Solubility of folic acid and protonation of folate in NaCl at different concentrations, even in physiological solution.

The solubility of folic acid was determined at 25 °C in 1.00 mol dm-3 and in 0.15 mol dm-3 NaCl (physiological solution) spectrophotometrically by measuring the absorbance of saturated solution at different hydrogen ion concentrations. Five protonation constants of folate were determined both from the dependence of the solubility on the hydrogen ion concentration as well as from potentiometric titrations carried out in the presence of solid folic acid and in alkaline solution, in which folate is relatively soluble. Corresponding to the protonation constants, nuclear magnetic resonance and florescence spectra were also obtained at different hydrogen ion concentrations to determine the protonation positions in acid, neutral and alkaline solutions. An approach through circular dichroism was also applied to study the eventual polymerization of folate in alkaline solution.