{{distinguish|Chlorine}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 445287858 | ImageFile = Chlorin.svg | ImageSize = | IUPACName = 2,3-Dihydroporphyrin <ref>{{Cite web|title=TP-4 Reduced Porphyrins Including Chlorins|url=https://iupac.qmul.ac.uk/tetrapyrrole/TP4.html|website=iupac.qmul.ac.uk|access-date=2025-11-27}}</ref> | OtherNames = 2,3-Dihydroporphine | Section1 = {{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 58616 | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEBI = 36303 | 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- | InChIKey = UGADAJMDJZPKQX-CEVVSZFKBJ | CASNo_Ref = {{cascite|correct|??}} | CASNo=2683-84-3 | PubChem=65106 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 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- | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = UGADAJMDJZPKQX-CEVVSZFKSA-N | SMILES = C(N1)(/C=C2N=C(C=C\2)/C=C3N/C(C=C\3)=C\4)=CC=C1/C=C5CCC4=N/5 }} | Section2 = {{Chembox Properties | Formula=C<sub>20</sub>H<sub>16</sub>N<sub>4</sub> | MolarMass=312.36784 | Appearance= | Density= | MeltingPt= | BoilingPt= | Solubility= }} | Section3 = {{Chembox Hazards | MainHazards= | FlashPt= | AutoignitionPt = }} }}
In organic chemistry, '''chlorins''' are tetrapyrrole pigments that are partially hydrogenated porphyrins.<ref>{{cite journal|journal=European Journal of Biochemistry|year=1988|volume=178|issue=2|pages=277–328|title=Nomenclature of Tetrapyrroles. Recommendations 1986|author=Gerard P. Moss|doi=10.1111/j.1432-1033.1988.tb14453.x|pmid=3208761|doi-access=free}}</ref> The parent chlorin is an unstable compound which undergoes air oxidation to porphine.<ref>{{cite journal |doi=10.1039/b002635m|title=Tetrapyrroles: The pigments of life|year=2000|last1=Battersby|first1=Alan R.|journal=Natural Product Reports|volume=17|issue=6|pages=507–526|pmid=11152419}}</ref> 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.
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.<ref>{{cite journal|last1=Spikes|first1=John D.|title=New trends in photobiology|journal=Journal of Photochemistry and Photobiology B: Biology|date=July 1990|volume=6|issue=3|pages=259–274|doi=10.1016/1011-1344(90)85096-F|pmid=2120404}}</ref>
==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 N''H'' centers in the parent.<ref name="Hand">{{cite book |last1=K. Eszter |first1=Borbas |title=Handbook of Porphyrin Science: 181: Chlorins |publisher=worldscientific |doi=10.1142/9789813149564_0001 |isbn=9814322326 }}</ref>
== Variation == {{see also|Porphyrin#In nature}} [[File:Porphyrin, chlorin, bacteriochlorins.png|class=skin-invert-image|440px|thumb|center|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 bond.<ref name=Maqueo>{{cite journal |doi=10.1146/annurev.micro.61.080706.093242 |title=Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity |year=2007 |last1=Chew |first1=Aline Gomez Maqueo |last2=Bryant |first2=Donald A. |journal=Annual Review of Microbiology |volume=61 |pages=113–129 |pmid=17506685 }}</ref> Isobacteriochlorins are found in nature mostly as sirohydrochlorin, a biosynthetic intermediate of vitamin B<sub>12</sub>, produced without going through a chlorin. In living organisms, both are ultimately derived from uroporphyrinogen III, a near-universal intermediate in tetrapyrrole biosynthesis.<ref>{{cite journal |doi=10.1039/B002635M |title=Tetrapyrroles: The pigments of life: A Millennium review |year=2000 |last1=Battersby |first1=Alan R. |journal=Natural Product Reports |volume=17 |issue=6 |pages=507–526 |pmid=11152419 }}</ref>
== Synthetic chlorins == Numerous synthetic chlorins with different functional groups and/or ring modifications have been examined.<ref>{{cite journal |doi=10.1021/acs.chemrev.5b00696|title=Synthetic Chlorins, Possible Surrogates for Chlorophylls, Prepared by Derivatization of Porphyrins|year=2017|last1=Taniguchi|first1=Masahiko|last2=Lindsey|first2=Jonathan S.|journal=Chemical Reviews|volume=117|issue=2|pages=344–535|pmid=27498781|osti=1534468}}</ref>
Contracted chlorins can be synthesised by reduction of B(III)subporphyrin or by oxidation of corresponding B(III)subbacteriochlorin.<ref>{{cite journal |last1=Osuka |first1=Atsuhiro |last2=Kim |first2=Dongho |title=Synthesis and Characterization of meso-Aryl-Substituted Subchlorins |journal=Journal of the American Chemical Society |year=2008 |volume=130 |issue=2 |pages=438–439 |doi=10.1021/ja078042b |pmid=18095693 |bibcode=2008JAChS.130..438T |url=https://pubs.acs.org/doi/10.1021/ja078042b |archive-date=2021-08-05 |access-date=2021-08-05 |archive-url=https://web.archive.org/web/20210805193601/https://pubs.acs.org/doi/10.1021/ja078042b |url-status=live |url-access=subscription }}</ref> 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<ref>{{cite journal |title=Meso-Free Boron(III)subchlorin and Its μ-Oxo Dimer with Interacting Chromophores |journal=Organic Letters |date=3 Dec 2020 |volume=22 |issue=24 |doi=10.1021/acs.orglett.0c03813 |url=https://pubs.acs.org/doi/full/10.1021/acs.orglett.0c03813|last1=Chandra |first1=Brijesh |last2=Soman |first2=Rahul |last3=Sathish Kumar |first3=B. |last4=Jose |first4=K. V. Jovan |last5=Panda |first5=Pradeepta K. |pages=9735–9739 |pmid=33270460 |s2cid=227282229 |url-access=subscription }}</ref><ref>{{cite journal |title=A2B- and A3-Type Boron(III)Subchlorins Derived from meso-Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration |journal=The Journal of Organic Chemistry |date=15 Jul 2021 |doi=10.1021/acs.joc.1c01001 |url=https://pubs.acs.org/doi/10.1021/acs.joc.1c01001 |last1=Soman |first1=Rahul |last2=Chandra |first2=Brijesh |last3=Bhat |first3=Ishfaq A. |last4=Kumar |first4=B. Sathish |last5=Hossain |first5=Sk Saddam |last6=Nandy |first6=Sridatri |last7=Jose |first7=K. V. Jovan |last8=Panda |first8=Pradeepta K. |volume=86 |issue=15 |pages=10280–10287 |pmid=34264670 |s2cid=235959639 |archive-date=5 August 2021 |access-date=5 August 2021 |archive-url=https://web.archive.org/web/20210805193600/https://pubs.acs.org/doi/10.1021/acs.joc.1c01001 |url-status=live |url-access=subscription }}</ref>
==See also== * Corrin * Photodynamic therapy
==Further reading== *{{cite journal|last1=Juse´lius|first1=Jonas|last2=Sundholm|first2=Dage|title=The aromatic pathways of porphins, chlorins and bacteriochlorins|journal=Physical Chemistry Chemical Physics|date=2000|volume=2|issue=10|pages=2145–2151|doi=10.1039/b000260g|url=https://zenodo.org/record/900813|bibcode=2000PCCP....2.2145J}}
==References== {{reflist}}
{{tetrapyrroles}}{{Plant pigments}} Category:Biomolecules Category:Metabolism Category:Tetrapyrroles