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51.
Redouane Chebout Didier Tichit Géraldine Layrac Akila Barama Bernard Coq Iuliana Cota Eliana Ramirez Rangel Francisco Medina 《Solid State Sciences》2010,12(6):1013-1017
A new route for the preparation of basic mixed oxides using nanocomposite precursors obtained from layered double hydroxides (LDH) was investigated. These nanocomposites have been prepared by intercalation of negatively charged guest entities containing Ca2+, Sr2+, Ba2+ or La3+ cations in the interlayer space of host Mg/Al LDH by anionic exchange. The guest entities have been previously prepared by complexation of the required cations in the presence of edta or citrate chelating anions. Intercalation of [Mn+(edta)](4?n)? or [La(cit)OH]? complexes is proved by elemental analysis, XRD analysis and FT-IR spectroscopy. However, in order to satisfy the charge equilibrium in the materials, (edta)4? and (citrate)3? species are also co-intercalated in the nanocomposites. The basic properties of the mixed oxides obtained after thermal decomposition of the nanocomposites precursors were evaluated in the disproportionation of 2-methyl-3-butyn-2-ol (MBOH) and the transesterification of 1-phenylethanol with diethylcarbonate (DEC). The Sr- and Ba-containing mixed oxides exhibit basicity close to the one of MgO and Mg(La)O mixed oxides. A comparative study of the reactivity of La-containing mixed oxides obtained following different preparation routes, i.e. coprecipitation or anionic exchange, allows to conclude that the nanocomposite route led to the most active samples. 相似文献
52.
Merli D Speltini A Ravelli D Quartarone E Costa L Profumo A 《Journal of chromatography. A》2010,1217(46):7275-7281
Presented hereafter is the novel application of differently functionalized multi-walled carbon nanotubes (f-MWCNTs) as stationary phases for the GC separation of C(1)-C(5) alcohols and esters. Low-cost packed columns, easily prepared in laboratory, were used with satisfactory results. Depending on the functional groups introduced on the pristine MWCNTs, remarkably different behaviours have been observed, thus indicating that derivatization is a key factor to achieve optimal resolution. The best performance was shown by the 2,2'-(ethylenedioxy)diethylamine derivatized MWCNTs, allowing the separation of alcohol isomers, for this reason chosen for the investigation of fermentation by-products in distilled spirits. The degree of derivatization has been assessed for each packing material by thermogravimetric analysis (TGA). A computational study has been performed to correlate the physico-chemical properties of alcohol probes with the retention behaviour. 相似文献
53.
54.
Structural effects in the kinetic behavior of the monomer-dimer surface reaction over nondeterministic fractal surfaces 总被引:2,自引:0,他引:2
A study is made of the segregation effect of adsorbed species related to the inner structure of two bidimensional adsorbent fractals, the incipient percolation cluster (IPC) and the backbone of the IPC, and their connection with the rate-determining step of the kinetic mechanism of the monomer-dimer (MD) surface reaction on those fractals. Production, R(AB), is proportional to the concentration of A in the gas phase y(A) and to the fraction of vacant superficial sites x(E) (R(AB)=y(A)x(E)), and it is shown that adsorption of the monomer is the rate-controlling step of the reaction mechanism. 相似文献
55.
Quinolones are degraded by light with loss of their antimicrobial activity, generating active species or radicals. Evidence exists that some fluoroquinolones (lomefloxacin, fleroxacin and enoxacin) induce damage to the cellular membrane and DNA cleavage by photosensitization. In this study, the genotoxic potential of the quinolones ofloxacin, nalidixic acid and ciprofloxacin (three antimicrobials frequently used in therapy) was evaluated upon irradiation with UV light by using the comet assay on cells of the Jurkat line. The results demonstrate that there are significant differences between the control groups (positive control with 50 microM H2O2, negative controls without drug and with and without irradiation) and the groups of irradiated quinolones (ofloxacin 2.76 x 10(-5) M, nalidixic acid 2.15 x 10(-4) M and ciprofloxacin 2.01 x 10(-5) M), indicating that, at the dose of irradiation employed (necessary to produce 50% photodegradation), the photodecomposition of the quinolones enhanced DNA damage. The unirradiated drugs also exhibited genotoxicity significantly different from that of the negative control. 相似文献
56.
