AbstractA variety of hostL‐alanine homo‐peptides (to the pentamer) containing one or two spin‐labelled TOAC (2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐4‐amino‐4‐carboxylic acid) residues were synthesized by solution methods and fully characterized. The conformational features of the terminally blocked, doubly spin‐labelled–TOAC–(Ala)2–TOAC–Ala– pentapeptide were examined in the crystal state by X‐ray diffraction and in solution using a combination of techniques (Fourier transform infrared, circular dichroism, cyclic voltammetry and electron spin resonance) in comparison with singly labelled shorter peptides. The 310‐helical structure of the pentapeptide, promoted by the two Cα,α‐disubstituted glycines under favourable experimental conditions, allows an interaction to take place between the two nitroxide TOAC side chains spaced by one turn of the helix. Taken together, these results suggest that TOAC is an excellent probe for exploring bends