Figure 3. Assignment of guanine imino protons and proposed structures.

(a) Imino-imino region of NOESY spectrum of d(G₂C₄)₄ at mixing time of 150 ms. (b) Assignment of imino protons of guanine residues involved in GC base pairs using 1D ¹⁵N-edited HSQC NMR spectra of residue specific (marked on the left side of each spectrum) ¹⁵N, ¹³C-isotopically labelled d(G₂C₄)₄. Top spectrum in B represents imino region of ¹H NMR spectrum. All spectra were acquired at pH 4.7 and 5 °C. (c) Proposed structures of i-motif and (d,e) hairpins adopted by d(G₂C₄)₄.