Biological reactions, stoichiometric

Reactive Zn OII (n = 1 or 2) species are proposed in the catalytic cycles of several zinc-containing enzymes. In order to gauge the chemical factors that influence the formation and reactivity of Zn OH species, synthetic model complexes have been prepared and systematically examined for biologically relevant stoichiometric and catalytic reactivity. Systems that promote the hydration of C02, the activation and oxidation of alcohols, and amide and phosphate ester cleavage reactions are discussed. 

Here, a is a stoichiometric coefficient for A in reaction 2. Reactions involving non-integer stoichiometric coefficients are common in biological reactions. The overall rate expression for A, r, is given by the peculiar kinetics (which has been fabricated for demonstration) as follows ... 

The representation of the biological conservation of substrate to cell mass by an overall chemical reaction. The stoichiometric relationships are then used to calculate various rates such as cell mass concentration [83]. 

Nonetheless, the topological and stoichiometric analysis of metabolic networks is probably the most powerful computational approach to large-scale metabolic networks that is currently available. Stoichiometric analysis draws upon extensive work on the structure of complex reaction systems in physical chemistry in the 1970s and 1980s [59], and can be considered as one of the few theoretically mature areas of Systems Biology. While the variety and amount of applications of stoichiometric analysis prohibit any comprehensive summary, we briefly address some essential aspects in the following. 

In Table 5.4 the contributions of the individual weathering reactions were assigned and combined in such a way as to yield the concentrations of Ca2+, Mg2+, Na+, K+, and H+ measured in these lakes the amounts of silicic acid and aluminum hydroxide produced and the hydrogen ions consumed were calculated stoichiometrically from the quantity of minerals assumed to have reacted. Corrections must be made for biological processes, such as ammonium assimilation and nitrification and the uptake of silicic acid by diatoms. Some of the H4Si04 was apparently lost by adsorption on aluminum hydroxide and Fe(III)(hydr)oxides, but the extent of these reactions was difficult to assess. 

Derivatives of quinones have always attracted attention because of their biological importance. As a consequence, a number of reactions have been investigated. After emerging as a fascinating alternative to most of the conventional stoichiometric... 

The oxidation of sulfides to sulfones has been the subject of extensive studies, since sulfones are useful synthons for the construction of various chemically and biologically significant moleculesJ Recently, a new catalytic system has been developed by exchanging potassium osmate onto chloride-saturated layered double hydroxides (Figure 9.1), which we have shown to be an efficient catalyst for the direct oxidation of sulfides to sulfones, using molecular oxygen as the stoichiometric oxidant and with delivery of two oxygen atoms simultaneously to the sulfide, reminiscent of olefin dihydroxylation reactions. 

Asymmetric Mannich reactions provide useful routes for the synthesis of optically active p-amino ketones or esters, which are versatile chiral building blocks for the preparation of many nitrogen-containing biologically important compounds [1-6]. While several diastereoselective Mannich reactions with chiral auxiliaries have been reported, very little is known about enantioselective versions. In 1991, Corey et al. reported the first example of the enantioselective synthesis of p-amino acid esters using chiral boron enolates [7]. Yamamoto et al. disclosed enantioselective reactions of imines with ketene silyl acetals using a Bronsted acid-assisted chiral Lewis acid [8]. In all cases, however, stoichiometric amounts of chiral sources were needed. Asymmetric Mannich reactions using small amounts of chiral sources were not reported before 1997. This chapter presents an overview of catalytic asymmetric Mannich reactions. 

Heteroatom transfer reactions to carbon-carbon double bonds using catalytic or stoichiometric amounts of transition-metal complexes have recently attracted considerable interest in the convenient synthesis of three-membered heterocycles (Eq. (1)). The latter are versatile building blocks for the construction of complex organic compounds, such as natural products and biologically active compounds (Eq. (1)) [11. 

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