Avidity of folic acid for carcinogenic metal ions aluminium(3), chromium(3), beryllium(II), lead(II) and uranium(VI).

Abstract

Stepwise formation constants of folic acid, N-[p-[[ (2-amino-4-hydroxy-6-pteridyl) methyl] amino] benzyl] glutamic acid, with the carcinogenic metal ions, aluminium (III), chromium (III), beryllium (II), lead (II) and uranium (VI) have been determined at 30 °C, and at various ionic strengths, viz. 0.01 ᴍ, 0.05 ᴍ, 0.10 ᴍ, maintained by potassium nitrate solution. The formation of the chelate is evident from the shift between the (i) ligand and (ii) ligand and metal titration curves. From the values for the stepwise protonation constants and metal-ligand stability constants at various ionic strengths, thermodynamic formation constants were evaluated by extrapolation to zero ionic concentration. Logarithms of the overall thermodynamic stability constants (log Kμ=0) are: 20.40 for H-; 15.15 for Al-; 10.10 for Cr-; 9.35 for Be-; 6.50 for Pb-; 9.00 for U-chelates. Corresponding free energy changes (ΔF0) are -28.47, -21.14, -14.09, -13.05, -9.07, -12.56 K · Cal · mol-1 respectively