ISSN:
1573-5001
Keywords:
1H NMR
;
Amide-proton chemical shifts
;
Helix
;
Temperature shift
;
Mixed solvents
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary 2D 1H NMR spectroscopy of two α-helical peptides which differ in their amphipathicity has been used to investigate the relationships between amide-proton chemical shifts, amide-proton exchange rates, temperature, and trifluoroethanol (TFE) concentration. In 50% TFE, in which the peptides are maximally helical, the amide-proton chemical shift and temperature coefficient patterns are very similar to each other in each peptide. Temperature coefficients from −10 to −6 ppb/K, usually indicative of the lack of intramolecular hydrogen bonds, were observed even for hydrophobic amino acids in the center of the α-helices. However, slow hydrogen isotope exchange for residues from 4 to 16 in both 18-mer helices indicates intact intramolecular hydrogen bonds over most of the length of these peptides. Based on these anomalous observations, we suggest that the pattern of amide-proton shifts in α-helices in H2O/TFE solvents is dominated by bifurcated intermolecular hydrogen-bond formation between the backbone carbonyl groups and TFE. The amide-proton chemical shift changes with increasing temperature may be interpreted by a disruption of intermolecular hydrogen bonds between carbonyl groups and the TFE in TFE/water rather than by the length of intramolecular hydrogen bonds in α-helices.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00198143
