Abstract
The formation constants of species formed in the system H+ + alanine and VO2+ +alanine have been determined in aqueous solution for 1.0<pH<7.0 and at different ionic strengths ranging from 0.1 to 1.0 mol dm-3 NaClO4, using a combination of potentiometric and spectrophotometric techniques.The compositions of the formd complexes and their stability constants were determined by curve fitting method and it was shown that dioxivanadium(V) forms two mononuclear 1:1 and 1:2 species with alanineof type VO2L and VO2L2-.The porotonation constant of the amino group of alanine has been determined using potentiometric techniques and calculated using a computer program wich employ a least-squares method. The dependence of the porotonation of alanine and the stability constants of the species on ionic strength are described by a deby-huckel type equation.
Highlights
Interactuon between amino acids, peptides and proteins with transition metal ions plays an important role in biochemistry and biology.Great attention has been paid to elucidating and interpreting the thermodynamic and structural characteristics of these biological ligands complexes
We have reported some interesting features of the function logβ=f(I), where β and I refer to the stability constant and ionic strength, respectively [6,7,8,9]
All formation constants seem to follow the same trend as a function of ionic strength, if allowance is made for different types of reaction stoichiometry and different charges of reactants and products
Summary
Interactuon between amino acids, peptides and proteins with transition metal ions plays an important role in biochemistry and biology.Great attention has been paid to elucidating and interpreting the thermodynamic and structural characteristics of these biological ligands complexes. In determining a formation constant at a fixed ionic strength, in all cases, some uncertainties are present. The 0.9 log unit difference in the stability constants determined at 0.1 and 0.7 mol dm−3 should be the result of the uncertainties in the numerical values. A Debye–Hückel type equation was established for the dependence of formation constant on ionic strength. This equation gives the possibility of estimating a formation constant at a fixed ionic strength when its value is known at another ionic strength in the range 0.1
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