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排序方式: 共有209条查询结果,搜索用时 531 毫秒
71.
C. Bisio K. Fajerwerg J. M. Krafft P. Massiani G. Martra 《Research on Chemical Intermediates》2008,34(5-7):565-576
Pt/Cs-BEA materials prepared by a classical ion-exchange procedure using two Cs-BEA supports with different Cs loadings, and a reference acidic Pt/H-BEA, have been studied to investigate the effect of the framework basicity (evaluated by FT-IR of adsorbed CO2) on the state of platinum species after the initial steps (introduction of Pt complex by ion-exchange and subsequent calcination) of the preparation procedure. DR-UV data revealed that the framework basicity affects the structure of the Pt2+ complexes introduced as countercations in the zeolite by ion exchange. FT-IR spectra of adsorbed CO indicated that zeolite basicity rules the fate of platinum species in the subsequent calcination. Hence, in Pt/H-BEA essentially well dispersed Ptδ+ (4≥δ≥1) are present, while PtO x particles progressively prevail as the basic character of the zeolite increases. 相似文献
72.
Cyrille Mbemba Katia Sigaud Florent Perret Kinga Suwinska Oleksandr Shkurenko Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2008,61(1-2):29-40
A series of mono-O-alkylated calix [4] arenes derivatives, with alkyl chain lengths of between 1 and 12 carbon atoms are reported. Monoalkylation is best achieved using potassium carbonate as the weak base and the respective alkyl iodide for chain lengths of one to three carbon atoms and using caesium fluoride as the base and the respective alkyl iodide for longer chain lengths. The mono-alkylated derivatives were converted into the tri-para-dimethylaminomethylene derivatives by the para-quinonemethide reaction in good yields. Surface tension measurements showed that at pH 2, 4, 6 and 8 all the tri-dimethylaminomethylene derivatives showed surfactant behaviour, and at pH 2 all show a Critical Micellar Concentration values. No correlation between Critical Micellar Concentration values and chain length is observed. Dynamic Light Scattering measurements showed that the CMC behaviour may be correlated with the observed aggregate sizes. The solid state structure of mono-O-ethoxy-calix[4]arene is described, in this structure a 1-D inclusion polymer is observed. 相似文献
73.
Saúde-Guimarães DA Perry KS Raslan DS Chiari E Barrero AF Oltra JE 《Magnetic resonance in chemistry : MRC》2007,45(12):1084-1087
The chemical transformations of eremantholide C (1), a trypanocidal sesquiterpene lactone isolated from Lychnophora trichocarpha Spreng., gave five new oxide derivatives: 3'-hydroxyeremantholide C (2), 1'-formyleremantholide C (3), 1'-carboxyeremantholide C (4), 1'-carbomethoxyeremantholide C (5) and sodium 1'-carboxylate of eremantholide C (6). The (1)H and (13)C NMR data of all these derivatives were assigned based on 1D and 2D techniques. The derivatives were evaluated against Y and CL strains of Trypanosoma cruzi. All of them were inactive against the Y strain. Compounds 2 and 5 displayed 100% activity on the CL strain while compounds 4 and 6 were partially active on the CL strain. 相似文献
74.
Giraudet J Dubois M Guérin K Delabarre C Hamwi A Masin F 《The journal of physical chemistry. B》2007,111(51):14143-14151
The conversion of (C2.5F)n fluorine-graphite intercalation compounds (GIC) into covalent graphite fluoride during a post-treatment in pure F2 gas is studied by solid-state NMR. First, a careful characterization of the starting material is performed; in particular, for the first time for fluorinated carbons, two-dimensional 19F--> 13C cross-polarization wide-line separation (CP-WISE) experiments were carried out. This completes the classical NMR data such as 19F and 13C chemical shifts, quantitative 13C solid echo, and C-F bond length measurements, which were estimated by dipolar recoupling using inverse CP MAS. The data of the raw (C2.5F)n and of the samples post-fluorinated at 350, 450, and 550 degrees C were compared to investigate the C-F bonding as a function of the treatment temperature. The C-F bonding is discussed taking into account a hyperconjugation of the C-F bonds with neighboring unfluorinated carbon atoms. 相似文献
75.
Dubois M Guérin K Batisse N Petit E Hamwi A Komatsu N Kharbache H Pirotte P Masin F 《Solid state nuclear magnetic resonance》2011,40(4):144-154
Solid state NMR measurements using 13C, 1H and 19F nuclei (MAS, CP-MAS) underline the surface chemistry of nanodiamonds from different synthesis (detonation, high pressure high temperature and shock compression). The comparison of the spin-lattice relaxation times T1 and physicochemical characterization (spin densities of dangling bonds, specific surface area and Raman and infrared spectroscopies) for the various samples, as synthesized, chemically purified and fluorinated allows the nature and the location of the various groups, mainly C-OH, C-H and C-F to be investigated. C-OH groups are located only on the surface whereas C-H and dangling bonds seem to be distributed in the whole volume. Fluorination was studied as a chemical treatment for purification and change of the hydrophobicity through the conversion of the C-OH groups into covalent C-F bonds. 相似文献
76.
