title: Nitroxides with two pK values--useful spin probes for pH monitoring within a broad range.
abstract: A series of 4-dialkylamino-2,5-dihydroimidazole nitroxides with pyridine-4-yl, 4-dimethylaminophenyl or 4-hydroxyphenyl groups in position 2 of the imidazole ring were prepared using the reaction of RMgBr with corresponding 5-dialkylamino-4,4-dimethyl-4H-imidazole 3-oxides. The EPR spectra of the nitroxides were shown to be pH-sensitive due to consecutive protonation of the amidino moiety and the basic group(s) at position 2 of the imidazole ring. The 5,5-dimethyl-4-(dimethylamino)-2-ethyl-2-pyridine-4-yl-2,5-dihydro-1H-imidazol-1-oxyl showed a monotonic increase in the isotropic nitrogen hyperfine (hfi) coupling constant alpha(N) of 1 .4 G over a pH range from 2 to 6.5. Such a broad range of pH-sensitivity could be useful for many biophysical and biomedical applications, including pH-monitoring in the stomach.
authors.affiliation: N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Academician Lavrent'ev 9, Novosibirsk, 630090, Russia. kirilyuk@nioch.nsc.ru
authors.forename: Igor A
authors.initials: IA
authors.lastname: Kirilyuk
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Bobko
authors.forename: Valery V
authors.initials: VV
authors.lastname: Khramtsov
authors.forename: Igor A
authors.initials: IA
authors.lastname: Grigor'ev
mesh_terms: D003497:Cyclic N-Oxides / Q000138:chemical synthesis / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013113:Spin Labels / Q000138:chemical synthesis*
chemical_list: D003497:Cyclic N-Oxides; D007093:Imidazoles; D011725:Pyridines; D013113:Spin Labels