Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices |
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Authors: | Contreras Miquel Angel Haack Thomas Royo Miriam Giralt Ernest Pons Miquel |
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Institution: | (1) Department de Química Orgànica, Divisió de Ciències Experimentals i Matemàtiques, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain |
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Abstract: | Summary Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients
are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational
shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation,
provide information on secondary structure. In particular, negative CHα conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations
within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the ocurse
of the study of differnet peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol
(HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary
to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably
weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature
affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes
in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients
in helical peptides can therefore be used to identify short or long hydragen bonds causing bending of the helix axis. |
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Keywords: | NMR Hydrogen bond Conformational shifts TFE |
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