Figure 4.

CW EPR spectra of RL2-MTSL at different temperatures and different pH levels (black curve: experimental, red one: simulated). (A) and (C) pH = 3.9, acetate buffer, 50% D₂O, 50% deuteroglycerol. (B) and (D) pH = 7.5. (A) and (B) T = 300 K. (C) and (D) T = 132 K. Parameters of the simulation were as follows: g_xx = g_yy = 2.0071, g_zz = 2.0022, A_xx = A_yy = 0.5 mT, A_zz = 3.7 mT, τ_corr = 1.95 ns. The additional curve in spectrum A corresponds to free nitroxide at a concentration ~4% of the attached MTSL with correlation time τ_corr = 0.27 ns and is clearly visible in spectrum (B).