Influerce of chemical structure of nitroxyl spin labels on their reduction by ascorbic acid

The Influence of structure on the reduction of nitroxyl spin labels by ascorbic acid was examined using both piperidine and pyrrolidine nitroxyls. A five-fold molar excess of ascorbic acid and pH of 7.4 were used. The nitroxyl concentration was measured by electron spin resonance spectrometry. The five-membered (pyrrolidine) nitroxyls were more stable than the six-meabered derivatives. Ring substituents also influenced the reaction. The anionic derivatives were more stable than the unionized compounds which, in turn, were more stable than the amines (cations at pH 7.4).