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Helix‐coil transition of poly( L ‐glutamic acid) in N ‐methylacetamide
Author(s) -
Harry John B.,
Franzen James S.
Publication year - 1969
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.1969.360080402
Subject(s) - chemistry , helix (gastropod) , solvent , hydrogen bond , molecule , acetamide , polymer , amide , crystallography , folding (dsp implementation) , titration , entropy (arrow of time) , protein folding , organic chemistry , thermodynamics , ecology , physics , snail , electrical engineering , biology , engineering , biochemistry
The folding of randomly coiled poly( L ‐glutamic acid) to the helical state has been studied in N ‐methylacetamide by titration methods. Since this solvent would be expected to form amide‐peptide group hydrogen bonds with the unfolded form of the polymer, to a first approximation no helix stabilization could come from intrapolymer hydrogen bonds. The titration data, collected from 30 to 70°C yield the following values per residue for the thermodynamic parameters governing the coil‐helix reaction for the uncharged polymer: Δ G 30°C °, −1. 9 ± 0.1 kcal; Δ H °, 0 ± 0.1 kcal; Δ S 30°C °, 6.3 ± 0.6 eu. In N ‐methyl acetamide, the helix is an order of magnitude more stable than in water, and this stabilization appears to be entirely the result of the entropy gained by solvent molecules which are released from the polymer upon folding.