Figure 9.

Three mechanisms associated with the transition from the syn-syn conformation to the anti-syn conformation. (a) The transition occurs through base flipping in the minor groove, following a path C1 → C2 → B1. (b) Shown here is the transition that occurs through base flipping in the major groove. (c) The two syn bases first stack on each other, one of them rotates while stacked, and then they become unstacked adopting anti-syn conformations. The insets show the A-A conformation in the vertical direction. See detailed descriptions in the text. To see this figure in color, go online.