Figure 9. Intrastrand bidentate and reverse tridentate cation/FSW orientations.

a) Bidentate orientation in 1enn between Mg19 FSW and TT step in which W21 simultaneously participates in a cation-pi interaction with T15 while hydrogen bonding with O4 of T16. b) Reverse tridentate orientation in the minor groove of 423d between Mg26 FSW and GC step in which W501 hydrogen bonds with O2 of C18 and forms cation-pi interactions with both the imidazole and pyrimidine ring of G19. FSW (light green); Mg²⁺ (dark green); base ring centroid (purple).