What metal atom is at the center of a chlorophyll molecule?

The metal atom at the center of a chlorophyll molecule is magnesium. A chlorin ring surrounds the magnesium ion, with four nitrogen atoms coordinating it inside the ring’s central cavity.

This structure is part of what makes chlorophyll effective at absorbing light. The magnesium-containing ring has delocalized electrons that can be excited by photons. Chlorophyll a then helps transfer that excitation energy toward photosynthetic reaction centers, where light energy drives electron-transfer reactions.

Magnesium is often confused with iron because the related pigment heme, found in hemoglobin, contains iron at the center of a porphyrin ring. Copper, zinc, and iron can occur in other biological molecules or laboratory pigments, but they are not the defining central metal of chlorophyll. Chlorophyll’s long phytol tail anchors the molecule in photosynthetic membranes, while small chemical differences in the ring’s side groups distinguish forms such as chlorophyll a and chlorophyll b.