Stability of fluorinated double-walled carbon nanotubes produced by different fluorination techniques

Double-walled carbon nanotubes (DWCNTs) have been fluorinated using (1) gaseous F2 at 200 °C, (2) a mixture of BrF3 and Br2 at room temperature, and (3) radio frequency CF4 plasma. The stability of the resultant samples was examined by thermogravimetric analysis in an inert atmosphere and by comparing the X-ray photoelectron spectra of the pristine samples with those after heating in vacuum at either 70 °C for 10 h or 120 °C for 20 h. The DWCNTs fluorinated by F2 showed the highest stability (the temperature of decomposition is around 396 °C), while the BrF3 and plasma-fluorinated DWCNTs lose fluorine from 150 °C. Prolonged annealing of the fluorinated DWCNTs in vacuum at a temperature below 150 °C also resulted in the defluorination of the samples. Fluorine atoms leave the DWCNT surface together with carbon atoms leading to defects in the graphitic network. These defects are likely to be centers for later functionalization by oxygen-containing groups during DWCNT storage

Synthesis and degradation of nucleic acid components by formamide and iron sulfur minerals

We describe the one-pot synthesis of a large panel of nucleic bases and related compounds from formamide in the presence of iron sulfur and iron-copper sulfur minerals as catalysts. The major products observed are purine, 1H-pyrimidinone, isocytosine, adenine, 2-aminopurine, carbodiimide, urea, and oxalic acid. Isocytosine and 2-aminopurine may recognize natural nucleobases by Watson-Crick and reverse Watson-Crick interactions, thus suggesting novel scenarios for the origin of primordial nucleic acids. Since the major problem in the origin of informational polymers is the instability of their precursors, we also investigate the effects of iron sulfur and iron-copper sulfur minerals on the stability of ribooligonucleotides in formamide and in water. All of the iron sulfur and iron-copper sulfur minerals stimulated degradation of RNA. The relevance of these findings with respect to the origin of informational polymers is discussed. © 2008 American Chemical Society