Пластохинон

Description

Plastoquinone is a lipophilic benzoquinone of plant and cyanobacterial origin, a key electron carrier in the photosynthetic electron transport chain. The natural and most common form is plastoquinone-9 (PQ-9, PQA), which has 2,3-dimethyl-1,4-benzoquinone at its core and a side chain of nine isoprenoid units attached to it.

Basic Attributes

• CAS No.: 4299-57-4
• Chemical formula: C53H80O2
• Molecular weight: 749.20
• XLogP3: 18.2
• Number of hydrogen bond acceptors: 2
• Number of links rotated: 26
• Number of heavy atoms: 55
• Related CAS numbers (isomers/forms): 1184-38-9, 20936-14-5, 26013-03-6

Synonyms

• Plastoquinone-9, Plastoquinone A, Plastoquinone 45, PQA, Q 254
• Koflerquinone 45, Kofler's Quinon
• 2,3-Dimethyl-5-[(2E,6E,10E,14E,18E,22E,26E,30E)-3,7,11,15,19,23,27,31,35-nonameth yl-2,6,10,14,18,22,26,30,34-hexatriacontanonaen-1-yl]-2,5-cyclohexadiene-1,4-dione

Physico-chemical properties

Due to the long unsaturated isoprenoid chain, the substance is extremely lipophilic (XLogP3 about 18) and practically insoluble in water. The molecule contains 26 rotatable bonds, reflecting the flexibility of the side chain, and 55 heavy atoms in the backbone. The melting point is not documented in open sources due to the difficulty of isolating an individual homologue in crystalline form - in practice, the substance works in the lipid phase of the membrane, and not as a general-purpose solid reagent.

Mechanism of action and role in photosynthesis

Plastoquinone is embedded in the lipid bilayer of the thylakoid membrane of chloroplasts and cyanobacteria. It accepts a pair of electrons and two protons from photosystem II, being reduced to plastoquinol, diffuses inside the membrane and transfers electrons to the cytochrome b6f complex, and releases protons into the thylakoid lumen - this is how a proton gradient is formed, due to which ATP synthase synthesizes ATP. This pool of plastoquinone/plastoquinol works as a shuttle transporter between two photosystems and at the same time as a sensor of the redox state of the chain, regulating the expression of photosynthetic genes and the distribution of energy between photosystems (state transitions).

Application

• biochemical and physiological studies of photosynthesis, study of the electron transport chain of chloroplasts
• reference compound for analysis of the redox state of thylakoid membranes
• component of formulations in cosmetics and nutraceuticals as a fat-soluble antioxidant, acting in a similar way to ubiquinone

Storage and handling

Like other polyunsaturated quinones, plastoquinone is sensitive to light, atmospheric oxygen and elevated temperature - the long chain of conjugated double bonds is prone to oxidation and isomerization. Store in an airtight container, in a cool place, protected from light, minimizing contact with air when the package is opened. Specific safety data sheets (GHS, transport codes) for preparative quantities have not been published in open sources - handle according to the general rules for working with organic reagents: gloves, eye protection, exhaust ventilation.