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Triplet chlorophyll is a potent photosensitiser of molecular oxygen forming singlet oxygen which can cause oxidative damage to the pigments, lipids and proteins of the photosynthetic thylakoid membrane. To counter this problem, one photoprotective mechanism is so-called non-photochemical quenching (NPQ), which relies upon the conversion and ...
The light-harvesting complex (or antenna complex; LH or LHC) is an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem. The antenna pigments are predominantly chlorophyll b, xanthophylls, and ...
Examples of atoms in singlet, doublet, and triplet states. In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin S = 1. It has three allowed values of the spin's projection along a given axis m S = −1, 0, or +1, giving the name "triplet".
In biology, a light-harvesting complex or LHC is an aggregate consisting of proteins bound with chromophores (chlorophylls and carotenoids) that play a key role in photosynthesis. LHCs are arrayed around photosynthetic reaction centers in both plants and photosynthetic bacteria and collect more of the incoming light than would be captured by ...
The P700 lies in the center of the protein. Once photoinduced charge separation has been initiated, the electron travels down a pathway through a chlorophyll α molecule situated directly above the P700, through a quinone molecule situated directly above that, through three 4Fe-4S clusters, and finally to an interchangeable ferredoxin complex. [10]
The excited, triplet state photosensitizer then reacts with a substrate molecule which is not molecular oxygen to both form a product and reform the photosensitizer. Type I photosensitized reactions result in the photosensitizer being quenched by a different chemical substrate than molecular oxygen.
The light harvesting complex in purple bacteria is multifunctional; at high light intensities, the light harvesting complex typically switches into a quenched state through a conformational change of the PPC, and at low light intensities, the light harvesting complex typically reverts to an unquenched state. [11]
Photosynthetic reaction centre proteins are main protein components of photosynthetic reaction centres (RCs) of bacteria and plants. They are transmembrane proteins embedded in the chloroplast thylakoid or bacterial cell membrane. Plants, algae, and cyanobacteria have one type of PRC for each of its two photosystems.