Catalysis of oxidation

Thermodynamic Disequilibrium and Microbial Catalysis of Oxidation Reactions... 

Yeast alcohol dehydrogenase, catalysis of oxidation by NAD of benzyl alcohol equilibrium interconversion of benzyl alcohol and benzaldehyde... 

Samuelsson (1966) concluded, on the basis of his studies, that the close proximity of a copper-protein complex to the phospholipids which are also associated with the fat globule membrane is an important consideration in the development of an oxidized flavor in fluid milks. Haase and Dunkley (1970) stated that although some aspects of catalysis of oxidative reactions in milk by copper still appear anomalous... the mechanism of oxidized flavor development with copper as catalyst involves a specific grouping of lipoprotein-metal complexes in which the spatial orientation is a critical factor. ... 

Catalysis of Oxidation Reactions by Electron Exchange wnh Metal Ions or Metal Complexes... 

Figure 2.17. Infrared spectra of the synthesized FA (MW > 1000 Da) in the Mn(IV) oxide-pyrogallol system and the FA extracted from a Borosaprist (Terric Humisol). Reprinted from Wang, M. C., and Huang, P. M. (2000). Characteristics of pyrogallol-derived polymers formed by catalysis of oxides. Soil Sci. 165, 737-747, with permission from Lippincott Williams Wilkins.

Pal et al. (1994) compared the catalysis of oxidative coupling reactions of various phenolic compounds by the enzymes, laccase and tyrosinase, and mineral catalyst, birnessite. Birnessite acts as a heterogeneous catalyst whereas laccase and tyrosinase function as homogeneous catalysts. Laccase and tyrosinase continue to oxidize catechol after repeated additions of the chemical, while birnessite lost its oxidizing activity after the first addition of catechol (Figure 2.20). In the case of birnessite,... 

Wang, M. C., and Huang, P. M. (2000a). Characteristics of pyrogallol-derived polymers formed by catalysis of oxides. Soil Sci. 165,737-747. 

In this context, the most successful will be the branch of pure catalysis of oxidation where the substrate is oxidized in close connection with the catalyst, i.e. the catalyst forms an active intermediate with the substrate or oxidant (or, probably, with both). 

These concepts are important for an understanding of the roles played by metal ions and their complexes in the catalysis of oxidation reactions via homo-lytic mechanisms. Thus, metal complexes may function as catalysts by interfering with any of the various initiation, propagation, and termination steps outlined earlier. 

Catalysis of oxidation reactions will continue to be of enormous importance in the future. Areas that continue to be of active interest are the development of efficient methods for the direct epoxidation of olefins, hydroxylation and substitution of aromatics as well as the selective oxidation of alkanes. The application of methods developed for industrial chemicals to the synthesis of more complex molecules is worthy of more attention. A few examples have been discussed in the text. On the whole, however, synthetic chemists have not exploited these methods. 

We shall now consider the biological functions of haemoproteins. These may be classified as (a) oxygen transport and storage, (b) electron transfer and (c) catalysis of oxidations by O2 and H2O2. 

The other major class of haemoproteins is involved in the catalysis of oxidations by O2 and H2O2. Such enzymes are known respectively as oxidases (14) and peroxidases (15). In these the ferric form is often the more important, and some, notably catalase, are almost impossible to reduce to the ferrous state. 

Ceruloplasmin binds eight copper atoms per molecule and is of an intense blue colour. The coding gene is localized on chromosome 3. (396) Ceruloplasmin is the most important transport protein for copper in circulating blood (about 75-95% binding capacity). Another important function of this protein is the catalysis of oxidative metabolic reactions it also possesses antioxida-tive features for the elimination of reactive oxygen intermediates. (s. tab. 3.25) The normal value in serum is 20-35 mg/dl. 

Niacin is a water-soluble vitamin. The RDA of niacin for the adult man is 19 mg. Niacin is converted in the bi>dy to the cofactor nicotinamide adenine dinucleotide (NAD). NAD also exists in a phosphorylated form, NADP The phosphate group occurs on the 2-hydrr>xyl group of the AMP half of the coenzyme, NAD and NADP are used in the catalysis of oxidation and reduction reactions. These reactions are called redox reactions. NAD cycles between the oxidized form, NAD, and the reduced form, NADH + H. The coenzyme functions to accept and donate electrons. NADP behaves in a similar fashion. It occurs as NADP and NADPH + HT The utilization of NAD is illustrated in the sections on glycolysis, the malatc-aspartate shuttle, ketone body metabolism, and fatty acid oxidation. The utilization of NADP is illustrated in the sectirrns concerning fatty acid synthesis and the pentose phosphate pathway. 

In systems where metal catalysis of oxidation is an issue, the use of a metal chelator such as ethylenediaminetetraacetic acid is recommended to inhibit oxidation. Additionally, as with previous degradation techniques, the oxidation samples should be stored at low temperature (below 5 °C) to preserve the... 

Fig. 9 Role of free iron in the catalysis of oxidative stress. Pathophysiological events can trigger the release of redox-active iron from transport and storage proteins. Ferric iron can be reduced by cellular reductants, resulting in autoxidation and subsequent HO radical formation...

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