news OH formation in human platelets The hydroxyl radical (OH) is considered the most damaging of all the reactive oxygen species. In the human body, it is particularly hazardous because it tends to stabilize itself by reacting with lipids and DNA. Because OH is extremely difficult to measure directly, researchers have turned to indirect methods to quantify it. One such method involves the determination of 2,3- and 2,5-dihydroxybenzoate (2,3-DHB and 2,5-DHB), which form by reacting OH with salicylate. F. Blandini and coworkers at the Neurological Institute “C. Mondino” and the University of Pavia (both in Italy) use this indirect method to measure increases in OH levels in human platelets after exposure to experimentally induced oxidative stress. Increases in OH are thought to play a role in the progression of neurodegenerative diseases, such as Parkinson’s disease. Experiments were performed to determine the effects of oxidative stress, including exposure to hydrogen peroxide/UV radiation and pyrogallol (a generator of superoxide-free radicals) on the conversion of sodium salicylate to 2,3-DHB and 2,5-DHB in human platelets. In all cases, reversed-phase HPLC with electrochemical (coulometric) detection quantified the formation of 2,3-DHB and 2,5-DHB. Detection limits were 10 and 5 fmol for 2,3DHB and 2,5-DHB, respectively. Upon exposure to UV radiation, platelets incubated with sodium salicylate and hydrogen peroxide showed
massive increases in DHB, particularly 2,3-DHB. These increases were nearly counteracted by addition of the free radical scavenger DMSO. On the other hand, less of an increase in DHB was observed in platelets exposed to pyrogallol. In this case, increases were completely counteracted by the addition of DMSO. The researchers also investigated the conversion of sodium salicylate to 2, 3-DHB and 2,5-DHB in platelets from Parkinson’s disease patients treated with L-DOPA to determine if the drug causes enhanced oxidative stress. It is currently being debated whether L-DOPA, the most commonly used treatment for Parkinson’s disease, contributes to the progression of the disease. The researchers found higher levels of 2,3-DHB and 2,5DHB in the platelets from Parkinson’s disease patients treated with L-DOPA than in platelets taken from normal subjects. Because platelets were not taken from untreated Parkinson’s disease patients, the authors could not conclude whether the increased levels of 2,3DHB and 2,5-DHB were caused by the treatment or the disease itself. However, they did observe a direct correlation between levels of 2,3-DHB and both LDOPA and its major metabolite, 3-O-methyldopa, suggesting that increased hydroxylation is, at least in part, related to the presence of the drug. (J. Chromatogr., B 1999, 732, 213–220)
Carbon nanotube electrochemistry Few discoveries have captured chemists’ imaginations as much as buckyballs and the closely related carbon nanotubes. Given the success electrochemists have had with graphite, it would follow that these new forms of carbon might also offer useful chemistry. Allen J. Bard and co-workers at the University of Texas–Austin and the University of California–Los Angeles investigate the electrochemistry of thin films of single-wall carbon nanotubes (SWCNTs) deposited on Pt or Au electrodes. They find a very high “effective capacitance”, which might make these materials of interest as electrodes in supercapacitors. The thin-film electrodes were cast from suspensions (generated by strong sonication) of SWCNTs in various solvents. The thin film was evaporated on the electrode, and the electrochemistry was performed in acetonitrile under an He atmosphere in a dry box. Cyclic voltammograms with the nanotube-modified electrodes are featureless, regardless of casting solvent, suspension concentration, or electrode temperature. The authors propose that the voltammograms appear featureless because they contain closely spaced peaks—representing different nanotubes—that average out. An alternative explanation is that the material behaves like a bulk carbon material rather than a collection of individual molecules. However, the electrochemical capacitance is found to increase significantly with SWCNTs. For example, at a potential of –0.5 V versus the Ag quasi-reference electrode, the increase in the effective capacitance-per-unit weight of SWCNT is 283 F/g, which is more than twice the largest value reported to date for an active carbon electrode in a nonaqueous solution. (Electrochem. Solid-State Let. 1999, 2, 577–578)
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