Editing Chlorophyll

{{short description|Green pigments found in plants, algae and bacteria}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Redirect|Leaf green|the RAL color|RAL 6002 Leaf green|the 2004 ''[[Pokémon]]'' video game|Pokémon LeafGreen{{!}}''Pokémon LeafGreen''}}
{{see also|bacteriochlorophyll}}
{{multiple image|caption_align=center|header_align=center
 | align = right
 | direction = vertical
 | width = 300
 | header = Chlorophyll at various scales
 | image1 = Mélisse Feuilles FR 2013b.jpg
 | alt1 = Lemon balm leaves
 | caption1 = Chlorophyll is responsible for the green color of many plants and algae.
 | image2 = Plagiomnium affine laminazellen.jpeg
 | alt2 = A microscope image of plant cells, with chloroplasts visible as small green balls
 | caption2 = Seen through a microscope, chlorophyll is concentrated within organisms in structures called [[chloroplast]]s &ndash; shown here grouped inside plant cells.
 | image3 = Why are plants green.svg
 | alt3 = A leaf absorbing blue and red light, but reflecting green light
 | caption3 = Plants are perceived as green because chlorophyll absorbs mainly the blue and red wavelengths but green light, reflected by plant structures like cell walls, is less absorbed.<ref name=JBE>{{cite journal |doi=10.1080/00219266.2020.1858930|doi-access=free  |title=Chlorophyll does not reflect green light – how to correct a misconception |year=2020 | vauthors = Virtanen O, Constantinidou E, Tyystjärvi E |journal=Journal of Biological Education |volume=56 |issue=5 |pages=1–8 }}</ref>
 | image4 = Chlorophyll d structure.svg
 | alt4 = The structure of chlorophyll d
 | caption4 = There are several types of chlorophyll, but all share the [[chlorin]] [[magnesium]] [[ligand]] which forms the right side of this diagram.
}}

'''Chlorophyll''' is any of several related green [[pigment]]s found in [[cyanobacteria]] and in the [[chloroplast]]s of [[alga]]e and [[plant]]s.<ref>{{cite web | title =Chlorophyll | vauthors = May P | publisher=[[University of Bristol]] | url=http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm}}</ref> Its name is derived from the [[Ancient Greek|Greek]] words {{lang|grc|χλωρός}} ({{transliteration|grc|khloros}}, "pale green") and {{lang|grc|φύλλον}} ({{transliteration|grc|phyllon}}, "leaf").<ref name=OnlineEtDict>{{cite encyclopedia |title=chlorophyll |dictionary=[[Online Etymology Dictionary]] |url=http://www.etymonline.com/index.php?term=chlorophyll&allowed_in_frame=0}}</ref> Chlorophyll allows plants to absorb [[energy]] from light. Those pigments are involved in [[oxygenic photosynthesis]], as opposed to [[bacteriochlorophyll]]s, related molecules found only in bacteria and involved in [[anoxygenic photosynthesis]].<ref>{{cite web | vauthors = Udayangani S | date = 31 March 2020 | work = differencebetween.com | title = Difference Between Bacteriochlorophyll and Chlorophyll| url = https://www.differencebetween.com/difference-between-bacteriochlorophyll-and-chlorophyll/}}</ref>

Chlorophylls absorb light most strongly in the [[Diffuse sky radiation|blue portion]] of the [[electromagnetic spectrum]] as well as the red portion.<ref>{{cite journal | vauthors = Muneer S, Kim EJ, Park JS, Lee JH | title = Influence of green, red and blue light emitting diodes on multiprotein complex proteins and photosynthetic activity under varying light intensities in lettuce leaves (Lactuca sativa L.) | journal = International Journal of Molecular Sciences | volume = 15 | issue = 3 | pages = 4657–70 | date = March 2014 | pmid = 24642884 | pmc = 3975419 | doi = 10.3390/ijms15034657 | doi-access = free }}</ref> Conversely, it is a poor absorber of green and near-green portions of the spectrum. Hence chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, is less absorbed.<ref name=JBE/> Two types of chlorophyll exist in the photosystems of green plants: [[chlorophyll a|chlorophyll ''a'']] and [[chlorophyll b|''b'']].<ref>{{cite web | vauthors = Speer BR | year = 1997 | title = Photosynthetic Pigments | work = UCMP Glossary (online) | publisher = [[University of California Museum of Paleontology]] | url = http://www.ucmp.berkeley.edu/glossary/gloss3/pigments.html | access-date = 2010-07-17 }}</ref>

