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Elongational flow field as a tool for investigating helix–coil transition: Observation of helix–coil transition in poly( L ‐glutamic acid) induced by pH change
Author(s) -
Hayakawa Ichiro,
Sasaki Naoki,
Hikichi Kunio
Publication year - 1995
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1995.070560603
Subject(s) - helix (gastropod) , flow birefringence , chemistry , dispersion (optics) , helix angle , polymer , birefringence , diffusion , anisotropy , flow (mathematics) , analytical chemistry (journal) , rotational diffusion , electromagnetic coil , crystallography , thermodynamics , molecule , materials science , chromatography , composite material , organic chemistry , optics , physics , mechanics , ecology , snail , biology , quantum mechanics
Elongational flow technique has been used to investigate helix–coil transition of poly( L ‐glutamic acid) (PGA) induced by pH change. The elongational flow field was generated by a four‐roller mill apparatus of the type originally used by G. I. Taylor 16 . The flow‐induced nonlocalized birefringence was observed all over the pH range measured. The birefringence, Δ n 176 , at a fixed strain rate ε = 176 s −1 decreases rapidly within a narrow pH range with increasing pH. The Δ n 176 value is considered to contain information about both helix content, θ, of the system and the degree of orientation of polymers in the elongational flow field. From the Δ n 176 value, using rotational diffusion coefficient, D r , the helix content, θ, was estimated at each iso‐pH measurement. pH dependence of θ was obtained and was found to correspond well to those determined by optical rotary dispersion (ORD) studies. Even in a hinged‐rod conformation, the PGA molecule is expected to be in an extended structure. On the basis of the hydrodynamic considerations about the molecular conformation, it is concluded that the elongational flow technique is useful to investigate conformational transitions of biopolymers. © 1995 John Wiley & Sons, Inc.