Studies on conformational transition of the maleic acid copolymer with styrene in aqueous salt solution by derivative spectroscopy

The first and second derivative spectra for the optical absorption of maleic acid copolymer with styrene were measured in aqueous 0.09 m NaCl at 25°C within a wavelength range of 240–280 nm, where contributions of groups, other than the phenyl ones, to the second derivatives seem to be negligible. The normal absorption spectra in the range were composed of seven absorption bands and the peak position of each band was determined from the derivative spectra. The peak position of the coiled form copolymer was found to shift to the shorter wavelength range compared with the compact form of the copolymer. From the extent of such blue shifts for each peak, the environment near the phenyl groups in the compact copolymer form was concluded to be similar to aqueous ethanol (40–50 vol%), by comparing with the derivative spectra for $\text{N-}\text{acetyl-}\text{l}\text{-rmphenylalanine}$ in a water-ethanol mixture. However, the first and second derivative spectra and various first derivative spectra were found to have 12 isoderivative points, and all the bands of the different spectra displayed the two-state character of the transition. The degree of transition was determined from the change in the peak height of each band and this coincided well with the pH-titration data.