Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The effect of LiCl, NaCl, and CsCl as univalent salts, and of CaCl2, ZnCl2, and MgCl2 as divalent salts, on the α and antiparallel β-sheet, and random conformations of poly(L-lysine) (PLL), in water at room temperature were examined by means of CD and compared quantitatively on the basis of elliptical strength at the maximal peak. Changes in the α-helical and antiparallel β-sheet helical conformations of PLL were markedly dependent on the salt concentrations of LiCl, NaCl, and CsCl, which induced decreases in negative intensity in that order. The CD spectrum of the random conformation, the most disordered form, displayed positive cotton effect in concentrations of these salts up to 3.0M and a negative peak in concentrations of 6.0M. The effect of these salts on the random conformation of PLL was stronger than that on the α- and β-conformations in higher concentrations. The CD spectrum of the random conformation in the presence of CaCl2, ZnCl2, and MgCl2, on the other hand, showed negative cotton effect in salt concentrations as low as 3.0M. It was impossible, however, to measure the effect on α- and β-conformations of ZnCl2 and MgCl2 above concentrations of 10 mM because of a solubility problem with salts in alkaline solution.
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