Figure 6.

Conformational switching of foldamer F4* with competing chiral ligands. [F4*] = 10 mM, CDCl₃, 296 K; all subsequent additions are of 1.5 equiv relative to F4*. Portions of the ¹³C NMR spectra of the mixtures containing the labeled signals of F4* are shown, with anisochronicity Δδ reported as the difference in chemical shift between the major and minor labeled signals of F4*, δ^maj – δ^min, measured in ppb. Protonated species available for interaction with the F4* binding site (represented by the pyridine in the colored rectangle) are indicated by blue/green (for chiral species) or gray (for achiral species) disks, and acids HA are stacked in order of pK_a in CDCl₃. The number of protons available is represented by the number of discs, building up from the bottom of the stack. Proposed conformation-inducing interactions with F4* (whether these are hydrogen-bonded or ion-paired is left undefined) are coded by matched colors: blue indicates induction of a P screw-sense; green indicates induction of an M screw-sense; red indicates no screw-sense induction. The most significant interaction is assumed to be between F4* and the top (typically the most acidic) protonated species in each multiply protonated stack.