Braga D D'Agostino S Grepioni F Gandolfi M Rubini K 《Dalton transactions (Cambridge, England : 2003)》2011,40(18):4765-4777
15-crown[5] or 18-crown[6] complexes of alkali, transition metal and ammonium cations together with polyprotic inorganic and organic anions have been used to construct crystalline molecular salts based on hydrogen bonded anionic networks. This new class of organic-inorganic complexes displays a variety of crystal-to-crystal transformations, mainly associated to the loss/uptake of water molecules and/or to the ionic reorganization accompanying phase transitions on varying the temperature. The dehydration and phase transition processes have been investigated by DSC, TGA and variable temperature X-ray powder diffraction. Most of the complexes described herein have been prepared by solid state mixing of the solid reactants. 相似文献
77.
Katia Liburdi Raffaello Straniero Ilaria Benucci Anna Maria Vittoria Garzillo Marco Esti 《Applied biochemistry and biotechnology》2012,166(7):1736-1746
In order to use lysozyme as an anti-microbial agent during the winemaking process, hen egg-white lysozyme (LYZ) was covalently
immobilized on two different micro-size magnetic particles (tosyl-activated and carboxylated, TSA and CA, respectively). A
cell suspension of Oenococcus oeni, an oenological strain involved in the winemaking process, was utilized as LYZ substrate. Both a kinetic study and a study
of the stability of free and immobilized LYZ were performed in McIlvane buffer at pH 3.2, that is the average minimum pH value
in wine. The activity and kinetic parameters measured for the free LYZ at pH 3.2 are lower than those reported at the optimum
pH (4.5); however the residual activity at pH 3.2 is sufficient to be of interest for further immobilization and applications
in winemaking. All kinetic parameters of both biocatalysts (LYZ-CA and LYZ-TSA) are altered after immobilization, probably
due to the structural modifications in the active site caused by covalent attachment to the supports. The half-life calculated
at 25 °C was 39 h for free LYZ, while it increased to 280 and 134 h for LYZ-TSA and LYZ-CA, respectively. This result indicates
that immobilization improves the enzyme stability and that LYZ can be utilized in wine applications in its immobilized forms.
In addition, LYZ-TSA seems to be the best biocatalyst for further applications in winemaking. 相似文献
78.
Lachezar Radev Katia Hristova Valery Jordanov Maria Helena V. Fernandes Isabel Margarida M. Salvado 《Central European Journal of Chemistry》2012,10(1):137-145
The 70SiO2-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF5 (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were
measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent
with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6
and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite
(CO3HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly,
compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower
than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses.
SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time. 相似文献
79.
Tianxiang Su Nathan Wicks Jahir Pabon Katia Bertoldi 《International Journal of Solids and Structures》2013,50(14-15):2468-2476
We present a theory to reveal for the first time the distinct mechanisms by which a compressed rod confined in a channel buckles in the presence of dry friction. Contrary to the case of a frictionless contact, with friction the system can bear substantially enhanced compressive load without buckling after its stiffness turns negative, and the onset of instability is strongly affected by the amount of perturbation set by the environment. Our theory, confirmed by simulations, shows that friction enhances stability by opening a wide stable zone in the perturbation space. Buckling is initiated when the applied compressive force is such that the boundary of the stable zone touches a point set by the environment, at a much higher critical load. Furthermore, our analysis shows that friction has a strong effect on the buckling mode; an increase in friction is found to lead to higher buckling modes. 相似文献
80.
Dirk C. de Graaf Wolfgang Ritter Frans J. Jacobs Marleen Brunain Hein Imberechts Koen Mintiens Yves Van der Stede Bart Verheyden Aud Kari Fauske Patrick Boujon Gabriela Chioveanu Daniel Dezmirean Giovanni Formato Franco Mutinelli Hendrik-Jan Roest Dalibor Titĕra Stephen F. Pernal Katia Knapen 《Accreditation and quality assurance》2009,14(5):273-276
We report on the first proficiency test in the context of honey bee disease testing on a broad international scale. Honey
samples were distributed to 12 participating laboratories for isolation and identification of spores of the etiological agent
of American foulbrood, Paenibacillus larvae. Of the 11 laboratories responding to this proficiency testing event, only 6 (54%) provided data that were in full agreement
with the previously determined status of the honey samples; eight (72%) laboratories fell within the threshold for qualification
as defined a priori in this proficiency test (=level of agreement of at least 90%). Some lessons can now be drawn from the
organizational point of view and will certainly improve new initiatives to be taken. 相似文献