Synthesis of new nitroxides modified with disulfide functionality to be used as spin label

Spin labels are molecules that contain a stable diamagnetic fragment, 1 such as the nitroxide group present in the 2,2,6,6-tetramethylpiperidine-1-oxyl compound (TEMPO) and derivatives. The synthesis of these labels is a strategy used to allow molecules that do not have a mismatched electron to be analyzed by Electronic Paramagnetic Resonance (EPR)1, which is a technique that detects electron-nucleus and electron-electron interactions, obtaining information about the environment next to the unpaired electron. The objective of this work is the synthesis of spin labels containing disulfide groups that can be coupled to the surface of gold nanoparticles for molecular dynamics studies. Lipoic acid 1 and 11-mercaptoundecanoic acid 5 (MUA) were chosen to be coupled to TEMPO derivatives (TEMPOL 3 and 4-amino-TEMPO 2) since they have sulfur atoms that have a great affinity for gold. The synthesis of the labels was performed according to the route shown in Scheme 1. Using this methodology, it was possible to obtain and characterize diamagnetic lipoic and MUA acids derivatives with good yields, which are being used as probes for EPR studies of spin-labeled Au nanoparticles