==History==
Chlorophyll was first isolated and named by [[Joseph Bienaimé Caventou]] and [[Pierre Joseph Pelletier]] in 1817.<ref>See:
* {{cite journal | vauthors = Delépine M | author-link = :fr:Marcel Delépine | date = September 1951 | title = Joseph Pelletier and Joseph Caventou | journal = [[Journal of Chemical Education]] | volume = 28 | issue = 9 | page = 454 | doi = 10.1021/ed028p454 | bibcode = 1951JChEd..28..454D }}
*  {{cite journal | vauthors = Pelletier PJ, Caventou JB | date = 1817 | url = https://archive.org/stream/journaldepharma22unkngoog#page/n444/mode/2up | title = Notice sur la matière verte des feuilles | trans-title = Notice on the green material in leaves | language = French | journal = Journal de Pharmacie | volume = 3 | pages = 486–491 }} On p. 490, the authors propose a new name for chlorophyll. From p. 490: ''"Nous n'avons aucun droit pour nommer une substance connue depuis long-temps, et à l'histoire de laquelle nous n'avons ajouté que quelques faits ; cependant nous proposerons, sans y mettre aucune importance, le nom de ''chlorophyle'', de ''chloros'', couleur, et ''{{math|φύλλον}}'', feuille : ce nom indiquerait le rôle qu'elle joue dans la nature."''  (We have no right to name a substance [that has been] known for a long time, and to whose story we have added only a few facts ; however, we will propose, without giving it any importance, the name ''chlorophyll'', from ''chloros'', color, and {{math|φύλλον}}, leaf :  this name would indicate the role that it plays in nature.)</ref>
The presence of [[magnesium]] in chlorophyll was discovered in 1906,<ref>{{cite journal | vauthors = Willstätter R | date = 1906 | title = Zur Kenntniss der Zusammensetzung des Chlorophylls | trans-title = Contribution to the knowledge of the composition of chlorophyll | language = de | journal = Annalen der Chemie | volume = 350 | issue = 1–2 | pages = 48–82 | doi = 10.1002/jlac.19063500103 | quote = From p. 49: ''"Das Hauptproduct der alkalischen Hydrolyse bilden tiefgrüne Alkalisalze. In ihnen liegen complexe Magnesiumverbindungen vor, die das Metall in einer gegen Alkali auch bei hoher Temperatur merkwürdig widerstandsfähigen Bindung enthalten."'' (Deep green alkali salts form the main product of alkali hydrolysis. In them, complex magnesium compounds are present, which contain the metal in a bond that is extraordinarily resistant to alkali even at high temperature.) | url = http://babel.hathitrust.org/cgi/pt?id=uva.x002455980;view=1up;seq=436}}</ref> and was the first detection of that element in living tissue.<ref name="motilva">{{Cite book | vauthors = Motilva MJ | contribution = Chlorophylls{{Snd}} from functionality in food to health relevance | year = 2008 | title = 5th Pigments in Food congress- for quality and health | publisher = University of Helsinki | type = Print | isbn = 978-952-10-4846-3 }}</ref>

After initial work done by German chemist [[Richard Willstätter]] spanning from 1905 to 1915, the general structure of chlorophyll ''a'' was elucidated by [[Hans Fischer]] in 1940. By 1960, when most of the [[stereochemistry]] of chlorophyll ''a'' was known, [[Robert Burns Woodward]] published a total synthesis of the molecule.<ref name="motilva"/><ref>{{cite journal | vauthors = Woodward RB, Ayer WA, Beaton JM, Bickelhaupt F, Bonnett R, Buchschacher P, Closs G, Dutler H, Hannah J, Hauck F, Itô S, Langemann A, Le Goff E, Leimgruber W, Lwowski W, Sauer J, Valenta Z, Volz H |date=July 1960|title=The total synthesis of chlorophyll|journal=[[Journal of the American Chemical Society]]|volume=82|issue=14|pages=3800–3802|doi=10.1021/ja01499a093|url=http://media.iupac.org/publications/pac/1961/pdf/0203x0383.pdf |archive-url=https://web.archive.org/web/20110410023814/http://media.iupac.org/publications/pac/1961/pdf/0203x0383.pdf |archive-date=2011-04-10 |url-status=live}}</ref> In 1967, the last remaining stereochemical elucidation was completed by [[Ian Fleming (chemist)|Ian Fleming]],<ref>{{cite journal | vauthors = Fleming I |author-link=Ian Fleming (chemist) |date=14 October 1967 |title=Absolute Configuration and the Structure of Chlorophyll |journal=[[Nature (journal)|Nature]] |volume=216 |issue=5111 |pages=151–152 |s2cid=4262313 |doi=10.1038/216151a0 |bibcode = 1967Natur.216..151F }}</ref> and in 1990 Woodward and co-authors published an updated synthesis.<ref>{{cite journal | vauthors = Woodward RB, Ayer WA, Beaton JM, Bickelhaupt F, Bonnett R, Buchschacher P, Closs GL, Dutler H, Hannah J, Hauck FP, Itǒ S, Langemann A, Le Goff E, Leimgruber W, Lwowski W, Sauer J, Valenta Z, Volz H |year=1990|title=The total synthesis of chlorophyll ''a''|journal=[[Tetrahedron (journal)|Tetrahedron]] |volume=46 |issue=22 |pages=7599–7659 |doi=10.1016/0040-4020(90)80003-Z }}</ref> [[Chlorophyll f|Chlorophyll ''f'']] was announced to be present in [[cyanobacteria]] and other oxygenic microorganisms that form [[stromatolites]] in 2010;<ref>{{cite journal | vauthors = Jabr F | date = August 2010 | url = http://www.scientificamerican.com/article.cfm?id=new-form-chlorophyll | title = A New Form of Chlorophyll? | journal = Scientific American }}</ref><ref>{{cite web | url = https://www.newscientist.com/article/dn19338-infrared-chlorophyll-could-boost-solar-cells.html | title = Infrared chlorophyll could boost solar cells. | work = New Scientist | date = 19 August 2010 | access-date = 15 April 2012 }}</ref> a molecular formula of C<sub>55</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg and a structure of (2-[[formyl]])-chlorophyll ''a'' were deduced based on NMR, optical and mass spectra.<ref name=ChlF>{{cite journal | vauthors = Chen M, Schliep M, Willows RD, Cai ZL, Neilan BA, Scheer H | title = A red-shifted chlorophyll | journal = Science | volume = 329 | issue = 5997 | pages = 1318–9 | date = September 2010 | pmid = 20724585 | doi = 10.1126/science.1191127 | bibcode = 2010Sci...329.1318C | s2cid = 206527174 }}</ref>

