排序方式: 共有95条查询结果,搜索用时 15 毫秒
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M. P. Fontaine-Aupart E. Renault L. Brian J. F. Delouis M. Garde
-Albert 《Journal of photochemistry and photobiology. A, Chemistry》1995,90(2-3):95-102
The triplet properties of the excited triplet state of pazelliptine (PZE), an antitumoral drug derived from ellipticine, were investigated in dioxane, ethanol and buffer aqueous solutions using the laser flash photolysis technique. The triplet absorption spectra and the kinetic parameters associated with the excited state decay were quite similar in the different solvents. 3PZE reacted with unexcited PZE in deaerated solutions (k = 6 × 1010 M−1 s−1) and was quenched by oxygen (k ≈ 2 × 107 s−1). The extinction coefficients of the triplet transition were estimated and used to calculate the singlet-triplet intersystem crossing quantum yields of about 5%.
A biphotonic ionization of PZE in buffer aqueous solution has been demonstrated in a previous work. This process was also observed in ethanol but not in dioxane. Mixed yttrium aluminum garnet laser harmonics (355 nm + 532 nm) and delayed-pulse experiments were carried out in order to determine the intermediate excited state involved in this photoionization process. The results indicate that pazelliptine radical cation and e−s are formed via a consecutive two-photon absoprtion in which the first excited singlet state is the only intermediate. 相似文献
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[reaction: see text] 1,3-Dimesitylimidazol-2-ylidene ruthenium benzylidene catalyst (RuCl2(=C(H)Ph)(PCy3)(IMes)) has been successfully employed in ring-closing metathesis reactions of acyclic diene sulfides, disulfides, and dithianes and in self-cross metathesis reactions of ene-sulfides, thioethers, and thiols. 相似文献
45.
Damoiseau X Tfibel F Hoebeke M Fontaine-Aupart MP 《Photochemistry and photobiology》2002,76(5):480-485
Bacteriochlorin a (BCA) is a potential photosensitizer for photodynamic therapy of cancer. It has been shown previously that the photoefficiency of the dye is mainly dependent on singlet oxygen (1O2) generation. Nanosecond laser flash photolysis was used to produce and to investigate the excited triplet state of the dye in methanol, phosphate buffer and dimiristoyl-L-alpha-phosphatidylcholine (DMPC) liposomes. The transients were characterized in terms of their absorption spectra, decay kinetics, molar absorption coefficients and formation quantum yield of singlet-triplet intercrossing. The lifetime of the BCA triplet state was measured at room temperature. The triplet-state quantum yield is quite high in methanol (0.7) and in DMPC (0.4) but only 0.095 in phosphate buffer. In the last case, BCA is in a monomer-dimer equilibrium, and the low value of the quantum yield observed was ascribed to the fact the triplet state is only formed by the monomers. 相似文献
46.
Marie-Pierre Gelin 《Journal of fluorine chemistry》2005,126(4):575-583
The radical copolymerisation in solution of vinylidene fluoride (or 1,1-difluoroethylene (VDF)) with hexafluoropropylene (HFP) initiated by di-tert-butyl peroxide is presented. A series of eight copolymerisation reactions was investigated with initial [VDF]o/[HFP]o molar ratios ranging from 5.0/95.0 to 85.2/14.8. Both co-monomers copolymerised in this range of copolymerisation. Moreover, only VDF homopolymerised in these conditions. The copolymer compositions of these random-type copolymers were calculated by means of 19F NMR spectroscopy which allowed the respective amount of each monomeric unit in the copolymer to be quantified. The Tidwell and Mortimer method led to the assessment of the reactivity ratios, ri, of both co-monomers showing a higher incorporation of VDF in the copolymer (rHFP = 0.12 ± 0.05 and rVDF = 2.9 ± 0.6 at 393 K). Alfrey-Price's Q and e values of HFP were calculated to be 0.002 (from QVDF = 0.008) or 0.009 (from QVDF = 0.015) and +1.44 (versus eVDF = 0.40) or +1.54 (versus eVDF = 0.50), respectively, indicating that HFP is an electron-accepting monomer. The thermal properties of these fluorinated copolymers were also determined. Except for those containing a high amount of VDF, they were amorphous. Each showed one glass transition temperature (Tg) only, and from known laws of Tg, that of the homopolymer of HFP was assessed. It was compared with that obtained from the literature after extrapolation and is discussed. 相似文献
47.
