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1.
The photoresponses of Phycomyces, including phototropism and photocontrol of sporangiophore development, are mediated primarily by blue and UV light. Recent results on these two responses indicated a subsidiary role for green light. We have measured in vivo light-induced absorbance changes (LIAC) in mycelial samples of a caroteneless (carB) strain to compare the effectiveness of UV, blue, and green light. In the dual-wavelength kinetic mode of the spectrophotometer, measuring wavelengths of 445 and 470 nm were chosen, because green light produces substantial absorbance changes between these two wavelengths. Fluence-response curves were measured for 13 wavelengths between 365 and 530 nm, and for variable exposure times between 0.5 and 320 s. With one exception (365 nm), the curves were biphasic. The low fluence component was generally sigmoidal with an abrupt rise. The high fluence component failed to reach saturation for the fluences tested (less than 70 μmol m−2 s−1). Using the inferred threshold fluences of these two components as criterion effects, we obtained two action spectra. For the low fluence component, the action spectrum showed major peaks at 394, 450, and 530 nm and a minor peak at 416 nm. The high fluence component action spectrum showed very little sensitivity in the blue region. The major sensitivity was in the near UV, and a relatively small peak appeared in the green part of the spectrum at 507 nm. The biphasic character of the fluence-response curves suggests that two photosystems are responsible for the absorbance changes. The low fluence photosystem is sensitive mainly to blue and UV light and may thus represent a physiological blue-light photoreceptor. The high fluence photosystem is clearly not of this type. It (and perhaps the low fluence system as well) may mediate some of the subsidiary physiological effects of green light. 相似文献
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Chafia Bennaceur Carlos Afonso Sandra Alves Anne Bossée Jean-Claude Tabet 《Journal of the American Society for Mass Spectrometry》2013,24(8):1260-1270
Structural elucidation and distinction of isomeric neurotoxic agents remain a challenge. Tandem mass spectrometry can be used for this purpose in particular if a “diagnostic” product ion is observed. Different vibrational activation methods were investigated to enhance formation of diagnostic ions through consecutive processes from O,O-dialkyl alkylphosphonates. Resonant and non-resonant collisional activation and infrared multiphoton dissociation (IRMPD) were used with different mass spectrometers: a hybrid quadrupole Fourier transform ion cyclotron resonance (Qh-FTICR) and a hybrid linear ion trap-Orbitrap (LTQ/Orbitrap). Double resonance (DR) experiments, in ion cyclotron resonance (ICR) cell, were used for unambiguous determination of direct intermediate yielding diagnostic ions. From protonated n-propyl and isopropyl O-O-dialkyl-phosphonates, a diagnostic m/z 83 ion characterizes the isopropyl isomer. This ion is produced through consecutive dissociation processes. Conditions to favor its formation and observation using different activation methods were investigated. It was shown that with the LTQ, consecutive experimental steps of isolation/activation with modified trapping conditions limiting the low mass cut off (LMCO) effect were required, whereas with FT-ICR by CID and IRMPD the diagnostic ion detection was provided only by one activation step. Among the different investigated activation methods it was shown that by using low-pressure conditions or using non-resonant methods, efficient and fast differentiation of isomeric neurotoxic agents was obtained. This work constitutes a unique comparison of different activation modes for distinction of isomers showing the instrumental dependence characteristic of the consecutive processes. New insights in the dissociation pathways were obtained based on double-resonance IRMPD experiments using a FT-ICR instrument with limitation at low mass values.
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Chafia Sobhi Abdelmalek Khorief Nacereddine Abdelhafid Djerourou M. José Aurell Luis R. Domingo 《Tetrahedron》2012,68(40):8457-8462
The role of the trifluoromethyl group in reactivity, regio-, and stereoselectivity in cycloaddition reactions has been analyzed by studying the 1,3-dipolar cycloaddition (13DC) reactions of nitrone 4 with 3,3,3-trifluoro-1-nitropropene 7b and 3,3,3-trifluoro-2-nitropropene 14 using density functional theory (DFT) methods at the B3LYP/6-311G(d) level. The recent M06-2X functional has also been evaluated but, although the thermodynamic performance is improved, the kinetic data are not necessarily better than those obtained by the popular B3LYP functional for cycloaddition reactions. Four reactive channels associated with the meta and ortho regio- and endo and exo stereoselective approach modes of the nitro group of these disubstituted ethylenes relative to nitrone 4 have been explored and characterized. Unlike other electron-withdrawing groups, the trifluoromethyl group increases the reactivity of the nitroethylene, but it does not modify the meta and endo selectivities when it is located at the β conjugated position of nitroethylene. Analysis of the global and local electrophilicity indices allows for an explanation of the role of the trifluoromethyl group in reactivity and regioselectivity of electrophilically activated ethylenes. 相似文献
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A DFT study of the mechanism and selectivities of the [3 + 2] cycloaddition reaction between 3‐(benzylideneamino)oxindole and trans‐β‐nitrostyrene
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Chafia Sobhi Abdelmalek Khorief Nacereddine Abdelhafid Djerourou Mar Ríos‐ Gutiérrez Luis R. Domingo 《Journal of Physical Organic Chemistry》2017,30(6)
The mechanism and regioselectivities and stereoselectivities of the [3 + 2] cycloaddition (32CA) reaction of 3‐(benzylideneamino) oxindole (AY) and trans‐β‐nitrostyrene have been studied using both B3LYP and ωB97XD density functional theory methods together with the standard 6‐31G(d) basis set. Four reactive pathways associated with the ortho and meta regioselective channels and endo and exo stereoselective approaches modes have been explored and characterized. While the B3LYP functional fails to predict the experimental regioselectivity, the ωB97XD one succeeds to predict the experimentally observed meta regioselectivity favoring the formation of meta/endo cycloadduct as the major isomer. Inclusion of solvent effects increases the regioselectivity and decreases the experimentally observed stereoselectivity. Analysis of the density functional theory global reactivity indices and the Parr functions of the reagents in its ground state allows explaining the reactivity and the meta regioselectivity of this zwitterionic‐type 32CA reaction, which account for the high polar character of this reaction. Non‐covalent interaction analysis of the most favorable meta/endo transition state structure reveals that the formation of a hydrogen‐bond between 1 nitro oxygen and the AY N–H hydrogen is responsible for the selectivity experimentally found in this polar zwitterionic‐type 32CA reaction. 相似文献
5.
