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Solution properties of synthetic polypeptiedes. XXI. Solvent effect on the helix-coil transition of poly(e-carbobenzoxy L-lysine)

✍ Scribed by Noboru Nishioka; Akio Maekawa; Akio Teramoto

Publisher
Wiley (John Wiley & Sons)
Year
1978
Tongue
English
Weight
549 KB
Volume
17
Category
Article
ISSN
0006-3525

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✦ Synopsis

Abstract

Helix‐coil transitions of poly(ϵ‐carbobenzoxy L‐lysine) in mixtures of dichloroacetic acid and 1,2‐dichloroethane were investigated by optical rotatory dispersion (ORD) measurements. The ORD data were analyzed according to the statistical mechanical approaches developed by Sayama et al. (1970) (Ref. 10) and by Karasz and Gajnos (1973) (Ref. 4) to obtain the enthalpy chage associated with the unfolding of helix in the inert solvent 1,2‐dichloroethane, Δ__H__~o~, and that for the solvation of the peptide backbone with the dichloroacetic acid dimer, Δ__H__~a~. The results were: Δ__H__~o~ = −(340 ∼ 620) cal/mol and Δ__H__~a~ = ‐(2.4 ∼ 3.6) kcal/mol. These values are favorably compared with those for poly(γ‐benzyl L‐glutamate) and poly(β‐benzyl L‐aspartage) in the same solvent system. On the other hand, the equilibrium constant for the solvation and hte cooperativity parameter in the inert solvent 1,2‐dichloroethane depended appreciably on the chemical structure of hte side chain. In terms of the Zimm‐Bragg parameter, s, which varied from 1.3 to 1.7 with polypeptied species, the helices of these three polypeptieds are far from complete even in the typical helix‐supporting solvent 1,2‐dichloroethane.

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