Co-reporter:Xiao-Feng Wang;Haoshen Zhou;Osamu Kitao;Shin-ichi Sasaki
The Journal of Physical Chemistry C May 7, 2009 Volume 113(Issue 18) pp:7954-7961
Publication Date(Web):Publication Date (Web): April 10, 2009
DOI:10.1021/jp900328u
Two dye sensitizers, methyl trans-32-carboxy-8-deethyl-7-ethyl-8-oxo-pyropheophorbide-a (BChlorin-1) and methyl trans-32-carboxy-7-demethyl-8-methyl-7-oxo-pyropheophorbide-a (BChlorin-2), with stable bacteriochlorin skeletons were synthesized and applied to dye-sensitized solar cells. Both sensitizers absorb the light all over the visible region owing to partial saturation of the two pyrrole rings on the Qx transition dipole. When they were deposited on a TiO2 film, the J-aggregates of the sensitizers are partially formed to give broad and red-shifted Qy bands. The surface coverage of TiO2 film by BChlorin-2 is much larger than by BChlorin-1, suggesting the former sensitizer forms more serious aggregation on the surface of TiO2, and this could cause more exciton annihilation to reduce the photocurrent of solar cell. The frontier molecular orbitals of both sensitizers obtained from the DFT calculations show no distinguishable difference. Extended calculations on the dye−TiO2Na model system suggest that additional LUMO + 2 orbital in BChlorin-1 may also contribute to the difference in photocurrent. The larger photovoltage in BChlorin-1 sensitized solar cell was attributed to a less efficient charge recombination in the dye−TiO2 interface to give a longer electron lifetime (τ). Additional 4-tert-butylpyridine in the electrolyte significantly reduced the photocurrent and the solar energy-to-electricity conversion efficiency (η) of the solar cells, especially when BChlorin-2 was employed as a sensitizer. This dramatic decrease was attributed to the shift of conduction band edge (CBE) of TiO2 to a negative potential above the molecular Fermi level (MFL) of the sensitizers and suppressed the electron injection from the MFL of sensitizer to CBE of TiO2. Coadsorption of BChlorin-1 with chenodeoxycholic acid (CDCA) could break the dye aggregate and improve the incident photon-to-current conversion efficiency at the absorption bands maxima. BChlorin-1 sensitized solar cells coadsorbed with CDCA gave a longer electron lifetime and a larger diffusion coefficient than the cell without CDCA. By coadsorbing with 5 mM CDCA in solution, the BChlorin-1 sensitized solar cell gave a highest performance with short-circuit photocurrent = 18.4 mA cm−2, open-circuit photovoltage = 0.54 V, fill factor = 0.66, and η = 6.6% under the air mass AM 1.5 (100 mW cm−2) illumination.
Co-reporter:Hitoshi Tamiaki, Yukihiro Okamoto, Yuji Mikata and Sunao Shoji
Photochemical & Photobiological Sciences 2012 vol. 11(Issue 6) pp:898-907
Publication Date(Web):02 Dec 2011
DOI:10.1039/C1PP05301A
Photoreaction of zinc methyl 20-substituted meso(pyro)pheophorbide-a prepared by modifying naturally occurring chlorophyll-a in the presence of oxygen molecules gave its C19–C20 oxidative cleavage (1-carbonyl-19-oxo-bilatrienes) as the major products and the regioisomeric C1–C20 cleavage (19-carbonyl-1-oxo-bilatrienes) as the minor products. The resulting zinc complexes of linear tetrapyrroles took a helical conformation and the P-conformers were preferential over the M-stereoisomers due to the presence of their 17S,18S-chiral centers. The helical conformers (diastereomers) of the corresponding nickel complexes were separated by reverse-phase or chiral HPLC and their conformational changes were observed in solution.
