Carotenoid interactions between

NPQ (Rakhimberdieva et al. 2004) exactly matches the absorption spectrum of the carotenoid, 3 -hydrox yech i nenone (Polivka et al. 2005) in the OCP. The OCP is now known to be specifically involved in the phycobilisome-associated NPQ and not in other mechanisms affecting the levels of fluorescence such as state transitions or D1 damage (Wilson et al. 2006). Studies by immunogold labeling and electron microscopy showed that most of the OCP is present in the interthylakoid cytoplasmic region, on the phycobilisome side of the membrane, Figure 1.2 (Wilson et al. 2006). The existence of an interaction between the OCP and the phycobilisomes and thylakoids was supported by the co-isolation of the OCP with the phycobilisome-associated membrane fraction (Wilson et al. 2006, 2007). 

While excited-state properties of monomeric carotenoids in organic solvents have been the subject of numerous experimental and theoretical studies (Polfvka and Sundstrom 2004), considerably less is known about excited states of carotenoid aggregates. Most of the knowledge gathered so far stems from studies of aggregation-induced spectral shifts of absorption bands of carotenoid aggregates that are explained in terms of excitonic interaction between the molecules in the aggregate. 

The aggregation-induced changes of absorption spectra result from intermolecular interactions between closely spaced carotenoid molecules. For two molecules whose transition dipole moment vectors, p, are located at places characterized by position vectors /- and r2, with the relative position vector defined as R=r1-r2, Figure 8.3, the interaction energy is expressed as (van Amerongen et al. 2000)... 

Carotenoid radical formation and stabilization on silica-alumina occurs as a result of the electron transfer between carotenoid molecule and the Al3+ electron acceptor site. Both the three-pulse ESEEM spectrum (Figure 9.3a) and the HYSCORE spectrum (Figure 9.3b) of the canthaxanthin/ A1C13 sample contain a peak at the 27A1 Larmor frequency (3.75 MHz). The existence of electron transfer interactions between Al3+ ions and carotenoids in A1C13 solution can serve as a good model for similar interactions between adsorbed carotenoids and Al3+ Lewis acid sites on silica-alumina. 

D is the dipole-dipole interaction between the slow relaxing carotenoid radical and the fast relaxing Ti3+ ion r is the interspin distance... 

FIGURE 17.4 Interactions between carotenoids during their transport through Caco-2 cell monolayers, (a) a-C effect on 3-C transport, (b) 3-C effect on a-C transport, (c) LUT effect on P-C transport, (d) P-C effect on LUT transport, (e) LYC effect on P-C transport, and (f) P-C effect on LYC transport. Data with error bars are mean + SD obtained from three or more independent experiments ( P < 0.05 compared with the carotenoid alone). (Modified from During, A. et al., J. Lipid Res., 43, 1086, 2002.)... 

Interaction between carotenoids-rich micelles and enterocyte... 

Hill TJ, Land EJ, McGarvey DJ, Schalch W, Tinkler JH, Truscott TG. (1995) Interactions between carotenoids and the CCl Oj radical. J Amer Chem Soc, 117 8322-8326. 

Triplet energy transfer from chlorophyll to carotenoid is not mechanistically anomalous. The dominant term describing the interaction between the donor triplet and the acceptor is an electron exchange integral, the magnitude of which depends directly on the overlap between the donor and acceptor n-... 

On the other hand, carotenoids in light-harvesting complexes of photosynthetic bacteria assume an all-trans configuration, either twisted (as in Rs. rubrum, Chromatium vinosum, md Rp. palustris) or planar (as in Rb. sphaeroides and Rp. capsulata). Note that chain twisting is not ascribed to the type of carotenoid, but rather to some specific interaction between the carotenoid and the protein environment and apparently affects the efficiency of singlet energy transfer. 

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