Carbon activation mechanism

Firstly, the difference between ethane and higher alkanes cannot be readily explained by mechanisms such as those proposed by Gault (Scheme 38) or 1,2-carbon-carbon activation mechanisms (Scheme 39), while the mechanism involving y-H activation does fully account for this observation. Given... 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Leconte and Basset [161-166] proposed two other possible mechanisms (Scheme 39) the first one implies a 1,2 carbon-carbon activation which invokes the de-insertion of a methylidene fragment from a surface metal-alkyl species, and the second implies a 1,3 carbon-carbon bond activation in which the key steps are the formation of a dimetallacyle by y-H activation from a metal-alkyl followed by carbon-carbon bond cleavage via a concerted electron transfer. 

E. Raymundo-Pinero, P. Azais, T. Cacciaguerra, D. Cazorla-Amoros. A. Linares-Solano, and F. Beguin, KOH and NaOH activation mechanisms of multiwalled carbon nanotubes with different structural organisation, Carbon, 43, 786-795 (2005). 

The metal dusting of pure metals, especially Fe, was studied extensively by Hochman2. The Hochman mechanism for the metal dusting of iron involves three steps. The first step is the formation of metastable iron carbide, FejC, on the surface of iron. This reaction requires carbon activities higher than unity. 

It is about an active mechanism depending on the Na+-K+-ATPase enzyme located in the lateral plasma membrane of the endothelial cells. It enables the penetration of potassium into the cell against the excretion of sodium into the aqueous humor. Then this latter becomes hypertonic in comparison with the stroma and thus drains the water. In normal conditions, the pump can adapt to the physiological needs. Actually, the moves of the sodium ion are relative to those of the bicarbonate ion (responsible for the negative polarization of the back side of the endothelial cell) and to the pH variation. And yet, the bicarbonate comes from the aqueous humor and from the intracellular transformation of carbon dioxide and water by carbonic anhydrase. All of this shows the good functioning of the pumps depends on the integrity of the plasma... 

The metabolism of apiose in plants has not been investigated extensively. It has been suggested80 that apiose could give rise to simple terpenes by condensation and reduction. Incubation of [ -,4C]apiose in parsley plants resulted in negligible, but unspecified, amounts of carbon-14 incorporated into apiin.66 The specific activity of the [ -14C]apiose administered was low (5 X 105 d.p.m./jumole) for this reason, the data suggested only that no highly active mechanism is available in parsley for the metabolism of this branched-chain sugar. 

Martin Jekel, Professor of Water Quality Control at the Technical University Berlin, has been involved in ozonation and oxidation research since 1976, especially concerning ozone/ biological activated carbon, microflocculation mechanisms of ozone and advanced oxidation processes for water and wastewaters. He studied chemistry, has a Ph.D. in chemical engineering and is a full professor since 1988. He contributed Chapter A 3 to this book. Technische Universitat Berlin, Institut fur Technischen Umweltschutz, Sekr. KF 4, Strasse des 17. Juni 135, D-10623 Berlin, Germany wrh itu201. ut.TU-Berlin.DE... 

Relative to the initiator/activator mechanism shown in Scheme 5, it is interesting to compare vinyl ether polymerizations initiated with the HI/I2 system and with iodine alone. The former system provides living polymers of controlled molecular weights and very narrow MWD [58], whereas the latter has been known for more than a century but fails to give such controlled polymerizations (cf., Sections IV.A) [49,55]. In the iodine-mediated polymerization, iodine serves as both the initiator and activator one molecule of iodine first slowly adds across the vinyl ether double bond to give an adduct. The a-carbon-iodine bond is activated by another molecule of iodine [34,95]. Thus, both systems would in fact form the identical growing chain end [ CH2CH(OR)+.I3 ], and the ob-... 

An alternative activity mechanism of metal compounds is their participation in pyrolytic reactions in the condensed phase, i.e. promotion of carbonization and reduction of the yield of volatile products. 

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