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Far ultraviolet optical rotatory properties of poly‐ L ‐tryptophan. Part I
Author(s) -
Cosani A.,
Peggion E.,
Verdini A. S.,
Terbojevich M.
Publication year - 1968
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.1968.360060707
Subject(s) - optical rotatory dispersion , chemistry , chromophore , circular dichroism , indole test , specific rotation , copolymer , optically active , side chain , optical rotation , tryptophan , polymer , solvent , dichloroacetic acid , ultraviolet , crystallography , stereochemistry , photochemistry , amino acid , organic chemistry , biochemistry , physics , quantum mechanics
Abstract A block copolymer [γ‐Et‐ DL ‐Glu] m [ L ‐Trp] n was prepared using N ‐carboxy anhydrides (NCA) of L ‐tryptohan and γ‐ethyl DL ‐glutamate. The block copolymer, dissolved in trifluoroethanol (TFE)–dichloroacetic acid (DCA) mixtures, exhibited a sharp change in the specific rotation at 546 mμ when the solvent composition reached 70–75% DCA content. Optical rotatory dispersion (ORD) and circular dichroism (CD) measurement were carried out in TFE solution in the spectral range 180–350 mμ. Indole side‐chain chromophores were found to be optically active in the polymer. On the other hand, these groups exhibit very small optical activity in the model compound C 6 H 3 CH 2 OCO( L ‐Trp) 2 OCH 3 . Indole groups therefore appear to be in a dissymmetric environment only in the polymer. From these data it was concluded that poly‐ L ‐Trp is in some type of helical conformation in TFE. Strong overlapping of CD bands from side‐chain chromophores and peptides chromophores in the wavelength range 185–240 mμ does not allow definite conclusions to be drawn about the type of helical conformation which exists in poly‐ L ‐Trp in TFE solution.