Abstract

The N hyperfine coupling constants (<TEX>$a_N$</TEX>) of di-t-butyl nitroxide (DTBN) radicals in water-solvent system were measured with EPR spectroscopy. Various kinds of the solvents with different polarity such as acetone, dimethylsulfoxide (DMSO), methanol, ethanol and 1-propanol were applied and studied. Equilibrium constants for the solvation equilibrium and the solvent parameters (<TEX>$E_T$</TEX>, molar transition energy) of various water-solvent system were obtained from the experimental results and are presented. The <TEX>$a_N$</TEX> values were plotted as a function of mole fraction of the solvent. In case of water-DMSO, water-ethanol and water-1-propanol system, slight negative deviations from the straight line were observed. In water-acetone system, the absorption wavelength (<TEX>${\lambda}$</TEX>) due to <TEX>${\eta}{\rightarrow}{\pi}^{\ast}$</TEX> transition increased linearly with the increase of mole fraction of acetone. The relationship between <TEX>$a_N$</TEX> of DTBN and <TEX>${\lambda}$</TEX> due to <TEX>${\eta}{\rightarrow}{\pi}^{\ast}$</TEX> transition in water-acetone and water-DMSO system was examined. It was found that the electronic structure of the nitroxide radicals is stablized from the fact that the N hyperfine coupling constants of DTBN radicals are greatly unaffected in the environment of water-solvent system.