. Author manuscript; available in PMC: 2014 Jul 6.

Published in final edited form as: J Am Chem Soc. 2011 Jan 5;133(5):1534–1544. doi: 10.1021/ja108943n

Table 2. ¹⁵N CSA Principal Values, Anisotropy Parameters (δ), Asymmetry Parameters (η), and Spans (Δσ) in Histidine; Hydrogen-Bond Distances Are Also Included.

state	site	δ_iso (ppm)	δ₃₃ (ppm)	δ₂₂ (ppm)	δ₁₁ (ppm)	δ (ppm)	η	Δσ (ppm)	H-bond (Å)
cationic	Nδ1–H	190	71	219	280	−119	0.51	209	2.63^a
	Nε2–H	176	63	195	270	−113	0.66	207	2.81^a
neutral τ tautomer	Nδ1	249	39	319	389	−210	0.33	350	2.76^b
	Nε2–H	171	73	184	256	−98	0.73	183	2.76^b
anionic τ tautomer	Nδ1	253	100	288	371	−153	0.54	271	–
	Nε2–H	167	71	175	255	−96	0.83	184	–
anionic π tautomer	Nδ1–H	172	69	189	258	−103	0.67	189	–
	Nε2	248	101	271	362	−147	0.62	261	–

The cationic histidine hydrogen-bonding distances are based on the crystal structure of histidine hydrochloride monohydrate C₆H₁₂ClN₃O₃, measured on the pH 4.5 sample.

The distances for the neutral τ tautomer are R_NN, based on the crystal structure of histidine C₆H₉N₃O₂, measured on the pH 8.5 sample.

Table 2. 15N CSA Principal Values, Anisotropy Parameters (δ), Asymmetry Parameters (η), and Spans (Δσ) in Histidine; Hydrogen-Bond Distances Are Also Included.

Table 2. ¹⁵N CSA Principal Values, Anisotropy Parameters (δ), Asymmetry Parameters (η), and Spans (Δσ) in Histidine; Hydrogen-Bond Distances Are Also Included.