La Specificite des Halogenations Atomiques VII. La photochloruration du chloroforme

The photochemical reaction between Cl2 and CHCl3 has been studied. The experimental rate equation can be explained from the general scheme previously proposed and yields two relations between elementary rate constants. Further two relations are obtained from the competition reaction in a mixture of Cl2, CHCl3 and C2Cl4: (Formula Presented.) Arguments are given to reject a mechanism of the Rollefson type. The chain breaking step previously proposed by Schumacher is in contradiction with the experimental results. Copyright © 1958 Wiley‐VCH Verlag GmbH & Co. KGaA, WeinheimSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Photochlorination of chloroform [35]

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La Specificite des Halogenations Atomiques VII. La photochloruration du chloroforme

The photochemical reaction between Cl2 and CHCl3 has been studied. The experimental rate equation can be explained from the general scheme previously proposed and yields two relations between elementary rate constants. Further two relations are obtained from the competition reaction in a mixture of Cl2, CHCl3 and C2Cl4: (Formula Presented.) Arguments are given to reject a mechanism of the Rollefson type. The chain breaking step previously proposed by Schumacher is in contradiction with the experimental results. Copyright © 1958 Wiley‐VCH Verlag GmbH & Co. KGaA, WeinheimSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Atomic chlorination of simple hydrocarbon derivatives in the gas phase

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Cytosolic calcium rises and related events in ergosterol-treated Nicotiana cells.

The typical fungal membrane component ergosterol was previously shown to trigger defence responses and protect plants against pathogens. Most of the elicitors mobilize the second messenger calcium, to trigger plant defences. We checked the involvement of calcium in response to ergosterol using Nicotiana plumbaginifolia and Nicotiana tabacum cv Xanthi cells expressing apoaequorin in the cytosol. First, it was verified if ergosterol was efficient in these cells inducing modifications of proton fluxes and increased expression of defence-related genes. Then, it was shown that ergosterol induced a rapid and transient biphasic increase of free [Ca\ub2\u207a](cyt) which intensity depends on ergosterol concentration in the range 0.002-10 \u3bcM. Among sterols, this calcium mobilization was specific for ergosterol and, ergosterol-induced pH and [Ca\ub2\u207a](cyt) changes were specifically desensitized after two subsequent applications of ergosterol. Specific modulators allowed elucidating some events in the signalling pathway triggered by ergosterol. The action of BAPTA, LaCl\u2083, nifedipine, verapamil, neomycin, U73122 and ruthenium red suggested that the first phase was linked to calcium influx from external medium which subsequently triggered the second phase linked to calcium release from internal stores. The calcium influx and the [Ca\ub2\u207a](cyt) increase depended on upstream protein phosphorylation. The extracellular alkalinization and ROS production depended on calcium influx but, the ergosterol-induced MAPK activation was calcium-independent. ROS were not involved in cytosolic calcium rise as described in other models, indicating that ROS do not systematically participate in the amplification of calcium signalling. Interestingly, ergosterol-induced ROS production is not linked to cell death and ergosterol does not induce any calcium elevation in the nucleus

Competition in atomic halogenation reactions

IT has been shown recently 1 that it is useful to consider a general mechanism for atomic halogenation reactions, which, in the case of the photochlorination of C 2Cl 4 and C 2HCl 5, is given by: © 1957 Nature Publishing Group.SCOPUS: le.jinfo:eu-repo/semantics/publishe

La Spécificité des Halogénations Atomiques VIII. La Mise Au Point D'Une Méthode Actinométrique

The quantum yield of the gas phase photochlorination of C2Cl4 and C2Cl3H have been measured. The light intensity of a Hg vapour lamp transmitted by a filter has been measured with a potassium ferrioxalate actinometer. The spectral intensity distribution of the light was measured and corrections were applied for intensity loss and multiple reflexions. The quantum yield is given by Φ = Ia −1/2k(Cl2) with log k = –(1065 ± 8)/T + 3.941 ± 0.021 for the photochlorination of C2HCl3. Conditions are described which permit one to use this reaction as an actinometer for other photochlorinations, so as to avoid the corrections mentioned above and permitting one to use the approximation Ia = 2,303. Ioϵl(Cl2) even at high absorption (up to about 180 mm Cl2 with light of about 4300 A). The photochlorination of C2Cl4 has a somewhat more complexe mechanism and is therefore not very adequate for actinometry. Copyright © 1959 Wiley‐VCH Verlag GmbH & Co. KGaA, WeinheimSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Kinetic isotope effect in photochlorination of H2, CH 4, CHCl3, and C2H6

The relative rates of hydrogen and deuterium abstraction by chlorine atoms from H2-D2, CH4-CD4, and C 2H6-C2D6 in direct competition have been studied by a mass spectrometer technique permitting direct determinations of rates. The pair CHCl3-CDCl3 was investigated by a substitution-addition competition with C2Cl4. Data were obtained between 300° and 475°K, and values of ka/kv ranged between 3.64 and 10.9 for CH4/CD4, 2.37 to 2.69 for C 2H6/C2D6,1.58 to 2.26 for CHCl 3/CDCl3, and 4.7 to 8.9 for H2/D2. For the family of reactions involving C-H-Cl, an extensive series of model calculations were made by the "bond-energy-bond-order" method. The expected variation of activation energy with heat of reaction was computed and compared with experiment. The expected variation of kinetic isotope effect with both temperature and heat of reaction was computed for a range of conditions much wider than these experiments. Simple activated complex theory predicts several strong trends of kinetic isotope effect with heat of reaction. The data, in a general semiquantitative way, follow these predicted trends, but in terms of fine details the data do not fit the theoretical lines. In view of the known simplifications in activated complex theory, this agreement with broad trends is all that anyone should expect.SCOPUS: ar.jinfo:eu-repo/semantics/publishe