 相似文献
923.
Giovanni Calaresu Patrizia Piras Gavina Carta Roberta Galarini Giannina Chessa 《Accreditation and quality assurance》2006,11(1-2):10-16
A measurement uncertainty estimated for aflatoxin M1 determination in milk sample has been calculated using data generated from analytical method validation studies. The protocol
adopted is described in detail in document LGC/VAM/1998/088. The uncertainty budget was based on precision, trueness and ruggedness
data. The individual contributions are described in detail. The expanded uncertainty for aflatoxin M
1 at a concentration of 20 ng L−1 was estimated as 2.81 ng L−1. This was calculated using a coverage factor of two which gives a level of confidence of approximately 95%.
Presented at AOAC Europe / Eurachem Symposium March 2005, Brussels, Belgium 相似文献
924.
Phillips ST Piersanti G Rüth M Gubernator N van Lengerich B Bartlett PA 《Organic letters》2004,6(24):4483-4485
The synthesis of @-tide beta-strand peptidomimetics has been improved such that oligomers now can be obtained from solution- and solid-phase synthesis protocols approaching the efficiency and flexibility of peptide chemistry. These methods enable the synthesis of @-tide oligomers with a variety of amino acids and with lengths up to 13 units. [reaction: see text] 相似文献
925.
Chillemi G Barone V D'Angelo P Mancini G Persson I Sanna N 《The journal of physical chemistry. B》2005,109(18):9186-9193
In this paper, we present a state-of-the-art 100 ns molecular dynamics simulation of a cadmium(II) aqueous solution that highlights a very flexible ion first coordination shell which transits between hexa- and heptahydrated complexes. From this investigation, a dynamical picture of the water exchange process emerges that takes place through an associative mechanism for the solvent substitution reaction. Our procedure starts from the generation of an effective two-body potential from quantum mechanical ab initio calculations in which the many-body ion-water terms are accounted for by the polarizable continuum method (PCM). This approach is computationally very efficient and has allowed us to carry out extremely long molecular dynamics simulations, indispensable to reproduce the dynamic properties of the cadmium(II) aqueous solution. Quantum mechanical ab initio calculations of the hexa- and heptahydrated complexes extracted from MD configurations have revealed stable minima for both clusters with the water molecules arranged in T(h)() and C(2) symmetries in the hexa- and heptahydrated complexes, respectively, with a slight energetic preference for the heptahydrated one. Finally, a comparison of the calculated hexa- and heptahydrated cluster IR and Raman spectra with the experimental data in the literature, has demonstrated that the IR spectroscopy is not able to distinguish between the two species, whereas the Raman spectrum of the Cd(2+)-(H(2)O)(7) cluster provides a better agreement with the experimental data. 相似文献
926.
Fast GC for the analysis of citrus oils 总被引:2,自引:0,他引:2
Mondello L Casilli A Tranchida PQ Costa R Dugo P Dugo G 《Journal of chromatographic science》2004,42(8):410-416
In this investigation, the gas chromatographic (GC) analysis of citrus essential oils is carried out in 3.3 min, with a speed gain of almost 14 times in comparison with traditional GC procedures. The fast method that is developed requires the application of severe experimental conditions (accelerated temperature program rates, high inlet pressures, and split ratios) and, thus, the support of adequate instrumentation. The samples investigated can be considered to be rather complex and, although a slight loss in peak resolution is observed, the overall analytical result is excellent. All data obtained are compared with that of a conventional application on the same matrices. This is done in order to evaluate the effectiveness and advantages of fast GC achieved with narrow bore columns. 相似文献
927.
Giovanni Alberti 《Annali di Matematica Pura ed Applicata》1993,165(1):49-86
We study conditions under which a functional F(u, B) admits an integral representation of the form $$F(u, B) = \int\limits_B {f(x, D^k u(x)) dx.} $$ 相似文献
928.
