One of the immune system’s many responsibilities is inhibiting pathogens from commandeering needed nutrients, such as transitional metals, from the host system. In the human immune system, the protein calprotectin strongly binds manganese, possibly in order to sequester it from the bacteria or pathogen, “starving” them of this essential nutrient. In calprotectin, the binding site for manganese is an unusual hexahistidine coordination site. Using this coordination site as inspiration, this work synthesized chelating ligands with polyimidazole donors to better understand this unprecedented binding site’s affinity for manganese. Using 1,4,7-triazocyclononane (tacn) as a scaffold, along with the incorporations of three imidazole rings, a coordinatingly saturated ligand was synthesized. Varying the steric bulk substituted on the imidazole ring was used as a means of changing the environment to study the effects on binding.<br/>The ligand binding to manganese and zinc was investigated using methods such as potentiometric titration and electron paramagnetic resonance in order to determine the affinity of the ligands towards the two relevant bioavailable transition metals. These complexes were also characterized spectroscopically, structurally, and computationally. This provided insight into the thermodynamic and structural aspects of the unusual calprotectin binding site’s affinity for manganese.

Biomimetic polyimidazole chelates as models to investigate Mn<sup>2+</sup> affinity in immune protein calprotectin

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Biomimetic polyimidazole chelates as models to investigate Mn2+ affinity in immune protein calprotectin

Biomimetic polyimidazole chelates as models to investigate Mn²⁺ affinity in immune protein calprotectin