Nitroxides with two pK values—useful spin probes for pH monitoring within a broad range
作者:Igor A. Kirilyuk、Andrey A. Bobko、Valery V. Khramtsov、Igor A. Grigor'ev
DOI:10.1039/b418707e
日期:——
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 aN 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.
通过 RMgBr 与相应的 5-二烷基氨基-4 的反应,制备了一系列在咪唑环的 2 位上具有吡啶-4-基、4-二甲基氨基苯基或 4-羟基苯基基团的 4-二烷基氨基-2,5-二氢咪唑硝基氧化物, 4-二甲基-4H-咪唑3-氧化物。由于脒基部分和咪唑环 2 位碱性基团的连续质子化,硝基氧的 EPR 光谱显示出 pH 敏感性。 5,5-二甲基-4-(二甲氨基)-2-乙基-2-吡啶-4-基-2,5-二氢-1H-咪唑-1-氧基显示各向同性氮超细(hfi)单调增加在 2 至 6.5 的 pH 范围内,耦合常数 aN 为 1 .4 G。如此广泛的 pH 敏感性可用于许多生物物理和生物医学应用,包括胃中的 pH 监测。