P. Hanson, G. Millhauser, F. Formaggio
Aug 14, 1996
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Influential Citations
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Journal
Journal of the American Chemical Society
Abstract
α-Aminoisobutyric acid (Aib) is a Cα-tetrasubstituted amino acid that strongly favors helical structure. Most of the conformational trends established for Aib-rich peptides have been determined by X-ray crystallography. Whether these conformational trends carry over to protic solvents is an open question. In order to develop a general strategy for probing the properties of peptides containing Cα-tetrasubstituted amino acids, the hexameric sequences Boc-TOAC-Alan-TOAC-Ala4-n-OtBu were synthesized where n = 0−3 and TOAC is a spin label Aib analog. The peptides were studied by electron spin resonance (ESR) in four alcohols: MeOH, EtOH, TFE, and HFIP. Biradical J-coupling and dipolar interactions between the TOACs within each peptide were used to determine peptide geometry as a function of solvent. In MeOH, strong biradical interactions were observed consistent with the geometry of a 310-helix. The solvents displayed differing tendencies to support helical structure with the ranking MeOH > EtOH > TFE > HFIP....