==Photosynthesis==
[[File:Chlorophyll ab spectra-en.svg|thumb|right|[[Absorbance]] spectra of free chlorophyll&nbsp;''a'' ('''<span style="color:#0169c9;">blue</span>''') and ''b'' ('''<span style="color:red;">red</span>''') in a solvent. The spectra of chlorophyll molecules are slightly modified ''in vivo'' depending on specific pigment-protein interactions.
{{legend|#0169C9|Chlorophyll&nbsp;''a''}}
{{legend|red|Chlorophyll&nbsp;''b''}}]]
Chlorophyll is vital for [[photosynthesis]], which allows plants to absorb energy from [[light]].<ref>{{cite web | vauthors = Carter JS | year =1996 | title =Photosynthesis | publisher =[[University of Cincinnati]] | url =http://biology.clc.uc.edu/courses/bio104/photosyn.htm | url-status =dead | archive-url = https://web.archive.org/web/20130629204107/http://biology.clc.uc.edu/courses/bio104/photosyn.htm | archive-date =2013-06-29 }}</ref>

Chlorophyll molecules are arranged in and around [[photosystem]]s that are embedded in the [[thylakoid]] membranes of [[chloroplast]]s.<ref>{{Cite web |title=Photosynthesis, Chloroplast {{!}} Learn Science at Scitable |url=https://www.nature.com/scitable/topicpage/photosynthetic-cells-14025371/ |access-date=2024-10-19 |website=www.nature.com |language=en}}</ref> In these complexes, chlorophyll serves three functions:
# The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light.
# Having done so, these same centers execute their second function: The transfer of that energy by [[resonance energy transfer]] to a specific chlorophyll pair in the [[reaction center]] of the photosystems.
# This specific pair performs the final function of chlorophylls: Charge separation, which produces the unbound protons (H{{sup|+}}) and electrons (e{{sup|−}}) that separately propel biosynthesis.

The two currently accepted photosystem units are {{nobr|[[photosystem I]]}} and {{nobr|[[photosystem II]],}} which have their own distinct reaction centres, named [[P700]] and [[P680]], respectively. These centres are named after the wavelength (in [[nanometer]]s) of their red-peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them.

The function of the reaction center of chlorophyll is to absorb light energy and transfer it to other parts of the photosystem. The absorbed energy of the photon is transferred to an electron in a process called charge separation. The removal of the electron from the chlorophyll is an oxidation reaction. The chlorophyll donates the high energy electron to a series of molecular intermediates called an [[electron transport chain]]. The charged reaction center of chlorophyll (P680<sup>+</sup>) is then reduced back to its ground state by accepting an electron stripped from water. The electron that reduces P680<sup>+</sup> ultimately comes from the oxidation of water into O<sub>2</sub> and H<sup>+</sup> through several intermediates. This reaction is how photosynthetic organisms such as plants produce O<sub>2</sub> gas, and is the source for practically all the O<sub>2</sub> in Earth's atmosphere. Photosystem&nbsp;I typically works in series with Photosystem&nbsp;II; thus the P700<sup>+</sup> of Photosystem&nbsp;I is usually reduced as it accepts the electron, via many intermediates in the thylakoid membrane, by electrons coming, ultimately, from Photosystem&nbsp;II. Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700<sup>+</sup> can vary.

The electron flow produced by the reaction center chlorophyll pigments is used to pump H<sup>+</sup> ions across the thylakoid membrane, setting up a [[proton-motive force]] a chemiosmotic potential used mainly in the production of [[Adenosine triphosphate|ATP]] (stored chemical energy) or to reduce NADP<sup>+</sup> to [[NADPH]]. NADPH is a universal [[redox|agent]] used to reduce CO<sub>2</sub> into sugars as well as other biosynthetic reactions.

Reaction center chlorophyll–protein complexes are capable of directly absorbing light and performing charge separation events without the assistance of other chlorophyll pigments, but the probability of that happening under a given light intensity is small. Thus, the other chlorophylls in the photosystem and antenna pigment proteins all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll&nbsp;''a'', there are other pigments, called [[accessory pigment]]s, which occur in these pigment–protein antenna complexes.

