2,2,6,6 - tetramethyl piperidinyl-1 -oxyl

In 1993, Georges et al. reported on the controlled radical polymerization of St initiated by benzoyl peroxide and mediated by 2,2,6,6-tetramethyl-l-piperidinyl-oxyl (TEMPO), a stable nitroxide radical [38]. TEMPO was able to bond reversibly to the polystyryl chain end and provide polystyrenes with predetermined molecular weights and low polydispersities. Nitroxides used earlier to control radical polymerizations were less successful [37, 57]. Scheme 3 illustrates the mechanism of the St polymerization, using a generalized structure of radical initiator I-I, and details the structure of TEMPO. Although several types of nitrox-... 

The ultimate loss of the HAS activity occurs by destruction of the heterocycle initiated thermally, photochemically, chemically or by high-energy radiation. An intramolecular H-abstraction from the p-carbon atom in thermolysis of 2,2,6,6-tetramethyl-4-oxo-piperidinyl-l-oxyl 133 via a general reaction (Eq. 8) was proposed as a pathway of thermal selfdestruction of the piperidine cycle [25] (Scheme 25). The respective hydroxylamine was isolated in the yield of 66.5%. The biradical intermediate 137 either dimerizes to nitroxide 138 or thermolyses via 139 to a nitrogen-free fragment 140 (phorone) and nitric oxide. 

In a 50 ml round-bottomed flask, 7.35 g (25 mmol) of 2 is dissolved in 20 ml of DMF. After the addition of 117 mg (0.75 mmol) of 2,2,6,6-tetramethyl-l-piperidinyl-N-oxyl (TEMPO) and 75 mg (CuCl)2 the solution is stirred vigorously and air is blown in. The reaction may be monitored by TLC (Silica 60, Merck F 254 cyclohexane/EtOAc 4 1) and is terminated within ca. 1 h. The reaction mixture is filtered (G4-filter) and is extracted five times with 20 ml hexane. The combined extracts are washed with 50 ml H2O, the solution is concentrated in the rotatory evaporator to ca. one-third volume and is stored for ca. 16 h at -5°C. The orange-red crystals are collected by filtration and dried in a stream of N2 to give 5.4 g (75.2%) of 3 (purity 94% according to HPLC). 

The structure of horse carboxyhaemoglobin reacted with the spin label iV-(l-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodoacetamide has been determined. The label has two orientations, which correspond to the weakly immobilized and strongly immobilized components of the e.s.r. spectra found in solution and in crystals. One is free and the other displaces the C-terminus of the )3-chain, causing perturbations in the P- and to a less extent in the a-chains. 

QH CljNOjP]- 0-(2,2,6,6-Tetramethyl-4-piperidinyl-l-oxyl) phosphoric acid dichloride Reaction of EPR/ 300 N 1.57 73Sos2... 

C H,NO,S,]- 2,2,6,6-Tetramethyl-4,4-di(ethylsulfonyl)- piperidinyl-l-oxyl Reaction of HjCHjSOj SOjCHjCH, +HjOj/ 300 N 1.48 76Zhal... 

Early EPR studies of normal human erythrocyte membranes labelled with N-( 1 oxyl-2,2,6,6- tetramethyl 4-piperidinyl ) maleimide ( see Figure 1. b ) which is a derivative of NEM indicated that 75 % of the total labelled sites belong to the spect rin-actin complex [lO], Membranes were incubated with N-Maleimide at 4 C. It was also indicated that the differences between the results of [4] and [lO] may be due to the difference of the molecules and different incubation temperatures used. 

C26H28N2 f trans-1-Cinnamyl-4-diphenylmethyl-piperazine, 4IB, 298 C2 6H3 0CIFN2O2, 1 (4-(3-Chlorophenyl)-1 -(4-fluorophenyl-4-oxobutyl)-4-piperidinylcarbonyl)-pyrrolidine, 42B, 194 C26H4 N20s, Di (2,2,6,6-tetramethyl-4-piperidinyl-1-oxyl) suberate, 38B, 115... 

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