Fig. 2.

Analysis of Cu(II)-treated Aβ₄₀ upon incubation with L1 by ESI–MS and ESI–MS². (A) ESI–MS spectra of the +3-charged Cu(II)-added Aβ₄₀ monomer incubated with L1 in the absence and presence of O₂. (B) ESI–MS spectra of the +3-charged Cu(II)-added Aβ₄₀ monomer treated with L2 and L3 under aerobic conditions. The peaks of the covalent adduct between Aβ₄₀ and 2-methylthiophene (1,475 m/z) and the singly oxidized Aβ₄₀ (1,449 m/z) are highlighted in orange and red, respectively. The singly oxidized covalent adduct (1,480 m/z) is presented as a green peak. Na⁺ adducts of Aβ₄₀ with or without Cu(II) are shown with blue and black dots. (C and D) ESI–MS² spectra of the covalent adduct (1,475 m/z) and the singly oxidized peptide (1,449 m/z). The gray, orange, and red boxes indicate b_x fragments corresponding to Aβ, Aβ bound to 2-methylthiophene, and singly oxidized Aβ, respectively. Conditions were as follows: [Aβ₄₀], 100 μM; [CuCl₂], 100 μM; [compound], 500 μM; incubation for 1 h; 20 mM ammonium acetate, pH 7.2; 37 °C; no agitation. The samples were diluted with H₂O by 10-fold prior to injection to the mass spectrometer.