Catalysis abiotic

These species are ubiquitous in soil (Kelly and Harrison 1989). In a recent laboratory investigation of the fate of ionic thiocyanate in six different soils, Brown and Morra (1993) concluded that microbial degradation is the primary mechanism for thiocyanate disappearance at or below 30 °C, with carbonyl sulfide proposed as a possible hydrolysis product. Loss of thiocyanate at higher temperatures (50-60 °C) did not appear to result from microbial degradation the observed decreases in thiocyanate concentrations of soil extracts with incubation time at elevated temperatures were postulated to result primarily from increased sorption or increased sorption kinetics, but abiotic catalysis of thiocyanate degradation was also noted as a possible cause. 

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. 

A. Naidja, and P. M. Huang, Significance of the Henri-MichaeUs-Menten theory in abiotic catalysis Catechol oxidation by 5-Mn02, Surf. Sci. 506(1-2), L243-L249 (2002). 

Abiotic catalysis is generally less important than biotic but may be important. Examples are Mn(lll,IV) and Fe(III) reduction by microbial metabolites, and Fe(ll) oxidation which is catalysed by sorption onto soil particles. 

In an extensive review on abiotic catalysis, Huang (2000) noted that the reactivity of hydrolyzable organic contaminants arises from the presence of electron-deficient (electrophilic) sites within the molecules. Figures 14.2 and 14.3 show the patterns of reactivity in two cases of nucleophihc substitution and monomolecular nucleophilic substitution. The Sj 2 mechanism (nucleophilic substitution) involves attack of the electrophilic sites by OH" or H O, generation of a higher coordination nnmber intermediate, subsequent elimination of the leaving group, and the formation of an hydrolysis product (Fig. 14.2). 

Haderlein SB, Pecher K (1988) PoUutant reduction in heterogeneous Pe(ll)/Pe(lll) systems. In Sparks DL, GrundlT (eds) Kinetics and mechanisms of reactions at the mineral/water interface. ACS Symposium Series vol 715 342-357, Washington, DC Huang OM (2000) Abiotic catalysis. In Sumner ME (ed) Handbook of sod science. CRC Press Boca Raton, Florida, pp 303-327... 

Little is known on the catalysis of the Maillard reaction and especially the integrated polyphenol-Maillard reaction by natural soils and sediments. Further work is warranted on this subject matter to advance our understanding of the role of abiotic catalysis in the formation of humic substances and related C turnover and N transformations in the environment. 

In the past the mineral matrix was considered as inert, only providing stabilization support for enzymes and humic substances however, due to the overwhelming amount of evidence at the molecular level, there is no doubt that minerals participate in abiotic catalysis of humification reactions in soils. Naidja et al. (2000) referred to mineral particles as the Hidden Half of enzyme-clay complexes, which not only prolong the activity of immobilized enzymes but also are readily able to participate in electron transfer reactions. Many environmental factors can negatively affect the... 

Huang, P. M. (2000). Abiotic catalysis. In Handbook of Soil Science, Sumner, M. E., ed., CRC Press, Boca Raton, FL, pp. B302-B332. 

Naidja, A., and Huang, P. M. (2002). Significance of the Henri-Michaelis-Menten theory in abiotic catalysis catechol oxidation by 8-Mn02. Surface Sci. 506, L243-L249. 

Oxidation Kinetics of Mn(II). This section addresses the question of whether the Mn(II) oxidation rates shown in Figure 4 can be explained by microbiological or abiotic pathways. Several incubation studies of Mn(II) with natural water, natural particulate matter, or pure cultures reported evidence for microbial catalysis of Mn(II) oxidation (4, 18, 54-58). In bottom waters of Lake Zurich (58) and in water samples from the marine fjord of Saanich Inlet (18) maximum Mn oxidation occurred at around 33 and 20 °C, respectively. These results strongly suggest microbial catalysis. In the case of abiotic catalysis, a steady increase in the oxidation rate with temperature is to be expected (16). Working with water samples from the bottom of Lake Zurich that were spiked with Mn(II) at 2 or 10 xM, Diem (58) found a Michaelis-Menten-type rate law for Mn(II) oxidation ... 

In natural systems microbiological oxidation may offer a faster pathway, particularly at pH < 8 and low concentrations (<5 jlM) of particulate oxides. Hastings and Emerson (17) showed that sporulated cultures of marine bacillus SG-1 at pH 7.5 accelerated the oxidation of Mn(II) by a factor of 104 with respect to the abiotic catalysis on a colloidal MnOz surface. A radiotracer study of microbial Mn oxidation in a marine fjord revealed half-lives as short as 2 days (18). Perhaps microorganisms can use the entire redox cycle of manganese. A study indicates that the vegetative cells of spores that mediate Mn(II) oxidation also reduce manganese oxides (19). 

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