Co-reporter:Hitoshi Tamiaki;Hiroshi Takebe;Shin-ichi Sasaki
Photosynthesis Research 2012 Volume 111( Issue 1-2) pp:1-8
Publication Date(Web):2012 March
DOI:10.1007/s11120-010-9616-y
Methyl pheophorbide-a/a′ derivatives covalently linked with oligomethylene chains at the 3-CH2OCO– and 132-COO– moieties in a molecule were prepared by modifying chlorophyll-a through intramolecular ring-closing metathesis of vinyl groups. At least, a C10-length between the 33- and 134-positions was necessary for the cyclization and connection of a C12-strap was the most suitable to achieve the highest closure yield. The oligomethylene chain in 132R-epimers derived from methyl pheophorbide-a covered the α-face of the chlorin π-plane and the strap in the corresponding 132S-epimers protected the β-face. Synthetic 132R-epimer with a dodecamethylene chain gave a flat chlorin π-plane, while the decamethylene chain in the 132R-epimer distorted the π-system due to its shorter linkage. The distortion by strapping in the 132R-epimer induced a slight blue-shift of Qy peak in dichloromethane. CD spectra of the 132R-epimers were similarly dependent on the chain length, i.e., the distortion of π-plane. Visible absorption and CD spectra of all the strapped 132S-epimers were almost identical and only slightly different from those of the unstrapped. The strapping in the 132S-epimers shifted the Qy peak bathochromically.
Co-reporter:Hitoshi Tamiaki, Daisuke Takekoshi, Tadashi Mizoguchi
Bioorganic & Medicinal Chemistry 2011 Volume 19(Issue 1) pp:52-57
Publication Date(Web):1 January 2011
DOI:10.1016/j.bmc.2010.11.056
3,8-Divinyl-chlorophyll(Chl)-a possessing a phytyl ester was hydrogenated in acetone by rhodium catalyst on alumina to afford 3-vinyl-8-ethyl-, 3-ethyl-8-vinyl- and 3,8-diethyl-Chls. The ratio of produced 3-ethyl-8-vinyl- over 3-vinyl-8-ethyl-Chls was determined to be 1.2, indicating that the reactivity of the 3-vinyl group was slightly higher than that of the 8-vinyl group. Catalytic hydrogenation of divinyl-protochlorophyll-a possessing a porphyrin π-skeleton (C17C18) instead of the above chlorin moiety (C17H–C18H) gave an equal amount of mono-reduced regioisomers. The slight (or no) selectivity is different from that in the enzymatic reduction of divinyl-(proto)chlorophyllides-a lacking a phytyl ester in the biosynthetic pathway of Chl-a where the sole 8-vinyl group is transformed to the ethyl group.
Co-reporter:Tadashi Mizoguchi, Taichi Yoshitomi, Jiro Harada, and Hitoshi Tamiaki
Biochemistry 2011 Volume 50(Issue 21) pp:
Publication Date(Web):April 21, 2011
DOI:10.1021/bi2002339
The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum (previously known as Chlorobium tepidum), which grows at an optimal temperature of around 45 °C, biosynthesized unique disaccharide rhamnosylgalactosyldiacylglyceride (RGDG) having a methylene-bridged palmitoleyl (17:Cyc) and a palmitoyl group (16:0) as the two acyl chains in a molecule [RGDG(17:Cyc,16:0)], together with the corresponding monosaccharide monogalactosyldiacylglyceride (MGDG). Here, we report changes in the structure and composition of the glycolipids that are dependent upon the temperature and period of cultivation. With a decrease in temperature to 25 °C, the two major glycolipids were almost completely eliminated, and MGDG with a palmitoleyl (16:1) and a (16:0) group concomitantly became the major glycolipid. MGDG(16:1,16:0) corresponded to the removal of an α-rhamnosyl and a cyclopropyl methylene group from RGDG(17:Cyc,16:0) and the lack of the CH2 group in MGDG(17:Cyc,16:0). The structural conversion was almost reversible when the Cba. tepidum adapted to low and high temperatures was cultured again at 45 and 25 °C, respectively. Moreover, during this cultivation, the structure and composition of glycolipids were sequentially changed: MGDG(16:1,16:0), MGDG(17:Cyc,16:0), and RGDG(17:Cyc,16:0) predominated in the exponential, stationary and late phases of the cultivation, respectively. On the basis of these time-dependent changes, the unique disaccharide RGDG(17:Cyc,16:0) was thought to be created by the site-specific transfer of an α-rhamnosyl group to MGDG(17:Cyc,16:0) after insertion of a methylene group into the precursor MGDG(16:1,16:0). These culturing temperature- and time-dependent changes in glycolipids at the molecular level allow us to discuss their biosynthesis as well as physiological function in green photosynthetic bacteria.
