AbstractThe optical rotatory dispersion of L‐lysine oligopeptides (Lysn, n = 2–22) in solution was measured in water and in 50% methanol. A gradual change with increasing chain length in the ORD curves of the oligomers was observed at pH 4. 3. Not even a chain of 22 residues had ORD identical with that of high molecular weight poly‐L‐lysine. A plot of the average molar residue rotation at 233 nm versus 1/n (where n is the chain length) resulted in a straight line with an intercept of −1900, representing the internal residue rotation of a lysine residue in the random conformation, and a slope of +6200 representing the large end effect. At pH 11.9 a stright line is obtained up to n = 12 after which it deviates from the initial slope indicating onset of helicity. Extrapolation of the initially straight line to tire higher n's provided the necessary zero‐helicity values for calculation of helicity. The highest oligolysine (n = 22) showed at pH 11. 9 13% helicity, which on adding methanol to 50% increased to about 50% helicity. It is shown that helix‐coil data which are usually obtained from the temperature dependence of helicity can be obtained from the dependence of helicity on chain length applying the statistical theory. For the methanol‐water system the cooperativity parameter v was calculated to be in the range 0.024–0.060, with corresponding equilibrium constants w of 1.32–1.43. The helical structure was calculated to be less stable in water than in methanol‐water by about 250 calories per residue.

Yaron, A., Katchalski, E., Berger, A., Fasman, G. D., & Sober, H. A. (1971). The chain length dependence of the conformation for oligomers of L‐lysine in aqueous solution: Optical rotatory dispersion studies. Biopolymers, 10(7), 1107–1120. Portico.