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Reaction Centers as Nanoscale Photovoltaic Devices
Published in Swee Ching Tan, Photosynthetic Protein-Based Photovoltaics, 2018
Reaction centers are membrane-embedded complexes of pigment and protein that are found in all organisms capable of chlorophyll-based photosynthesis.1–5 They work together with light-harvesting complexes to capture solar energy and trap it in the form of a metastable separation of electrical charge across the photosynthetic membrane. Ensuing reduction/oxidation reactions are coupled to proton translocation to establish a transmembrane proton electrochemical gradient that can power a variety of reactions including the synthesis of adenosine triphosphate (ATP). In oxygenic photosynthetic organisms, plants, algae, and cyanobacteria, two types of reaction center operate in series to transfer electrons along a linear pathway from water to nicotinamide adenine dinucleotide phosphate (NADP +), thus also generating reducing power for biosynthesis.6–10 These reaction centers form part of Photosystem I (PSI) and Photosystem II (PSII). In anoxygenic purple photosynthetic bacteria, a single type of reaction center powers a cyclic flow of electrons that reduces NADP + indirectly.1,11–16 The high ATP/ADP and NADPH/NADP + ratios resulting from the capture of solar energy power biosynthesis including, in photoautotrophic organisms, the fixation of carbon. An excellent, in-depth, and comprehensive treatise covering the primary events of photosynthesis has been written by Blankenship.5
Oxidative Phosphorylation— Photosynthesis
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
It is chlorophyll which drives the absorbed light energy to reaction centers. The light-absorbing pigments of thylakoid membranes are arranged in functional arrays called photosystems. All the pigment molecules of a photosystem can absorb photons, but a few chlorophyll associated with the photochemical reaction center can transduce light into chemical energy. The other pigment molecules of a photosystem are called antenna molecules or light-harvesting molecules. They absorb light energy and transmit it rapidly and efficiently to the reaction center.
Natural Organic Photosynthetic Solar Energy Transduction
Published in Sun Sam-Shajing, Sariciftci Niyazi Serdar, Organic Photovoltaics, 2017
The conversion of pure energy of excited states to chemical bonds in molecules takes place in the reaction center. The reaction center is a multisubunit integral–membrane pigment-protein complex, incorporating both chlorophylls and other electron transfer cofactors such as quinones or iron–sulfur centers, along with hydrophobic peptides that thread back and forth across the membrane several times.
Polyethylene glycol-modified mesoporous zerovalent iron nanoparticle as potential catalyst for improved reductive degradation of Congo red from wastewater
Published in Journal of Environmental Science and Health, Part A, 2023
Ipsita Som, Mouni Roy, Rajnarayan Saha
Based on the m/z value obtained from the GCMS analysis degraded products, a plausible mechanistic pathway of CR degradation has been illustrated in Scheme 2. At first significant adsorption of CR molecule on the surface of synthesized nZVI-PEG6000 occur. Then, an electron-deficient reaction center (carbocation ion) is generated in the catalytic cavity of CR molecule. This carbocation ion is highly prone to react with nucleophile, i.e., BH4- ion which transfer electrons to nano catalyst. Later, this electrons attacked the carbocation ion, which leads to the cleavage of electronically unstable azo bond. The color of CR is due to the presence of azo bond along with chromophores.[74] Thus, cleavage of azo bond causes its decolorization gradually. Later, the various steps including demination (–NH2), desulphonation (–SO3H) and ring cleavage or rupturing process leads to the formation of several low molecular weight intermediate compounds. The obtained low molecular weight compounds (dicarboxylic acid, other organic acid) are finally mineralized to CO2 and H2O.
Cotyledonary leaves effectively shield the true leaves in Ricinus communis L. from copper toxicity
Published in International Journal of Phytoremediation, 2021
Chlorophyll a fluorescence kinetics can provide the details regarding the structure and function of the photosynthetic apparatus especially PSII under different environmental stresses (Stirbet and Govindjee 2011). Various chlorophyll a fluorescence parameters were analyzed to study the effects of Cu stress on PSII efficiency of first true leaves of R. communis in the presence and absence of cotyledonary leaves on 6th day of CuSO4 exposure (Table 4). The area above the chlorophyll a fluorescence curve between Fo and Fm (Area), which is proportional to the pool size of the electron acceptor QA on the reducing side of PSII (Strasser et al. 2004), was decreased in both types of leaves as a result of CuSO4 treatment. The reduction was about 77% in the case of true leaves in the absence of cotyledonary leaves, but only a slight decrease (upto 25%) was noticed in true leaves in the presence of cotyledonary leaves, along with a significant reduction (upto 90%) in the cotyledonary leaves. This significant decline in the “Area” with the increasing metal stress in the cotyledonary leaves is a clear indication of blockage of electron transfer from the reaction center to the quinone pool (Mathur et al. 2016). The value of maximal chlorophyll fluorescence (Fm) showed a decrease of only 14% in true leaves with the treatment of 200 μM CuSO4 in the presence of cotyledonary leaves, while the decrease was 35% in the case of the true leaves in the absence of cotyledonary leaves.
Non-stomatal limitation of photosynthesis by soil salinity
Published in Critical Reviews in Environmental Science and Technology, 2021
Ting Pan, Minmin Liu, Vladimir D. Kreslavski, Sergey K. Zharmukhamedov, Chenrong Nie, Min Yu, Vladimir V. Kuznetsov, Suleyman I. Allakhverdiev, Sergey Shabala
The intrinsic proteins are also affected by the salt stress. Sudhir, Pogoryelov, Kovacs, Garab, and Murthy (2005) reported a significant change in D1 content in cyanobacterium Spirulina platensis as well as diminishing in content of intrinsic Chl-binding protein CP47 and a core membrane linker protein 94 kDa that can attach phycobilisome to thylakoid; at the same, an increase in 17-kDa protein content was observed. The decrease in 47-kDa and 94-kDa proteins led to a reduced energy transfer from the light-harvesting complex of PSII to reaction center of PSII. This occurred simultaneously with a decrease in PSII photochemical activity that can be due to reduced content (by 40%) of PSII key protein D1 (Sudhir et al., 2005).