Co-reporter:Toru Oba, Yuki Uda, Kohei Matsuda, Takanori Fukusumi, Satoshi Ito, Kazuhisa Hiratani, Hitoshi Tamiaki
Bioorganic & Medicinal Chemistry Letters 2011 Volume 21(Issue 8) pp:2489-2491
Publication Date(Web):15 April 2011
DOI:10.1016/j.bmcl.2011.02.054
The C3-vinyl group of a chlorophyll derivative, methyl pyropheophorbide-a, was converted into the formyl group by a novel one-pot reaction with thiophenol at room temperature. The mild reaction can provide insight into development of ‘green’ catalysts displacing OsO4 or O3, and into elucidation of unknown biosynthetic processes of chlorophyll-d.A chlorophyll-a derivative (3-vinyl-chlorin) was smoothly converted into the corresponding chlorophyll-d derivative (3-formyl-chlorin) under mild conditions: treatment with thiophenol in an acidic solution at room temperature.
Co-reporter:Xiao-Feng Wang ; Li Wang ; Naoto Tamai ; Osamu Kitao ; Hitoshi Tamiaki ;Shin-ichi Sasaki
The Journal of Physical Chemistry C 2011 Volume 115(Issue 49) pp:24394-24402
Publication Date(Web):November 1, 2011
DOI:10.1021/jp206206x
Purpurin sensitizers with and without the central zinc, ZnP and H2P, have been synthesized and used in dye-sensitized solar cells. Both the sensitizers readily formed aggregates on the semiconductor surface. The DFT and TD-DFT calculations suggest that the major difference between the two sensitizers is ascribable to the energy levels of their four molecular orbitals. With biased potential in the solid-state photovoltaic diodes, the photoresponse of ZnP and H2P started from −2 and −2.5 V, respectively, and the observed difference is in agreement of the difference of calculated LUMO energy level for the two sensitizers. ZnP gave much better photovoltaic performance than H2P, when TiO2 electrode and 4-tert-butylpyridine (TBP)-free electrolyte were employed. The decrease of photocurrent of ZnP-based solar cell in TBP-containing electrolyte is attributed to the change in energy level of the electron acceptor, while that of H2P-based solar cell in TBP-containing electrolyte is ascribed to the change of electron donor state. The replacement of TiO2 with SnO2 substantially improved the photocurrent of solar cells because the electron injection from LUMO orbital of the dye sensitizers becomes favorable. A clear observation of photocurrent generation from the dye aggregate suggests that the photon-generating excitons can diffuse over the dye aggregate and finally reach the semiconductor surface. TBP in electrolyte can disturb the dye aggregation, and this will reduce the possibility of exciton annihilation in dye layer, which was supported by the sub-picosecond time-resolved absorption spectra.
Co-reporter:Shin-ichi Sasaki, Keisuke Mizutani, Michio Kunieda, Hitoshi Tamiaki
Tetrahedron 2011 67(33) pp: 6065-6072
Publication Date(Web):
DOI:10.1016/j.tet.2011.06.020
Co-reporter:Yukihiro Okamoto, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology A: Chemistry 2011 Volume 219(2–3) pp:250-254
Publication Date(Web):15 April 2011
DOI:10.1016/j.jphotochem.2011.02.027
Co-reporter:Hitoshi Tamiaki;Jun Komada;Michio Kunieda;Kazuhiro Fukai
Photosynthesis Research 2011 Volume 107( Issue 2) pp:133-138
Publication Date(Web):2011 February
DOI:10.1007/s11120-010-9603-3
Bacteriochlorophyll(BChl)-f which has not yet been found in natural phototrophs was prepared by chemically modifying chlorophyll-b. The retention time of reverse-phase high-performance liquid chromatography of the synthetic monomeric BChl-f as well as its visible absorption and fluorescence emission spectra in a solution were identified and compared with other naturally occurring chlorophyll pigments obtained from the main light-harvesting antenna systems of green sulfur bacteria, BChls-c/d/e. Based on the above data, BChl-f was below the level of detection in three strains of green photosynthetic bacteria producing BChl-e.