Mauro Vaccaro Dr. Gaetano Mangiapia Dr. Luigi Paduano Prof. Eliana Gianolio Dr. Antonella Accardo Dr. Diego Tesauro Dr. Giancarlo Morelli Prof. 《Chemphyschem》2007,8(17):2526-2538
The structural and relaxometric characterization of a novel class of supramolecular aggregates, as potential tumor‐specific contrast agents in magnetic resonance imaging (MRI), is reported. The aggregates are based on a new monomer with an upsilon shape (MonY) that contains, in the same molecule, all three fundamental tasks that are required: 1) a hydrophobic moiety that allows the formation of supramolecular aggregates; 2) the bioactive CCK8 peptide for target recognition; and 3) a chelating agent able to give stable gadolinium complexes. As indicated by dynamic light scattering and small‐angle neutron scattering (SANS) measurements, MonY and its gadolinium complex MonY(Gd) aggregate in aqueous solution to give ellipsoidal micelles with a ratio between the micellar axes of ≈1.7 and an aggregation number Nagg of ≈30. There are no differences in the aggregation behavior of MonY and MonY(Gd), which indicates that the presence of metal ions, and therefore the reduction of the net charge, does not influence the aggregation behavior. When MonY or MonY(Gd) are blended with dioleoyl phosphatidylcholine (DOPC), the aggregation behavior is dictated by the tendency of DOPC to give liposomes. Only when the amount of MonY or MonY(Gd) is higher than 20 % is the coexistence of liposomes and micelles observed. The thickness d of the bilayer is estimated by SANS to be ≈35–40 Å, whereas cryogenic transmission electron microscopy images show that the diameter of the liposomes ranges from ≈50 to 150 nm. Self‐assembling micelles of MonY(Gd) present high relaxivity values (r1p=15.03 mM ?1 s?1) for each gadolinium complex in the aggregate. Liposomes containing MonY(Gd) inserted in the DOPC bilayer at a molar ratio of 20:80 present slightly lower relaxivity values (r1p=12.7 mM ?1 s?1), independently of their internal or external position in the liposome. 相似文献
57.
Silvio Aime Eliana Gianolio Davide Corpillo Camilla Cavallotti Giovanni Palmisano Massimo Sisti GiovanniB. Giovenzana Roberto Pagliarin 《Helvetica chimica acta》2003,86(3):615-632
The three novel pyridine‐containing 12‐membered macrocyclic ligands 1 – 3 were synthesized. The coordinating arms are represented by three acetate moieties in 1 and 3 and by one acetate and two phosphonate moieties in 2 . In all three ligands, the acetate arm in the distal position is substituted, with a benzyl group in 1 and 2 and with an arylmethyl moiety in 3 . The relaxivities r1p (20 MHz, 25°) of GdIII complexes are: GD?1 , r1p=8.3 mM ?1 s?1; GD?2 , r1p8.1 mM ?1 s?1; Gd?3 , r1p10.5 mM ?1 s?1. 1H‐NMRD and 17O‐NMR T2 data show that Gd?1 and Gd?3 contain two H2O molecules in the inner sphere, whereas the presence of two phosphonate arms allows the coordination of only one H2O molecule in Gd?2 . Interestingly, the exchange lifetime of coordinated H2O in the three complexes is similar in spite of the difference in the coordination number of the GdIII ion (i.e., 9 in Gd?1 and Gd?3 , and 8 in Gd?2 ). 1H‐Relaxometric measurements at different pH and in the presence of lactate and oxalate were carried out to get some insight into the formation of ternary complexes from Gd?1 and Gd?3 . Finally, it was found that binding to human‐serum albumin (HSA) of Gd?1 and Gd?2 , though weak, yields limited relaxivity enhancements, likely as a consequence of effects on the hydration sphere caused by donor atoms on the surface of the protein. 相似文献
58.
The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber. 相似文献
59.
Leonardo Manzoni Laura Belvisi Eliana Di Carlo Carlo Scolastico 《Tetrahedron letters》2004,45(33):6311-6315
By a stereoselective alkylation approach a synthesis of eight enantiopure, sterically constrained Cα-tetrasubstituted azabicycloalkane amino acids was carried out. 相似文献
60.
The problem of classifying finite projective planes
of order n with an automorphism group G and a point orbit
on which G acts two-transitively is investigated in considerable detail, under the assumption that
has length at last n. Combining old and new results a rather satisfying classification is obtained, even though some cases for orbit lengths n and n + 1 remain unsolved. 相似文献