In aqueous solution OH radicals react with chloride ions to form initially ClOH-, the rate constant being 4.3 k 0 . 4 ~ lo9 1. mol-' s-'. The rate constant for the dissociation of ClOH-back to OH radicals and chloride ions is 6.1 k0.8 x lo9 s-I. ClOH-is converted to chlorine atoms via the reaction, C10H-+H++C1+H20 (k = 2.1 k 0.7 x 10'O 1. mol-' s-' at an ionic strength of unity), the rate constant for the reverse reaction being 1.3 x lo3 1. mol-' s-' (0.3-3.0 x lo3 1. mol-' s-').Chlorine atoms combine with chloride ions to form Cl, (k = 2.1 x 1O'O 1. mo1-' s-I), the rate constant for the dissociation of Cl, back to chlorine atoms and chloride ions being 1.1 k 0.4 x lo5 s-'.Cl, absorption has a maximum at 340 nm where the extinction coefficient is 8.8 t-0.5 x lo3 1. mol-' cm-', whereas ClOH-has a maximum at 350 nm with an extinction coefficient of 3.7k0.4 x lo3 1. mol-' cm-l. The reactions of chlorine atoms and Cl, with ferrous ions have also been investigated and the constants are 5.9k0.6 x lo9 and 1.4k0.2 x lo7 1. mol-' s-' (ionic strength = 0.1 moll.-') respectively. The effect of chloride ions on the mechanism of the Fricke dosimeter is discussed.The absorption spectra of ClOH-and Cl, have been measured in the range 230-450 nm.

The rate of the reaction between H02 radicals and Fe2+ is dependent on temperature, the rate constant at 20°C being 9.1 f0.4 x lo5 M-' s-I (1.2 2 0.05 x lo6 M-' s-I at 25°C) and the activation energy 10.0+ 1.0 kcal mol-' (42 kJ mol-I). The initial reaction product is considered to be an outer-sphere complex between Fe3+ and HO;. This hydroperoxide complex appears to react with Fe2+ in a fast reversible reaction to give a bridge compound. The absorption spectra of the two complexes have been measured. The molar extinction coefficients at 450 nm are 140f: 50 M-* cm-' and 1240rf: 100 M-I cm-l, respectively. The equilibrium constant for the formation of the bridge compound varies from 22 k 2 M-' at 20°C to 37.5 rf: 0.5 M-I at 40°C. The hydroperoxide complex dissociates unimolecularly with a rate constant at 20 or 25°C of 1.8 & 0.1 x lo3 s-l, activation energy 2.1 k 0.2 kcal mol-l. The bridge compound dissociates unimolecularly with a rate constant at 20°C of 1.8k0.1 x lo4 s-I (2.5rf:O.l x lo4 s-I at 25"C), activation energy 11.4f 1.1 kcal mo1-'. The final product of the whole reaction is the hydrated ferric ion.

The relative contribution of the different ROS and RNS intermediates to GCX degradation in vivo, the immunogenic potential of the shed GCX fragments, and the role of heparanase in liver I/R injury all warrant further investigation.

Abstract— Primary photochemical processes in aqueous solution have been characterised for FMN. The influence of pH on these processes is attributed to protonation of the neutral triplet and not to the presence of a dimeric species as postulated earlier. Second order rate constants for reaction between the neutral triplet and some naturally occurring amino acids are reported.

The UV-VIS absorptive and emissive properties of three laser dyes, viz. Rhodamine 6G, Rhodamine B and Rhodamine 101, have been studied in ethanolic and methanolic solutions. Time-resolved methods were used to study the decay of the first excited singlet state of each dye. The absorptive properties of the lowest excited singlet states of Rhodamine 6G, Rhodamine B and Rhodamine 101 were generated using picosecond laser pulses. Values for the molar absorption coefficient for the S, t S, absorption process were measured, for each dye, by both comparative and complete-depletion methods. Values for the S, t S, absorption process, in ethanol, were found to be 3.7 x lo4 (452 nm), 4.4 x lo4 (428 nm) and 4.3 x lo4 (430 nm) dm3 mol-' cm-' for Rhodamine 101, Rhodamine 6G and Rhodamine 6 respectively with the corresponding values for the S, t S, absorption process being measured as 7.7 x lo4 (576 nm), 6.4 x lo4 (532 nm) and 3.8 x lo4 (566 nm) dm3 mol-' cm-' . These results are compared and contrasted with available literature values.