(Phys.org)—Macrocyclic and chelating molecules are important in physiological processes and pharmaceuticals. Hemoglobin,for example, is a chelating molecule in which iron is coordinated to donor atoms in a porphyrin ring. Often the donor atoms are some combination of nitrogen, or oxygen,phosphorous, and sulfur. For example, and nitrogen serves as the donor atoms in hemoglobin. Sometimes carbon acts as a donor atom,but it is normally as a heterocycle with one of these other atoms.
Source: phys.org