1-Oxyl-4-carboxyl-2,2,6,6-tetramethylpiperidine 1-Piperidinyloxy, 4-carboxy-2,2,6,6-tetramethyl- 37149-18-1 4-Carboxyl-2,2,6,6-tetramethylpiperidinoxyl Tca meglumine Tempo carboxylate Tempo carboxylic acid