**2.2 Myoglobin and hemoglobin fibril preparation**

Myoglobin and hemoglobin were dissolved (15 and 20 mg/mL, respectively) in 20 mM phosphate buffer at pH 7.4; samples of Mb and Hb solutions were mixed with 45% of 2,2,2-trifluoroethanol and incubated at 37°C for 24 hours to form the fibrils (control conditions). Another batch of samples was prepared with sodium sulfide nonahydrate salt (60–300 μM, 12 mM) under the same control conditions, to evaluate H2S effect [28, 34].