Co-reporter:Xiao-Feng Wang and Hitoshi Tamiaki
Energy & Environmental Science 2010 vol. 3(Issue 1) pp:94-106
Publication Date(Web):09 Nov 2009
DOI:10.1039/B918464C
In this Perspective, recent progress on dye-sensitized solar cells (DSSCs) based on cyclic tetrapyrrole type sensitizers including porphyrins, (bacterio)chlorins, and phthalocyanines has been reviewed. Cyclic tetrapyrrole type molecules have been studied extensively with respect to their photochemical and photophysical properties as well as to various applications. The photophysical properties of tetrapyrrole molecules can be readily controlled upon molecularly structural modification. Their low-lying singlet states are also suitable for studying excited state dynamics in the electron donor–acceptor systems. Here, we selected the most representative porphyrin, (bacterio)chlorin, and phthalocyanine sensitizers to discuss how those structural modifications on the cyclic tetrapyrrole rings affect the performance of DSSCs. The most important factors that strictly determine the power conversion efficiencies of DSSCs based on tetrapyrrole type sensitizers are also discussed in detail.
Co-reporter:Shin-ichi Sasaki;Mari Yoshizato;Michio Kunieda
European Journal of Organic Chemistry 2010 Volume 2010( Issue 27) pp:5287-5291
Publication Date(Web):
DOI:10.1002/ejoc.201000541
Abstract
C3-vinyl and C13-keto-carbonyl groups of methyl pyropheophorbide-a, a chlorophyll-a derivative, were systematically modified to investigate the substituent effects along the y-axis of chlorin macrocycles. C131 deoxygenation resulted in blueshifts of the Qy absorption maxima and a large reduction of their redox potentials, whereas introduction of the dicyanomethylene group at the 131-position caused the opposite effect on both optical and electrochemical properties. Among the nine chlorins examined, the Qy peak positions could be varied from 647 to 736 nm by the cooperative effects of the diagonal substituents' combinations.
Co-reporter:Tadashi Mizoguchi;Yuki Kimura
Photochemistry and Photobiology 2010 Volume 86( Issue 2) pp:311-315
Publication Date(Web):
DOI:10.1111/j.1751-1097.2009.00667.x
Abstract
Chiral high-performance liquid-chromatography (HPLC) for quantitative analysis of optically active chlorophyll(Chl)-c molecules, which are seen in many marine photosynthetic organisms, was developed. Chls-c have a single asymmetric carbon at the 132-position, so their stereoisomers are (132R)- and (132S)-enantiomers. After the separation of each enantiomer, the stereochemistry was unambiguously characterized using its circular dichroism spectrum in comparison with that of the structure-related compound, protochlorophyllide-a. Moreover, Chls-c were carefully extracted from the cells of a diatom Chaetoseros calcitrans without racemization and were subjected to the chiral HPLC. The results clearly demonstrated that naturally occurring Chl-c molecules are enantiomerically pure (132R)-forms, which are generally found in photosynthetically active chlorophyllous pigments.
