Article

Mechanism of Stabilization of Helical Conformations of Polypeptides by Water Containing Trifluoroethanol

Contribution from the Department of Chemistry, Room 18-582, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J. Am. Chem. Soc., 1996, 118 (13), pp 3082–3090
DOI: 10.1021/ja952900z
Publication Date (Web): April 3, 1996
Copyright © 1996 American Chemical Society

Abstract

For conjugates Ac-Hel1-Alan-OH, n = 1−6, of the previously characterized reporting, conformational template Ac-Hel1, increases in helicity induced by trifluoroethanol (TFE) in water have been related to a simple function of the peptide length n, yielding the helix propagation constant sAla, which increases from 1.0 to 1.5 for χTFE = 0−20 mol %. The per-residue helicity increase is similar to the increase in te state stability induced by TFE in monoamide conjugates Ac-Hel1-NHR. Addition of TFE to water significantly increases the rate of interconversion of s-cis/s-trans amide conformers for Ac-Pro-NHMe, consistent with a significant and selective destabilization of the planar resonance-stabilized amide. In dilute aqueous solution TFE increases helicity by selectively destabilizing amide functions that are solvent exposed, with the consequence that compact conformations such as helices that maximize intramolecular amide−amide hydrogen bonding and minimize amide solvent exposure are selectively favored.

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Article Views: 560 Times
Received 22 August 1995
Published online 3 April 1996
Published in print 1 January 1996
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