Using cyclodextrin-capillary zone electrophoresis (CD-CZE), baseline separation of baclofen, a potent GABA(B) agonist; was achieved. A method for the enantioresolution of this gamma-aminobutyric acid (GABA) and determination of enantiomeric purity was developed using CDs (highly sulfated-CD or highly S-CD) as chiral selectors and capillaries dynamically coated with polyethylene oxide (PEO). Operational parameters, such as the nature and concentration of the chiral selectors, buffer concentration, organic modifiers, and applied voltage, were investigated. The use of charged CDs provides a driving force in the opposite direction of the positively charged baclofen in the running buffer and enantiomeric resolution by inclusion of compounds in the CD cavity. Highly S-beta-CD was found to be the most effective complexing agent, allowing good enantiomeric resolution. The complete resolution was obtained using 25 mM phosphate buffer, pH 2.5, containing 3% w/v highly S-beta-CD at 25 degrees C with aN applied field of 0.40 kV/cm. The apparent association constants of the inclusion complexes were calculated. This optimized method was validated in terms of repeatability and limits of detection (0.13 microg x mL(-1)) and quantification. The migration order was determined. 相似文献
48.
Lipka E Daniel C Vaccher MP Glaçon V Ewing D Mackenzie G Len C Bonte JP Vaccher C 《Electrophoresis》2004,25(3):444-453
Baseline separation of some new acyclic nucleosides which are potential antiviral agents was achieved using cyclodextrin capillary zone electrophoresis (CD-CZE). A method for the enantiomeric resolution of these compounds and determination of their enantiomeric purity was developed using anionic CDs (highly sulfated-CD or highly S-CD) as chiral selectors and capillaries, which were dynamically coated with polyethylene oxide (PEO). Operational parameters including (i) the nature and concentration of the chiral selectors, (ii) organic modifiers, (iii) temperature, and (iv) applied voltage were investigated. The use of charged CDs provides (i) a supplementary driving force for the compounds in a running buffer and (ii) enantiomeric resolution by inclusion of compounds in the CD cavity. The highly S-CD was found to be the most effective complexing agent and allowed good enantiomeric resolution. The complete resolution of five nucleoside analogs was obtained using 25 mM phosphate buffer, pH 2.5, containing either highly S-alpha-CD, S-beta-CD or S-gamma-CD at 30 degrees C with an applied field of 0.30 kV/cm. The apparent association constants of the inclusion complexes were calculated. The enantiomer migration order for the molecules investigated was determined and the detection limit of enantiomeric impurities was found to vary between 0.34 to 3.56 ng.mL(-1) for the first enantiomer. 相似文献
49.
Dupouy C Iché-Tarrat N Durrieu MP Vigroux A Escudier JM 《Organic & biomolecular chemistry》2008,6(16):2849-2851
Introduction of alpha,beta-D-CNA featuring canonical values of the torsional angles alpha and beta within oligonucleotides leads to an overall stabilization and improved rigidity of the duplex DNA as demonstrated by UV experiments, circular dichroism and corroborated by molecular dynamics simulations. 相似文献
50.
The influence of structure and composition of a reverse SDS microemulsion on enzymatic activities and electrical conductivities 总被引:3,自引:0,他引:3
Bauduin P Touraud D Kunz W Savelli MP Pulvin S Ninham BW 《Journal of colloid and interface science》2005,292(1):244-254
The activity of the enzyme horse radish peroxidase (HRP) is studied in a series of reverse microemulsions composed of dodecane, aqueous buffer, sodium dodecylsufate (SDS) and alcohols of the homologous series 1-butanol to 1-octanol. The HRP catalyzed reaction is the oxidation of a classical water soluble substrate, the 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) by hydrogen peroxide. In parallel electrical conductivity measurements are performed on the same solutions. The structural changes in the microemulsions, as inferred by the conductivity measurements, correlate remarkably well with the changes in the enzymatic activities. In particular it is found that (a) the maximum activity of the enzyme is always related to its optimum hydration and that this hydration can be related to the microemulsion structures, (b) the enzyme inhibition caused by the alcohols in microemulsions is a consequence of both the solubility of the alcohols in the buffer and the rigidity of the interfacial film. Consequently, it can be concluded that enzymatic activity measurements are a valuable tool to study confined systems such as microemulsions and, in particular, the amount of available hydration water. Enzymatic activities can be finely tuned by small changes in microemulsion structures, probably in a predictive way. 相似文献