Co-reporter:Hitoshi Tamiaki, Shingo Tateishi, Shosuke Nakabayashi, Yutaka Shibata, Shigeru Itoh
Chemical Physics Letters 2010 Volume 484(4–6) pp:333-337
Publication Date(Web):7 January 2010
DOI:10.1016/j.cplett.2009.12.018
Abstract
Absorption spectra of chlorosomes isolated from several species of photosynthetic green sulfur bacteria using linearly polarized light were measured in a compressed polyacrylamide gel at three-dimensional geometric orientations. Chlorosomes containing self-aggregates of bacteriochlorophyll(BChl)-e gave two distinct Soret absorption peaks, which were assigned to By and Bx bands at longer and shorter wavelengths, respectively. The transition dipole of By band was determined to be parallel to the long axis of ellipsoid-shaped chlorosomes, while that of Bx parallel to the short axis. Analysis of linear dichroism and polarization degrees supported the above orientation, while the alignment of Bx transition dipoles was limited. The features are also observed in chlorosomes having BChls-c and d. The absorption bands in the Soret region by linearly polarized light are shown for the first time to be useful for the investigation of supramolecular structures of chlorosomal self-aggregates, as in the redmost Qy bands reported earlier.
Co-reporter:Xiao-Feng Wang, Hitoshi Tamiaki, Li Wang, Naoto Tamai, Osamu Kitao, Haoshen Zhou and Shin-ichi Sasaki
Langmuir 2010 Volume 26(Issue 9) pp:6320-6327
Publication Date(Web):April 9, 2010
DOI:10.1021/la1005715
Five chlorophyll-a derivatives, chlorins-1−5 possessing C32-carboxy and O174-esterified hydrocarbon groups including methyl, hexyl, dodecyl, 2-butyloctyl, and cholesteryl were synthesized. Their performance as sensitizers in dye-sensitized solar cells (DSSCs) was compared. These sensitizers have similar surface coverage on the unit surface of TiO2 film and their absorption spectra on transparent TiO2 films were identical. On the basis of DFT and TD-DFT calculations of these sensitizers in ethanol, a major difference between them was the geometry of the hydrocarbon ester group, to affect their electron injection and charge recombination with the TiO2 electrode rather than the energy level of their molecular orbitals. DSSC based on chlorin-3 with a dodecyl ester group gave a solar energy-to-electricity conversion efficiency of 8%, which was the highest among all the chlorophyllous sensitizers. The large photocurrent in the chlorin-3 sensitized solar cell can be explained by the least impedance in the electrolyte−dye−TiO2 interface in electrical impedance spectroscopy measurements. Subpicosecond time-resolved absorption spectroscopic studies have also been carried out to evaluate the electron injection and charge recombination dynamics in the dye−TiO2 interface. For the electron injection and charge recombination processes, a charge separated state of the dye−TiO2 complex has been found to be free from the type and concentration of dye sensitizer, reflecting the same type of electron transfer process for all the five chlorin sensitizers. A new quenching pathway of the dye excitation, which is probably from the exciton annihilation, in addition of the charge recombination has been observed for chlorin-1 and chlorin-5, but not for chlorin-3. The higher open-circuit photocurrent observed in the present dyes with larger ester groups can be attributed to the reduced leaking of charges in the TiO2−electrolyte interface, which was supported by the longer electron lifetimes.
Co-reporter:Hidetada Morishita;Tadashi Mizoguchi
Photosynthesis Research 2010 Volume 105( Issue 3) pp:257-263
Publication Date(Web):2010 September
DOI:10.1007/s11120-010-9590-4
The 3- and 7-formyl groups of chlorophyll-d (Chl-d) and bacteriochlorophyll-e (BChl-e), respectively, were regioselectively labeled with an isotopically stable oxygen-18 (18O) atom to give 31-18O-labeled Chl-d and 71-18O-labeled BChl-e (ca. 90% 18O) by exchanging the carbonyl oxygen atoms in the presence of acidic H218O (ca. 95% 18O). Another photosynthetically active chlorophyll, BChl-a possessing the 3-acetyl group was treated under similar acidic conditions to afford a trace amount of 31-18O-labeled BChl-a and further demetallated compound, the corresponding 31-18O-labeled bacteriopheophytin-a as the major product with 55% 18O-degree. The FT-IR spectra of 18O-(un)labeled chlorophylls in the solution and the solid states showed that the 3- and 7-carbonyl stretching vibration modes moved to about a 30-cm−1 lower wavenumber by 18O-labeling at the 31- and 71-oxo moieties. In artificial chlorosome-like self-aggregates of BChl-e, the 18O-labeled 7-carbonyl stretching mode was completely resolved from the specially hydrogen-bonded 13-C=O stretching mode, evidently indicating no interaction of the 7-CHO with other functional groups in the supramolecules.
