Effect of aliphatic alcohols on the conformation of poly (l-ornithine hydrobromide) as studied by square-pulse and reversing-pulse electric birefringence |
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Authors: | Koshiro Yoshioka Mitsuo Fujimori Kiwamu Yamaoka Kazuyoshi Ueda |
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Institution: | Department of Chemistry, College of General Education, University of Tokyo, Komaba, Meguroku, Tokyo 153, Japan;Faculty of Science, Hiroshima University, Higashisenda-machi, Hiroshima 730, Japan |
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Abstract: | The electric birefringence and circular dichroism spectra of poly(l-ornithine hydrobromide) have been measured in ethanol/water, 2-propanol/water and tertiary butyl alcohol/water mixtures of various compositions. This charged polypeptide underwent a transition from the coil conformation to the helical conformation at high alcohol content in every case tested. Anomalous birefringence signals, indicative of a field-induced helix-to-coil transition. were observed at high electric fields only in the case of ethanol/water mixtures. The reversing-pulse electric birefringence of this polypeptide has been studied in ethanol/water mixtures and in neutral aqueous solution. Upon rapid reversal of the pulse field, no transient could be observed. This confirms that the electric-field orientation of poly(l-ornithine hydrobromide) results predominantly from the contribution of the counterion-induced dipole moment, regardless of its molecular conformations. It is very probable that the backbone permanent dipole moment of the helical conformation is largely suppressed by the counterion-induced dipole moment in the ionized form. |
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Keywords: | Birefringence electric fields polyornithine helix coil transition |
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