Stability of (pyrrolidone-5-hydroxamato)iron (III) chelates

Overall stability constants of mono-, bis-, and tris(pyrrolidone-k-hydroxamato)iron(III) chelates were determined in aqueous solutions at 25 degrees as log beta1=1.49, log beta11=1.55, and log betaIII=0.21, respectively, where beta1=[Fe(C5H7O3N2)2+][H+]/[F=E3+][HC5H7O3N2], betaII=[Fe(C5H7O3N2)2+][H+]2/[Fe3+][hc5h7o3n2]2, and betaIII=[Fe(C5H7O3N2)3][H+]3/[Fe3+][HC5H7O3N2]3. Stability constants of all three chelates were determined potentiometrically in the 3.00-3.23 pH region. The stability constant of the mono chelate also was determined spectrophotometrically at 25 degrees as log beta1-1.52 by measuring absorbance at 500 nm (absorbance maximum), where the molar absorptivity was epsilon=1124 liters/(mole cm). Biological implications of hydroxamic acid-containing compounds are discussed.