| Popis: |
The influence of pH on the ESR spectra of six nitroxyl radicals was studied. Hyperfine splitting constants, a N , and g factors differ in protonated (RH + ) and nonprotonated (R) forms of the radicals. Proton exchange rates between R and RH + are either fast, moderate, or slow on the ESR time scale, depending on the p K a of the radical. For moderate exchange rates, the temperature dependence of the proton exchange rate was studied. Quantum chemical methods were used to calculate the magnetic parameters of ESR spectra in R and RH + forms for four of the radicals studied. All the radicals studied may be used as “pH probes.” One of the radicals was covalently bound to protein to give a macromolecular probe, which is recommended for pH studies in biological systems. |
