Catalysis in nature

The rates of Mn(II) oxidation in natural waters, although slow, are typically orders of magnitude faster than the rate of oxidation of Mn(II) in solution (8,12). It has been suggested that the enhanced rate of Mn(II) oxidation in natural waters is due either to bacterial oxidation (13-16) or to the "catalytic" effects of surfaces such as metal oxides (8, 17-19). The existing evidence suggests that in certain environments bacterial mediation of the reaction is important (13-15). But in many cases the relative importance of bacterial and abiotic "catalysis" in natural waters has not been clearly defined. 

Life is sustained by a complex web of chemical reactions. Catalysts, molecules that accelerate the rate of a chemical reaction but that are unchanged by the overall reaction, are essential for life as most reactions would otherwise occur far too slowly. Indeed, it can be argued that the evolution of life is essentially the story of the evolution of catalysis. In nature, most catalysts are proteins and these catalytic proteins, or enzymes, are one of the most remarkable classes of molecules to have been generated during evolution. Enzymes catalyze an enormous range of different reactions and their performances typically far exceed those of man-made catalysts. They can accelerate reactions by anything up to 10 -fold relative to the uncatalyzed reaction, enabling reactions that would otherwise have half-lives of tens of millions of years to be performed in milliseconds. 

For a better understanding of the enzyme catalysis in nature, experimental and theoretical studies characterize the free energy profiles and catalytic efficiencies of enzymes under different conditions, which may define the performance of an enzyme in maintaining a constant flux or a constant pool concentration of the product, working under irreversible or reversible conditions etc. (Albery and Knowles, 1976 Stackhouse et al., 1985 Pettersson, 1992 Somogyi, Welch and Damjanovich, 1984). Only a few enzyme reactions have been analyzed in detail and further experimental investigations are necessary to characterize the enzymes, to draw general conclusions, and to deduce how much their evolution approximated the requirements for optimal catalysis . 

Parmon VN. Abiogenic catalysis in Nature. Colloids and Surfaces A Physicochemical and Engineering Aspects 1999 151 351-65. 

Homogeneous Catalysis Heterogeneous Catalysis Catalysis in Nature... 

The discovery [4, 5] of naturally occurring ribozymes - RNA molecules with catalytic activity - made it clear that proteins are not the only biopolymers capable of catalysis in nature. At present, a large number of natural RNAzymes are known. 

The complexity of natural aquatic ecosystems necessitates that we examine the ability of naturally occurring species and surfaces to alter the hydrolysis rates of organic pollutants. Failure to realize the potential for catalysis to occur in natural systems can lead to underestimations of hydrolysis rates when extrapolating from laboratory studies. Although this discussion will focus primarily on hydrolytic catalysis in natural water systems, several examples will be presented which demonstrate that components of natural systems also can impede hydrolysis. 

A CoimectiOTi Between Site-Selective Catalysis in Natural Products and Remote... 

Although Diels-Alder reactions provided the first examples for the great potential of asymmetric iminium catalysis, it must be pointed out that by far the most applications of this type of catalysis in natural product syntheses have been reported for conjugate additions of different nucleophiles to iminium-activated a, 3-tmsatu-rated acceptor molecules. The following sections will give an overview based on the type of nucleophiles employed in such transformations. 

J. Tsuji, Pure Appl. Chem., 1981, 55, 2371-2378. Palladium Catalysis in Natural Product Synthesis. 

Much related work has occxured based on organized catalysis in natural and synthetic macrocycles, polymers, and modified surfaces, which can only be hinted at briefly in such a review. We highlight Lehn s application of crown-ethers (83) and (84) in the catalysis of hydrolysis of chiral dipeptide esters (S R up to 50 1) and hydride transfer to ketones, respectively, Knowles s successful preparation of specifically substituted a-cyclodextrins (85) and their involvement in phosphate ester hydrolysis, and Murakami s syntheses of catalytically active p-cyclophanes. " The long-standing contribution of... 

The Basis of Catalytic Action 531 Homogeneous Catalysis 531 Heterogeneous Catalysis 532 Catalysis in Nature 533... 

Cycle-specific cascade catalysis in natural product synthesis... 

Cycle-Specific Cascade Catalysis in Natural Product Synthesis... 

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