Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
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Chapter 6<br />
Figure 6.6 Cyclic voltammograms <strong>of</strong> (A) MPEG-b-PTAm <strong>and</strong> (B) MPEG-b-PLA-b-PTAm<br />
micelles in 0.1 M HCl aqueous solution.<br />
6.5 EPR study <strong>of</strong> the micelles in PBS containing ascorbic acid<br />
It is known that a reducing environment is necessary for biological systems. The<br />
antioxidants such as ascorbic acid (Vc) <strong>and</strong> glutathione (GSH) are important to keep the<br />
redox status in living cells <strong>and</strong> exist in most <strong>of</strong> parts in vivo. Thus, we evaluated the reduction<br />
resistance <strong>of</strong> the micelles in the presence <strong>of</strong> antioxidants. Since the reduction <strong>of</strong> nitroxyl<br />
radical into hydroxylamine group by GSH is much slower than Vc <strong>and</strong> there is higher<br />
concentration <strong>of</strong> Vc in the blood stream, 22, 23 we selected antioxidant Vc for our study. The<br />
EPR measurements were conducted in the presence <strong>of</strong> Vc at concentration <strong>of</strong> 5.0 mM which<br />
is 50 times more than the concentration <strong>of</strong> Vc in the blood.<br />
As shown in Figure 6.7 A, the EPR signal decreased over time in PBS solution<br />
containing Vc, ascribing to the reduction <strong>of</strong> nitroxyl radicals. And the EPR signal pattern <strong>of</strong><br />
both MPEG-b-PTAm <strong>and</strong> MPEG-b-PLA-b-PTAm micelles were broad single, which is<br />
distinct from typical triplet signal <strong>of</strong> free TEMPOL radical in diluted solution, due to the<br />
spin-spin interaction <strong>of</strong> TEMPO in the side chains. 19, 24, 25 Furthermore, we observed that the<br />
EPR signal in aqueous media is broader than in chlor<strong>of</strong>orm, which is consisted with previous<br />
report. 18 These results indicated that the polymer segment containing nitroxyl radicals had<br />
been incorporated into micelles in aggregated state in the hydrophobic core. By virtue <strong>of</strong> the<br />
micelle structure, the nitroxyl radicals in the core could resist reduction for a longer time than<br />
free TEMPOL radical even in the presence <strong>of</strong> higher concentration <strong>of</strong> Vc (Figure 6.7 B). The<br />
half-life time for both MPEG-b-PTAm <strong>and</strong> MPEG-b-PLA-b-PTAm micelles were about 8<br />
‐ 120 ‐