N n dimethyl p phenylenediamine

All reagents were purchased from commercial suppliers and used as received unless otherwise stated. N,N-Dimethyl-p-phenylenediamine was purchased from Sigma-Aldrich (St. Louis, MO, USA). Aβ₄₀ and Aβ₄₂ were purchased from AnaSpec (Fremont, CA, USA) (Aβ₄₂ = DAEFRHDSGYEVHHQKL-VFFAEDVGSNKGAIIGLMVGGVVIA). An Agilent 8453 UV–visible (UV–vis) spectrophotometer (Santa Clara, CA, USA) was used to measure optical spectra. Anaerobic reactions were performed in a N₂-filled glovebox (Korea Kiyon, Bucheon-si, Gyeonggi-do, Korea). TEM images were taken using a Philips CM-100 transmission electron microscope (Microscopy and Image Analysis Laboratory, University of Michigan, Ann Arbor, MI, USA) or a JEOL JEM-2100 transmission electron microscope (UNIST Central Research Facilities, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea). Absorbance values for cell viability assay were measured on a SpectraMax M5 microplate reader (Molecular Devices, Sunnyvale, CA, USA). All IM–MS experiments were carried out on a Synapt G2 (Waters, Milford, MA, USA). NMR studies of DMPD with and without Zn(II) were carried out on a 400 MHz Agilent NMR spectrometer. NMR studies of Aβ with DMPD were conducted on a 900 MHz Bruker spectrometer equipped with a TCI triple-resonance inverse detection cryoprobe (Michigan State University, Lansing, MI, USA).