Antenna function

The sol-gel co-immobilization of a non-fluorescent blue indicator bromothymol blue (BTB) with an europium (Ill)-complex intense antenna mediated lanthanide dye represents a new scheme for the fluorescence analysis38. Luminescence spectra of europium (Ill)-complex shown in Figure 12 were found to be independent of pH changes in the range 1-10. Therefore, BTB, a non-fluorescent pH indicator with alkaline absorption maximum close to main europium emission band was added to the sol-gel mixture to shield reversibly the emission of the europium (Ill)-complex at different pH s without quenching of the antenna function. 

Li and coworkers49 reported a molecular motion of /1-carotene and a carotenopor-phyrin dyad (composed of a porphyrin, a trimethylene bridge and a carotenoid polyene) in solution. Internal rotational motions in carotenoid polyenes and porphyrins are of interest because they can mediate energy and electron transfer between these two moieties when the pigments are joined by covalent bonds. Such internal motions can affect the performance of synthetic model systems which mimic photosynthetic antenna function,... 

The two cationic dyes, Py+ as a donor and Ox" as an acceptor, were found to be very versatile for demonstrating photonic antenna functionalities for light harvesting, transport, and capturing, as illustrated in Fig. 7. They can be incorporated into zeolite L by means of ion exchange, where they are present as monomers because of the restricted space. In this form they have a high fluorescence quantum yield and favourable spectral properties. The insertion of the dyes can be visualised by means of fluorescence microscopy. The fluorescence anisotropy of Ox -loaded zeolite L has recently been investigated in detail by conventional and by confocal microscopy techniques [15],... 

These two molecules were the antecedents of a variety of oligomeric porphyrin and chlorophyll derivatives which were constructed as mimics of the reaction center special pair. Many of these systems exhibit interesting optical properties which allow modelling of the electronic interactions within the special pair and/or the antenna function of chlorophyll, which involves singlet-singlet energy transfer... 

Energy transfer studies of 11 and related molecules demonstrated that the carotenoid moiety is active in antenna function (singlet-singlet energy transfer) and photoprotection (triplet-triplet energy transfer) in these molecules, just as it is in natural reaction centers [51, 62]. 

The core complex (CC 1, CP 1) with RC P700 (10-65 BChl a, 1-2 )3-carotenes found in various preparations of pea, spinach, barley and C. reinhardtii) contains two main types of polypeptides (60-70 kDa) and small amounts of three to five polypeptides of unknown function (some may also have an antenna function) [165,186]. The relatively large number of bound Chi a molecules in the core com-... 

We shall begin with a brief description of natural photosynthetic electron transfer, and then discuss some of the simplest man-made devices which attempt to mimic this process. We shall see how these devices have evolved into more complicated molecular constructions which are much more successful. The preparation and study of synthetic species which mimic photosynthetic antenna function will then be reviewed. Finally, model systems which have provided insight into the process whereby carotenoid... 

Thus, chlorophyll-based triad species can also successfully mimic the multistep strategy of natural photosynthesis to yield long-lived, energetic charge-separated states. Triad 13 and related molecules also mimic carotenoid photoprotection from singlet oxygen and carotenoid antenna function. These aspects of the molecules will be discussed in later sections. 

The LHC 11 antenna functionally exists as either an inner or a more peripheral component. An inner ( i, also called bound ) LHC II contains exclusively the 27-kDa apoprotein and is located closer to the PS-11 reaction center. The other, more peripheral or ijuter complex ( o, also called mobile ) contains... 

W Ortiz, E Lam, M Ghirardi and R Malkin (1984) Antenna function of a chlorophyll alb protein complex of photosystem I. Biochim Biophys Acta 766 505-509... 

Most of the proteins of PS II are embedded within the photosynthetic membrane although portions are exposed to the aqueous media on the inside and on the outside of the membrane. A fully developed PS II is composed of hundreds of Chi a and Chi b molecules, carotenoids, plastoquinones (Figure 1), a-tocopheryl quinone or a-tocopherol, cytochrome b-559, the Mn-protein responsible for O2 evolution, and other electron transport agents. The diameter of a fully-developed PS II has been estimated at 160 A from electron micrographs of freeze-fractured photosynthetic membranes (46). The bulk of the chlorophyll molecules in PS II have only an antenna function, i.e., they absorb photons (reaction 1) and transfer the resultant electronic... 

Heptakis 6-0-t-butyldimethylsilyl-P-cyclodextrin, on reaction with 4-chloro-methyl-A -methyl-2-nitroaniline, affords the mono-3-substituted benzyl ether. P-Cyclodextrin carrying a 2-(naphthylmethyl) group at 0-6 exists with the aromatic rings within the cavity to an extent which is very temperature dependent. Temperature can therefore be used to control the degree of complexing of the aromatic system with a fluorescent naphthalene compound. Heptakis-[2,3-di-0-acetyl-6-deoxy-6-iodo]-P-cyclodextrin treated with 6-methoxycarbonyl-2-naphthol allowed access to the compound having naphthoic acid substituents at all of the primary positions, and this forms a very stable 1 1 complex with a merocyanine laser dye which is a mimic of the antenna function in photosynthesis and shows promise as a photochemical microreactor. Mono-[6-0-(8-qui-nolyl)]-P-cyclodextrin has been reported, and the stabilities of inclusion complexes with amino acid guests have been described. ... 

Nagata, N. Kugimiya. S. Kobuke. Y. Antenna functions of 5,15- i5(imidazol-4-yl)-10,20- i5(4-dodecyloxy-phenyl)-porphyrin supramolecular assembly through imidazole-imidazole hydrogen bonding. Chem. Commun. 2000, (15), 1389-1390. 

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