Figure 66.

Revealing hydrogen bonding and protonation states. (a) N–H···N hydrogen bond is detected through measurement of a ^2HJ_NN coupling (blue and green) for H37 of Influenza A M2. In black and red, this hydrogen bond is broken upon addition of the inhibitor rimantadine. Reproduced from ref (389). Copyright 2020 American Chemical Society. (b) Long-range CP transfers were used in the NH spectra to identify tautomer states of histidine, as well as a hydroxyl proton hydrogen bonded to a histidine side-chain nitrogen. These histidine residues are at the heart of active chemistry in carbonic anhydrase. Reprinted with permission from ref (271). Copyright 2019 John Wiley & Sons. (c) Low- and high-temperature spectra were used to identify the chemical shift of a water proton hydrogen-bonded to a histidine side-chain nitrogen in the M2 protein from Influenza A. Reproduced with permission from ref (391). Copyright 2021 John Wiley & Sons. (d) Selective TEDOR sequence was used to identify tautomer states in the C-terminal domain of the HIV capsid protein with SP1 using fractional deuteration. Reprinted with permission from ref (392). Copyright 2021 Frontiers Media SA.