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Salt effects on the conformation of α‐poly‐ L ‐glutamic acid
Author(s) -
Jacobson A. L.
Publication year - 1964
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.1964.360020305
Subject(s) - chemistry , divalent , salt (chemistry) , tetramethylammonium , glutamic acid , polymer , chloride , aqueous solution , helix (gastropod) , ionization , optical rotatory dispersion , ionic strength , inorganic chemistry , magnesium , ionic bonding , crystallography , amino acid , circular dichroism , organic chemistry , ion , biochemistry , ecology , snail , biology
The optical rotatory dispersion in the range 630–340 mμ has been measured for aqueous solutions of the tetramethylammonium salt of α‐poly‐ L ‐glutamic acid to compare the effects produced by added tetramethylammonium chloride and magnesium chloride at equivalent ionic strengths. The addition of magnesium chloride significantly decreased the apparent pK of the α‐poly‐ L ‐glutamic acid. This large decrease in apparent pK makes the use of pH inadequate as a rough criterion of polymer conformation. Both the Moffitt b 0 and the modified Drude constants λ c have been calculated to compare helix content in presence and absence of divalent cation. Both estimations of helix content show the same trends with increased polymer ionization. At equivalent polymer ionization the divalent cation caused a significant increase in the helix content in the helix‐coil transition region.