==Chemical structure==
[[Image:Chlorophyll-a-3D-vdW.png|thumb|Space-filling model of the chlorophyll&nbsp;''a'' molecule]]
Several chlorophylls are known. All are defined as derivatives of the parent [[chlorin]] by the presence of a fifth, ketone-containing ring beyond the four pyrrole-like rings. Most chlorophylls are classified as [[chlorin]]s, which are reduced relatives of [[porphyrins]] (found in [[hemoglobin]]). They share a common biosynthetic pathway with porphyrins, including the precursor [[uroporphyrinogen III]]. Unlike hemes, which contain iron bound to the N4 center, most chlorophylls bind [[magnesium]]. The axial [[ligand]]s attached to the Mg<sup>2+</sup> center are often omitted for clarity. Appended to the chlorin ring are various side chains, usually including a long [[phytyl]] chain ({{chem2|C20H39O}}). The most widely distributed form in terrestrial plants is chlorophyll ''a''. Chlorophyll ''a'' has [[methyl]] group in place of a [[formyl]] group in chlorophyll ''b''. This difference affects the absorption spectrum, allowing plants to absorb a greater portion of visible light.

The structures of chlorophylls are summarized below:<ref>{{cite book |doi=10.1007/1-4020-4516-6_1 |chapter=An Overview of Chlorophylls and Bacteriochlorophylls: Biochemistry, Biophysics, Functions and Applications |title=Chlorophylls and Bacteriochlorophylls |series=Advances in Photosynthesis and Respiration |year=2006 | vauthors = Scheer H |volume=25 |pages=1–26 |isbn=978-1-4020-4515-8 }}</ref><ref>{{cite journal | vauthors = Taniguchi M, Lindsey JS | title = Synthetic Chlorins, Possible Surrogates for Chlorophylls, Prepared by Derivatization of Porphyrins | journal = Chemical Reviews | volume = 117 | issue = 2 | pages = 344–535 | date = January 2017 | pmid = 27498781 | doi = 10.1021/acs.chemrev.5b00696 | osti = 1534468 }}</ref>{{clear}}

{| class="wikitable"
|
! [[Chlorophyll a|Chlorophyll ''a'']]
! [[Chlorophyll b|Chlorophyll ''b'']]
! [[Chlorophyll c1|Chlorophyll ''c<sub>1</sub>'']]
! [[Chlorophyll c2|Chlorophyll ''c<sub>2</sub>'']]
! [[Chlorophyll d|Chlorophyll ''d'']]
! [[Chlorophyll f|Chlorophyll ''f'']]<ref name=ChlF />
|-
! [[Molecular formula]]
| C<sub>55</sub>H<sub>72</sub>O<sub>5</sub>N<sub>4</sub>Mg
| C<sub>55</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg
| C<sub>35</sub>H<sub>30</sub>O<sub>5</sub>N<sub>4</sub>Mg
| C<sub>35</sub>H<sub>28</sub>O<sub>5</sub>N<sub>4</sub>Mg
| C<sub>54</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg
| C<sub>55</sub>H<sub>70</sub>O<sub>6</sub>N<sub>4</sub>Mg
|-
! C2 group
| [[methyl group|−CH<sub>3</sub>]]
| −CH<sub>3</sub>
| −CH<sub>3</sub>
| −CH<sub>3</sub>
| −CH<sub>3</sub>
| −CHO
|-
! C3 group
| [[Vinyl group|−CH=CH<sub>2</sub>]]
| −CH=CH<sub>2</sub>
| −CH=CH<sub>2</sub>
| −CH=CH<sub>2</sub>
| [[formyl|−CHO]]
| −CH=CH<sub>2</sub>
|-
! C7 group
| −CH<sub>3</sub>
| −CHO
| −CH<sub>3</sub>
| −CH<sub>3</sub>
| −CH<sub>3</sub>
| −CH<sub>3</sub>
|-
! C8 group
| [[ethyl group|−CH<sub>2</sub>CH<sub>3</sub>]]
| −CH<sub>2</sub>CH<sub>3</sub>
| −CH<sub>2</sub>CH<sub>3</sub>
| −CH=CH<sub>2</sub>
| −CH<sub>2</sub>CH<sub>3</sub>
| −CH<sub>2</sub>CH<sub>3</sub>
|-
! C17 group
| −CH<sub>2</sub>CH<sub>2</sub>COO−Phytyl
| −CH<sub>2</sub>CH<sub>2</sub>COO−Phytyl
| [[acrylate|−CH=CHCOOH]]
| −CH=CHCOOH
| −CH<sub>2</sub>CH<sub>2</sub>COO−Phytyl
| −CH<sub>2</sub>CH<sub>2</sub>COO−Phytyl
|-
! C17−C18 bond
| Single<br />(chlorin)
| Single<br />(chlorin)
| Double<br />(porphyrin)
| Double<br />(porphyrin)
| Single<br />(chlorin)
| Single<br />(chlorin)
|-
! Occurrence
| Universal
| Mostly plants
| Various algae
| Various algae
| Cyanobacteria
| Cyanobacteria
|}
<div class="skin-invert-image><gallery caption="Structures of chlorophylls">
chlorophyll a.svg|chlorophyll ''a''
chlorophyll b.svg|chlorophyll ''b''
chlorophyll c1.svg|chlorophyll ''c<sub>1</sub>''
chlorophyll c2.svg|chlorophyll ''c<sub>2</sub>''
Chlorophyll d.svg|chlorophyll ''d''
Chlorophyll f_vert.svg|chlorophyll ''f''
</gallery></div>

