ELECTRON SPIN RESONANCE OF TRITYL ALKYL NITROXIDES . SPIN-LABELED AMINO ACIDS

The electron spin resonance spectra of a variety of trityl alkyl nitroxides have been obtained by the reaction of p-nitroperbenzoic acid with the appropriate secondary amine in dioxane (or aqueous solution in some cases). Included are the nitroxides of certain trityl amino acids (or esters) and trityl dipeptides (or esters). The β-hydrogen hyperfine coupling constant is characteristic for the structure of the alkyl group. Evidence is obtained for restricted freedom of motion about the β-carbon atom. Different stable conformations are detected in the nitroxides of certain trityl dipeptides. Trityl alkyl (but no aryl) nitroxides with substituted α-carbon atoms dissociate to produce trityl radicals. Preliminary evidence indicates that this reaction may be reversible. © 1969, American Chemical Society. All rights reserved.