Co-reporter:Hitoshi Tamiaki, Keishiro Ogawa, Keisuke Enomoto, Kazutaka Taki, Atsushi Hotta, Kazunori Toma
Tetrahedron 2010 66(9) pp: 1661-1666
Publication Date(Web):
DOI:10.1016/j.tet.2010.01.002
Co-reporter:Michio Kunieda, Kohei Yamamoto, Hitoshi Tamiaki
Tetrahedron 2010 66(6) pp: 1228-1235
Publication Date(Web):
DOI:10.1016/j.tet.2009.12.029
Co-reporter:Teodor Silviu Balaban ; Anil Dnyanoba Bhise ; Gerhard Bringmann ; Jochen Bürck ; Cyril Chappaz-Gillot ; Andreas Eichhöfer ; Dieter Fenske ; Daniel C. G Götz ; Michael Knauer ; Tadashi Mizoguchi ; Dennis Mössinger ; Harald Rösner ; Christian Roussel ; Michaela Schraut ; Hitoshi Tamiaki ;Nicolas Vanthuyne
Journal of the American Chemical Society 2009 Volume 131(Issue 40) pp:14480-14492
Publication Date(Web):September 21, 2009
DOI:10.1021/ja905628h
Diacylation of copper 10,20-bis(3,5-di-tert-butylphenylporphyrin) using Friedel−Crafts conditions at short reaction times, high concentrations of catalyst, and 0−4 °C affords only the 3,17-diacyl-substituted porphyrins, out of the 12 possible regioisomers. At longer reaction times and higher temperatures, the 3,13-diacyl compounds are also formed, and the two isomers can be conveniently separated by normal chromatographic techniques. Monoreduction of these diketones affords in good yields the corresponding acyl(1-hydroxyalkyl)porphyrins, which after zinc metalation are mimics of the natural chlorosomal bacteriochlorophyll (BChl) d. Racemate resolution by HPLC on a variety of chiral columns was achieved and further optimized, thus permitting easy access to enantiopure porphyrins. Enantioselective reductions proved to be less effective in this respect, giving moderate yields and only 79% ee in the best case. The absolute configuration of the 31-stereocenter was assigned by independent chemical and spectroscopic methods. Self-assembly of a variety of these zinc BChl d mimics proves that a collinear arrangement of the hydroxyalkyl substituent with the zinc atom and the carbonyl substituent is not a stringent requirement, since both the 3,13 and the 3,17 regioisomers self-assemble readily as the racemates. Interestingly, the separated enantiomers self-assemble less readily, as judged by absorption, fluorescence, and transmission electron microscopy studies. Circular dichroism spectra of the self-assemblies show intense Cotton effects, which are mirror-images for the two 31-enantiomers, proving that the supramolecular chirality is dependent on the configuration at the 31-stereocenter. Upon disruption of these self-assemblies with methanol, which competes with zinc ligation, only very weak monomeric Cotton effects are present. The favored heterochiral self-assembly process may also be encountered for the natural BChls. This touches upon the long-standing problem of why both 31-epimers are encountered in BChls in ratios that vary with the illumination and culturing conditions.
