Circular Dichroism and Optical Rotatory Dispersion Spectra of Poly[γ-(1-naphthylmethyl)-l-gIutamate] and Its Charge-transfer Complex

Abstract

Abstract Poly-γ-(1-naphthylmethyl)-l-glutamate was synthesized and its structure analyzed by the measurements of circular dichroism and absorption spectra. When the circular dichroism band at 219 nm in the circular dichroism spectrum of the polymer can be assigned to the band due to n–π* transition in the peptide main chain of the polymer, the calculated content of the right hand helix in the polymer is about 54% in ethylene chlorohydrin solution. It was also found that the polypeptide can form a charge-transfer complex with an organic electron acceptor in ethylene chlorohydrin solution. In the charge-transfer complex, a circular dichroism band could be observed at the wavelength corresponding to that of the charge-transfer band in the absorption spectrum of the complex. From the results, it was confirmed that the charge-transfer complex contains α-helix structure of this polypeptide. The temperature dependence of the charge-transfer complex formation was discussed in terms of the formation constant and thermodynamic parameters. The polypeptides having various portions of the 1-naphthylmethyl-d-glutamate residue were synthesized from poly-γ-methyl-d-glutamate by a polymer reaction using p-toluenesulfonic acid. The values of b0 for the polypeptides derived from poly-γ-methyl-d-glutamate were estimated by means of Moffitt-Yang’s equation, and the correlation between the b0 values and the contents of 1-naphthylmethyl residue in the polypeptides was discussed.