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.

Dynamics of pH-sensitive nitroxide radicals in water adsorbed in ordered mesoporous molecular sieves by EPR Spectroscopy

“…Double-distilled water was employed in all experiments. The nitroxide radicals used (Table 1) were synthesized at the Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences (Novosibirsk) [16,17].…”

Development and Application of Spin Traps, Spin Probes, and Spin Labels

“…2 to 5.5 (Kirilyuk, Bobko, Khramtsov, & Grigor'ev, 2005). This spin probe is most useful in studies of heterogeneous systems.…”

Interaction of imidazoline- and imidazolidine-based nitroxides with chloroplasts

“…21, nitroxide KG-1 was synthesized as descfibed in ref. 22. The nitroxide KG-3 was prepared from 4,4-dimethyl-2-phenyl-4H-imidazole-5-carbonitrile 3-oxide [21] according to the following scheme: (2).…”