Chlorin

In organic chemistry, chlorins are tetrapyrrole pigments that are partially hydrogenated porphyrins.[1] The parent chlorin is an unstable compound which undergoes air oxidation to porphine.[2] The name chlorin derives from chlorophyll. Chlorophylls are magnesium-containing chlorins and occur as photosynthetic pigments in chloroplasts. The term "chlorin" strictly speaking refers to only compounds with the same ring oxidation state as chlorophyll.

Not to be confused with chlorine.
Chlorin
Names
Other names
2,3-Dihydroporphine
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
  • InChI=1S/C20H16N4/c1-2-14-10-16-5-6-18(23-16)12-20-8-7-19(24-20)11-17-4-3-15(22-17)9-13(1)21-14/h1-6,9-12,22-23H,7-8H2/b13-9-,14-10-,15-9-,16-10-,17-11-,18-12-,19-11-,20-12- checkY
    Key: UGADAJMDJZPKQX-CEVVSZFKSA-N checkY
  • InChI=1/C20H16N4/c1-2-14-10-16-5-6-18(23-16)12-20-8-7-19(24-20)11-17-4-3-15(22-17)9-13(1)21-14/h1-6,9-12,22-23H,7-8H2/b13-9-,14-10-,15-9-,16-10-,17-11-,18-12-,19-11-,20-12-
    Key: UGADAJMDJZPKQX-CEVVSZFKBJ
  • C(N1)(/C=C2N=C(C=C\2)/C=C3N/C(C=C\3)=C\4)=CC=C1/C=C5CCC4=N/5
Properties
C20H16N4
Molar mass 312.36784
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chlorins are excellent photosensitizing agents. Various synthetic chlorins analogues such as m-tetrahydroxyphenylchlorin (mTHPC) and mono-L-aspartyl chlorin e6 are effectively employed in experimental photodynamic therapy as photosensitizer.[3]

Chlorophylls

The most abundant chlorin is the photosynthetic pigment chlorophyll. Chlorophylls have a fifth, ketone-containing ring unlike the chlorins. Diverse chlorophylls exists, such as chlorophyll a, chlorophyll b, chlorophyll d, chlorophyll e, chlorophyll f, and chlorophyll g. Chlorophylls usually feature magnesium as a central metal atom, replacing the two NH centers in the parent.[4]

Variation
See also: Porphyrin § In nature
Structures comparing porphin, chlorin, bacteriochlorin, and isobacteriochlorin.

Microbes produce two reduced variants of chlorin, bacteriochlorins and isobacteriochlorins. Bacteriochlorins are found in some bacteriochlorophylls; the ring structure is produced by Chlorophyllide a reductase (COR) reducing a chlorin ring at the C7-8 double boud.[5] Isobacteriochlorins are found in nature mostly as sirohydrochlorin, a biosynthetic intermediate of vitamin B12, produced without going through a chlorin. In living organisms, both are ultimately derived from uroporphyrinogen III, a near-universal intermediate in tetrapyrrole biosynthesis.[6]

Synthetic chlorins

Numerous synthetic chlorins with different functional groups and/or ring modifications have been examined.[7]

Contracted chlorins can be synthesised by reduction of B(III)subporphyrin or by oxidation of corresponding B(III)subbacteriochlorin.[8] The B(III)subchlorins were directly synthesized as meso-ester B(III)subchlorin from meso-diester tripyrromethane, these class of compound showed very good fluorescence quantum yield and singlet oxygen producing efficiency[9][10]

See also

Further reading
  • Juse´lius, Jonas; Sundholm, Dage (2000). "The aromatic pathways of porphins, chlorins and bacteriochlorins". Physical Chemistry Chemical Physics. 2 (10): 2145–2151. Bibcode:2000PCCP....2.2145J. doi:10.1039/b000260g.

References
  1. Gerard P. Moss (1988). "Nomenclature of Tetrapyrroles. Recommendations 1986". European Journal of Biochemistry. 178 (2): 277–328. doi:10.1111/j.1432-1033.1988.tb14453.x. PMID 3208761.
  2. Battersby, Alan R. (2000). "Tetrapyrroles: The pigments of life". Natural Product Reports. 17 (6): 507–526. doi:10.1039/b002635m. PMID 11152419.
  3. Spikes, John D. (July 1990). "New trends in photobiology". Journal of Photochemistry and Photobiology B: Biology. 6 (3): 259–274. doi:10.1016/1011-1344(90)85096-F. PMID 2120404.
  4. K. Eszter, Borbas. Handbook of Porphyrin Science: 181: Chlorins. worldscientific. doi:10.1142/9789813149564_0001. ISBN 9814322326.
  5. Chew, Aline Gomez Maqueo; Bryant, Donald A. (2007). "Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity". Annual Review of Microbiology. 61: 113–129. doi:10.1146/annurev.micro.61.080706.093242. PMID 17506685.
  6. Battersby, Alan R. (2000). "Tetrapyrroles: The pigments of life: A Millennium review". Natural Product Reports. 17 (6): 507–526. doi:10.1039/B002635M. PMID 11152419.
  7. Taniguchi, Masahiko; Lindsey, Jonathan S. (2017). "Synthetic Chlorins, Possible Surrogates for Chlorophylls, Prepared by Derivatization of Porphyrins". Chemical Reviews. 117 (2): 344–535. doi:10.1021/acs.chemrev.5b00696. OSTI 1534468. PMID 27498781.
  8. Osuka, Atsuhiro; Kim, Dongho (2008). "Synthesis and Characterization of meso-Aryl-Substituted Subchlorins". Journal of the American Chemical Society. 130 (2): 438–439. doi:10.1021/ja078042b. PMID 18095693.
  9. Chandra, Brijesh; Soman, Rahul; Sathish Kumar, B.; Jose, K. V. Jovan; Panda, Pradeepta K. (3 Dec 2020). "Meso-Free Boron(III)subchlorin and Its μ-Oxo Dimer with Interacting Chromophores". Organic Letters. 22 (24): 9735–9739. doi:10.1021/acs.orglett.0c03813. PMID 33270460. S2CID 227282229.
  10. Soman, Rahul; Chandra, Brijesh; Bhat, Ishfaq A.; Kumar, B. Sathish; Hossain, Sk Saddam; Nandy, Sridatri; Jose, K. V. Jovan; Panda, Pradeepta K. (15 Jul 2021). "A2B- and A3-Type Boron(III)Subchlorins Derived from meso-Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration". The Journal of Organic Chemistry. 86 (15): 10280–10287. doi:10.1021/acs.joc.1c01001. PMID 34264670. S2CID 235959639.
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