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581.
Cp*Rh(bpy)(H2O)]2+ as a coenzyme substitute in enzymatic oxidations catalyzed by Baeyer-Villiger monooxygenases 总被引:1,自引:0,他引:1
de Gonzalo G Ottolina G Carrea G Fraaije MW 《Chemical communications (Cambridge, England)》2005,(29):3724-3726
[Cp*Rh(bpy)(H2O)]2+ was applied as a flavin regenerating reagent in BVMO catalyzed oxidations of organic sulfides to chiral sulfoxides. 相似文献
582.
Bruno Danieli Andrea Bertario Giacomo Carrea Barbara Redigolo Francesco Secundo Sergio Riva 《Helvetica chimica acta》1993,76(8):2981-2991
A chemo-enzymatic approach to some 6″-O-(3-arylprop-2-enoyl) derivatives of the flavonol glucoside isoquercitrin ( 2a ) was explored to overcome the inability to directly introduce these acyl moieties by an enzyme-catalyzed reaction of 2a with the corresponding activated esters. This new approach was based on the regioselective introduction of a methyl malonate residue at the CH2OH of the sugar moiety by catalysis with the protease subtilisin (→ 22a ). The mixed diester 22a was then subjected to chemoselective hydrolysis of the methoxycarbonyl function by another enzyme, biophine esterase (→ 23 ). Finally, the malonic monoester 23 was reacted in a Knoevenagel-type condensation with benzaldehyde, 4-hydroxybenzaldehyde, or 4-hydroxy-3-methoxybenzaldehyde to afford the target 6″-O-(3-arylprop-2-enoyl) isoquercitrins 2b–d . 相似文献
583.
We have investigated the performance of several computational protocols in predicting the NMR spectrum of a molecular ion in a complex liquid phase such as an ionic liquid. To do this, we computed the proton NMR chemical shifts of the 1-ethyl-3-methylimidazolium cation [emim](+) in [emim][Cl]. Environmental effects on the imidazolium ring proton chemical shifts are quite significant and must be taken into account explicitly. Calculations performed on the isolated imidazolium cation as well as on the [emim][Cl] ion pair grossly fail to reproduce the correct spacing between proton signals. In contrast, calculations performed on clusters extracted from the trajectory of a Car-Parrinello molecular dynamics simulation yield very good results. 相似文献
584.
Ruzziconi R Ricci G Gioiello A Couthon-Gourvès H Gourvès JP 《The Journal of organic chemistry》2003,68(3):736-742
Tetraethyl vinylidenebis(phosphonate) (VBP) reacts smoothly with substituted 1,3-dienes at 90-110 degrees C without solvent to give the corresponding cyclohex-3-ene-1,1-bis(phosphonates) in good yields (60-85%). With nonsymmetrically substituted dienes, mixtures of regioisomers are obtained, the regioisomeric ratio being exclusively controlled by electronic effects. Danishefsky's diene allows tetraethyl 4-oxocyclohex-2-ene-1,1-bis(phosphonate) to be obtained in an 81% overall yield after the acid-catalyzed hydrolysis of the Diels-Alder cycloadduct. With 2,3-dimethoxy-1,3-butadiene, a mixture of regioisomeric dimethoxycyclohexene-1,1-bis(phosphonates) is formed by the VBP-catalyzed isomerization of the normal Diels-Alder cycloadduct. The mixture converges into tetraethyl 3,4-dimethoxycyclohex-2-ene-1,1-bis(phosphonate) at prolonged reaction times. 相似文献
585.
Mauro Aglietto Luca Cioni Giacomo Ruggeri Elisa Taburoni Edoardo Tomei 《Journal of polymer science. Part A, Polymer chemistry》1986,24(6):1337-1349
The preparation of 2-methoxy-5-t-butylphenyl vinyl ketone (MeOBVK), 2-hydroxy-5-t-butylphenyl vinyl ketone (HOBVK), and 2-methoxy-5-isooctylphenyl vinyl ketone (MeOOVK) is reported. These compounds can be considered as precursors of polymerizable derivatives of polyoxyethylated alkylphenols—a very important class of nonionic surface active compounds. The homopolymerization and copolymerization of MeOBVK, HOBVK, and MeOOVK with butylacrylate (BA), (–) menthylacrylate [(–)MtA], styrene (STY), and vinylacetate (VA) by free radical initiators, both in solution and emulsion, have been investigated. Copolymer formation has been demonstrated by fractionation and by the presence of induced optical activity in the electronic transitions of the achiral MeOBVK and HOBVK units in copolymers with the optically active comonomer (—)MtA. MeOBVK, HOBVK and MeOOVK give substantially random copolymers with STY, BA, or VA under all conditions investigated, and always show larger reactivity; thus, depending on feed composition, sequences of the vinyl ketone units can be expected in the macromolecules. 相似文献
586.
