Figure 2.

Standard and ¹⁵N-filtered 1D ¹H NMR spectra of d(G₃T₄G₄)₂ at 25°C and pH 5.0 in 10% ²H₂O in the presence of 20 mM ¹⁵NH₄Cl and 0 (a and d), 2 (b and e) and 8.5 mM (c) KCl. Assignments of individual imino resonances are indicated (a–c). Labels U (δ7.25 p.p.m.), L (δ7.45 p.p.m.), L^m (δ7.41 p.p.m.) and B (δ7.11 p.p.m.) indicate ${}^{15}\text{NH}_4^{+}$ ions at distinct binding sites within the architecture of d(G₃T₄G₄)₂ and in bulk solution, respectively. Downfield shoulders of the main peaks in (d) and (e) are due to isotopomers like ¹⁵NH₃D⁺. The oligonucleotide concentration was 3.5 mM in strand.