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151.
Travert A Nakamura H van Santen RA Cristol S Paul JF Payen E 《Journal of the American Chemical Society》2002,124(24):7084-7095
Hydrogen adsorption on Mo[bond]S, Co[bond]Mo[bond]S, and Ni[bond]Mo[bond]S (10 1 macro 0) surfaces has been modeled by means of periodic DFT calculations taking into account the gaseous surrounding of these catalysts in working conditions. On the stable Mo[bond]S surface, only six-fold coordinated Mo cations are present, whereas substitution by Co or Ni leads to the creation of stable coordinatively unsaturated sites. On the stable MoS(2) surface, hydrogen dissociation is always endothermic and presents a high activation barrier. On Co[bond]Mo[bond]S surfaces, the ability to dissociate H(2) depends on the nature of the metal atom and the sulfur coordination environment. As an adsorption center, Co strongly favors molecular hydrogen activation as compared to the Mo atoms. Co also increases the ability of its sulfur atom ligands to bind hydrogen. Investigation of surface acidity using ammonia as a probe molecule confirms the crucial role of sulfur basicity on hydrogen activation on these surfaces. As a result, Co[bond]Mo[bond]S surfaces present Co[bond]S sites for which the dissociation of hydrogen is exothermic and weakly activated. On Ni[bond]Mo[bond]S surfaces, Ni[bond]S pairs are not stable and do not provide for an efficient way for hydrogen activation. These theoretical results are in good agreement with recent experimental studies of H(2)[bond]D(2) exchange reactions. 相似文献
152.
Paolesse R Nardis S Venanzi M Mastroianni M Russo M Fronczek FR Vicente MG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(5):1192-1197
5,10,15-Triphenylcorrole (1) reacts with the Vilsmeier reagent (POCl(3)/DMF) to give the corresponding 3-formyl derivative 3 as the major product. The regioselectivity of the reaction was proven by X-ray crystallography and only traces of the 2-formyl isomer were observed. A more polar product is also observed and this compound becomes the major product when an excess of DMF is used for the preparation of the Vilsmeier reagent, while the formation of the 3-formyl isomer is almost completely suppressed. X-ray crystallography allowed us to identify this compound as the fully substituted N-ethane bridged derivative 4, formed from the attack of the Vilsmeier reagent at the inner core of the macrocycle. This compound is unique among porphyrinoid macrocycles, and further confirms the peculiarity of corrole chemistry. 相似文献
153.
Summary A
tail-made polymer matrix is proposed to remove strontium ions from aqueous
solutions. The removal behavior of strontium ions on a crosslinked copolymer
containing methacrylic acid as functional groups was investigated as a function
of sorptive concentration, time, temperature and pH. It was observed that an
increase of these parameters enhanced the removal of Sr(II) ions from aqueous
solution. It is found that a maximum adsorption of Sr(II) ions can be obtained
on the crosslinked copolymer after 30 minutes and at pH 8. The increase of
Sr(II) ion concentration in the solution resulted in an increase in the amount
of Sr(II) ions adsorbed on the crosslinked copolymer containing methacrylic
acid as functional groups. However, after a maximum of Sr(II) concentration in
the solution, the percentage of adsorbed Sr(II) ions decreased. The adsorption
data are well represented by the Freundlich, Langmuir and Dubinin-Radushkevich
(D-R) isotherms. The adsorption capacity of the copolymer and the free energy
change were calculated by using the D-R isotherm. For the adsorption of Sr(II)
ions on the crosslinked copolymer the thermodynamic parameters (DH°,DS° andDG°) were
calculated.</p>
</p> 相似文献
154.
Mustafa Şenyel T. Raci Sertbakan Güneş Kürkçüoğ Ergün Kasap Ziya Kantarci 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(1-2):175-180
Three Hofmann-diaminododecane-type clathrates of the form M(1,12-diaminododecane) Ni(CN)4G (M = Co, Ni or Cd; G = benzene, naphthalene, anthracene, phenanthrene or biphenyl) have been prepared in powder form. The 1,12-diaminododecane molecules in the host lattice permit the inclusion of bulky guest molecules. The spectral features suggest that these compounds are similar in structure to the other Hofmann-diam-type clathrates. 相似文献
155.
