magnesiumporphyrin

Magnesium porphyrin, or magnesiumporphyrin, is a class of metalloporphyrins in which a magnesium ion sits at the center of a porphyrin macrocycle. Like chlorophyll, magnesium porphyrins are planar, highly conjugated rings capable of absorbing visible light and coordinating axial ligands. The term covers both naturally occurring Mg-containing porphyrins and synthetic derivatives.

In nature, magnesium porphyrins are key intermediates in chlorophyll biosynthesis. The enzyme magnesium chelatase inserts Mg2+ into protoporphyrin IX to form Mg-protoporphyrin IX, which is then processed to chlorophyll after further modifications. Magnesium protoporphyrin IX and its esters occur in plants, algae, and cyanobacteria.

Spectroscopically, Mg-porphyrins exhibit intense Soret bands around 400 nm and Q bands in the 500-700 nm range. The electronic and photophysical properties can be tuned by substituents on the porphyrin ring, core size (porphyrin vs chlorin), and axial ligation of the magnesium.

Synthetically, magnesium porphyrins are prepared by metal insertion into free-base porphyrins or by metallation of metal-free porphyrins. They have applications as photosensitizers in photodynamic therapy and as models for photosynthesis research, as well as in catalysis and dye- or fluorescence-based materials. See also chlorophyll and porphyrin chemistry.