Oxygen separation inefficiencies

Deprotonation provides the necessary electron push to kick out the electron pair joining C(6) with the nitrobenzene oxygen. If, however, N(l) is alkylated (as with the nucleosides and nucleotides), OH catalysis is much less efficient since it now proceeds by deprotonation from N(3) (with the uracils) or from the amino group at C(4) (with the cytosines). In these cases the area of deprotonation is separated from the reaction site by a (hydroxy)methylene group which means that the increase in electron density that results from deprotonation at N(3) is transferable to the reaction site only through the carbon skeleton (inductive effect), which is of course inefficient as compared to the electron-pair donation from N(l) (mesomeric effect) [26]. Reaction 15 is a 1 1 model for the catalytic effect of OH on the heterolysis of peroxyl radicals from pyrimidine-6-yl radicals (see Sect. 2.4). 

The key CBB cycle enzyme, RubisCO, is the most abundant protein in the world [8], as it can comprise up to 50% of the total soluble protein in the chloro-plasts or in bacteria using this cycle. This fact is a consequence of the notorious catalytic inefficiency of RubisCO, that is, a low affinity for C02, a slow catalytic turnover rate, and a wasteful oxygenase side reaction responsible for photorespiration, resulting in a futile cleavage of the substrate to form phosphoglycolate as a side product. However, the CBB cycle enzymes are oxygen-insensitive and can easily be controlled, because the whole pathway is separated from... 

In an effort to explore this aspect further, a paper written by Gyftopoulos and Benedict concerning the maximum potential efficiency of an air separation plant provided some insight (4 ). Compressed air is separated by cryogenic distillation into oxygen and nitrogen. In a unique approach, the authors developed an idealized process wherein all thermodynamic inefficiencies which could be corrected by capital investment were eliminated. The losses in the distillation tower were not much affected by this approach. Their thermodynamic analysis for the practical and idealized processes are compared in Figure 7. 

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