Chlorophyll ''e'' is reserved for a pigment that has been extracted from algae in 1966 but not chemically described. Besides the lettered chlorophylls, a wide variety of sidechain modifications to the chlorophyll structures are known in the wild. For example, ''[[Prochlorococcus]]'', a cyanobacterium, uses 8-vinyl Chl ''a'' and ''b''.<ref name="Chen19">{{cite journal | vauthors = Chen M |title=Chlorophylls d and f: Synthesis, occurrence, light-harvesting, and pigment organization in chlorophyll-binding protein complexes |journal=Advances in Botanical Research |date=2019 |volume=90 |pages=121–139 |doi=10.1016/bs.abr.2019.03.006|isbn=9780081027523 |s2cid=149632511 }}</ref>

==Measurement of chlorophyll content==
[[File:Chlorophyll Extraktion.jpg|thumb|Chlorophyll forms deep green solutions in organic solvents.]]
Chlorophylls can be extracted from the protein into organic solvents.<ref name=Marker1972>{{Cite journal | vauthors = Marker AF | year = 1972 | title = The use of acetone and methanol in the estimation of chlorophyll in the presence of phaeophytin in plant | journal = Freshwater Biology | volume = 2 | pages = 361–385 | doi = 10.1111/j.1365-2427.1972.tb00377.x | issue = 4 }}</ref><ref name=Jeffrey1969>{{Cite journal | vauthors = Jeffrey SW, Shibata | date = February 1969 | title = Some Spectral Characteristics of Chlorophyll c from Tridacna crocea Zooxanthellae | journal = [[Biological Bulletin]] | volume = 136 | issue = 1 | pages = 54–62 | doi = 10.2307/1539668 | jstor = 1539668 | url = https://www.biodiversitylibrary.org/part/25503 }}</ref><ref>{{cite web | vauthors = Gilpin L |date=21 March 2001 |title=Methods for analysis of benthic photosynthetic pigment |publisher=School of Life Sciences, [[Napier University]] |url=http://www.lifesciences.napier.ac.uk/teaching/MB/benchl01.html |access-date=2010-07-17 |url-status=dead |archive-url=https://web.archive.org/web/20080414215124/http://www.lifesciences.napier.ac.uk/teaching/MB/benchl01.html |archive-date=April 14, 2008 }}</ref> In this way, the concentration of chlorophyll within a leaf can be estimated.<ref>{{cite journal | vauthors = Cate TM, Perkins TD | title = Chlorophyll content monitoring in sugar maple (Acer saccharum) | journal = Tree Physiology | volume = 23 | issue = 15 | pages = 1077–9 | date = October 2003 | pmid = 12975132 | doi = 10.1093/treephys/23.15.1077 | doi-access = free }}</ref> Methods also exist to separate [[chlorophyll a|chlorophyll ''a'']] and [[chlorophyll b|chlorophyll ''b'']].

In [[diethyl ether]], chlorophyll ''a'' has approximate absorbance maxima of 430&nbsp;nm and 662&nbsp;nm, while chlorophyll ''b'' has approximate maxima of 453&nbsp;nm and 642&nbsp;nm.<ref>{{cite book | vauthors = Gross J | year = 1991 | title = Pigments in vegetables: chlorophylls and carotenoids | publisher = Van Nostrand Reinhold | isbn = 978-0442006570 }}</ref> The absorption peaks of chlorophyll ''a'' are at 465&nbsp;nm and 665&nbsp;nm. Chlorophyll ''a'' [[fluorescence|fluoresces]] at 673&nbsp;nm (maximum) and 726&nbsp;nm. The peak [[Molar absorptivity|molar absorption coefficient]] of chlorophyll ''a'' exceeds 10<sup>5</sup>&nbsp;M<sup>−1</sup>&nbsp;cm<sup>−1</sup>, which is among the highest for small-molecule organic compounds.<ref>{{Cite journal | vauthors = Porra RJ, Thompson WA, Kriedemann PE |year=1989|title=Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by atomic absorption spectroscopy|journal= Biochimica et Biophysica Acta (BBA) - Bioenergetics|volume= 975|issue=3|pages=384–394 |doi=10.1016/S0005-2728(89)80347-0}}</ref> In 90% acetone-water, the peak absorption wavelengths of chlorophyll ''a'' are 430&nbsp;nm and 664&nbsp;nm; peaks for chlorophyll ''b'' are 460&nbsp;nm and 647&nbsp;nm; peaks for chlorophyll ''c<sub>1</sub>'' are 442&nbsp;nm and 630&nbsp;nm; peaks for chlorophyll ''c<sub>2</sub>'' are 444&nbsp;nm and 630&nbsp;nm; peaks for chlorophyll ''d'' are 401&nbsp;nm, 455&nbsp;nm and 696&nbsp;nm.<ref>{{cite book | veditors = Larkum AW, Douglas S, Raven JA | title = Photosynthesis in algae|year=2003|publisher=Kluwer|location=London|isbn=978-0-7923-6333-0}}</ref>

