The G:G:G:G tetrad and G(:A):G:G(:A):G hexad planes, and the dimeric architecture of R12. NH (imino)-NH (A) and NH-H8 (B) cross-peaks in the NOESY spectrum with the mixing time of 230 ms at 30°C. Cross-peaks are denoted by mutual residue numbers. In (A), the cross-peaks between the tetrad and hexad planes are underlined, and the intermolecular one between two hexad planes is double-underlined, respectively. In (B), the cross-peaks as to G:A base pairs are underlined, and those between the tetrad and hexad planes are double-underlined, respectively. The G:G:G:G tetrad (C) and G(:A):G:G(:A):G hexad (D) planes identified for R12. The observed NOESY cross-peaks are indicated by lines. Hydrogen bonds are indicated by dotted lines. (E) The G(:A):G(:A):G(:A):G heptad plane found in D12 (15) is shown for reference. (F) The dimeric architecture of two R12 parallel quadruplexes formed in a tail-to-tail manner through hexad-hexad stacking. (G) Intermolecular A3H2-A3H1′ and A9H2-A9H1′ NOESY cross-peaks confirming the dimeric architecture. (H) Imino proton spectra in H2O (upper) and D2O (lower) at 30°C with the assignments.