Tetzuya Katoh

Calculation of the excitation transfer matrix elements between the S2 or S1 state of carotenoid and the S2 or S1 state of bacteriochlorophyll

Formalism of the excitation transfer matrix element applicable for any multiconfigurational wave functions is made. On the basis of the resultant formulas, the excitation transfer matrix elements between the S2 or S1 state of a carotenoid, neurosporene, and the S2 or S1 state of bacteriochlorophyll a are calculated at various stacked configurations of the two molecules. The results show that the excitation transfer from the carotenoid S1 state to the bacteriochlorophyll S1 state via the Coulomb mechanism including multipole–multipole interactions takes place very efficiently in a speed more rapid than that via the electron‐exchange mechanism. The results also show that the excitation transfer from carotenoid to bacteriochlorophyll occurs directly from the carotenoid S2 state, as well as from the carotenoid S1 state. Furthermore, it is shown that the excitation transfer matrix element due to the electron‐exchange interaction has an oscillatory dependence on the displacement of one molecule from the other w...

Carotenoids in photosynthesis: absorption, transfer and dissipation of light energy

The functioning of carotenoids in photosynthesis is discussed in relation to the reaction mechanism. The energy transfer process from the allenic carotenoid, fucoxanthin, to chl a was intensively investigated in the newly isolated fucoxanthin-chl a/c protein assembly (FCPA) from a brown alga Dictyota dichotoma. The transfer time was shorter than 3 ps at 15°C. The energy level responsible for transfer may not be the Qx band of chl a, contrary to the proposal for the transfer in the bacterial antenna system.

Light-harvesting particles isolated from a brown alga, Dictyota dichotoma. A supramolecular assembly of fucoxanthin-chlorophyll-protein complexes

Using a new type of detergent, decylsucrose, light-harvesting pigment proteins of a brown alga, Dictyota dichotoma , were isolated as brown-colored particles (17.1 S). They are supramolecular assemblies consisting of 7 units of 4.8 S fucoxanthin-chlorophyll a/c protein complexes, but theirmolecular association is rather unstable, and they are readily dissociated to the 4.8 S complexes. The 4.8 S complexes have a very high pigment content (0.37 mg/mg protein); 10 fucoxanthin, 1 violaxanthin, 3 chlorophyll c and 13 chlorophyll a being confined in a 54 kDa protein to form a 4.8 S pigment-protein (molecular weight 74 · 10 3 ). In the intact assemblies, excitation energy migrates through two separate paths, from fucoxanthin to chlorophyll a and from chlorophyll c to chlorophyll a , both with the efficiencies as high as from chlorophyll a itself. Fucoxanthin and chlorophyll a are assumed to form donor-acceptor couples at a 1:1 ratio, and this would probably be the case for chlorophyll c and chlorophyll a . On contact with Triton X-100 (0.01%), these particles were dissociated into component proteins with a concomitant blue-shift of fucoxanthin, and consequent breakdown of the coupling between fucoxanthin and chlorophyll a .

Molecular structure and optical properties of carotenoids for the in vivo energy transfer function in the algal photosynthetic pigment system

Common fluorescence properties of carotenoids functioning as an efficient antenna in algal pigment systems are elucidated in relation to their molecular structure. Those carotenoids contain eight conjugated double bonds and one keto group associated with the double bond. The origin of the fluorescence is the optically forbidden S 1 state and its radiative lifetime is longer than that of carotenoids without a keto group. These characteristics are discussed in relation to the excited state of polyenes.

Spatial arrangement of pigments and their interaction in the fucoxanthin-chlorophyll ac protein assembly (FCPA) isolated from the brown alga Dictyota dichotoma. Analysis by means of polarized spectroscopy

Molecular interaction and energy transfer between pigments in the fucoxanthin-chlorophyll (Chl) ac protein assembly (FCPA) isolated from the brown alga Dictyota dichotoma was investigated mainly by polarized spectroscopy. FCPA consists of 7 identical units of 54 kDa apoprotein, each of them containing 13 Chl a, 3 Chl c, 10 fucoxanthin and 1 violaxanthin. Spectral heterogeneity was found in the component pigments; two types of Chl a (Chl a673 and Chl a669), two types of Chl c (Chl cl, long-wavelength form of Chl c and Chl cs, short-wavelength form). In fucoxanthin, two functionally active and one inactive species were found. Energy flow in the FCPA is attained by a direct coupling of donor-acceptor pair and those are classified into four types: from fucoxanthin to Chl a669, from fucoxanthin to Chl a673, from Chl cl to Chl a669 and from Chl cs to Chl a669. The number of those four pathways was estimated to be 7, 2, 2 and 1, respectively, per unit peptide. Energy migration in the Chl a molecules is always functioning. Dissociation of FCPA into unit peptides induces the uncoupling of energy transfer between the respective donor and acceptor Chl a. The spatial orientation of individual pigments, investigated by linear dichroism and polarized fluorescence spectroscopy, was shown to be favorable for an efficient energy transfer. Based on the results of polarized spectroscopy, a spatial orientation of individual chromophores in the peptide was proposed.

