Abstract
A set of four hexapeptide sequences, each characterized by four strongly helicogenic Aib residues and all combinations of two isomeric Ile/__a__Ile residues at positions 2 and 5, was synthesized by solution methods and fully characterized. A detailed solution (by FT–IR absorption, NMR, and CD techniques) and solid/crystalline state (by X‐ray diffraction) conformational investigation allowed us to validate our assumption that all four peptides are folded in well‐developed 3~10~‐helical structures. However, the most relevant conformational conclusion extracted from the present 3D‐analysis is that the handedness of the 3~10~‐helical structures formed does not seem to be sensitive to the configurational change at the β‐carbon atom of the constituent Ile versus the diastereomeric __a__Ile residues (in other words, the dominant control on this important structural parameter appears to be exerted by the chirality of the amino acid α‐carbon atom). These results complement published findings on the diverging relative stabilities of the intermolecularly H‐bonded β‐sheet structures generated by Ile versus __a__Ile homo‐oligopeptides. © 2006 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 84: 490–501, 2006
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