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The reactions of indole semiquinone radicals produced following one-electron oxidation of 5,6dihydroxyindole (DHI) and its N-methyl-substituted analogue (MeDHI) have been studied using pulse radiolysis with spectrophotometric detection in the p H range 5-1 0 using different dose/pulse values (1-20 Gy/pulse). Using a dose/pulse of 18.5 Gy the semiquinone radicals of DHI and MeDHl decay predominantly by second order kinetics. The second order rate constants for disappearance of the semiquinone radicals are dependent upon the pH. Values of rate constants for decay of the semiquinone radical of DHI (pK, = 6.8) at p H 5.5 and 9.1 are 3.8 x lo9 and

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The "in-pulse" luminescence emission from solid DNA produced upon irradiation with electron pulses of energy below 260 keV has been investigated in vacuo at 293 K to gain an insight into the existence of radiation-induced charge/energy migration within DNA. The DNA samples contained misonidazole in the range 3 to 330 base pairs per misonidazole molecule. Under these conditions greater than 90% of the total energy is deposited in the DNA. The in-pulse radiation-induced luminescence spectrum of DNA was found to be critically dependent upon the misonidazole content of DNA. The luminescence intensity from the mixtures decreases with increasing content of misonidazole, and at the highest concentration, the intensity at 550 nm is reduced to 50% of that from DNA only. In the presence of 1 atm of oxygen, the observed emission intensity from DNA in the wavelength region 350-575 was reduced by 35-40% compared to that from DNA in vacuo. It is concluded that electron migration can occur in solid mixtures of DNA over a distance of up to about 100 base pairs.

BackgroundThe number of waterpipe tobacco smokers has been increasing worldwide. Smokers can be exposed to a number of toxicants, some of which are metals. The aim of this study is to quantitatively determine if the water filtration stage of the waterpipe smoking process successfully decreases exposure to Bi, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, V, and U.MethodsFour samples of commercially available tobacco (Moassel) were compared in terms of the total amount of metal contained within the fresh tobacco sample and the amount of metal distributed into each compartment of the waterpipe after a smoking session.ResultsFor all metals analysed, the concentration of metal ‘filtered’ out during the water bubbling stage is around 3% (±1%) of the total metal.ConclusionsIt can be concluded that this small fraction would not protect the user against exposure to the majority of the potentially toxic metals.