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

Fluorescence and FTIR spectroscopy have been used to investigate the pi-I-d ependent conformational change of poly(methacrylic acid) (PMA) in aqueous s olutions. Fluorescence intensity and lifetime, and other fluorescence param eters of the 1-pyrenemethanol probe were measured as a function of pH in PM A 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 FTI R 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 ioniz ation of the carboxyl groups takes place progressively, the conformational change of PMA is brought about abruptly.