Salt effect on the conformation of an alternating copolymer of l-leucine and l-lysine

The ‘statistical’ copoly(l-leucyl-l-lysine) is shown to undergo a coil to α-helix transition by either adding salt or raising the pH. However, the corresponding alternating copolymer undergoes a conformational transition from a coil to a b-structure, which is accomplished by adding various salts or by raising the pH. The b-structure fraction of the alternating copoly(l-leucyl—l-lysine) is especially enhanced by either water structure, breaking or making anion (e.g., ClO^?₄ or SO^2?₄), in which the β-structure may be induced by a different molecular mechanism. As a consequence of the strong shielding effect due to the specific binding of ClO^?₄ with charged side chain as well as its electrochemical monovalency, an intramolecular cross-β-structure is formed at lower salt concentration (e.g., 0.10 moll^?1). However, in the presence of SO^2?₄, due to its divalency, intermolecular β-pleated sheet structure occurs even at very low salt concentration (e.g., 0.002 moll^?1). Furthermore, in both cases the resulting β-structure is stable up to 90°C.