The iso-Aβ1–42 peptide was synthesized in the solid phase using tert-butyloxycarbonyl (Boc)-chemistry in-house, as reported earlier [113 (link)]. A stock solution of this peptide was prepared using distilled water, to yield a concentration of 1 mg/mL (200 μM, pH = 7), and it was sonicated for 3 min. The solution was incubated for 10 min at room temperature (RT), then the pH level was adjusted (pH = 11), and it was further incubated for 2 h. After a 3-min-long sonication process, the Aβ1–42 solution was diluted in phosphate buffer (PBS, 20 mM) to a final peptide concentration of 50 μM (26.67 mM phosphate, 1.2% NaCl, pH = 7.4). The solution was stored at 4 °C until further use on the same day.
The oligomeric state of the Aβ peptide was verified by a transmission electron microscope (JEM-1400, JEOL USA Inc., Peabody, MA, USA) operating at 120 kV. Images were taken by an EM-15300SXV system, routinely at a magnification of 25,000 and 50,000, and were processed by the SightX Viewer Software (EM-15300SXV Image Edit Software, JEOL Ltd., Tokyo, Japan).
The oligomeric state of the Aβ peptide was verified by a transmission electron microscope (JEM-1400, JEOL USA Inc., Peabody, MA, USA) operating at 120 kV. Images were taken by an EM-15300SXV system, routinely at a magnification of 25,000 and 50,000, and were processed by the SightX Viewer Software (EM-15300SXV Image Edit Software, JEOL Ltd., Tokyo, Japan).