Clay minerals often are recognized as the slimy slurry of minerals that slicks rivers' banks. Understanding clay's structure is integral to answering questions about the mechanisms behind its antibacterial activity. Negatively charged surfaces attract positively charged elements, such as iron, copper, silver and other metals. In turn, water is absorbed between layers of the crystal structure creating a cation sandwich with aqueous filling or interlayer.
Antibacterial activity in leachates, extracted from the mineral mixtures, confirm that the antibacterial activity is chemically-based, rather than a result of physical interactions with microbes.
Because of the tendency of clay to attract multivalent ions, particularly metals, the scientists next examined the leachates' chemistry and antibacterial activity in the presence of chelators, which bind metals. The researchers also used thiourea, a hydroxyl radical scavenger, at various pH levels. Chelation of the minerals with ethylenediaminetetraacetic acid (EDTA) or desferrioxamine eliminated or reduced toxicity, respectively.
Further testing of the mineral leachates confirmed that there are higher concentrations of chemically-accessible metal ions in leachates from antibacterial samples than from non-bactericidal mineral samples.
In addition, acidic conditions were found to increase the availability of metal ions and their toxicity. Overall, these findings suggest a role of an acid soluble metal species, particularly iron or other sequestered metal cations, in mineral toxicity.
However, whatever advances the study puts forward also present researchers with further challenges. Acidity may complicate deve
|Contact: Margaret Coulombe|
Arizona State University