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Conformation of poly‐S‐carboxyethyl‐ L ‐cysteine in aqueous solutions
Author(s) -
Makda Hiroshi,
Ikeda Rhoichi
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.360100917
Subject(s) - chemistry , optical rotatory dispersion , aqueous solution , polymer , circular dichroism , chloroform , crystallography , random coil , dichroic glass , infrared spectroscopy , organic chemistry , materials science , nanotechnology
Poly‐S‐carboxyethyl‐ L ‐cysteine, a higher side‐chain homolog of poly‐S‐carboxymethyl‐ L ‐cysteine, has been prepared from poly‐S‐carbobenzoxyethyl‐ L ‐cysteine with hydrogen bromide in chloroform or acetic acid. The polymer is found to be in the β‐conformation of an antiparallel arrangement of polypeptide chains in solid films, both in acid and salt forms, when examined by infrared spectra. Aqueous solutions of t he polymer have been investigated by measurements of rotatory dispersion and circular dichroism as well as by infrared spectra in D 2 O. These properties show sharp changes around pH 5.5, as the pH of solution is varied. At higher ionization the polymer is randomly coiled, but at lower ionization it is in the β‐conformation. Dependence of the rotatory properties upon polymer concentration as well as on ionic strength has been observed even at the lowest degree of ionization attained, and this has been attributed to the formation of intermolecular β‐conformation in solutions. The β‐structure is characterized by a negative circular dichroic band at 223 mμ and a positive dichroic band at a wavelength lower than 200 mμ, and furt her by a negative b o value, −140°. The pH‐induced coil‐β transition of the polymer is compared with that of poly‐S‐carboxymethl‐ L ‐cysteine.