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| Names | |
|---|---|
| IUPAC name Chlorophylla | |
| Systematic IUPAC name Magnesium [methyl (3S,4S,21R)-14-ethyl-4,8,13,18-tetramethyl-20-oxo-3-(3-oxo-3-{[(2E,7R,11R)-3,7,11,15-tetramethyl-2-hexadecen-1-yl]oxy}propyl)-9-vinyl-21-phorbinecarboxylatato(2−)-κ2N,N′] | |
| Other names α-Chlorophyll | |
| Identifiers | |
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3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.006.852 |
| EC Number |
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| RTECS number |
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| UNII | |
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| Properties | |
| C55H72MgN4O5 | |
| Molar mass | 893.509 g·mol−1 |
| Appearance | Dark green powder |
| Odor | Odorless |
| Density | 1.079 g/cm3[1] |
| Melting point | ~ 152.3 °C (306.1 °F; 425.4 K)[2] decomposes[1] |
| Insoluble | |
| Solubility | Very soluble inethanol,ether Soluble inligroin,[2]acetone,benzene,chloroform[1] |
| Absorbance | See text |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Chlorophylla is a specific form ofchlorophyll used inoxygenicphotosynthesis. It absorbs most energy fromwavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum.[3] Chlorophyll does not reflect light but chlorophyll-containing tissues appear green because green light is diffusively reflected by structures like cell walls.[4] Thisphotosynthetic pigment is essential for photosynthesis ineukaryotes,cyanobacteria andprochlorophytes because of its role as primary electron donor in theelectron transport chain.[5] Chlorophylla also transfers resonance energy in theantenna complex, ending in thereaction center where specific chlorophyllsP680 andP700 are located.[6]
Chlorophylla is essential for mostphotosynthetic organisms to releasechemical energy but is not the only pigment that can be used for photosynthesis. All oxygenic photosynthetic organisms use chlorophylla, but differ inaccessory pigments likechlorophyllb.[5] Chlorophylla can also be found in very small quantities in thegreen sulfur bacteria, ananaerobicphotoautotroph.[7] These organisms usebacteriochlorophyll and some chlorophylla but do not produce oxygen.[7]Anoxygenic photosynthesis is the term applied to this process, unlikeoxygenic photosynthesis where oxygen is produced during the light reactions ofphotosynthesis.
The molecular structure of chlorophylla consists of achlorin ring, whose four nitrogen atoms surround a centralmagnesium atom, and has several other attachedside chains and ahydrocarbon tail formed by aphytolester.
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| Structure of chlorophylla molecule showing the phytol tail | |
Chlorophylla contains a magnesiumion encased in a large ring structure known as achlorin. The chlorin ring is aheterocyclic compound derived frompyrrole. Four nitrogen atoms from the chlorin surround and bind the magnesium atom. The magnesium center uniquely defines the structure as a chlorophyll molecule.[8] The porphyrin ring ofbacteriochlorophyll is saturated, and lacking alternation of double and single bonds causing variation in absorption of light.[9]
Side chains are attached to the chlorin ring of the various chlorophyll molecules. Different side chains characterize each type of chlorophyll molecule, and alters the absorption spectrum of light.[10][11] For instance, the only difference between chlorophylla andchlorophyllb is that chlorophyllb has analdehyde instead of a methyl group at the C-7 position.[11]
The phytol ester of chlorophylla (R in the diagram) is a longhydrophobic tail which anchors the molecule to other hydrophobic proteins in thethylakoid membrane of thechloroplast.[5] Once detached from the porphyrin ring, phytol becomes the precursor of twobiomarkers,pristane andphytane, which are important in the study ofgeochemistry and the determination of petroleum sources.[12]
The Chlorophyllabiosynthetic pathway utilizes a variety ofenzymes.[13] In most plants, chlorophyll is derived fromglutamate and is synthesised along a branched pathway that is shared withheme andsiroheme.[14][15][16]The initial steps incorporate glutamic acid into5-aminolevulinic acid (ALA); two molecules of ALA are thenreduced toporphobilinogen (PBG), and four molecules of PBG are coupled, formingprotoporphyrin IX.[8]
Chlorophyll synthase[17] is the enzyme that completes the biosynthesis of chlorophylla[18][19] by catalysing the reactionEC2.5.1.62
This forms an ester of the carboxylic acid group inchlorophyllidea with the 20-carbonditerpene alcoholphytol.
Chlorophylla absorbs light within theviolet,blue andred wavelengths. Accessory photosynthetic pigments broaden the spectrum of light absorbed, increasing the range of wavelengths that can be used in photosynthesis.[5] The addition of chlorophyllb next to chlorophylla extends theabsorption spectrum. In low light conditions, plants produce a greater ratio of chlorophyllb to chlorophylla molecules, increasing photosynthetic yield.[10]
Absorption of light by photosynthetic pigments converts photons into chemical energy.Light energy radiating onto thechloroplast strikes the pigments in thethylakoid membrane and excites their electrons. Since the chlorophylla molecules only capture certain wavelengths, organisms may use accessory pigments to capture a wider range of light energy shown as the yellow circles.[6] It then transfers captured light from one pigment to the next as resonance energy, passing energy one pigment to the other until reaching the special chlorophylla molecules in the reaction center.[10] These special chlorophylla molecules are located in bothphotosystem II andphotosystem I. They are known asP680 for Photosystem II andP700 for Photosystem I.[20] P680 and P700 are the primaryelectron donors to the electron transport chain. These two systems are different in their redox potentials for one-electron oxidation. The Em for P700 is approximately 500mV, while the Em for P680 is approximately 1,100-1,200 mV.[20]
Chlorophylla is very important in the energy phase of photosynthesis. Twoelectrons need to be passed to anelectron acceptor for the process of photosynthesis to proceed.[5] Within thereaction centers of both photosystems there are a pair of chlorophylla molecules that pass electrons on to thetransport chain throughredox reactions.[20]
The concentration of chlorophyll A is used as an index of phytoplankton biomass. In the ocean, phytoplankton all contain the chlorophyll pigment, which has a greenish color.
Phytoplankton are microscopic organisms that live in watery environments and changes in the amount of phytoplankton indicate the change in productivity of the ocean. Phytoplankton can be affected indirectly by climatic factors, such as changes in water temperatures and surface winds.[21]