Summary New separation procedures for alkaloids of similar polarity and structure or of very different polarity and structure, based upon two-dimensional thin-layer chromatography on unmodified silica gel under mild conditions are described. Separation factors and separation mechanisms based on the structure of the bases and mobile phase composition are discussed for some examples of very efficient procedures.Proportions in solvent mixtures are v/v except where otherwise indicated. 相似文献
156.
157.
Fernando J. S. Oliveira Francisca P. de França 《Applied biochemistry and biotechnology》2005,122(1-3):581-591
Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing
press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This
article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor
inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 g/m3 of C6H14, and a temperature of 28°C. The results of hexane removal efficiencies were presented as a function of the inoculum size
(approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension
of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The
steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent
from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using
reused cells at an initial microbial concentration of 0.2 g/L. 相似文献
158.
Odile Meyer Jean-Franois Hoeffler Catherine Grosdemange-Billiard Michel Rohmer 《Tetrahedron》2004,60(52):12153-12162
An optimised gram scale synthesis allows the production of 1-deoxy-d-xylulose and 1-deoxy-d-xylulose 5-phosphate with possible deuterium labelling at C-5. Such substrates are required for investigations on the mevalonate-independent 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis in bacteria and chloroplasts of phototrophic eukaryotes and for the biosynthesis of vitamins B1 (thiamine diphosphate) and B6 (pyridoxol phosphate) in bacteria. 相似文献
159.
I. M. Miranda Salvado F. M. A. Margaça J. Teixeira 《Journal of Sol-Gel Science and Technology》1994,2(1-3):289-294
Silica-titania gels, prepared in acidic conditions, with contents of TiO2 up to 6 mol%, have been studied by small angle neutron scattering (SANS) as wet gel with increasing aging times. In all samples, small primary particles have been found with a diameter of about 3 nm. At the gel point, cylindrical clusters, ca. 10 nm long, were observed as well. These grow with aging time, becoming branched. The cluster-cluster diffusion limited aggregation model is found to be consistent with the SANS results. The growth process is independent of the TiO2 content. It is mainly influenced by the ratio of the aging time to the gelation time. 相似文献
160.
David R. Benson Robert Valentekovich Suk-Wah Tam Franois Diederich 《Helvetica chimica acta》1993,76(5):2034-2060
Following a known synthetic procedure, the porphyrin-cyclophane 1 having a porphyrin attached by two straps to an apolar cyclophane binding site was prepared. Upon metallation, the ZnII and FeIII derivatives 2 and 3 , respectively, were obtained in good yields. Treatment of 3 with base yielded the μ-oxo dimer 4 in which the two oxo-bridged porphyrins moieties are both capped by cyclophane binding sites. All compounds 1–4 are freely soluble in protic solvents such as MeOH and CF3CH2OH, and the FeIII derivatives 3 and 4 are active cytochrome P-450 mimics in these protic environments. Strong inclusion complexation of polycyclic aromatic hydrocarbons by 1 and 3 in alcoholic solvents was observed and quantified by 1H-NMR and UV/VIS titrations. Acenaphthylene binds in an ‘equatorial’ orientation which locates its reactive 1,2-double bond near the porphyrin center, whereas phenanthrene binds ‘axially’ with the reactive 9,10-double bond oriented away from the porphyrin. The reduction potential of 3 was not significantly altered by substrate binding. In the unbound form, the FeIII center in porphyrin 3 was found by ESR and 1H-NMR to prefer a high-spin state (S = 5.2). In CF3CH2OH, using iodosylbenzene as O-transfer agent, the FeIII derivative 3 catalyzed the oxidation of acenaphthylene to acenaphthen-1-one ( 14 ). Phenanthrene inhibited the reaction, possibly as a result of strong but nonproductive binding. Under similar conditions, isotetralin ( 18 ) was aromatized with high turnover to 1,4-dihydronaphthalene. The μ-oxo dimer 4 also showed high activity in the oxidation of acenaphthylen in MeOH, a result which provides strong evidence for efficent supramolecular catalysis. Due to as yet unknown reaction channels leading to polymeric products, poor mass balances were generally obtained in the oxidations effected in MeOH and CF3CH2OH in the presence of PhIO. 相似文献