Benjamin A. Horwitz Chafia H. Trad Edward D. Lipson † 《Photochemistry and photobiology》1986,44(2):207-214
Abstract— The unidentified receptor pigments responsible for phototropism and other blue light responses of Phycomyces are expected to contribute only a minuscule fraction of the in vivo absorption spectra, even for carotene-deficient ( car genotype) albino strains. The variable amount of residual carotenoids in strains with mutations in the carA gene precluded their use for the comparison of phototropism (mad) mutants with phototropically normal controls. We turned instead to carB albino strains, all of which have negligible carotene content. For various mad genes, we isolated carB mad strains by crosses and mutagenesis, and compared them with carB controls, in search of spectral differences associated with the mad photoreception defects. The spectra and their second derivatives show cytochrome bands, as well as a minor peak near 480 nm. This peak was present in carB strains, so it is probably not due to carotenoids. Strains L26 and L136 (both carB madE , but with different genetic backgrounds) showed modifications in the480–500 nm region. Sporangiophores that lacked the green material that usually interferes with in vivo spectroscopy were obtained by the addition of potassium iodide to the culture medium. Dark-grown carB sporangiophores have a more pronounced second-derivative peak at 480 nm than do light-grown sporangiophores. Growth in the light, though, did not significantly alter the spectra of sporangiophores of L131 (carB madB) or L130 (carB madC). The spectral differences may be useful in the biochemical search for the receptor pigments. 相似文献
6.
Sousna Sahnoun Mokhtar Boutahala Chafia Tiar Abdelkrim Kahoul 《Comptes Rendus Chimie》2018,21(3-4):391-398
A modified bentonite was prepared at different surfactant (ODTMA) loadings through ion exchange. The obtained organobentonite adsorbent materials were then used for the removal of an anionic dye, tartrazine, from an aqueous solution. The bentonite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Brunauer- Emmett-Teller (BET) method. The modification of organophilic bentonite by ODTMA increases the basal spacing d001 from 24.1 to 39.1 Å when the cation exchange capacity increases from 1 to 4. The increase in the spacing, due to the basic organic modifications, was confirmed by the results of thermogravimetric analysis, Fourier transform infrared spectroscopy, and BET. The effects of contact time, initial concentration, and solution pH onto an adsorbed amount of tartrazine were investigated. To predict adsorption isotherm, the experimental data were analyzed using the Langmuir and Freundlich isotherm equations. It was determined that the isotherm data were fitted to the Langmuir isotherm. The adsorption process was also found to follow a pseudo-second-order kinetic model. 相似文献
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Applications of Mathematics - We propose a feasible primal-dual path-following interior-point algorithm for semidefinite least squares problems (SDLS). At each iteration, the algorithm uses only... 相似文献
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Chafia Sobhi Abdelmalek Khorief Nacereddine Lilia Nasri Zohra Lechtar Abdelhafid Djerourou 《Molecular physics》2013,111(21):3193-3200
A DFT study of the (32CA) reaction of a series of some nitrile oxides with electron-deficient alkyne (3-phenylpropionlaldehyde) in gas phase and in toluene has been carried out using B3LYP functional with 6-31G(d) basis set. Two reactive channels 4- and 5-associated with the two regioisomeric modes have been located and characterised. These 32CA reactions are characterised by a low asynchronous one-step mechanism with a low-polar character. Analysis of the DFT reactivity indices indicates that the nucleophilic centre of the different nitrile oxides accounts for the 4-regioselectivity. Our calculations are in a good agreement with the experimental findings. 相似文献
10.
Chafia Bouchelta Mohamed Salah Medjram Odile Bertrand Jean-Pierre Bellat 《Journal of Analytical and Applied Pyrolysis》2008,82(1):70-77
Activated carbons are produced from wastes of Algerian date stones by pyrolysis and physical activation in the presence of water vapor into a heated fixed-bed reactor. The effect of pyrolysis temperature and activation hold time on textural and chemical surface properties of raw date stones and carbon materials produced are studied. As expected, the percentage yield decreases with increase of activation temperature and hold time. The characterization of carbon materials is performed by scanning electron microscopy (SEM). X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption (BET). Results show the presence of cellulose and hemicellulose in the raw material, and the predominance of carbon and graphite after pyrolysis. Different oxygen-containing functional groups are found in the raw material while aromatic structures are developed after pyrolysis and activation. The best specific surface area (635 m2 g−1) and microporous volume (0.716 cm3 g−1) are obtained when the date stones are grinded, pyrolysed at 700 °C under a 100 cm3 min−1 nitrogen flow and then activated under water vapor at 700 °C for 6 h. 相似文献