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Solution properties of synthetic polypeptides. XV. Helix–coil transition in poly (ε‐carbobenzyloxy L ‐lysine)
Author(s) -
Matsuoka Mikio,
Norisuye Takashi,
Teramoto Akio,
Fujita Hiroshi
Publication year - 1973
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1973.360120707
Subject(s) - chemistry , cooperativity , helix (gastropod) , enthalpy , crystallography , lysine , dichloroacetic acid , cresol , polymer chemistry , stereochemistry , analytical chemistry (journal) , thermodynamics , chromatography , organic chemistry , amino acid , biochemistry , ecology , physics , phenol , snail , biology
Helix–coil transitions of poly(ε‐carbobenzyloxy L ‐lysine) (PCBL) in m ‐cresol and in mixtures of dichloroacetic acid (DCA) and ethylene dichloride (EDC) were investigated by optical rotation measurements, with special interest in the molecular‐weight dependence of helical content. The data obtained were analyzed according to an approximate expression for the helical content of Okita et al. The values obtained for the cooperativity parameter σ and transition enthalpy Δ H ε (at the transition temperature) were: √σ = (0.25 ± 0.06) × 10 −2 and Δ H c = 930 ± 130 cal/mole in m ‐cresol, and √σ = (0.49 ± 0.10) × 10 −2 , and Δ H c = 350 ± 150 kcal/mole in a DCA–EDC mixture (33 vol % DCA). The Δ H c value in the DCA–EDC mixture is much smaller than that derived by Giacometti et al. from heat of solution measurements. The transition in m ‐cresol was extremely sharp. This was attributed to the unusually small value of √σ and the moderately large value of Δ H c obtained.