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991.
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
992.
Henri Edouard Audier Georges Sozzi Arielle Milliet Steen Hammerum 《Journal of mass spectrometry : JMS》1990,25(7):368-374
The reactions of propyl ether radical cations close to threshold are initiated by (reversible) formation of γ-disitonic isomers, R$ \mathop {\rm O}\limits^ + $ (H)CH2CH2CH2·. The three methylene groups in these ions lose their positional identity by ring closure/ring opening via [cyclopropane + alcohol]+· intermediates. Extensive hydrogen exchange occurs within the C3-chain. When R is not methyl the γ-distonic isomer undergoes further intramolecular hydrogen atom transfer reactions that lead to formation of α- and β-distonic ions. The α-distonic isomers expel ethyl and propyl radicals by C? O bond cleavage. 相似文献
993.
The synthesis of 11 oligosaccharides (4-14) containing beta-arabinofuranosyl residues is reported. The glycans are all fragments of two polysaccharides, arabinogalactan and lipoarabinomannan, which are found in the cell wall complex of mycobacteria. In the preparation of the targets, the key step was a low-temperature glycosylation reaction that installed the beta-arabinofuranosyl residues with good to excellent stereocontrol. 相似文献
994.
Francis J. Bonner Romain Wolf Pier Luigi Luisil 《Applied biochemistry and biotechnology》1980,5(4):255-268
Three proteins (horse liver alcohol dehydrogenase, ribonuclease, lysozyme) were solubilized in hydrocarbon with the help of reverse micelles formed by aqueous di(2-ethyl-hexyl) sodium sulfosuccinate (AOT). Sedimentation and diffusion coefficients of the micellar aggregates were measured with an analytical ultracentrifuge. Partial specific volumes were also evaluated from density measurements. The molecular weight of the protein-containing reverse micelles (M t ) could thus be determined for each protein system at various w0 values (w0 - [H2O]/[AOT]). For horse liver alcohol dehydrogenase at w0 = 46.4, for example,M t is ca. 2,670,000 Daltons; for lysozyme at wo = 22.5,M t is ca. 323,000 Daltons and increases by increasing w0. On the basis of these experimentally determined molecular weights, a structural model for the protein-containing reverse micelle is proposed. The model is based upon the assumption that the protein is confined in the water pool of a spherical micelle, and that the inner core volume is the sum of the protein volume and the volume of all water molecules present in a micelle. It is possible then to calculate the micellar structure at each w0 value. For example, in the case of ribonuclease at w0 = 20, the inner core radius is ca. 37.5 A, and a layer of water of ca. 22 A separates the protein surface from the surfactant layer. The possible implications of this model for the reactivity of enzymes solubilized in hydrocarbons by reverse micelles are discussed. 相似文献
995.
Talbot FO Tabarin T Antoine R Broyer M Dugourd P 《The Journal of chemical physics》2005,122(7):074310
We have coupled a quadrupole ion trap with a frequency doubled optical parametric oscillator laser. The photodissociation spectrum of the protonated tryptophan ion from 215 to 320 nm is reported. The yields of fragmentation on each mass channel as a function of the laser wavelength were obtained. We also report experiments involving multiple stages of laser induced dissociation and discuss possible structures for the fragmentation products. 相似文献
996.
WAVELENGTH DEPENDENCE FOR AMT CROSSLINKING OF pBR322 DNA 总被引:1,自引:0,他引:1
Francis P. Gasparro Wilma A. Saffran Charles R. Cantor† Richard L. Edelson‡ 《Photochemistry and photobiology》1984,40(2):215-219
Abstract The wavelength dependence for 4'aminomethyl-4,5',8-trimethylpsoralen crosslinking of a linearized plasmid DNA (pBR322) by narrow band UV-A light (298–382 nm) has been determined. Maximal levels of crosslinking occurred with light in the 322–346 nm range. Crosslinks were shown to be photoreversible by shorter wavelength photons (298 and 310 nm). The correlation between the wavelength dependence for crosslink formation and the optimal wavelength for most psoralen action spectra further supports the notion that crosslinks are the major lesion responsible for the effectiveness of psoralen plus ultraviolet A therapies. 相似文献
997.
