In short, FB18 generates accurate (i.e., within ∼0.5 Hz) predictions of backbone scalar couplings across all residues examined, but especially for the deprotonated phosphorylated residues that have the largest charge perturbation relative to the unmodified residues. This gives us some confidence that the differences in backbone conformational preferences between ff99SB and FB18 that are shown in Figure are meaningful and that FB18's predictions are likely as accurate as -and in some cases substantially more accurate than -ff99SB.