Vibrational spectroscopic study of L-phenylalanine: Effect of pH

Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectra of L-phenylalanine in aqueous solution were recorded in the pH range 0-13. The vibrational molecular spectroscopic study of this amino-acid, a well-kn own component of human tissue,, showed that L-phenylalanine undergoes struc tural changes under the influence of pH. Characteristic bands of each ionic species were highlighted and the pKa values were determined from IR measur ements by using an intensity ratio method. ATR-FTIR spectroscopy appears to be a powerful tool for obtaining valuable information on the building bloc ks of proteins and for measuring tissue damage, in aqueous environments.