Different Micellar Packing and Hydrophobicity of the Membrane Probes TEMPO and TEMPOL Influence Their Partition Between Aqueous and Micellar Phases Rather than Location in the Micelle Interior
✍ Scribed by Luı́s E. Almeida; Iouri E. Borissevitch; Victor E. Yushmanov; Marcel Tabak
- Book ID
- 102581043
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 182 KB
- Volume
- 203
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
These characteristics depend strongly on the chemical and spa-We report the investigation of the distribution of two stable tial structures of the radical and the microheterogeneous sysnitroxyl radicals, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) tems. In the present work we report the investigation of the and 4-hydroxy-TEMPO (TEMPOL), between aqueous and miceldistribution of two stable nitroxyl radicals with different hydrolar phases and in the micelle interior by quenching of fluorescence phobicities, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) of dipyridamole (DIP) and by 1 H NMR, ESR, and optical absorpand 4-hydroxy-TEMPO (TEMPOL) (Fig. 1), between aquetion spectroscopies. Cationic cetyltrimethylammonium chloride ous and micellar phases and in the micelle interior by 1 H NMR (CTAC), anionic sodium dodecylsulfate (SDS), zwitterionic Nand optical absorption spectroscopies, as well as by quenching hexadecyl-N,N-dimethyl 3-ammonio-1-propanesulfonate (HPS), of fluorescence of 2,6-bis(diethanolamino)-4,8-dipiperidinoand non-ionic octylphenoxypolyethoxyethanol (Triton X-l00) micelles were used. In all types of micelles the binding constants for pyrimido [5,4-d] pyrimidine, dipyridamole (DIP), which has more hydrophobic TEMPO appear higher than those for TEMa very high quantum yield of fluorescence in neutral solutions, POL. At the same time the 1 H NMR and optical absorption data high affinity to the micellar phase, and known site of location show that the distribution of both radicals in the micelle interior in micelles (4, 7, 8). On the other hand, DIP is widely used is practically the same: The paramagnetic fragments are localized as a coronary vasodilator (9, 10) and has been considered as in the interface between the polar headgroup region and the hyan antitumor drug coactivator (11, 12). Its antioxidant effect drophobic interior of micelles. There is no clear correlation beand participation in radical reactions have also been docutween K b and the micelle charge. Indeed, K b for TEMPO with SDS mented (13, 14). Thus, the interaction of DIP with free radicals (2150 M 01 ) is lower than with CTAC (3250 M 01 ), but higher constitutes a matter of special interest. Some of the data in than with Triton X-l00 (1300 M 01 ) or HPS (1000 M 01 ). The K b this work are presented in comparison to pyrene fluorescence values correlate quite well with the packing of the monomers in
quenching since this fluorophore is intensively used in quenchthe micelle, being higher for the loosely packed micelles (higher cmc). Besides, the micelle headgroup hydration water seems to ing studies (5,6, 15, 16).
decrease the binding constant.