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Volume and sound velocity changes associated with coil‐β transition of poly (S‐carboxymethyl L ‐cysteine) in aqueous solution
Author(s) -
Makino Shio,
Noguchi Hajime
Publication year - 1971
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.360100714
Subject(s) - chemistry , aqueous solution , mole , salt (chemistry) , polymer , solvation , volume (thermodynamics) , polymer chemistry , ion , crystallography , analytical chemistry (journal) , chromatography , organic chemistry , thermodynamics , physics
The measurements were made for the volume and the sound velocity changes (Δ V and Δ U ) on titrating the sodium salt of poly (S‐carboxymethyl L ‐cysteine) with dilute HCl. For the reaction, COO − + H + → COOH, Δ V per mole of H + bound was + 12. 7 ml and +11. 4 ml in salt‐free and 0. 2 M NaCl solutions, respectively. Corresponding Δ U was about −13 cm/sec in salt‐free polymer solution where 11.5 mM carboxylate ion reacts with equimolar hydrogen ion. Δ V associated with the coil‐to‐β transition was found to be +2. 35 ml in H 2 O and +1. 90 ml in 0. 2 M NaCl per mole of amino acid residue, respectively. These values are larger than those obtained for the coil‐to‐helix transition of poly ( L ‐glutamic acid). Δ U for the transition was about −30 cm/sec in salt‐free solution of polymer concentration 0.0115 mole/liter. Possible sources of Δ V and Δ U for reaction; coil → β, are ( 1 ) the formation of void volume and ( 2 ) the changes in the extent of solvation in amide linkage and in side chain.