Editing Conjugated system (section)

===Porphyrins and similar compounds===
[[Porphyrin]]s have conjugated molecular ring systems ([[macrocycle]]s) that appear in many [[enzyme]]s of biological systems. As a [[ligand]], porphyrin forms numerous [[complex (chemistry)|complexes]] with metallic ions like [[iron]] in [[hemoglobin]] that colors blood red. Hemoglobin transports oxygen to the cells of our bodies. Porphyrin–metal complexes often have strong colors. A similar molecular structural ring unit called [[chlorin]] is similarly complexed with [[magnesium]] instead of iron when forming part of the most common forms of [[chlorophyll]] molecules, giving them a green color. Another similar macrocycle unit is [[corrin]], which complexes with [[cobalt]] when forming part of [[cobalamin]] molecules, constituting [[Vitamin B12]], which is intensely red. The corrin unit has six conjugated double bonds but is not conjugated all the way around its macrocycle ring.  
{| class="wikitable" style="margin: 1em auto 1em auto; text-align: center;"
| | [[File:Heme b.svg|class=skin-invert-image|230 px]]||[[File:C-3 position Chlorophyll a.svg|class=skin-invert-image|200px]] || [[File:Cobalamin.svg|class=skin-invert-image|200px]]
|-
| |<small>[[Heme]] group of [[hemoglobin]]</small> ||<small>The [[chlorin]] section of the [[chlorophyll a]] molecule. The green box shows a [[Functional group|group]] that varies between [[chlorophyll]] types.</small>|| <small>[[Cobalamin]] structure includes a [[corrin]] macrocycle.</small>
|}