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Chlorophyll a contains a magnesium ion encased in a large ring structure known as a chlorin. The chlorin ring is a heterocyclic compound derived from pyrrole. Four nitrogen atoms from the chlorin surround and bind the magnesium atom. The magnesium center uniquely defines the structure as a chlorophyll molecule. [8]
Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life. Some tetrapyrroles form the active core of compounds with crucial biochemical roles in living systems, such as hemoglobin and chlorophyll.
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.
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. [20]
The chlorin ring system features a five-membered carbon ring E is created when one of the propionate groups of the porphyrin is cyclised to the carbon atom linking the original pyrrole rings C and D. A series of chemical steps catalysed by the enzyme Magnesium-protoporphyrin IX monomethyl ester (oxidative) cyclase [ 7 ] gives the overall ...
A cyclic compound or ring compound is a compound in which at least some its atoms are connected to form a ring. [1] Rings vary in size from three to many tens or even hundreds of atoms. Examples of ring compounds readily include cases where: all the atoms are carbon (i.e., are carbocycles),
In these two examples, a metal is complexed at the center of a tetrapyrrole macrocycle ring: the metal being iron in the heme group (iron in a porphyrin ring) of hemoglobin, or magnesium complexed in a chlorin-type ring in the case of chlorophyll. The highly conjugated pi-bonding system of the macrocycle ring absorbs visible light.
With a total of 26 π-electrons, of which 18 π-electrons form a planar, continuous cycle, the porphyrin ring structure is often described as aromatic. [2] [3] One result of the large conjugated system is that porphyrins typically absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored.