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. Author manuscript; available in PMC: 2016 Dec 1.
Published in final edited form as: Structure. 2015 Oct 30;23(12):2300–2308. doi: 10.1016/j.str.2015.09.011

Figure 2. Aromatic/Aliphatic and Aromatic/Aromatic Regions of 2D 13C-13C Correlation Spectra with 50-ms Mixing Time Using PARIS Irradiation Recorded at −10°C on His37-Labeled M2FL as a Function of pH.

Figure 2

(A) pH 7.3. Apparent doubling of the backbone Cα, Cβ and side-chain Cδ2, Cγ/Cε1 resonances; only neutral τ and π tautomers are present.

(B) pH 6.6. Charged H37 resonances are first observed at this pH. Cγ and Cε1 resonances of the charged tautomers are resolved.

(C) pH 6.2. Heterogeneity is apparent in the contour shapes for both charged and neutral species. Some of the Cδ2 resonances are missing in the aliphatic/aromatic spectrum. A subset of cross-peaks between neutral and charged H37 are indicated with arrows in the aromatic-aromatic region.

(D) pH 5.8. Cross-peaks between neutral and charged H37 are becoming prominent at this pH, and heterogeneity is clear in the contoured line shapes.