Kimia Talebi - Chemistry Department, Islamic Azad University, Ardabil Branch, Ardabil, Iran
Ali Shamel - Chemistry Department, Islamic Azad University, Ardabil Branch, Ardabil, Iran
Farrokh Gharib - Chemistry Department, Shahid Beheshti University, Tehran, Evin, Iran

The macrospic protonation of different species of valine as well as microscopic and the tautomeric protonation constants of valine were studied in thepH range of 1.5 - 11 at 25 C using potentiometric technique. Investigations were performed in sodium chloride as background electrolytes at I(0.1, 0.3, 0.5, and 0.5) mol dm-3. The parametersbased on the protonation constants were calculated, and their dependences on ionic strength aredescribed by a Debye-Huckel type equation. The dependence on ionic strength of the protonation constants was also analyzed by the specific ioninteraction theory (SIT) model. The constants at infinite dilution were obtained using this model. The specific interaction coefficients are alsoreported.

Macrioscopic and microscopic protonation constant; Valine