Study of equilibria in aluminum(III)-L-glutamic acid or -L-serine solutions

Hydrolytic and complex formation equilibria in L-glutamic acid (H(2)Glu) and L-serine (HSer) + Al-III systems have been studied by glass electrode potentiometric titrations in 0.1 mol/dm(3) LiCl medium, at 298 K. In the concentration range 0.6 less than or equal to [Al-III] less than or equal to 5.0 mmol/dm(3), aluminum(III)-ion hydrolyzes between pH 3.5 and 4.5. The model which gives the best fit to the experimental data includes the species: Al(OH)(2+), Al(OH)(2)(+), Al-2(OH)(2)(4+), Al-3(OH)(4)(5+) and Al-13(OH)(32)(7+). In the L-glutamic acid + Al-III system, in the concentration ranges 1.0 less than or equal to [Al-III] less than or equal to 5.0, 1.5 less than or equal to [Glu(2-)] less than or equal to 12.5 mmol/dm(3) and pH rbetween 3.0 and 5.5, besides pure hydrolytic species formation of the following complexes (stability constants given in parenthesis) has been evidenced: Al(HGlu)(2+)( log beta(1,1,1) = 12.02 +/- 0.04), Al(Glu)(+) (log beta(1,0,1) = 7.86 +/- 0.01), AlH_2Glu(-) ( log beta(1,-2,1) = -2.30 +/- 0.08) and AlH_3Glu(2-) (log beta(1,-3,1) = -8.44 +/- 0.10). In the L-serine + Al-III system, in the concentration ranges 1.0 less than or equal to [Al-III] less than or equal to 10.0, 5.0 less than or equal to [Ser] less than or equal to 25.0 mmol/dm(3) and pH between 2.7 and 4.8, the following complexes are formed: AI(HSer)(3+) (log beta(1,1,1) = 11.16 +/- 0.03), Al(Ser)(2+) (log beta(1,0,1) = 5.71 +/- 0.02), Al(2)H(-1)Ser(4+) (log beta(2,-1,1) = 4.65 +/- 0.03), AIH_3Ser (log beta(1,-2,1) = -2.51 +/- 0.04) and AlH_3Ser(-) (log beta(1,-3,1) = -7.5 +/- 0.1) as well as several pure hydrolytic complexes. The mechanism of the formation of the complexes is discussed. Their role in absorption, transport, excretion and cellular uptake of aluminium is briefly discussed.