Electroanalytical characterization of Zn (II) complexes with D-mannosamine and Glycine in aqueous solutions

• Combination of voltammetry and potentiometry was used for the study of Zn(II) solutions containing ManN and Gly.
• Formation of binary [ZnManN]2+, and ternary [ZnManNGly]+/[ZnManNGlyH-1] complexes were detected.
• Redox processes of [ZnManN]2+ and [ZnManNGly]+ were registered at Ep ∼ −1.01 V, and −1.12 V at pH = 8.
• Quantitative characterization of Zn(II) complexes was performed by potentiometric measurements.
• log β[ZnMan]2+log β[ZnMan]2+ = 2.7, log β[MaNZnGly]+log β[MaNZnGly]+ = 7.7 and log β[MaNZnGlyH−1]log β[MaNZnGlyH−1] = −0.15.

A detailed study of Zn(II)-D-mannosamine and mixed ligand complex Zn(II)-D-mannosamine-glycine in aqueous solution (θ = 25 °C, Ic = 0.55 mol L−1) was carried out by voltammetry and potentiometry, allowing their characterization. Redox process of the [ZnManN]2+ complex was registered at Ep ∼ −1.01 V, [ZnGly]+ at −1.02 V, ZnGly2 at −1.18 V, while [ZnManNGly]+ at −1.12 V (pH = 8.0). Stoichiometry and stability constants of Zn (II) complexes were determined by potentiometric titrations. Calculated stability constants were found to be: log βZnManN2+log βZnManN2+ = 2.7, log βMaNZnGly+log βMaNZnGly+ = 7.7 and log βMaNZnGlyH−1log βMaNZnGlyH−1 = −0.15. Voltammetric and potentiometric data were in good agreement, both indicating formation of two different ternary complexes, i.e. [ZnGlyManN]+ and [ZnGlyManNH−1]. Calculated speciation revealed the presence of the [ZnManN]2+ complex, as well as ternary complexes ([ZnManNGly]+) in significant amount. This study was the first attempt to quantify complexation processes of Zn (II) with naturally occurring amino sugar and mixed complex with amino acid, important for bioavailability of zinc (II) in seawater.

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