Fig. 3.

Solid state NMR allows characterization of growing low abundance Aβ_1–40 oligomers. (A) AFM image showing the presence of Aβ_1–40 oligomers (left) after separation from fibers after 4 days (scale bar is 100 nm). (B) CD spectra show that the filtered Aβ_1–40 oligomers (blue) are disordered, similar to the freshly dissolved monomers (red), and differ from the β-sheet rich fibers (black). (C–E) 2D ¹H/¹H NMR spectra obtained via RFDR recoupling of ¹H-¹H dipolar couplings show high-resolution cross-peaks for oligomers (blue) and freshly dissolved Aβ_1–40 monomers (red); spectra recorded at 25 °C under 2.7 kHz MAS on a 600 MHz solid-state NMR spectrometer. The spectrum highlights the observation of cross-peaks due to the recoupled ¹H-¹H dipolar couplings for (C) side-chain to Hα, (D) side-chain, and (E) Hβ-Hα and Hα-Hα regions. The acquisition time was 4 days. The 2.7 kHz MAS and RFDR mixing enabled the suppression of signals from monomers and fibers and selective observation of low molecular weight oligomers in a non-perturbative manner. The NMR samples were prepared in 10 mM phosphate buffer, pH 7.4, and 10% D₂O. Copyright © 2015, Springer Nature. This figure is reproduced from Scientific Reports: https://doi.org/10.1038/srep11811. Further details can be found in the referenced work.¹⁰³