Synthesis of whey peptide-iron complexes: Influence of using different iron precursor compounds

- Peptide-iron complexes with two iron sources (FeCl2 or FeSO4) were synthesized.
- Evidence of bidentate fashion coordination of iron with all ligands was obtained.
- Structure of the coordination complexes depends on the iron precursor.
- Counterions (SO4− 2 and Cl−) play a central role in complexes characteristics.

Iron-binding peptides are an alternative for increasing the bioavailability of iron and to decreasing its pro-oxidant effect. This study aimed to synthesize and characterize peptide-iron complexes using FeCl2 or FeSO4 as the iron precursor compounds. Whey protein isolate (WPI), WPI hydrolyzed with pancreatin, and its fractions obtained via ultrafiltration (cut-off 5 kDa) were used as ligands. The fluorescence intensity of the ligands significantly decreased as the iron concentration increased as a result of metal coordination with the iron-binding sites, which may have led to changes in the microenvironment of tryptophan. For both iron precursor compounds, the primary iron-binding site was carboxylate groups, and the linkage occurred via a bidentate coordination mode with two vibrational modes assigned to the COOFe linkage. However, infrared spectroscopy and thermal analysis results showed that the dynamics of the interaction is different for the iron precursor. The iron source may be of great importance because it may impact iron absorption and the pro-oxidant effect of the mineral.

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