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Isodichroic point and the β–random coil transition of poly(S-carboxymethyl-L-cysteine) and poly(S-carboxyethyl-L-cysteine) in the absence of added salt

✍ Scribed by Hiroshi Maeda; Kenta Ooi

Publisher
Wiley (John Wiley & Sons)
Year
1981
Tongue
English
Weight
774 KB
Volume
20
Category
Article
ISSN
0006-3525

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✦ Synopsis

The p-coil transition of poly(S-carboxymethyl-L-cysteine) (poly[Cys(CHzCOpH)]) and poly(S-carboxyethyl-L-cysteine) (poly[Cys((CHz)zCOzH)]) was followed by CD, potentiometric titration, and viscosity in the absence of added salt. These different properties give consistent results for poly[Cys((CHz)zCO~H)]. The CD spectra of poly[Cys(CHzCOzH)] change considerably with the degree of neutralization a even for a low-molecular-weight sample incapable of forming the p-structure. Because of the superposition of this additional effect, the dependence of CD on a is inconsistent with titration data for the case of poly-[Cys(CHzCOzH)], particularly when the n** transition is used to follow the p-coil transition. The change of CD inherent to the 0-coil transition is characterized by an isodichroic point: 215 nm for poly[Cys((CHz)2CO~H)] and 218 nm for poly[Cys(CHzCOzH)]. A criterion supporting the stacking of the pleated sheet is suggested based on the isodichroic point.

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