Giacomo Bondietti Gianfranco Suardi Renzo Ros Raymond Roulet Fabrizia Grepioni Dario Braga 《Helvetica chimica acta》1993,76(8):2913-2925
The synthesis of [Ir2Rh2(CO)12] ( 1 ) by the literature method gives a mixture 1 /[IrRh3(CO)12] which cannot be separated using chromatography. The reaction of [Ir(CO)4]? with 1 mol-equiv. of [Rh(CO)2(THF)2]+ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir2Rh2(CO)5(μ2-CO)3(norbornadiene)2] which were analysed using X-ray diffraction. The ground-state geometry of 1 in solution has three edge-bridging CO's on the basal IrRh2 face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D- and VT-13C-NMR. Substitution of CO by X? in 1 takes place at a Rh-atom giving [Ir2Rh2(CO)8(μ2-CO)3X]? (X = Br, I). Substitution by bidentate ligands gives [Ir2Rh2(CO)7(μ2-CO)3(η4-L)] (L = norbornadiene, cycloocta-1,5-diene) where the ligand L is chelating a Rh-atom of the basal IrRh2 face. Carbonyl substitution by tridentate ligands gives [Ir2Rh2(CO)6(μ2-CO)3(μ3-L)] (L = 1,3,5-trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C3 axis on the apical Ir-atom. 相似文献
587.
Giacomo Bergamini Paola Ceroni Vincenzo Balzani Fritz V?gtle Sang-Kyu Lee 《Chemphyschem》2004,5(3):315-320
The photochemical and photophysical behavior of two dendrimers consisting of a benzophenone core and branches that contain dimethoxybenzene units has been investigated. Such dendrimers can undergo a variety of photochemical and photophysical processes, namely: 1) quenching of the fluorescence and phosphorescence of the dimethoxybenzene units by energy transfer to the benzophenone core (antenna effect), 2) direct and sensitized phosphorescence (and delayed fluorescence) of the benzophenone core, 3) hydrogen abstraction by the triplet excited state of the benzophenone core from solvent molecules, 4) intramolecular hydrogen abstraction by the triplet excited state of the benzophenone core from the dendrimer branches, 5) quenching of the phosphorescence and hydrogen abstraction reaction of the benzophenone core by energy transfer to terbium ions and dioxygen; 6) conversion of the UV light absorbed by the dendrimer branches into visible (Tb3+) or near infrared (O2) emission via the sequence of processes 1) and 5). The results obtained emphasize the great potential of suitably designed dendrimers for a multiple use of light signals. 相似文献
588.
A product and time-resolved kinetic study on the reactivity of tertiary arylcarbinyloxyl radicals bearing alpha-cyclopropyl and alpha-cyclobutyl groups has been carried out. Both the 1-cyclopropyl-1-phenylethoxyl (1.) and alpha,alpha-dicyclopropylphenylmethoxyl (2.) radicals undergo beta-scission to give cyclopropyl phenyl ketone as the major or exclusive product with rate constants higher than that measured for the cumyloxyl radical. It is proposed that in the transition state for beta-scission of 1. and 2., formation of the C=O double bond is assisted by overlap with the C-C bonding orbitals of the cyclopropane ring. With tertiary arylcarbinyloxyl radicals bearing alpha-cyclobutyl groups such as the 1-cyclobutyl-1-phenylethoxyl (4.) and 1-cyclobutyl-1-phenylpropoxyl (5.) radicals, the fragmentation regioselectivity is essentially governed by the stability of the radical formed by beta-scission. Accordingly, 4. undergoes exclusive C-cyclobutyl bond cleavage to give acetophenone, whereas with 5., competition between C-cyclobutyl and C-ethyl bond cleavage, leading to propiophenone and cyclobutylphenyl ketone in a 2:1 ratio, is observed. 相似文献
589.
Clara Musa Roberto Orr Roberta Licheri Giacomo Cao 《Physica C: Superconductivity and its Applications》2009,469(22):1991-1995
Following recent theoretical studies based on electronic structure calculations conducted on Ag- and Au-borides which estimated their superconducting behaviour at elevated transition temperatures, the preparation of AgB2 was attempted in this work by reactive Spark Plasma Sintering (SPS) from Ag and B elemental powders. It was found that, independently from the processing conditions adopted, the formation of a new phase, which corresponds to a small peak on the XRD pattern at 2θ equal to about 28°, cannot be attributed to AgB2. In fact, it was shown that the new phase detected on sintered pellets is most likely boric acid which is formed only if the sample is left in contact with air. If SPSed samples were stored under inert (Ar) atmosphere, no additional phases other than unreacted elements were observed. 相似文献
590.
A. De Giacomo M. Dell'Aglio R. Gaudiuso G. Cristoforetti S. Legnaioli V. Palleschi E. Tognoni 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
The Stark broadening of hydrogen Balmer α line is often measured in Laser-Induced Breakdown Spectroscopy (LIBS) to evaluate the electron number density of the plasma. When measurements are carried out in air, hydrogen atoms are supposedly supplied by the atmosphere. This hypothesis casts some doubts on the validity of hydrogen as an indicator of the conditions in the inner part of the plasma. In this experiment, we acquired spectrally resolved images of a Laser-Induced Breakdown Spectroscopy plasma generated in air on an aluminum target by irradiation with the Nd:YAG fundamental emission. The evolution of the plasma was studied by acquiring images at several delay times. In particular, we imaged the spatial distribution of plasma emitters along the direction orthogonal to the target surface. The spatial distribution of hydrogen emission was compared to the one of the species ablated from the sample. Moreover, electron density and temperature were evaluated in the time- and space-resolved spectra extracted from the images, obtaining thus a picture of the propagation and internal structure of the plasma. The fluid dynamics implications of the plasma expansion were discussed. The z-resolved characterization was compared with the picture of the plasma obtained by processing space-integrated spectra. 相似文献