Chlorin

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Chlorin
Structures comparing porphin, chlorin, bacteriochlorin, and isobacteriochlorin. Note relocation of C=C double bond between the two bacteriochlorin isomers. There are two π electrons (symbolized by π e−) for every double bond in the macrocycle.

In the realm of organic chemistry, chlorins occupy a significant niche. These large heterocyclic aromatic rings are closely related to porphyrins, which are vital to various biological processes. While both structures share a number of similarities, key differences set them apart, notably the extent of aromaticity. This article delves into the structural details of chlorins, their significance in nature, and their potential applications.

Structural Characteristics[edit | edit source]

At its core, a chlorin molecule consists of three pyrrole units and one pyrroline unit. These are interconnected through four methine (=CH-) bridges. This arrangement makes the chlorin ring predominantly aromatic but not fully aromatic around its entire circumference, a marked distinction from its close relative, the porphin ring.[1]

Comparative Structures[edit | edit source]

  • Porphin: The central aromatic ring structure of porphyrins, it is aromatic throughout its circumference.
  • Chlorin: Like porphin but with one of the double bonds reduced, breaking full aromaticity.
  • Bacteriochlorin: Contains two pyrroles and two pyrrolines. Note that pyrrolines are akin to pyrroles but with one of their double bonds reduced to a single bond.
  • Isobacteriochlorin: Similar to bacteriochlorin but has a relocated C=C double bond.
  • In essence, for every double bond present in these macrocycles, there are two π electrons (denoted as π e−).[2]

Biological Relevance[edit | edit source]

Magnesium-containing chlorins are better known as chlorophylls. These pigments are pivotal for photosynthesis, capturing light energy and converting it into chemical energy within the chloroplasts of plants and some microorganisms.[3]

Applications and Uses[edit | edit source]

Because of their inherent photosensitivity, chlorins are gaining traction as photosensitizing agents in experimental photodynamic therapy. In this medical treatment, a photosensitizing agent is introduced into the body and subsequently activated by light to produce a form of oxygen that can kill nearby cells. This therapy is under investigation for treatments of various conditions, including cancer.[4]

Conclusion[edit | edit source]

Chlorins are not just structural wonders but are also fundamental to life processes and potential therapeutic applications. Their versatility and functionality make them a topic of keen interest and research in organic chemistry and biomedicine.

See also[edit | edit source]

References[edit | edit source]

  1. ↑ Smith, K. M. (2011). Porphyrins and Metalloporphyrins. Elsevier.
  2. ↑ Harper, J. D., & Dolphin, D. (1999). The Porphyrins: Physical Chemistry, Part A. Academic Press.
  3. ↑ Renger, G. (2012). Photosynthesis: Plastid Biology, Energy Conversion and Carbon Assimilation. Springer Science & Business Media.
  4. ↑ Agostinis, P., Berg, K., Cengel, K. A., Foster, T. H., Girotti, A. W., Gollnick, S. O., ... & Kessel, D. (2011). Photodynamic therapy of cancer: an update. CA: a cancer journal for clinicians, 61(4), 250-281.
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Contributors: Prab R. Tumpati, MD