Figure 1.

(A) Ramachandran plot with the structures in the ff99SB Ala₃ training set³ shown as circles, with the Hu and Bax²⁵ H-Hα Karplus curve data shown in the background as a color gradient. Vertical lines indicate the φ values where the Karplus curve matches the scalar coupling value from either NMR¹⁰ (black) or ff99SB simulations (gray). Note that ff99SB training data were limited near the maximum of the Karplus curve (φ=−120°), suggesting that the ff99SB energies may be poorly defined in this region. (B) Free energy surface for alanine dipeptide in ff99SB, showing that the β-ppII transition region near φ,ψ=−120°,160° has significant population despite lack of training data in Figure 1A.