Charge active

Similar reaction mechanisms, involving general base and metal ion catalysis, in conjunction with an OH nucleophilic attack, have been proposed for thermolysin (Ref. 12) and carboxypeptidase A (Refs. 12 and 13). Both these enzymes use Zn2+ as their catalytic metal and they also have additional positively charged active site residues (His 231 in thermolysin and... 

There are several choices for the adsorbent. Activated carbon still remains the most widely used, especially for VOCs. Activated carbon is by far the most commonly used adsorbent in odor control applications and many VOC recovery applications. Because of its relatively uniform distribution of surface electrical charge, activated carbon is not selective toward polar molecules. 

Co-ordination of an alkene to an electronegative metal (often it may carry a positive charge) activates the alkene toward attack of nucleophiles. After the nucleophilic attack the alkene complex has been converted into a c-bonded alkyl complex with the nucleophile at the (3-position. With respect to the alkene (in the "organic" terminology) the alkene has undergone anti addition of M and the nucleophile Nu, see Figure 2.25. 

In some cases they were able to quench deton completely by an applied magnetic field, and in one experiment they determined the temperature coefficient of voltage required to quench detonation in 20 mol % acetylene and 80% air to be positive. Malinovskii Lavrov stated that negative charges actively propagate the deton wave in 25/75 mol % acetylene... 

The C02 hydration activity of cat isoenzyme III is independent of pH in the range of 5.0 < pH < 8.5 (148). The pKa value of zinc-H20 is outside this pH range and probably quite low due to electrostatic effects from positively charged active-site groups such as Lys-64 and Arg-67 (143). 

The charged electrophile can then either add to a susceptible monomer molecule producing a positively charged active centre... 

Fig. 4.6. Schematic pattern of the tunnelling recombination of positively changed Vk centre with neutral electron centre (e.g., F centre) (a) and with oppositely charged activator atom (e.g., Tl°) (b). In the second case the Coulomb field traps Vk at long distance R n, but electron transfer itself occurs at much shorter distance.

FIGURE 5.19 Postulated interaction between (positively charged) activated carbon cloth surface and (negatively charged) bentazone under anodic polarization. (From Ania, C.O. and Beguin, F., Water Res. 41, 3372, 2007.)... 

Stainless Steel Element Copper Element i Activated Alumina Element Activated Charcoal Element Magnetic Element Synthetic Zeolite Charge Activated Alumina Charge Liquid Nitrogen Dry-Ice Slurry Water-Cooled Polyester Element 1 a. s a... 

When ammonium chloride is used as the supporting electrolyte in the anodic oxidation of enecarbamates in acetonitrile or methanol, chlorination at the -position takes place. In the mechanism of this -chlorination, the electron transfer from the unsaturated bond of the enecarbamate may not be involved, but the chloride ion is anodically oxidized to a positively charged active species which subsequently adds to the -position of the... 

The initiation of an electrogenic process causes an adjustment of the passive ionic fluxes across the membrane. In particular, the net charge actively brought in is soon electrically compensated by appropriate passive movements of that ion and other ions into or out of the cell. The actual electrical potential difference across the membrane then results from the diffusion potential caused by these new passive fluxes plus a steady-state contribution from the electrogenic process involving the active transport of various charged species. We can represent the electrical potential difference generated by the active transport of species/, atj, by... 

Substituents which are electron donating, and can stabilize a positive charge, activate the ring towards electrophilic attack and direct further substitution to the ortho and para positions. Substituents which are electron withdrawing deactivate the ring towards electrophilic attack and direct further substitution to the meta position. 

The most commonly used type of catalyst is a relatively small, bifunctional molecule that contains both a Lewis base and a Bronsted acid center, the catalytic properties being based on the activation of both the donor and the acceptor of the substrates. The majority of organocatalysts are chiral amines, e.g. amino acids or peptides. The acceleration of the reaction is either based on a charge-activated reaction (formation of an imminium ion 4), or involves the generalized enamine catalytic cycle (formation of an enamine 5). In an imminium ion, the electrophilicity compared to a keton or an oxo-Michael system is increased. If the imminium ion is deprotonated to form an enamine species, the nucleophilicity of the a-carbon is increased by the electron-donating properties of the nitrogen. ... 

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