Proton exchange in stable nitroxyl radicals of the imidazoline and imidazolidine series |
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| Institution: | 1. Institute of Chemical Kinetics and Combustion, Novosibirsk 630090, USSR;2. Institute of Organic Chemistry, Novosibirsk 630090, USSR;1. Department of Physics of Polymers and Crystals, Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 119991, Moscow, Russia;2. A.N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, Vavilova St. 28, INEOS, 119991, Moscow, Russia;3. Institute of Advanced Energy-Related Nanomaterials, University of Ulm, Albert-Einstein-Allee 11, D-89069, Ulm, Germany;4. D.I. Mendeleev University of Chemical Technology of Russia, Moscow, Russia;1. Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia;2. Green Chemistry Department, National Research Centre, Dokki, Cairo 12622, Egypt;3. Chemistry Department, Faculty of Science, Cairo University, Giza 12613, Egypt;4. Chemistry Department, College of Science, King Saud University, P.O.Box 2455, Riyadh 11451, Saudi Arabia;1. School of Mechanical and Electric Engineering, Guangzhou University, Guangzhou 510006, China;2. School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China;1. Tsinghua University. Beijing, China;2. University of Maryland, College Park, MD, U.S.A.;3. Shanghai Jiao Tong University, Shanghai, China;4. University of California, Berkeley, CA, U.S.A.;5. Lawrence Berkeley National Laboratory, Berkeley, CA, U.S.A. |
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| Abstract: | The influence of pH on the ESR spectra of six nitroxyl radicals was studied. Hyperfine splitting constants, aN, 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 pKa 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. |
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