Reactions of dichloride anion radicals with pyrimidine and its derivatives.
Rate constants for the reactions of dichloride anion radicals with pyrimidine and its derivatives were determined by a conventional flash photolysis. Kinetic treatment was carried out by assuming that second-order self decay of the anion radicals and the reaction with a substrate proceed simultaneously. Values of the rate constants were found within 1.1 × 107 to 4.1 × 109 M-1 s-1; the lowest reactivity was observed for pyrimidine and the highest for 2, 4, 6triaminopyrimidine. Comparison of the rate constants with those for hydroxyl radicals suggests that the dichloride anion radicals undergo a different reaction with pyrimidine bases from that of the hydroxyl radicals. A transient absorption due to an intermediate produced in the reaction with the anion radicals was observed for 5-aminouracil. This is only a case where relatively long-lived absorption was observed. The absorption was used to determine the rate constants for the reactions with the anion radicals.
Photoelectron spectroscopy of carbonyls. Ureas, uracils, and thymine 1,2.
The photoelectron spectra of the six possible methyl ureas, two acyl ureas, and four uracils have been obtained. Many of the low-energy set of ionization events in these molecules have been assigned empirically on the basis of methylation and other substitution effects. The data are then correlated with CNDO/s MO energies and are compared with other semiempirical and ab initio computational results which are available in the literature.
Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the Fricke dosimeter
In aqueous solution OH radicals react with chloride ions to form initially ClOH–, the rate constant being 4.3 ± 0.4 × 109 l. mol–1 s–1. The rate constant for the dissociation of ClOH– back to OH radicals and chloride ions is 6.1 ± 0.8 × 109 s–1. ClOH– is converted to chlorine atoms via the reaction, ClOH–+ H+→ Cl + H2O (k= 2.1 ± 0.7 × 1010 l. mol–1 s–1 at an ionic strength of unity), the rate constant for the reverse reaction being 1.3 × 103 l. mol–1 s–1(0.3–3.0 × 103 l. mol–1 s–1). Chlorine atoms combine with chloride ions to form Cl–2(k= 2.1 × 1010 l. mol–1 s–1), the rate constant for the dissociation of Cl–2 back to chlorine atoms and chloride ions being 1.1 ± 0.4 × 105 s–1.The absorption spectra of ClOH– and Cl–2 have been measured in the range 230–450 nm. Cl–2 absorption has a maximum at 340 nm where the extinction coefficient is 8.8 ± 0.5 × 103 l. mol–1 cm–1, whereas ClOH– has a maximum at 350 nm with an extinction coefficient of 3.7 ± 0.4 × 103 l. mol–1 cm–1.The reactions of chlorine atoms and Cl–2 with ferrous ions have also been investigated and the constants are 5.9 ± 0.6 × 109 and 1.4 ± 0.2 × 107 l. mol–1 s–1(ionic strength = 0.1 mol l.–1) respectively. The effect of chloride ions on the mechanism of the Fricke dosimeter is discussed.