PROXYL

Several reports indicate the involvement of superoxide in the mediation of tolerance [67-69]. Based on these reports, a bifunctional superoxide dismutase-mimic NO donor was designed by Haj-Yehia s group [70]. The nitrate ester was incorporated into a nitroxide such as 3-hydroxymethyl-2,2,5,5-tetramethyl-l-pyrroHdinyloxy (HMP) by its conversion into 3-nitratomethyl-PROXYL (NMP) (Scheme 1.7). HMP is a stable, metal-independent, low-molecular weight SOD-mimic with excellent cell-permeability. So NMP is the first compound that can simultaneously generate NO and destroy superoxide. This may lead to novel nontolerance-inducing nitrovasodila-tors. 

The encapsulation of small guest molecules was achieved by constructing the dendrimer shell in the presence of the guest molecules followed by extensive dialysis to remove free guest molecules in solution [11]. A variety of probe molecules were applied, including Rose Bengal, 7,7,8,8,-tetracyano-quino-dimethane (TCNQ) and 3-carboxy-PROXYL. UV-Vis, fluorescence and EPR... 

TABLE 13.1 Comparison of Calculated Line Broadening Effects with Experimentally Determined Line Broadening Effects of PROXYL Functionalized Dendrimers... 

Figure 2,2 Computed HCC and isotropic g tensor shift along a Car-Parrinello molecular dynamic trajectory of PROXYL in the gas phase.

As case studies, let us consider the aqueous solutions of the derivatives 1, 2 and 3 shown in Figure 2.1, namely dimethyl-nitroxide (DMNO), the di-terr-butyl-nitroxide (DTBN) and the 2,2,5,5-tetramethyl-pyrroline-A-oxyl (PROXYL). 

Figure 2.9 Number of solute-solvent H-bonds along CPMD trajectories for (a) PROXYL and (b) DTBN.

An other interesting example of copolymer is given by Georges et al. [52,59] who first demonstrated the living character of the polymerization of styrene initiated by dibenzoyl peroxide in the presence of Tempo or Proxyl (2,2,5,5-tetramethyl-l-pyrrolydinyloxy). Polystyrene with a narrow polydispersity (Mw/Mn = 1.2) is obtained and block copolymers with butadiene, isoprene, acrylate and methacrylate sequences are prepared ... 

By carrying out the encapsulation reaction in the presence of a varying concentration of 3-carboxy-PROXYL, the number of entrapped radicals could be varied from 0.3 to 6.0 molecules per dendritic box as determined by electron spin resonance (ESR) spectroscopy [36]. Tbe number of 3-carboxy-PROXYL radicals in the dendritic box does not increase above six (Figure 9), clearly demonstrating that... 

Figure 9 Number of 3-carboxy-PROXYL radicals trapped in the dendritic box, as determined by ESR spectroscopy, versus the molar ratio of radical and dendrimer in the initial solution prior to the encapsulation reaction...

Figure 10 = 2 ESR spectram of a solid sample of 3-carboxy-PROXYL DAB- e afr-...

C15H19N205 3-(4-nitrophenoxycarbonyl)-proxyl, free radi 21913-97-3 25.00 1.2313 2 28835 C15H2804 dimethyl brassylate 1472-87-3 25.00 0.9868 2... 

This has stimulated in recent years several theoretical studies on nitroxides, either as spin probes [133] and molecular magnets [164]. Pyrrolidine-1-oxyl (hereafter Proxyl), belongs to the class of five membered ring nitroxides, which have been most used as spin probes (see figure 20) [156]. 

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