Ratio fluorescence emission can be used to measure chlorophyll content. By exciting chlorophyll ''a'' fluorescence at a lower wavelength, the ratio of chlorophyll fluorescence emission at {{val|705|10|u=nm}} and {{val|735|10|u=nm}} can provide a linear relationship of chlorophyll content when compared with chemical testing. The ratio ''F''<sub>735</sub>/''F''<sub>700</sub> provided a [[correlation coefficient|correlation value of ''r''<sup>2</sup>]] 0.96 compared with chemical testing in the range from 41&nbsp;mg&nbsp;m<sup>−2</sup> up to 675&nbsp;mg&nbsp;m<sup>−2</sup>. Gitelson also developed a formula for direct readout of chlorophyll content in mg&nbsp;m<sup>−2</sup>. The formula provided a reliable method of measuring chlorophyll content from 41&nbsp;mg&nbsp;m<sup>−2</sup> up to 675&nbsp;mg&nbsp;m<sup>−2</sup> with a correlation ''r''<sup>2</sup> value of 0.95.<ref>{{cite journal| vauthors = Gitelson AA, Buschmann C, Lichtenthaler HK |date=1999 |title=The Chlorophyll Fluorescence Ratio ''F''<sub>735</sub>/''F''<sub>700</sub> as an Accurate Measure of Chlorophyll Content in Plants |journal=Remote Sens. Environ. |volume=69 |issue=3 |pages=296–302|doi=10.1016/S0034-4257(99)00023-1 |bibcode=1999RSEnv..69..296G }}</ref>

Also, the chlorophyll concentration can be estimated by measuring the light transmittance through the plant leaves.<ref>{{cite journal | vauthors = Najm AA, Kashani A, Paknejad F, Ardakani MR, Hadi MR |title= Using by rapid field test methods to assess the Potato canopy nitrogen status in the presence of organic and inorganic nitrogen fertilizer|journal= International Journal of Advanced Life Sciences |volume=8 |issue=3|pages=328–339|year=2015|issn=2320-1827|url=https://unitedlifejournals.in/ms_files/ijals/14._Using_rapid_filed_test_methods_to_assess_the_potato_canopy.pdf }}</ref> The assessment of leaf chlorophyll content using optical sensors such as [[Dualex]] and SPAD allows researchers to perform real-time and non-destructive measurements.<ref>{{Cite web | vauthors = Cerovic ZG |title=New proximal sensors of vegetation: towards a non destructive quantitative estimation of plant constituents |url=http://www.ese.u-psud.fr/IMG/pdf/CerovicEbernburg2012.pdf |url-status=dead |archive-url=https://web.archive.org/web/20140822115631/http://www.ese.u-psud.fr/IMG/pdf/CerovicEbernburg2012.pdf |archive-date=2014-08-22 |date=October 2012 |place=Ebernburg |access-date=2024-07-12 }}</ref><ref>{{cite journal | vauthors = Huan YU, Hua-Song WU, Zhi-Jie WA |title= Evaluation of SPAD and Dualex for In-Season Corn Nitrogen Status Estimation |journal= Acta Agronomica Sinic |volume=36 |issue=5|pages=840–847|year=2010| ISSN= 1875-2780|doi=10.1016/S1875-2780(09)60051-1}}</ref> Research shows that these methods have a positive correlation with laboratory measurements of chlorophyll.<ref>{{cite journal | vauthors = Vos J, Bom H |title= Hand-held chlorophyll meter: a promising tool to assess the nitrogen status of potato foliage |journal= Potato Res |volume=36|issue= |pages=301–308 |year=1993|doi=10.1007/BF02361796}}</ref>

