SMECTITE CATALYZED DEHYDRATION OF GLUCOSE

Authors: Gonzalez, Javier; Laird, David

Submitted to: Clays and Clay Minerals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2005
Publication Date: 2/1/2006
Citation: Gonzalez, J.M., Laird, D.A. 2006. Smectite catalyzed dehydration of glucose. Clays and Clay Minerals. 54(1):38-44.

Interpretive Summary: Developing new agricultural management techniques that increase the amount of soil organic matter (SOM) is a high national priority. Soil organic matter improves the ability of soils to supply air, water, and nutrients to growing plants, and may help mitigate global warming by removing greenhouse gasses from the atmosphere. The mechanisms by which plant residue are transformed into new SOM are only partially understood. We discovered that smectite, a type of clay mineral found in soils, abiotically catalyzes the dehydration of glucose in aqueous systems to form furfural compounds. Furfural compounds are a group of highly reactive molecules that may join together with other molecules to form new SOM. We also discovered that iron coatings on the surfaces of the clay minerals inhibits the reaction. The results of this study will help soil scientists to develop new farm management strategies that increase SOM. In the long run, this study may also help scientists to identify soils with high potential for building new SOM, which will help action agencies to better target conservation and other national programs.

Technical Abstract: A better understanding of the formation of humic materials in soils is necessary to develop suitable soil management practices that enhance the formation of new soil organic matter (SOM). The objective of this study was to determine whether smectites abiotically catalyze transformation of glucose under conditions relevant to SOM formation. Four cation-saturated smectites were incubated under abiotic conditions with glucose solutions for 21 days at 37°C. After the incubations, soluble organic carbon (C) recoveries ranged from 95 to 109.3%, relative to the amount of C added as glucose; however, glucose recoveries in the solutions ranged from 18.3 to 98.3%. The results indicate that a significant amount of the added glucose was abiotically transformed to soluble organic compounds other than glucose during the incubations. Higher glucose recoveries were obtained for 'Fe-rich' smectites relative to 'Fe-poor' smectites, suggesting that Fe-oxyhydroxy coatings on smectite surfaces inhibit the transformation of glucose. Chromatographic analysis of the incubation solutions revealed small peaks for 5-(hydroxymethyl)-2-furfural along with larger peaks for other unknown compounds. The results suggest that under conditions similar to those found in soils, smectites catalyze glucose dehydration to form furfural compounds. Polymerization of furfural compounds may be a major pathway leading to formation of new humic materials in soils.