SOLUTION EQUILIBRIA IN L-GLUTAMIC ACID AND L-SERINE PLUS IRON(III) SYSTEMS

Complex formation equilibria in L-glutamic acid (H(2)Glu) and L-serine (HSer) + iron(III) ion systems have been studied by a combination of glass electrode potentiometric and visible spectrophotometric measurem ents in 0.5 mol dm(-3) (Na)NO3 ionic medium at 25 degrees C. In the co ncentration range 1.0 < [Fe3+] less than or equal to 5.0; 3.0 less tha n or equal to [Glu(2-)] less than or equal to 30.0 mmol dm(-3) ([Glu]/ [Fe] = 3:1 to 30:1) and pH between 1.5 and 4.5. iron(III) and glutamic acid form the Fe(Glu)(2)(-), Fe(Glu)(+), Fe(HGlu)(2+), Fe(OH)Glu, Fe- 2(OH)(2)Glu(2+), Fe(OH)Glu(2)(2-) complexes: and several pure hydrolyt ic products. Iron(III) and L-serine, beside pure hydrolytic complexes of iron(III), form the Fe(HSer)(3+), Fe(Ser)(2+), Fe(OH)Ser(+), Fe(OH) (2)Ser(0), Fe(OM)Ser(2) and Fe-2(OH)(2)(Ser)(2)(2+) complexes, over a broad concentration range of serine to iron ([Ser]/[Fe] = 5:1 to 500:1 ), from pH 1.5 to 4.0. The stability constants of the complexes are gi ven and their formation mechanism is suggested. The possible structure of the complexes, in solution, is discussed.