STUDY OF EQUILIBRIA IN ALUMINUM(III)-L-GLUTAMIC ACID OR ALUMINUM(III)-L-SERINE SOLUTIONS

Hydrolytic and complex formation equilibria in L-glutamic acid (H(2)Gl u) and L-serine (HSer) + Al-III systems have been studied by glass ele ctrode 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-II I system, in the concentration ranges 1.0 less than or equal to [Al-II I] 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 (stabili ty constants given in parenthesis) has been evidenced: Al(HGlu)(2+)( l og 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_3Gl u(2-) (log beta(1,-3,1) = -8.44 +/- 0.10). In the L-serine + Al-III sy stem, in the concentration ranges 1.0 less than or equal to [Al-III] l ess than or equal to 10.0, 5.0 less than or equal to [Ser] less than o r equal to 25.0 mmol/dm(3) and pH between 2.7 and 4.8, the following c omplexes 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 sev eral 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.