Fluorescence and FTIR studies on the pH-dependent conformational change of poly(methacrylic acid) in aqueous solutions

Fluorescence and FTIR spectroscopy have been used to investigate the pi-I-dependent conformational change of poly(methacrylic acid) (PMA) in aqueous solutions. Fluorescence intensity and lifetime, and other fluorescence parameters of the 1-pyrenemethanol probe were measured as a function of pH in PMA aqueous solutions. The fluorescence data obtained show that PMA undergoes a sharp coiling <-> uncoiling change around pH 5. FTIR spectra of PMA were successfully observed by an attenuated total reflection technique. The FTIR data show that the carboxyl groups of PMA are ionized progressively over the wide pH range from 3 to 8, and that PMA takes an expanded conformation under basic conditions. These results make it clear that although the ionization of the carboxyl groups takes place progressively, the conformational change of PMA is brought about abruptly.