Positive catalysis definition

From the mere fact that CF, can be released from the membrane by EDTA treatment and the enzyme stays in solution without detergents, it is apparent that the catalytic sector has minimal, if any, direct interaction with the lipids of the chloroplast membrane. It is a globular protein that is held to the surface of the membrane via interaction with the membrane sector. Recently it was shown that the y subunit is in immediate contact with the membrane sector and the 8 and e subunits may induce proper binding for catalysis [17,18], The enzyme contains a few well-defined sites that were used for localization experiments by the method of fluorescent energy transfer [19,56-61], These studies revealed the position of those sites and helped to localize the various subunits of CF, in space relative to the chloroplast membranes (for a model of CF, see Refs. 61 and 62). These experiments are awaiting analysis of the amino acid sequence of the y subunit that is now under investigation in Herrmann s laboratory [148], Definite structural analysis could be obtained only after good crystals of the enzyme become available. 

The position is similar in basic catalysis. The hydroxyl ion has no strong claims to uniqueness, being merely the anion of a weak acid. According to the Bronsted-Lowry acid-base definition, a base is any species which has a tendency to accept a proton. This obviously includes anions like OH-, CH3COO, HPCL , as well as uncharged basic molecules like ammonia and the amines. Catalysis by all these species was first found in the decomposition of nitramide (Bronsted and Pedersen, 15), and subsequently in many other reactions. 

The problem of the nature and the extent of a relationship between catalytic activity and position in the periodic table is important not only in the formulation of a general theory of catalysis but also in respect to the more fundamental problem of interaction between solid surfaces and surrounding phases. There is definite evidence on the important role of unfilled d-bands of transition metals for low-temperature chemisorption of hydrogen ). 

Better results were obtained for the catalysis of the dehydrofluorination of 4-fluoro-4-(4-nitrophenyl)butanone by Shea et al. [94] and Mosbach et al [147]. Shea used benzyl-malonic acid as the template to position two polymerizable amines in a definite arrangement in the cavity. After removal of the template, dehydrofluorination was enhanced by this catalyst by a factor of 8.6. 

A definition that is still valid today is due to Ostwald (1895) a catalyst accelerates a chemical reaction without affecting the position of the equilibrium. Ostwald recognized catalysis as a ubiquitous phenomenon that was to be explained in terms of the laws of physical chemistry. 

The word "catalysis" was first used by Berzelius in 1836 to describe a number of experimental observations, including Thenard s discovery in 1813 that ammonia is decomposed by metals. The most general definition of a catalyst states that "it is a substance which modifies the rate at which a chemical system attains equilibrium, without itself undergoing a chemical change". It follows that a catalyst can only accelerate a thermodynamically feasible reaction and cannot displace the position of the equilibrium in the case of a reversible reaction because the forward and the reverse reactions are accelerated to the same extent. 

The term catalysis was coined by Berzelius in 1835, and catalysts are defined as substances which by their mere presence evoke chemical reactions that would not otherwise take place. Ostwald was the first to emphasize that a catalyst influences the rate of a chemical reaction but has no effect on the position of equilibrium because it accelerates the forward and the reverse reactions with equal intensity. Ostwald s famous definition was A catalyst is a substance that changes the rate of a chemical reaction without itself appearing in the end products . A catalyst is adequately compared to a coin that activates a slot machine to yield a valuable product, along with the coin. 

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