Molecular Design of pH-Sensitive Spin Probes in the 2,3,4,6,7,8-Hexahydroimidazo[1,5-a]pyrimidine Series with Different Lipophilic/Hydrophilic Properties - Khlestkin, Vadim K; Butakov, Vladimir V; Grigor’ev, Igor A; Bobko, Andrey A; Khramtsov, Valerii V (Synthesis, 2005)