Neglected tropical diseases cause great concern in developing countries where there are millions of reported infected humans. It is well known that chelating agents inhibit parasite growth by depriving them of iron, an essential nutrient for cell growth and division; therefore, in this work, we use computational methods to explore the Fe3+ chelating abilities of a set of 10 quinoline-hydrazone hybrids (28 substructures in total) whose cytotoxicity, leishmanicidal, and trypanocidal activities are known. We quantify stabilizing effects in the bare molecules as well as in the iron complexes and show how iron complexation reduces the structural space. Most noticeably, we provide evidence to support a direct relationship between biological activity and the Fe3+ chelating ability.