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Reactions on Polymers
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
The light-harvesting antenna complex LH II is composed of two bacteriochlorophyll a (BCHl) molecules that can be classified into two categories. The first one is a set of 18 molecules arranged in a slipped face-to-face arrangement and is located close to the membrane surface perpendicular to these molecules. The second ring is composed of 9 BCHl in the middle of the bilayer. The first 18 BCHl have an absorption maximum at 850 nm and are collectively called B850, while the second 9 BCHl have an absorption maximum at 800 nm and are called B800. These structures are contained within the walls of protein cylinders with radii of 1.8 and 3.4 nm. Once the LH II complex antenna absorbs light, a series of very complex nonradiative photophysical processes are triggered. First, the excitation energy migrates via energy transfers involving the hopping of excitation energy within almost isoenergetic subunits of a single complex. This is followed by a fast energy transfer to a lower-energy complex with minimal losses (Figure 16.11). These ultrafast events occur in the singlet state (S1) of the BCHl pigments and are believed to occur by a Förster mechanism occurring over relatively long distances (30–100 Å).
Exploring the potential of microalgae cell factories for generation of biofuels
Published in Biofuels, 2023
Dixita Chettri, Ashwani Kumar Verma, Anil Kumar Verma
Other effective strategies to increase biomass include changes in the intrinsic characteristics of algal species. One important strategy is to optimize algal biology, which involves optimizing light capture and conversion efficiency by adjusting the size of the photosynthetic light-collecting antenna and developing highly potent breeding methods [83]. In photosynthetic algae, more than 70% of chlorophyll pigments are localized in the light-collecting antenna (LHA), where the antenna complex captures photons and transmits them to reaction centers, i.e. PSI and PSII. The efficient quantum coherence processes are involved in energy migration in the antenna complex, and the large light capture by the antenna confers selective advantages in mixed populations by limiting light capture by competing species and mediating light capture at high densities and low light flux [91]. Promising results were obtained in studies in which the size of the light-harvesting antenna complex was adjusted, resulting in improved biomass yield. Cazzaniga et al. [92] performed random ultraviolet light (UV)-mediated mutagenesis in Chlorella sorokiniana followed by selection of the mutant strains. The results showed the presence of six strains with truncated antenna complexes that exhibited lower fluorescence output compared to the wild type. When analyzed, the strains with truncated antenna mutants (TAM) showed half the chlorophyll content compared to the wild type and had an improved chlorophyll a/chlorophyll b ratio in TAM4 and TAM2. Further analysis by deriphatic polyacrylamide gel electrophoresis followed by densitometry revealed a significant reduction in the light-harvesting complex II and a reduction by ∼50% in PSI/PSII. This reduction in the antenna complex of the TAM2 mutant resulted in a nearly 30% increase in biomass yield under laboratory conditions and in outdoor photobioreactors [92].