Fluorescence studies of the self-organization of a cholesterol-bearing polymethacrylate in n-hexane solution
✍ Scribed by Shin-Ichi Yusa; Mikiharu Kamachi; Yotaro Morishima
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 261 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
A copolymer of cholesteryl 6-(methacryloyloxy)hexanoate and a small amount of (1-pyrenylmethyl) 6-(methacryloyloxy)hexanoate (Py-C 5 -MA) was prepared by free radical copolymerization. A copolymer of 1-eicosanylmethacrylate and a small amount of Py-C 5 -MA was also prepared as a reference copolymer. A wide-angle X-ray diffraction pattern for an n-hexane solution of the cholesterol(Chol)-containing copolymer showed a peak corresponding to a spacing of 5.3 Å. In n-hexane, the hydrodynamic radius (R h ) for the Chol-containing copolymer (M w ϭ 7.8 ϫ 10 4 ) was 8.1 nm, while that of the eicosanyl-containing copolymer (M w ϭ 4.9 ϫ 10 4 ) was 9.6 nm, R h for the former being smaller than that for the latter, although M w for the former was higher than that of the latter. 1 H-NMR spectra of the Chol-containing polymer in n-hexane-d 14 indicated a strong restriction of local motions of pendant Chol groups. Fluorescence spectra of the Chol-containing copolymer in n-hexane indicated that each pyrene group was isolated from others. In n-hexane/benzene mixed solutions of the Chol-containing polymer, the ratio of the intensity of the excimer relative to the monomer emission decreased with increasing the ratio of n-hexane in the mixed solvent. Electron transfer from N,Ndimethylaniline to singlet-excited pyrene chromophores was suppressed in the Cholcontaining copolymer in n-hexane. The pyrene chromophores exhibited a long triplet lifetime in n-hexane. These observations led us to conclude that Chol groups formed stacks in n-hexane, and that the pyrene chromophores were trapped in the Chol stacks, leading to the "protection" of pyrene from the bulk phase.