Excitation energy transfer in phycobilisomes at −196°C isolated from the cyanobacterium Anabaena variabilis (M-3): evidence for the plural transfer pathways to the terminal emitters

Excitation energy transfer in phycobilisomes at −196°C was studied by means of the time-resolved fluorescence spectroscopy in the picosecond time-range. Supplemental data were obtained from the allophycocyanin-core complex. When the phycobilisomes were excited at 580 nm, at leastnine fluorescence components were resolved by the time-resolved spectra and deconvolution of thosespectra. Energy transfer among these components is not straightforward. At the phycocyanin level, two transfer pathways are probable; one may be among the β-155 chromophores, and another among α-84 chromophores along the long axis of the phycobilisome rods. The β-84 chromophores in intermediate discs of the rods might function as an energy pool by a fast equilibrium between αa-84 and β-84 chromophores. The β-84 chromophores in the trimer next to the core-complex is the energy donor to the core-complex. At allophycocyanin level, two pathways of the energy transfer were also found; one from F660 to F686 through the F673. This corresponds to the energy flow from β-84 chromophore without linker to 18.3 kDa polypeptide and finally to the ‘anchor’ polypeptide. The other pathway is from the F666 to F680, i.e., from the β-84 with a linker polypeptide to the α-subunit of allophycocyanin B. Two independent pathways in the energy transfer shown in this study basically agreewith the assembly model of the core components proposed by Glazer (cf. Biochim. Biophys. Acta 768 (1984) 29–51).

Fluorescence properties of the allenic carotenoid fucoxanthin: Implication for energy transfer in photosynthetic pigment systems

The fluorescence spectrum of an allenic carotenoid, all-trans-fucoxanthin isolated from a brown alga, has been reported for the first time. This carotenoid is known to function efficiently as a primary photosynthetic antenna pigment in marine algae. The emission bands were located around 630, 685 and 750 nm in CS2 at 20°C, absorption bands being located at 448, 476 and 505 nm. The energy difference between the 0-0 bands of absorption and emission spectra was about 3900 cm-1 and location of the emission maximum was less sensitive to the polarizability of solvents than that of the absorption maximum. These clearly indicate that the emission originates from the optically forbidden singlet state (2Ag). This is in contrast to other carotenoids whose emission is assigned to 1Bu state, probably due to the symmetric structure of the conjugated double bond responsible for the absorption in the visible region. A rapid internal conversion from 1Bu to 2Ag state might be facilitated by distorted structure of the conjugated double bond of fucoxanthin. The energy level responsible for the emission is almost identical to the Qy level of the acceptor molecule (Chl a), thus we propose an energy transfer pathway from the optically forbidden 2Ag state of the carotenoid to the Qy transition of Chl a in algal pigment systems.

A novel peridinin—chlorophyll a protein (PCP) from the marine dinoflagellate Alexandrium cohorticula: A high pigment content and plural spectral forms of peridinin and chlorophyll a

A new type of peridinin—chlorophyll a protein (PCP) was isolated from the marine dinoflagellate Alexandrium cohorticula. Unlike previous studies, PCP was obtained as a single component in the presence of a protease inhibitor. The monomer had a molecular mass of 37 kDa with 12 peridinin molecules associated with 2 chl a molecules. This pigment content was much higher than that reported previously. We observed a partial amino acid sequence of the N‐terminus that is novel among photosynthetic pigment—protein complexes. Magnetic circular dichroism clearly indicated that chl a in PCP had monomeric features. Multiple spectral components were suggested for both chl a and peridinin. Based on the high pigment content, the optical properties were compared with those for a reported PCP containing 4 chl a and 1 peridinin.

Direct measurement of the low-lying singlet excited (2 1Ag) state of a linear carotenoid, neurosporene, in solution☆

Abstract The forbidden singlet excited (2 1Ag) state of a linear carotenoid, neurosporene, in solution was directly detected by a single-proton absorption spectrum at 20°C. The absorption maximum in n-hexane was located at 623 ± 2 nm with its extinction coefficient of about 60 and an oscillator strength of 3.4 × 10−4. This is the first identification of the S1 state of long polyenes by the single-photon absorption spectroscopy, which leads to understanding of the excited stae of polyenes by using parameters directly obtained by absorption spectrum.

The effect of molecular structure on the relaxation processes of carotenoids containing a carbonyl group

Abstract Relaxation processes of the singlet excited states of carotenoids containing a carbonyl group were investigated in relation to the molecular structure around the carbonyl group. The relative quantum yield of fluorescence from the allowed S2 state to the forbidden S1 state follows the energy gap law of internal conversion. Further, increase in the fluorescence yield from the S1 state was strongly correlated with increase in the degree of conjugation of a carbonyl group to polyene chain. These were discussed in relation to (1) the coplanarity of π-electron system including a carbonyl group in the ground state and (2) the nature of transition and the molecular structure in the excited states.