[Effect of covalent functionalization on DNA cleavage activity and ROS formation of single-walled carbon nanotubes].

Biotoxicity of selected covalent functionalizaed single-walled carbon nanotubes (SWNTs) was investigated by plasmid DNA cleavage assay. The effect of covalent functionalization on the physical structural and chemical activity of SWNTs was also studied by Vis-NIR spectroscopy, Raman spectroscopy and ROS assay. The DNA cleavage intensity was promoted by covalent functionalization, and the intensity of DNA damage caused by the three types of carbon nanotubes in a descending order was found to be carboxylated SWNTs (SWNT-COOH) > polyethyleneglycol-lated SWNTs (SWNT-PEG) > uncovalent functionalized SWNTs (uSWNTs). SWNTs were efficient intermediate to trigger electron transfer from electron donor to O2 in dark condition which lead to superoxide radical (O2*-) formation. The electron transfer intensity caused by selected SWNTs was also SWNT-COOH > SWNT-PEG > SWNTs. The reason is that defect sites which changed from sp2-hybridized carbon atom on the side wall of carbon nanotubes were more reactive than the perfect ones.

The passivation of pyrrhotite by surface coating.

The potential of triethylenetetramine (TETA) to inhibit the oxidation of three pyrrhotites, Garson, McCreedy and Po-97 has been studied systematically and confirmed by comparing the release of Fe and SO4(2-) from samples with and without coating treatment. Each sample, original or coated by TETA, was exposed to oxygen, 1 x 10(-3) M FeCl3, and Acidithiobacillus ferrooxidans, respectively, for specific oxidation periods. Both abiotic and biotic oxidation of samples treated by this passivating agent has been reduced significantly in this study. Under the aerobic condition, lower concentrations of ferric, total Fe or SO4(2-) were obtained from the coated samples than those from the uncoated samples. In the presence of 1 x 10(-3) M FeCl3 at 30 degrees C, TETA was able to reduce oxidation rates of Garson, McCreedy and Po-97 by 83%, 79%, and 81% (based on Fe release), respectively. A higher pH, lower Eh, and lower concentrations of total Fe and SO4(2-) were also observed in the biotic oxidation of coated Garson by Acidithiobacillus ferrooxidans. The protection of pyrrhotite surface from oxidant attack by TETA barrier and the alkaline property of this coating agent can be used to interpret the inhibition of oxidation.