Bhaumik A Ramakanth M Brar LK Raychaudhuri AK Rondelez F Chatterji D 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5891-5896
Here, we report a system we have developed where long double-stranded DNAs (dsDNAs) are immobilized on a monolayer of Zn-arachidate. We have applied the Langmuir-Blodgett technique to form the monolayer of Zn-arachidate where Zn(II) is bound to arachidic acid through charge neutralization. Because tetrahedral Zn(II) participates in DNA recognition through coordination, we have been able to layer DNA over the Zn-arachidate monolayer. The DNA layer shows a typical compression and expansion cycle in a concentration-dependent fashion. Interestingly, the DNA monolayer is available for enzymatic degradation by DNaseI. The detection of DNA and its accessibility towards biological reaction is demonstrated by imaging through fluorescence microscopy. The conformation of the DNA, immobilized on the monolayer, was studied with the help of atomic force microscopy (AFM). We observed that the dsDNAs were aligned in a stretched manner on the surface. To investigate further, we also demonstrate here that the small single-stranded DNA (ssDNA) immobilized on the air-water interface can act as a target molecule for the complementary ssDNA present in the subphase. The study of DNA hybridization done with the help of fluorescence spectroscopy clearly supports the AFM characterization. 相似文献
998.
Babajide I. Alo Oluwole B. Familoni Francis Marsais Guy Queguiner 《Journal of heterocyclic chemistry》1992,29(1):61-64
4-Lithio-N-t-butylpyridine-3-sulphonamide reacted with benzophenone and carbon dioxide respectively to give the corresponding intermediates which on appropriate treatment gave isothiazolo[5,4-c]pyridin-3-one 1,1-dioxides. Metalation of 2- and 4-(N,N-dialkylaminosulphonyl)pyridines with lithium diisopropylamide (LDA) gave anions which reacted with benzophenone to give carbinols which thermally cyclised to 1,2-oxathiolo[3,4-b]pyridine and 1,2-oxathiolo[4,3-c]pyridine respectively. 相似文献
999.
An Unexpected Spectrum of p53 Mutations from Squamous Cell Carcinomas in Psoriasis Patients Treated with PUVA 总被引:2,自引:0,他引:2
Xiao Mei Wang Jennifer Madison McNiff Vincent Klump Maryam Asgari Francis P. Gasparro 《Photochemistry and photobiology》1997,66(2):294-299
Photochemotherapy employing 8-methoxypsoralen and long-wavelength ultraviolet radiation (UVA, 320-400 nm) is widely used in the treatment of psoriasis. The pho-toactivation of psoralens in skin cells leads to formation of DNA photoadducts which may be responsible, at least in part, for the efficacy of these photochemotherapies. However, mutations arising from these adducts may also lead to the well-characterized increased incidence of squamous cell carcinoma. Mutations in the p53 tumor suppressor gene have been detected in many human cancers. To determine whether p53 mutations occur in squamous cell carcinomas in PUVA patients, PCR was used to amplify the exons (5-9) in which other studies have found a high frequency of point mutations. Gel electrophoresis was used to detect single-strand conformational polymorphisms. Aberrantly migrating bands were excised, reamplined and sequenced. Thirty-four specimens from 10 patients were examined. Specimens from one patient who had received no phototherapy as well as from normal controls were also analyzed. Five of the 10 patients showed at least one p53 mutation. In contrast to previously reported psoralen-induced p53 mutations in mice, the expected psoralen type mutations at alternating AT sites were not detected. All but two of the altered sequences occurred at dipyrimidine sites which is typical of solar type mutations. Two C→T mutations and two dipyrimidine mutations (CC→TT) were found. Other mutations included: C→G, G→T, C→A and an 18 bp deletion. A review of therapeutic history of these patients showed that some had also received UVB phototherapy. Furthermore, because sunlight is thought to be beneficial for psoriasis, nontherapeutic, casual UVB exposure cannot be excluded. Our observations suggest that the SCC may have arisen from the solar mutations and that PUVA may enhance tumor progression or immune suppression 相似文献
1000.
Jean-Cyrille Hierso Francis Lacassin Régine Amardeil 《Journal of organometallic chemistry》2004,689(4):766-769
We previously reported the easy access to mixed ferrocenediyl ligands bearing phosphine and phosphonite moieties. Using this strategy, a new enantiopure phosphine-menthylphosphonite ferrocenediyl has been synthesised. This mixed ligand leads to original unsymmetrical dinuclear rhodium coordination-complexes. One example of this new class of “quasi-close bridging A frame” dinuclear rhodium complexes, fully characterised by multinuclear 1H, 13C, 31P and 103Rh NMR and optical rotation measurements, is presented. Preliminary tests have shown an activity improvement in the hydroformylation of oct-1-ene using the phosphine-menthylphosphonite ferrocenediyl auxiliary compared to known phosphine-phosphonite ligands. 相似文献