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Porphyrins are Colored & Fluoresce

المؤلف:  Peter J. Kennelly, Kathleen M. Botham, Owen P. McGuinness, Victor W. Rodwell, P. Anthony Weil

المصدر:  Harpers Illustrated Biochemistry

الجزء والصفحة:  32nd edition.p318

2025-08-24

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While porphyrinogens are colorless, the various porphyrins are colored. The conjugated double bonds in the pyrrole rings and linking methylene groups of porphyrins (absent in the porphyrinogens) are responsible for their characteristic absorption and fluorescence spectra. The visible and the ultraviolet spectra of porphyrins and porphyrin derivatives are useful for their identification (Figure 1). The sharp absorption band near 400 nm, a distinguishing feature shared by all porphyrins, is termed the Soret band after its discoverer, the French physicist Charles Soret.

Fig1. Absorption spectrum of hematoporphyrin.The spectrum is o a dilute (0.01%) solution o hematoporphyrin in 5% HCl.

Porphyrins dissolved in strong mineral acids or in organic solvents and illuminated by ultraviolet light emit a strong red fluorescence, a property often used to detect small amounts of free porphyrins. The photodynamic properties of porphyrins have suggested their possible use in the treatment of certain types of cancer, a procedure called cancer phototherapy. Since tumors often take up more porphyrins than do normal tissues, hematoporphyrin or related compounds are administered to a patient with an appropriate tumor. The tumor is then exposed to an argon laser to excite the porphyrins, producing cytotoxic effects.

Spectrophotometry Is Used to Detect Porphyrins & Their Precursors

Coproporphyrins and uroporphyrins are excreted in increased amounts in theporphyrias. When present in urine or feces, they can be separated by extraction with appropriate solvents, then identified and quantified using spectrophotometric methods.