Synthesis and use as spin-trap of 5-methyl-5-phosphono-1-pyrroline N-oxide (DHPMPO).: pH dependence of the EPR parameters of the spin adducts

5-Methyl-5-phosphono-1-pyrroline N-oxide (DHPMPO); the acid analogue of DEPMPO; is synthesized by hydrolysis of the diethoxyphosphoryl moiety of DEPMPO. A variety of carbon- and oxygen-centred radicals are trapped with DHPMPO and the corresponding EPR spectra are analysed. We investigate the influence of pH on the coupling-constant-values of DHPMPO-CH3, which behaves like a pH-sensitive probe. The two pK(a)-values (1.31 and 7.58) are obtained from the simultaneous calculation of ten EPR spectra recorded in the pH range 0.5-9, using new two-dimensional simulation software.