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Conformational studies on poly‐ L ‐tryptophan: Circular dichroism and X‐ray diffraction studies
Author(s) -
Peggion E.,
Cosani A.,
Verdini A. S.,
Del Pra A.,
Mammi 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.1968.360061010
Subject(s) - chemistry , circular dichroism , tryptophan , ethylene glycol , chromophore , helix (gastropod) , random coil , crystallography , conformational change , polymer , solvent , copolymer , polymer chemistry , stereochemistry , photochemistry , organic chemistry , amino acid , biochemistry , ecology , snail , biology
Circular dichroism (CD) measurements were carried out on various copolymers of L ‐tryptophan and γ‐ethyl L ‐glutamate in ethylene glycol monomethyl ether as the solvent. On increasing the L ‐tryptophan content of the copolymers a gradual change in the CD spectra was observed. The typical spectrum of the right‐handedα‐helix becomes more and more evident as the L ‐tryptophan content decreases. On the basis of these results we assumed that no conformational transition occurs on proceeding from pure poly (γ‐ethyl L ‐glutamate) to pure poly‐ L ‐tryptophan in ethylene glycol monomethyl ether: therefore the conformation of poly‐ L ‐tryptophan should be that of a right‐handed α‐helix. Moreover we observed that the change in the CD spectra of the copolymers is gradual but not linear on increasing the tryptophan content. The deviations from linearity were attributed to interactions among side‐chain chromophores whose contributions to the optical activity are not simply additive. An x‐ray analysis carried out on oriented films of poly‐ L ‐tryptophan casted from solutions of the polymer in dimethylformamide shows conclusively that the solid‐state conformation of the polymer is that, of an α‐helix.