==Biosynthesis==
{{Main|Chlorophyllide}}
In some plants, chlorophyll is derived from [[glutamate]] and is synthesised along a branched [[biosynthetic pathway]] that is shared with [[heme]] and [[siroheme]].<ref>{{cite journal | vauthors = Battersby AR | title = Tetrapyrroles: the pigments of life | journal = Natural Product Reports | volume = 17 | issue = 6 | pages = 507–26 | date = December 2000 | pmid = 11152419 | doi = 10.1039/B002635M }}</ref><ref name="akhtar94">{{cite book |doi=10.1002/9780470514535.ch8|chapter=The Modification of Acetate and Propionate Side Chains During the Biosynthesis of Haem and Chlorophylls: Mechanistic and Stereochemical Studies|title=Ciba Foundation Symposium 180 - the Biosynthesis of the Tetrapyrrole Pigments|series=Novartis Foundation Symposia|year=2007| vauthors = Akhtar M |volume=180|pages=131–155|pmid=7842850|isbn=9780470514535}}</ref><ref name="Review" >{{cite journal | vauthors = Willows RD | title = Biosynthesis of chlorophylls from protoporphyrin IX | journal = Natural Product Reports | volume = 20 | issue = 3 | pages = 327–41 | date = June 2003 | pmid = 12828371 | doi = 10.1039/B110549N }}</ref>
[[Chlorophyll synthase]]<ref>{{cite journal | vauthors = Schmid HC, Rassadina V, Oster U, Schoch S, Rüdiger W | title = Pre-loading of chlorophyll synthase with tetraprenyl diphosphate is an obligatory step in chlorophyll biosynthesis | journal = Biological Chemistry | volume = 383 | issue = 11 | pages = 1769–78 | date = November 2002 | pmid = 12530542 | doi = 10.1515/BC.2002.198 | url = https://epub.ub.uni-muenchen.de/17847/1/bc.2002.198.pdf | s2cid = 3099209 }}</ref> is the enzyme that completes the biosynthesis of chlorophyll ''a'':<ref>{{cite journal | vauthors = Eckhardt U, Grimm B, Hörtensteiner S | title = Recent advances in chlorophyll biosynthesis and breakdown in higher plants | journal = Plant Molecular Biology | volume = 56 | issue = 1 | pages = 1–14 | date = September 2004 | pmid = 15604725 | doi = 10.1007/s11103-004-2331-3 | s2cid = 21174896 | url = https://boris.unibe.ch/102079/ }}</ref><ref>{{cite journal | vauthors = Bollivar DW | title = Recent advances in chlorophyll biosynthesis | journal = Photosynthesis Research | volume = 90 | issue = 2 | pages = 173–94 | date = November 2006 | pmid = 17370354 | doi = 10.1007/s11120-006-9076-6 | s2cid = 23808539 }}</ref>
:chlorophyllide ''a'' + phytyl diphosphate <math>\rightleftharpoons</math> chlorophyll ''a'' + diphosphate
This conversion forms an ester of the carboxylic acid group in [[chlorophyllide|chlorophyllide ''a'']] with the 20-carbon [[diterpene]] alcohol [[phytol]]. Chlorophyll ''b'' is made by the same enzyme acting on [[chlorophyllide|chlorophyllide ''b'']]. The same is known for chlorophyll ''d'' and ''f'', both made from corresponding chlorophyllides ultimately made from chlorophyllide ''a''.<ref name="Tsuzuki">{{cite journal | vauthors = Tsuzuki Y, Tsukatani Y, Yamakawa H, Itoh S, Fujita Y, Yamamoto H | title = Effects of Light and Oxygen on Chlorophyll ''d'' Biosynthesis in a Marine Cyanobacterium ''Acaryochloris''&nbsp;''marina'' | journal = Plants | volume = 11 | issue = 7 | pages = 915 | date = March 2022 | pmid = 35406896 | doi = 10.3390/plants11070915 | pmc = 9003380 | doi-access = free }}</ref>

In [[Angiosperm]] plants, the later steps in the biosynthetic pathway are light-dependent. Such plants are pale ([[etiolation|etiolated]]) if grown in darkness. [[Non-vascular plant]]s and green algae have an additional light-independent [[enzyme]] and grow green even in darkness.<ref>{{cite journal | vauthors = Muraki N, Nomata J, Ebata K, Mizoguchi T, Shiba T, Tamiaki H, Kurisu G, Fujita Y | title = X-ray crystal structure of the light-independent protochlorophyllide reductase | journal = Nature | volume = 465 | issue = 7294 | pages = 110–4 | date = May 2010 | pmid = 20400946 | doi = 10.1038/nature08950 | bibcode = 2010Natur.465..110M | s2cid = 4427639 }}</ref>

Chlorophyll is bound to [[proteins]]. [[Protochlorophyllide]], one of the biosynthetic intermediates, occurs mostly in the free form and, under light conditions, acts as a [[photosensitizer]], forming [[free radicals]], which can be toxic to the plant. Hence, plants regulate the amount of this chlorophyll precursor. In angiosperms, this regulation is achieved at the step of [[aminolevulinic acid]] (ALA), one of the intermediate compounds in the biosynthesis pathway. Plants that are fed by ALA accumulate high and toxic levels of protochlorophyllide; so do the mutants with a damaged regulatory system.<ref>
{{cite journal | vauthors = Meskauskiene R, Nater M, Goslings D, Kessler F, op den Camp R, Apel K | title = FLU: a negative regulator of chlorophyll biosynthesis in Arabidopsis thaliana | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 98 | issue = 22 | pages = 12826–31 | date = October 2001 | pmid = 11606728 | pmc = 60138 | doi = 10.1073/pnas.221252798 | bibcode = 2001PNAS...9812826M | jstor = 3056990 | doi-access = free }}</ref>

