FT-IR study of pyridoxal phosphate

Films of pyridoxal phosphate were studied using FT-IR spectroscopy at different pH values using the ATR (attenuated total reflection) technique. With increasing pH of the films, very intense changes in the spectra were observed due to concentration changes of the hydrogen-bonded species N ... H-O-P reversible arrow N+-H ...O--P, O-... H-O-P reversible arrow O-H ...O--P and (P-O ... H ... O-P)(-). The spectra are characterised by pH-dependent continua which indicate that the above mentioned hydrogen bridges show very large proton polarizability. Other striking features in the spectra are due to the change in tautomeric equilibrium between aldehyde and ketol forms. (C) 1998 Elsevier Science B.V.