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. Author manuscript; available in PMC: 2013 Feb 28.
Published in final edited form as: J Am Chem Soc. 2011 Oct 21;134(8):3703–3713. doi: 10.1021/ja2081185

Fig. 3.

Fig. 3

2D 13C-13C and 15N-13C correlation spectra of His37 at 273 K or 243 K as a function of pH. (a) pH 4.5. (b) pH 5.2. (c) pH 6. (d) pH 8.5. States 1–4 denote different backbone conformations41. 13C-13C 2D correlation spectra were measured with mixing times of 40 ms or 60 ms. No neutral-cationic Cδ2(τ)-Cδ2(+) cross peak was observed (yellow shade) at pH 6.0. A 300 ms spectrum (Fig. S3a) confirms the lack of imidazole-imidazolium contact.