Catalysis autocatalysts

The key NMR observations (i) that the proportion of homo- and heterochiral dimers is near-equal, and (ii) that their interconversion by a dissociative process is rapid compared to catalytic turnover, preclude the possibility of a monomer autocatalyst. In Kagan s classification, monomer catalysis with a positive NLE may only arise when there is an unequal concentration of homo- and heterochiral oligomers, in favour of the heterochiral form, which acts as a reservoir for the deficient enantiomer. NMR results show that the resting state for Soai s autocatalysis is an equal mixture of homo-and heterochiral species, predominantly dimeric. The lack of ground-state stereo-discrimination requires that the number of chiral entities in the resting state must be less than or equal to the number in the enantioselectivity-determining transition state, else there is no possibility of the vital non-linear effect. Even after the publication of these results in late 2004, their consequences are not always applied. For recent discussions where a monomeric catalyst for Soai s system is permitted or promoted, see [91-93]. 

Autocatalysis is a distinctive phenomenon while in ordinary catalysis the catalyst re-appears from the reaction apparently untouched, additional amounts of catalyst are actively produced in an autocatalytic cycle. As atoms are not interconverted during chemical reactions, this requires (all) the (elementary or otherwise essential) components of autocatalysts to be extracted from some external reservoir. After all this matter was extracted, some share of it is not introduced in and released as a product but rather retained, thereafter supporting and speeding up the reaction(s) steadily as amounts and possibly also concentrations of autocatalysts increase. At first glance, such a system may appear doomed to undergo runaway dynamics ( explosion ), but, apart from the limited speeds and rates of autocatalyst resupply from the environment there are also other mechanisms which usually limit kinetics even though non-linear behavior (bistability, oscillations) may not be precluded ... 

But what is it about this system that makes us call it self-replicating How could we show that the system progresses through directed template catalysis rather than through simple chemical autocatalysis After all, (6) bristles with functional groups. The imide, amide, ribose and purine functionalities must all be considered as possible explanations for the autocatalysis observed. For example, imidazole is a well-known catalyst for acylation reactions, and the purine contains such a subunit. Could not this functionality be the cause The potentially catalytic functions of the product molecule had to be individually tested in the structural context of (6) and under the conditions where (6) acts as an autocatalyst. 

The role of the oxygen vacancies at the support in the CO oxidation on Rh/Ce02 and Rh/ Ti02 autocatalysts, in Catalysis and Automotive Pollution Control II, ed. A. Crucg (Elsevier, Amsterdam) pp. 207-219. 

Autocatalysis corresponds to prtxiesses involving a product as a catalyst in a chemical step leading to its own formation. As noticed above for catalysis, a direct interaction of the autocatalyst with the transition state of the non-catalysed upstream reaction is formally not needed since autocatalysis can result from the architecture of a reaction network in which a product or intermediate is involved as a component of a metabolic cycle (catalytic cycle) [24] (Fig. 8.5). This observation on metabolic cycles is important since any metabolism requires that every component is reproduced. 

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