Reducing agent holding reductants

Why are there two pyridine nucleotides, NAD+ and NADP+, differing only in the presence or absence of an extra phosphate group One important answer is that they are members of two different oxidation-reduction systems, both based on nicotinamide but functionally independent. The experimentally measured ratio [NAD+] / [NADH] is much higher than the ratio [NADP+] / [NADPH]. Thus, these two coenzyme systems also can operate within a cell at different redox potentials. A related generalization that holds much of the time is that NAD+ is usually involved in pathways of catabolism, where it functions as an oxidant, while NADPH is more often used as a reducing agent in biosynthetic processes. See Chapter 17, Section I for further discussion. 

The overall process involves a stoichiometric reducing agent which is plain old NaBH4 and another boron species Et2BOMe. We shall see in a minute that it is the job of this second boron species to hold the P-hydroxy ketone 156 in a ring as the reduction proceeds.39... 

An enzyme that catalyzes an oxidation reaction or a reduction reaction requires a coenzyme because none of the amino acid side chains can act as oxidizing or reducing agents. The coenzyme is the oxidizing or reducing agent. The enzyme s role is to hold the substrate and coenzyme together so that the oxidation or reduction reaction can take place. 

Miktoarm stars of the type (PS-b-PI)n(PI)m prepared using DVB as linking agent were employed in adhesive compositions, showing a good balance of tack, peel strength and hold power near room temperature due to their reduced cohesive strength and viscosity without any reduction in the service temperature... 

Except in tracer level solutions where its concentration is often difficult to ascertain, PuOj is normally present in a mixture of Pu oxidation states in which that of PuOj is much lower than PuOj and Pu , PuOj can be formed in good yield and maintained with a holding oxidant (which may be a complexor itself). Conversely, PuOj may be reduced by many complexing agents, (18), leading to calculation of erroneous stability constants if the extent of reduction is not taken into account. Photochemical... 

Initial experiments were performed to verify and demonstrate the feasibility of the electrolytic reduction method with uranium, followed by experiments with a mixture of uranium and plutonium. Experiments were conducted batchwise in a small electrolytic cell. Basic parameters, such as concentration of solutes and type of holding agents (in the aqueous phase) for removal of any nitrite which would reoxidize the reduced heavy metal, electrode material and geometry, off-gas composition and type of diaphragm, were also determined. These data were valuable in the conceptual design of the first continuously operating column for the electrolytic reduction process. 

Before being fed to Contactor III, the aqueous feed solution was treated to reduce Pu to the Pu(III) state, to prevent its extraction and ensure its recovery in the aqueous Pu product stream (3PP). The reference reductant for the flow sheet was hydroxyla-mine nitrate (HAN) at 0.3 mol/L with hydrazine nitrate (0.1 mol/L) as a holding agent or HNO2 scavenger (10). Use of HAN as Pu reductant was considered desirable because in reaction with Pu, as well as in subsequent reactions where the reductant is destroyed, only gaseous products are formed (equations 1 and 2). 

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