siRNA potency enhancement via chemical modifications of nucleotide bases at the 5′-end of the siRNA guide strand

Simultaneous fitting for determination of the dissociation constant. Chemical shift upon nucleotide titration of (A) AMP, (B) 8-Br AMP, and (C) 6-mCEPh-purine. Profiles of backbone ¹HN/¹⁵N chemical shift differences (Δ_H/N). For the determination of K_d, the following signals were selected, (1) isolated from other signals in each titration and (2) CSP > 20 Hz (shown). Sixteen signals were used for simultaneous fitting (right edge, ×200 means unassigned signal; single letters represent the amino acid).