M. Strlic 1, J. Kolar2, B. Pihlar1
1Faculty of Chemistry and Chemical Technology, University of Ljubljana,
Aškeceva 5, SI-1000 Ljubljana, Slovenia,
2 National and University Library, Turjaška 1, SI-1000 Ljubljana, Slovenia
The N,N'-(5-nitro,1,3-phenylene)bisglutaramide hydroxylation assay for rapid spectrophotometric determination of the rate of oxidising species production in Fenton-like systems has been evaluated and modified for use in different reaction conditions, i.e. at different temperatures, pH and transition metal used. The two predominant hydroxylated derivates were isolated and their spectral properties were demonstrated to depend significantly on pH. The ratio of products was found to be constant at different reaction temperatures, but dependent on pH, therefore it has to be determined by high-pressure liquid chromatography to enable us to calculate the apparent activation energies of the oxidising species production, as used for the systems Fe(III)/phosphate buffer/H2O2 (~70 kJ/mol) or Cu(II)/phosphate buffer/H2O2 (~95 kJ/mol) at pH 6.5-8. The rate of hydroxylation increases with pH in both systems and is ~5·103-104´ higher in the system containing Cu(II), probably reflecting its higher rate of reaction with superoxide anion and the higher rate of reaction of Cu(I) with H2O2.