Catalyst Enzymes Hydrogenation

Hydrogen will not reduce ketones or imines using CATHy or related catalysts. Inorganic hydrogen donors that have been used include dithionite and di-hydrogenphosphite salts, metal hydrides such as sodium borohydride, and sodium cyanoborohydride. Recently, amines have been shown to function as hydrogen donors with some catalysts. The enzymic cofactor NADH can be used stoichiometrically, and the potential exists to use this catalytically [56]. 

Like most other catalysts, enzymes can be poisoned if the active sites become clogged by an unwanted molecule. Inorganic metal catalysts are easily spoiled by hydrogen sulfide (H2S) or arsenic, whereas enzymes are particularly vulnerable to changes in hydrogen ion concentrations (pH) and temperature. Enzymes work best at temperatures around 37 °C (body temperature) and at a pH around 7 (neutral), although the digestive enzymes in the stomach work at a much lower pH. 

Two different catalysts for hydrogen peroxide decomposition, the enzyme peroxidase (isolated from the horseradish root, HRP), and polymer-supported catalyst (acid form of poly-4-vinylpyri-dine functionalized by ferric sulfate, apFe) [99,100], are examined with an aim to compare their activity. The active center in the peroxidases is the ferric ion in protoporphyrin IX. Besides the complex made of ferric ion and protoporphyrin IX, that is ferricprotoporphyrin IX, also known as ferric heme or hemin, peroxidase possesses a long chain of proteins [101,102]. On the other hand, the macroporous acid form of polyvinyl pyridine functionalized by ferricsulfate is obtained from cross-linked polyvinyl pyridine in macroporous bead form [103]. Pyridine enables it to form coordination complexes or quaternary salts with different metal ions such as iron (111) [104]. An active center on the polymeric matrix functionalized by iron, as metallic catalyst immobilized on polymer by pyridine, has similar microenvironment conditions as active center in an enzyme [105]. 

Analyzing different catalysts by means of an oscillatory reaction conducted in open and closed reactors as a matrix, it was shown that their characterization under mentioned conditions is, generally, possible and useful. Thus, by comparison with respect to dynamical effects of several catalysts in the matrix reaction system, the stmcture of active centers should be discussed. Particularly, analyzing two catalysts for hydrogen peroxide decomposition, the natural enzyme peroxidase and synthetic polymer-supported catalyst, the similarity in their catalytic activity is found. Hence, we can note that the evolution of the matrix oscillatory reaction can be used for determination of the enzyme activity. Moreover, one can see that the analysis of the granulation and active surface may also be performed by the oscillatory reaction. 

Pejic, N., Cupic, Z., Anic, S., Vukojevic, V., and Kolar-Anic, Lj., The oscillatory Bray Liebhafsky reaction as a matrix for analyzing enzyme and polymeric catalysts for hydrogen peroxide, Sci. Sintering, 33, 107-115, 2001. 

In order to facilitate hydrogen peroxide detection, a third enzyme, horseradish peroxidase has been employed as a catalyst for hydrogen peroxide reduction with the enzymatic oxidation of an electrode donor substance. Horseradish peroxidase has been used as a catalyst for hydrogen peroxide reduction with the enzymatic oxidation of a electrode donor (AH) ... 

Catalysts speed up chemical reactions in which they do not actually enter. They are typically used in small quantities. Raney nickel is used as a catalyst in hydrogenation of oils and sodium methoxide (sodium methanoate) in the transesterification of fats. Acids are used as catalysts in the production of certain modified starches. Catalysts also include the enzymes used as food additives, such as amylase (El 100), proteases (El 101, for example papain, bromelain and ficin), glucose oxidase (El 102), invertase (E1103) and lipases (El 104). 

The specificity of enzymes is associated with their geometrical (special structure), as the substrates have to fit (geometry), as weU as with their affinity provided by formation of hydrogen bonds, electrostatic interactions, and hydrophobicity. Enzymes have been named by adding the suffix -ase to the name of the substrate or to a word or phrase describing their activity. Enzymes are classified according to reaction type. The classification according to the Enzyme Commission emphasizes the ability of the enzyme to catalyze a process in one direction however, as with other catalysts, enzymes also catalyze the reverse reactions. 

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