==Senescence and the chlorophyll cycle==
The process of [[plant senescence]] involves the degradation of chlorophyll: for example the enzyme [[chlorophyllase]] ({{EC number|3.1.1.14}}) [[hydrolysis|hydrolyses]] the phytyl sidechain to reverse the reaction in which chlorophylls are biosynthesised from chlorophyllide ''a'' or ''b''. Since chlorophyllide ''a'' can be converted to chlorophyllide ''b'' and the latter can be re-esterified to chlorophyll ''b'', these processes allow cycling between chlorophylls ''a'' and ''b''. Moreover, chlorophyll ''b'' can be directly reduced (via {{nowrap|7<sup>1</sup>-hydroxychlorophyll ''a''}}) back to chlorophyll ''a'', completing the cycle.<ref>{{cite web |url=https://www.qmul.ac.uk/sbcs/iubmb/enzyme/reaction/tetrapyr/porphyrin7.html |title=Chlorophyll Cycle |publisher=	IUBMB |date=2011 |access-date=2020-06-04}}</ref><ref name="pmid16669755" >{{cite journal | vauthors = Hörtensteiner S | title = Chlorophyll degradation during senescence | journal = Annual Review of Plant Biology | volume = 57 | pages = 55–77 | year = 2006 | pmid = 16669755 | doi = 10.1146/annurev.arplant.57.032905.105212 }}</ref>
In later stages of senescence, chlorophyllides are converted to a group of colourless [[tetrapyrrole]]s known as nonfluorescent chlorophyll catabolites (NCC's) with the general structure:
:[[Image:Nonfluorescentchlorophilcatabolites.svg|class=skin-invert-image|Nonfluorescent chlorophyll catabolites]]
These compounds have also been identified in ripening fruits and they give characteristic [[Autumn leaf color|autumn colours]] to [[deciduous]] plants.<ref name="pmid16669755" /><ref>{{cite journal | vauthors = Müller T, Ulrich M, Ongania KH, Kräutler B | title = Colorless tetrapyrrolic chlorophyll catabolites found in ripening fruit are effective antioxidants | journal = Angewandte Chemie | volume = 46 | issue = 45 | pages = 8699–702 | year = 2007 | pmid = 17943948 | pmc = 2912502 | doi = 10.1002/anie.200703587 }}</ref>

==Distribution==
Chlorophyll maps from 2002 to 2024, provided by [[NASA]], show milligrams of chlorophyll per cubic meter of seawater each month.<ref name=GlobalMap>{{cite web |url=https://earthobservatory.nasa.gov/global-maps/MY1DMM_CHLORA |title = Chlorophyll : Global Maps |website = Earthobservatory.nasa.gov |access-date = 5 November 2024 }}</ref> Places where chlorophyll amounts are very low, indicating very low numbers of [[phytoplankton]], are blue. Places where chlorophyll concentrations are high, meaning many phytoplankton were growing, are yellow. The observations come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. Land is dark gray, and places where MODIS could not collect data because of sea ice, polar darkness, or clouds are light gray. The highest chlorophyll concentrations, where tiny surface-dwelling ocean plants are, are in cold polar waters or in places where ocean currents bring cold water to the surface, such as around the equator and along the shores of continents. It is not the cold water itself that stimulates the phytoplankton. Instead, the cool temperatures are often a sign that the water has welled up to the surface from deeper in the ocean, carrying nutrients that have built up over time. In polar waters, nutrients accumulate in surface waters during the dark winter months when plants cannot grow. When sunlight returns in the spring and summer, the plants flourish in high concentrations.<ref name=GlobalMap/>

==Uses==
=== Culinary ===
Synthetic chlorophyll is registered as a food additive colorant, and its [[E number]] is [[E number#E100–E199 (colours)|E140]]. Chefs use chlorophyll to color a variety of foods and beverages green, such as pasta and spirits. [[Absinthe#Production|Absinthe]] gains its green color naturally from the chlorophyll introduced through the large variety of herbs used in its production.<ref name=Adams2004>{{cite book | vauthors = Adams J | year = 2004 | title = Hideous absinthe : a history of the devil in a bottle | page = 22 | isbn = 978-1860649202 | publisher = I.B.Tauris, 2004 | location = United Kingdom | url = https://books.google.com/books?id=b7FwE6EpNPoC&pg=PA22 }}</ref> Chlorophyll is not soluble in water, and it is first mixed with a small quantity of [[vegetable oil]] to obtain the desired [[Solution (chemistry)|solution]].{{citation needed|date=May 2020}}

===In marketing===
In years 1950–1953 in particular, chlorophyll was used as a marketing tool to promote toothpaste, sanitary towels, soap and other products. This was based on claims that it was an odor blocker — a finding from research by F. Howard Westcott in the 1940s — and the commercial value of this attribute in advertising led to many companies creating brands containing the compound. However, it was soon determined that the hype surrounding chlorophyll was not warranted and the underlying research may even have been a hoax. As a result, brands rapidly discontinued its use. In the 2020s, chlorophyll again became the subject of unsubstantiated medical claims, as [[Social media marketing|social media influencers]] promoted its use in the form of "chlorophyll water", for example.<ref name=O'Hagan>{{cite journal |doi=10.1108/jhrm-11-2021-0057 |doi-access=free |title=All that glistens is not (Green) gold: Historicising the contemporary chlorophyll fad through a multimodal analysis of Swedish marketing, 1950–1953 |date=2022 | vauthors = O'Hagan LA |journal=Journal of Historical Research in Marketing |volume=14 |issue=3 |pages=374–398 }}</ref>

== See also ==
{{Commons category|Chlorophyll}}
* [[Bacteriochlorophyll]], related compounds in phototrophic bacteria
* [[Chlorophyllin]], a semi-synthetic derivative of chlorophyll
* [[Deep chlorophyll maximum]]
* [[Chlorophyll fluorescence]], to measure plant stress
* [[Purple Earth hypothesis]], a [[scientific hypothesis]] that explains the [[evolution]] of red-blue spectral affinity of chlorophyll.

== References ==
{{reflist}}

{{Botany}}
{{Plant Pigments}}
{{Authority control}}

[[Category:Tetrapyrroles]]
[[Category:Photosynthetic pigments]]
[[Category:Articles containing video clips]]
[[Category:E-number additives]]