Organic interaction with clays

A. S. Boyd and M. M. Mortland, Enzyme interactions with clays and clay-organic matter complexes. Soil Biochemistry, Vol. 6 (J.-M. Bollag and G. Stotzky, eds.), Marcel Dekker, New York, 1990, p. I. 

The experimental studies of interactions of organic molecules adsorbed or intercalated in the interlayer space of clay minerals are very extensive. These experimental investigations were reviewed in several monographs [15-17]. In this part, we will review only experimental studies concerning systems of kaolinitic minerals (specifically dickite and kaolinite) with formamide (FA), N-methylformamide (MFA) and dimethylsulfoxide (DMSO) since theoretical studies of interactions of small organic molecules with clay minerals are devoted to intercalates and adsorbates of kaolinitic minerals with these organic molecules. This will allow to compare theoretical results with available experimental data. 

All together, these data agree with those obtained for models prepared in alkaline conditions [15], and confirm that the interactions with clay minerals and polyvalent cations substantially protect the organic component of the aggregates even under strong oxidative conditions. 

Other inorganic constituents. Many soils, especially in dry climates, are rich in forms of calcium carbonate such as limestone some soils may contain over 50% CaC03. This mineral is quite alkaline and contributes to elevated pH values which may exceed 8.0. Metal oxides in varying amorphous and crystalline forms may also be important constituents of some soils oxisols, for example, may contain as much as 80% Fc203 (Wolfe et al., 1990). Metal oxides may interact with clays and also with organic constituents of soils. 

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

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