Ambrosi G Formica M Fusi V Giorgi L Guerri A Lucarini S Micheloni M Paoli P Rossi P Zappia G 《Inorganic chemistry》2005,44(9):3249-3260
The synthesis and characterization of new polydentate ligand 2-(N),2'-(N')-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1(N'),2(N),2'(N')-trimethyl-2,2'-diaminodiethylamine (L3) is reported. The coordination properties of L3 and of two analogous macrocyclic ligands (L1 and L2) toward Cu(II) and Zn(II) metal ions are reported. All three ligands show the 3-hydroxy-2(1H)-pyridinone (HPO) groups attached as sidearms to a polyaza fragment, which is a macrocyclic framework in the case of L1 and L2 while it is an open chain in the case of L3. The role of the polyaza fragments in preorganizing the two sidearms was investigated. The basicity of L3 and the binding properties of L1-L3 were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). UV-vis spectra as well 1H and 13C NMR experiments were used to understand the role of the HPO and of the polyaza fragments in the stabilization of the cations. While L1 forms stable mono- and dinuclear complexes, L2 and L3 can form only mononuclear species with each of the metal ions investigated. In the main mononuclear species of L2 and L3, the two HPO moieties stabilize the M(II) in a square planar geometry due to the two oxygen atoms of each HPO. The coordination sphere of the metal is completed by adding a secondary ligand such as water molecules in the case of Cu(II) systems or OH- in the Zn(II) systems. These results are confirmed by the crystal structures of the [CuH(-1)L2]+ and [CuH(-1)L3]+ species reported herein. Two conformations of L1 can be hypothesized in the formation of the dinuclear species, as suggested by NMR experiments on the [ZnH(-2)L1] species, which shows two conformers slowly interchanging on the NMR time scale, one of which was found to be more insoluble. 相似文献
929.
Complexes of the type syn-(R,S)-Me(3)dienPtL (Me(3)dien = N,N',N' '-trimethyldiethylenetriamine; L = guanine or hypoxanthine derivative) have two rotamers, a feature useful for assessing hydrogen-bond interactions between a Me(3)dien NH group and either the O6 or the phosphate group of the coordinated L. The two rotamers are defined as endo and exo for the rotamer with the six-membered ring of the purine on the same side and on the opposite side, respectively, of the coordination plane as the N-Me's. For L = 5'-GMP and 5'-IMP the endo rotamer is the exclusive form (at neutral and basic pH) or is present at 90% and more (low pH where 5'-phosphate group is protonated). A 5'-phosphate group can be positioned to form a direct H-bond with a Me(3)dien NH group only in the endo form; such an H-bond explains this high endo preference. Such a direct phosphate-NH H-bond is not possible for other complexes used in this study because either L has no phosphate group (9-EtG, Guo) or the phosphate is at the 3'-position (3'-GMP and 3'-IMP), too far for H-bonding. Nevertheless, a preference for the endo rotamer was observed for these L also. This result is opposite to that expected both from potential steric repulsion of the L O6 with the N-Me groups and also from the lack of a potential favorable H-bond interaction between L O6 and a Me(3)dien NH. For the 9-EtG adduct, the temperature dependence of the endo/exo equilibrium and the activation parameters for endo/exo interconversion suggest that the preference for the endo rotamer arises from the hydration of the Me(3)dien NH groups; such hydration is favorable in the endo rotamer. At basic pH, N1H deprotonation increases the H-bond capacity of O6, and the exo rotamer increases in stability, becoming the dominant rotamer for the 9-EtG and Guo adducts. For L = 3'-GMP and 3'-IMP, stabilization of the endo form upon phosphate deprotonation at neutral pH was observed. This result is attributed to an H-bonding network involving water, the 3'-phosphate, and the Me(3)dien NH groups. 相似文献
930.
Paolo Ganis Donatella Furlani Daniele Marton Giuseppe Tagliavini Giovanni Valle 《Journal of organometallic chemistry》1985,293(2):207-212
The crystal structure of (C6H5)3SnCH2CHCH2 has been determined. The asymmetric unit consists of two molecules of triphenylallyltin having virtually the same conformation. Their geometrical parameters exclude pπ-dπ bonding between the metal and the allyl double bond, and seem to be in a better agreement with a σ-π conjugation effect. 相似文献