ReGeneraTing Agents

The peroxide decomposer will drastically reduce the number of radicals, which can then be more effectively mopped up by the chain-breaking materials. A widely used combination is 4-methyl-2,6,di-t-butylphenol and dilauryl thiodipropionate. It is possible to envisage most powerful combinations where a chain-breaking antioxidant, a regenerating agent, a peroxide decomposer, a metal deactivator and an ultraviolet absorber are all employed together. 

Solvent recovery with adsorption is most feasible when the reusable solvent is valuable and is readily separated from the regeneration agent. When steam-regenerated activated-carbon adsorption is employed, the solvent should be immiscible with water. If more than one compound is to be recycled, the compounds should be easily separated or reused as a mixture. Only very large solvent users can afford the cost of solvent purification by distillation. ... 

In regenerating agents for waste oils from washing of mechanical parts, based on sodium silicate and water, salts of alkylphosphates are used as surfactants on account of their good solubility [232]. 

In the original process the cellulose nitrate itself was used as the fiber (hence its satirical description as mother-in-law silk ). The regenerating agent is ammonium hydrosulfide. The basic process was first demonstrated by J. W. Swan in London in 1885 but commercialized by Count L. M. H. B. de Chardonnet ( Father of the rayon industry ) in France in 1891 and operated there until 1934. The last working factory, that in Brazil, was burnt down in 1949. The other processes for making rayon fibers by regenerating cellulose ( viscose, cupram-monium) gave superior products. See also Rayon. 

The use of redox enzymes in organic synthesis, while having a large potential for broad application in the selective formation of high-value compounds, has been limited by the necessity of cofactor regeneration or enzyme reactivation. Electrochemistry offers an attractive and, in principle, simple way to solve this problem because the mass-free electrons are used as regenerating agents. No... 

The catalytic system has been successfully extended to polymer-bound lithium amide co-bases of type 65 (see Table 4) which, like C—Li bases of type 63 and 64, are efficient regenerating agents of HCLA and poorly reactive toward oxiranes. For instance, the isomerization of cyclohexene oxide by 0.05 equiv of HCLA 55 in the presence of 1.45 equiv of 65 affords ( l-cyclohexenol in 92% ee (entry 15). It is of interest to note that, similarly to co-bases 63 and 64, the use of 65 leads to an increase of selectivity compared to the stoichiometric reaction at room temperature (Table 2, entry. ... 

Benzoquinone has been used as an alternative oxidizing agent to oxygen in the oxidation of olefins catalyzed by palladium acetate (1). Presumably it has the same role as a regenerating agent in oxidizing some... 

The over-all process is catalytic both in metal and regenerating agent. 

While this type of reaction has been demonstrated with most of the group VIII noble metals, palladium has the highest activity and, therefore, is normally used. Regenerating agents (co-catalysts) are most frequently CuCl2, FeCl3, and quinone. Reaction details are complex (6). 

As described below, tolerance is an important consideration in the use of nitrates. While tolerance may be caused in part by a decrease in tissue sulfhydryl groups, it can be only partially prevented or reversed with a sulfhydryl-regenerating agent. The site of this cellular tolerance may be in the unknown reaction responsible for the release of nitric oxide from the nitrate, since other agents, eg, acetylcholine, that cause vasodilation via release of nitric oxide from endogenous substrates do not show cross tolerance with the nitrates. 

An advantage of electrochemical cofactor regeneration is the use of mass-free electrons as regenerating agents. The low cost of electricity can be exploited. 

The MesSiCl/col couple has also proved to be a suitable regenerating agent for Cp2TiCl-catalyzed cascade cyclizations of epoxypolyprenes [53]. Thus, the catalytic cyclization of epoxyfarnesyl acetate (4) (Scheme 12), for example, provided substantially increased yields of alkene 5 (40% versus the 25% obtained by the stoichiometric version) whilst employing lower titanocene proportions and dilution levels by one and two orders of magnitude, respectively. 

