Far ultraviolet optical rotatory properties of poly-L-tryptophan. Part I

✍ Scribed by A. Cosani; E. Peggion; A. S. Verdini; M. Terbojevich

• Publisher: Wiley (John Wiley & Sons)
• Year: 1968
• Tongue: English
• Weight: 433 KB
• Volume: 6
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1968.360060707

✦ Synopsis

A block copolymer [y-Et-~~-Glu], [~-Trp], was prepared using N-carboxy anhydrides (NCA) of L-tryptophan and y-ethyl DL-glutamate. The block copolymer, dissolved in trifluoroethanol (TFE)-dichloroacetic acid (DCA) mixtures, exhibited a sharp change in the specific rotation a t 546 mp when the solvent composition reached 70-7595 DCA content. Optical rotatory dispersion (ORD) and circular dichroism (CD) measurements were carried out in TFE solution in the spectral range 180-350 mp. 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~H~-CH2--O-CO-(tTrp)~-O-CH~.

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 mp does not allow definite conclusions to be drawn about the type of helical conformation which exists in poly-L-Trp in TFE solution.