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. Author manuscript; available in PMC: 2013 Oct 5.
Published in final edited form as: J Am Chem Soc. 2012 Feb 16;134(8):3667–3670. doi: 10.1021/ja2117816

Figure 3.

Figure 3

C7-purine substitution preserves WC geometry but suppresses 13C chemical exchange. (a) Substitution of N7 with C7H7 in 7-deazaadenine (c7A) eliminates the potential for N-H⋯N H-bond and inhibits transient HG base pairs (T N3 and c7A C7H7 are highlighted). (b) c7-modified constructs A6-DNAc7A16 and A6-DNAc7G10, modified residues are highlighted in red and blue respectively. (c) NOE cross-peaks between H8/H6/H1’ of c7A16 or c7G10 with adjacent nucleotides supporting WC geometry, highlighted as in (b). (d) R1ρ and (e) CPMG 13C relaxation dispersion profiles (effective R1ρ or R2,CPMG designated as R2 + Rex) showing chemical exchange is suppressed at c7A16•T9 in A6-DNAc7A16 (pH 6.8) and c7G10•C15 in A6-DNAc7G10 (pH 5.2) but retained at the unmodified neighboring base pairs G10•C15 and A16•T9 (pH 5.2). Solid lines represent average R2+Rex in the case of no detectable exchange or best fits to Eq. S2 (A16 C8 CPMG profile not fitted due to too fast exchange).