Conformation of poly(<Emphasis Type="SmallCaps">l</Emphasis>-glutamic acid) in bipolar amphiphiles with alkyl ammonium cations of different hydrophobicity |
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| Authors: | Katsuhiko?Kamio Yoshifumi?Kusumoto Masashi?Sakai Email author" target="_blank">Katumitu?HayakawaEmail author |
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| Institution: | (1) Department of Industrial Chemistry, Faculty of Engineering, Kyushu Sangyou University, Matsukadai, Higashi-ku, Fukuoka 813 8503, Japan;(2) Department of Chemistry and BioScience, Faculty of Science, Kagoshima University, Korimoto, Kagoshima 8900065, Japan; |
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| Abstract: | The conformation of the sodium salt of poly(l-glutamic acid) (P(Glu)) in solutions of the cationic bipolar amphiphile 1, 20-isosanediylbis(alkylammonium chloride) (C 20(RA) 2) with different alkyl head groups as a function of amphiphile concentration was investigated using circular dichroism (CD). RA included methylammonium (MA), ethylammonium (EA), propylammonium (PA), butylammonium (BA), and pentylammonium (PeA) cationic groups. The CD spectrum of each C 20(RA) 2 had a double minima corresponding to the a-helix of P(Glu), which was replaced by CD spectra with a single minimum at wavelengths larger than 222 nm as concentration increased. These changes in the CD spectrum were ascribed to the conformational change from random coil to a-helix and to aggregates of helices. In C 20(EA) 2 solutions, a step-like change in the CD intensity was observed at 222 nm as a function of the ratio of C 20(RA) 2 to P(Glu). At the step, the CD spectrum of the complete a-helix was observed. At 10–35 °C, an a-helix was induced in P(Glu) in the order: C 20(EA) 2>C 20(MA) 2>C 20(PA) 2>C 20(BA) 2>C 20(PeA) 2. This order was ascribed to the best fit of ethylammonium to the P(Glu) side chain. |
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