We have also achieved imusual 7-endo-dig and 7-endo-trig radical cyclizations employing the MesSiCl/col combination as titanocene-regenerating agent [69]. Moreover, we have provided theoretical and experimental evi-... 

Employing the MesSiCl/col couple as titanocene-regenerating agent, we have prepared both monocyclic sesquiterpenoids, such as the metabolite 19 found in the fragrant plant Artemisia chamaemelifolia (Scheme 24), and monocyclic triterpenoids, such as achilleol A (9), starting from epoxygeranylacetone derivative 8 and using only substoichiometric proportions (0.2 equiv) of the titanocene catalyst [53]. 

To reach high reaction rates, the hydride ion abstraction must be fast and very effective. The chemical regeneration agent frequency used for NAD" " is FMN, a quinoid system. It is most applied as a stoichiometric oxidant. It can also be introduced in the presence of oxygen, thus producing hydrogen peroxide, which has to be destroyed by catalase [10,13,14,114]. In this case, in principle, less than stoichiometric amounts of FMN should be sufficient. However, due to the low reactivity, even in this case more than stoichiometric amounts of the catalyst are applied. Thus, with FMN, the problem is a... 

Receptor tyrosine kinases (RTKs) are activated (phosphorylated) by inhibition of a negatively regulating phosphatase upon treatment with UV (A, B, or C), hydrogen peroxide, or iodoacetamide. The phosphatase activity, (i.e., dephosphorylation and inactivation of RTKs) is restored upon the addition of thiol-regenerating agents, if not inhibited irreversibly by iodoacetamide [20]. H2O2 not only inactivates membrane-bound phosphatases but also diminishes cytosolic general protein tyrosine phosphatase activity in mouse fibroblasts [21]. Further, the activation of JNK by sodium arsenite, which is reactive towards thiols (especially vicinal dithiols), is by inactivation of a JNK phosphatase [22]. 

The regeneration agent was either 2mg/mL pepsin in 50mM phosphate solution adjusted to pH 2 or 500mM formic acid (BZE-DADOO-modified sensors), respectively (see Note 3). The suggested measuring cycle consisted of the following steps (20,21) ... 

In this case we had to use 2mg/mL pepsin in phosphate solution at pH 2 to achieve a reproducible regeneration. Figure 5 shows a comparison of formic acid and pepsin as regeneration agents. In both cases 50pg/mL Drosphila AChE was allowed to interact with the propidium-modified QCM. In case of pepsin, a... 

Figure 1. General scheme for cofactor regeneration (top) and structures of adenosine and nicotinamide cofactors (bottom). Key X, Y, cofactors A, regenerating agent and B, product from this reagent.

Fig. 5.18. Fluidized bed adsorber. 1 — impure gas inlet, 2 — adsorber, 3 — clean gas outlet, 4 — regenerating agent, 5 — regenerating bed, 6 — desorbed vapour, 7 — surge bin, 8 — elevator for saturated adsorbent...

This method implies a reaction of the adsorbate with a regeneration agent, which eliminates it from the carbon. For example, sodium hydroxide or sodium bicarbonate reacts with phenol to form sodium phenolate which is soluble in water. Acids can also be used at elevated temperatures to remove heavy metals from exhausted carbons. Treatment with these chemicals may also affect the structure of the carbon, causing changes to the porosity and in most cases impairing its adsorption capacity after a few regeneration cycles. 

The regeneration step is the key to the implementation of the anion exchange system on the commercial scale. Desorption studies help to evaluate the nature of adsorption process. Desorption experiments were performed using different regenerating agents such as 1M NaCl, 1 M Na2S04,1 M N32C03,1 M NaOH, 1 M FECI and even 1 M KSCN. As previously stated [2, 15,20,23,25-31], the aqueous solutions mentioned above were ineffective for the dyes removal from the resin phase. 

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