Figure 10.

NMR-based (a) folding topology and (b) solution structure of the bimolecular G-quadruplex formed by the d(GCGGT₃GCGG) sequence in Na⁺ solution (coordinates deposition: 1A6M) (164). Schematics illustrating mixed tetrad pairing alignments observed for (c) direct and (d) slipped G–C–G–C tetrads, associated with pairing along the major groove edges. A monovalent cation (gray ball) most likely bridges the acceptor atoms along the major groove edges of opposing guanines in the slipped G–C–G–C tetrad.