Hydrogen Bonding of Carboxyl Groups in Solid-State Amino Acids and Peptides: Comparison of Carbon Chemical Shielding, Infrared Frequencies, and Structures

Abstract

We previously reported that the protonation state of the carboxyl group of amino acids and peptides in the solid state can easily be determined by the carbon chemical shielding tensors but not by the isotropic shifts. In this report the substantial variation in the 22 element for both protonated and deprotonated forms is shown to be a result of hydrogen bonding. We have correlated this tensor element with established measures of hydrogen bonding, namely the IR stretching frequencies of the carbonyl and the asymmetric stretching frequency for the protonated and deprotonated carboxy groups, respectively. We also observed a strong correlation between the 22 values and previously reported O-H hydrogen bonding distances from the carbonyl of protonated acids to the nearest proton donor. In the database, we found a fixed geometry for the protonated acids and a variable and complicated geometry for hydrogen bond interaction in deprotonated carboxylate. Correspondingly, the correlation betweeen NMR, IR, and diffraction data is more convincing for the protonated acids.

Phase transition of L‐Ser monohydrate crystal studied by 13C solid‐state NMR

“…15,18 This is similar to the correlation between the hydrogen bonding of the carbonyl group and υ 22 of its carbonyl carbon. 8,9,19 The hydrogen bonding in L-Ser monohydrate differs completely from that in the anhydrate.…”

“…COO and the Cˇand C˛carbons were 175.3, 63.2, and a doublet at 56.1 and 55.7 ppm respectively. 15 To stroboscopically monitor the transition process, the 13 C CP/MAS spectra of L-Ser monohydrate were observed at 2-min intervals until 536 min. The temperature of the sample space in the NMR probe was held at 323 K. Five spectra were selected, and the expansions of the COO and C˛/Cˇregions are shown in Fig.…”

Protonation state of E71 in KcsA and its role for channel collapse and inactivation

“…To establish quantitatively the protonation state of E71 and D80, we analyzed the magnitude of the δ11 tensor component, which is typically oriented in the plane of carboxyl oxygens and is known to be one of the clearest indicators of protonation. A comparison of our values of the δ11 tensor component for E71, D80, and E51, to a distribution of values from a known database (22) of 43 deprotonated and 31 protonated carboxyls is shown in Fig. 5B.…”

Crystal Polymorphism of Protein GB1 Examined by Solid-State NMR Spectroscopy and X-ray Diffraction

“…23,24 Carbonyl chemical shifts also show a dependence on hydrogen bonding, as well as backbone conformation. 19,25,26 However, the C', CA and backbone 15 N chemical shifts are not the most prominent reporters on the subtle changes among crystal formulations including intermolecular crystal contacts, protonation state of the ionizable sidechains, aromatic ring interactions and salt bridge geometry. Rather, sidechain residues, especially charged sidechains, are involved in all of these events; 27 therefore these sites are expected to demonstrate the largest changes in chemical shifts upon minor changes in formulation.…”