Reactive oxygen species are known to induce DNA strand cleavage and have been explored as treatments for cancer. The development of aqueous-soluble dibenzothiophene-S-oxide (DBTO) derivatives has made it possible to investigate the mechanism of DNA cleavage by these photoactivatable precursors of atomic oxygen. In addition to the release of atomic oxygen, DBTO can also undergo other processes such as a-cleavage. An objective of this work was to establish whether the extent of strand scission could be attributed to a direct reaction between atomic oxygen and DNA. To accomplish this aim, the extent of strand cleavage upon irradiation of three different DBTO derivatives was measured by the conversion of circular pUC19 plasmid (Form I) to nicked (Form II) as monitored by gel electrophoresis. The interaction of the sulfoxides with DNA was systematically studied by optical melt and fluorescence anisotropy experiments. Thiols are susceptible to rapid oxidation by atomic oxygen, and thus, glutathione was used as a ROS scavenger to determine if DNA cleavage was induced by the release of atomic oxygen. The results from these experiments indicated atomic oxygen was at least partially responsible for the observed strand scission.

Pyrroloquinoline quinone (PQQ) is an important electrocatalyst and redox cofactor for many enzymes used in bioanalytical applications. Careful selection of electrode modifications and buffer compositions is required due to PQQ's tendency to be irreversibly reduced on bare electrodes and the strong effect of pH on its electrochemistry. Multi-walled carbon nanotubes (MWCNTs) can effectively modify glassy carbon electrodes, but PQQ's behavior at these surfaces has not been investigated. While phosphate buffers have been used extensively to characterize PQQ's electrochemistry, phosphate buffers can act as chelating agents for important metal ions needed by PQQ and biomolecules. Different physiological buffers could overcome these challenges and expand the buffer options for biofuel cells. Using cyclic voltammetry, we studied PQQ in HEPES, MOPS, TRIS, and phosphate buffers at pH 7 with MWCNT-modified electrodes. While there were no significant differences in PQQ's behavior with the various buffers, the ionic composition of the non-phosphate buffers was very important. We observed that K + and Mg 2+ were the most influential ions for the reversible reduction-oxidation of PQQ. PQQ's electrochemistry was also affected by the length of and the functional groups on the MWCNTs, indicating that the electron transfer kinetics were quite sensitive to the surface chemistry of the electrodes. Pyrroloquinoline quinone (PQQ) is a redox cofactor found in the active sites of a number of enzymes. Most of these quinoproteins are dehydrogenases capable of catalyzing the oxidation of a broad range of substrates, such as alcohols, acids, aldehydes and sugars. 1 PQQ-dependent glucose dehydrogenase, for example, is capable of oxidizing several mono-and disaccharides, including glucose, maltose, lactose, galactose, xylose and mannose.1 The uniqueness of the quinoproteins and their broad substrate specificities have led to their use in bioanalytical applications, including biosensors and biofuel cells.In the absence of an enzyme, PQQ itself is capable of catalyzing redox reactions, including the oxidation of thiols, 2,3 amino acids, 4 and the redox cofactor nicotinamide adenine dinucleotide (NAD + ). 5The electrochemistry of PQQ has been studied quite extensively in both solution and immobilized forms via cyclic voltammetry (CV) and potentiometric titration studies. 6,7 These studies can be challenging due to the pH dependence of the redox potentials. 6,8,9 Using a cystamine-monolayer Au-modified electrode, Katz et al.6 studied the electrochemistry of PQQ in solution using CV and reported the change in potential with pH to be about 60 mV pH −1 at pH < 6.2; 30 mV pH −1 at 6.2 < pH < 8.6; and about 60 mV pH −1 at pH > 8.6. In another study using PQQ immobilized on few-walled carbon nanotube (FWCNT)-modified glassy carbon electrodes, the change in PQQ's redox potential was estimated to be approximately 67 mV pH −1 , with the highest reversible reduction-oxidation observed at ∼pH 2. The nature of the modified electrode surface can also affect P...

Newly identified DNA aptamers for PQQ provide an environment in which PQQ is still accessible for redox chemistry.

No abstract

Relatively inexpensive biosorbents, made from coconut shell, were explored as alternatives to high-quality activated carbon for use in small-scale, wastewater treatment in developing economies. Simple charring and activation procedures were followed to produce CaCl2-activated coconut shell charcoal and its effectiveness was compared with raw coconut shell powder for removal of mercury (Hg) and arsenic (As) from contaminated water. From atomic absorption spectroscopy analyses, the removal efficiency of As and Hg with the use of activated charcoal were 67% (vs 65% for the raw form), and 53% (vs 49% for the raw form), respectively, from their corresponding &ldquo;artificially&rdquo;-contaminated wastewater. These results suggest that despite the slightly improved removal efficiencies recorded for activated coconut shells, the raw version could equally be used in treating wastewater towards the removal of the toxic metals- As and Hg. In order to understand the chemistry of the adsorption processes, FT-IR spectroscopy was employed to study similarities and differences in chemical compositions of the raw versus activated coconut shells before and after the biofiltration processes. To further investigate the effect of this biofiltration process on the overall quality of water, the physicochemical parameters (pH, conductivity, colour, turbidity, TDS and TSS) were measured on river water samples, pre-treated with the biosorbents. For both the raw and activated coconut shell, there was general improvement, although the conductivity of the water treated with the activated version was slightly elevated, was likely due to leaching of CaCl2 that was used for activation.