Co-reporter:Tadashi Mizoguchi, Chihiro Nagai, Michio Kunieda, Yuki Kimura, Atsushi Okamura and Hitoshi Tamiaki
Organic & Biomolecular Chemistry 2009 vol. 7(Issue 10) pp:2120-2126
Publication Date(Web):18 Mar 2009
DOI:10.1039/B900802K
Chlorophyll (Chl)-c1 and Chl-c2 were extracted from a commercially available diatom Chaetoseros calcitrans, and the former (8-ethyl) and the latter (8-vinyl) were efficiently separated by reverse-phase HPLC using a polymeric octadecylsilyl column to afford analytically pure compounds in an amount adequate for further chemical modification. The conformation of the unique acrylate moiety at the 17-position of isolated Chls-c in THF was unambiguously determined to be “cisoid” around the C17–C171 bond using 1H-1H NOE correlations: C171C172 was on the same side as C17C18. Interestingly, correlations originating from the “transoid” conformer could not be observed under the present NMR conditions, indicating that the rotation of the acrylate was considerably restricted. To elucidate the function of the rigid acrylate in Chls-c, we examined their electronic absorption properties using two synthetic types of esters possessing a porphyrin π-system: acrylate-type (17-CHCH–COOR) prepared by esterification of natural Chl-c1 and Chl-c2, and propionate-type (17-CH2–CH2–COOR) by 17,18-oxidation of natural Chl-a and its 8-vinyl analog. The Soret absorption bands at around 450 nm of the acrylate-type were red-shifted and broadened more than those of the propionate-type. Consequently, the unique acrylate in Chls-c serves as an aid for expanding the absorption region around 400–500 nm in order to capture intense irradiation from the sun for photosynthesis.
Co-reporter:QianMing Wang, Keishiro Ogawa, Kazunori Toma, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 201(2–3) pp:87-90
Publication Date(Web):25 January 2009
DOI:10.1016/j.jphotochem.2008.10.005
A luminescent hydrogel was successfully prepared by immobilizing an europium(III) tetrakis(β-diketonate) complex into a gallate-based hydrogelator. The Eu(III) emission in hydrogel media was switched reversibly “on-off” as a function of pH and the corresponding thermal and photostabilities dramatically increased compared with its solution sample.
Co-reporter:Hidetada Morishita, Hitoshi Tamiaki
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2009 Volume 72(Issue 2) pp:274-279
Publication Date(Web):March 2009
DOI:10.1016/j.saa.2008.09.016
Metal complexes of methyl 131-18O-labelled pyropheophorbide-a1-M–18O (M = Zn, Cu and Ni) were prepared by metallation of the 18O-labelled free base (1-18O) and 18O-labelling of unlabelled nickel complex (1-Ni). The FT-IR spectra of 1-Zn and 1-Zn–18O in CH2Cl2 showed that the 13-keto carbonyl stretching vibration mode moved to about a 30-cm−1 lower wavenumber by 18O-labelling of the 131-oxo moiety. In 1-Cu–18O and 1-Ni–18O, the 13-C18O stretching modes were close to the highest-energy wavenumber mode of chlorin skeletal C–C/C–N vibrations at around 1650 cm−1 and they were coupled in CH2Cl2 to give two split IR bands (Fermi resonance). A similar coupling was observed in the resonance Raman scattering of 1-Ni–18O in the solid state. The hydrogen-bonded 13-C16O vibration mode of 1-Ni similarly coupled with the skeletal C–C/C–N mode in CCl4 containing 1% (v/v) 1,1,1,3,3,3-hexafluoro-2-propanol, while such a coupling was not observed in a neat CCl4 solution of 1-Ni possessing the 13-C16O free from any interaction. The skeletal C–C/C–N band selectively coupled with the 13-CO, not with the 3-CO, when the difference in their peak maxima was less than 20 cm−1.
Co-reporter:Hitoshi Tamiaki, Yuki Kotegawa, Shin-ichiro Nitta, Shin-ichi Sasaki, Keisuke Mizutani
Tetrahedron 2009 65(3) pp: 628-637
Publication Date(Web):
DOI:10.1016/j.tet.2008.11.015
Co-reporter:Hitoshi Tamiaki, Ai Shinkai, Yumiko Kataoka
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 207(Issue 1) pp:115-125
Publication Date(Web):5 September 2009
DOI:10.1016/j.jphotochem.2009.01.008
Co-reporter:Tadashi Mizoguchi, Megumi Isaji, Jiro Harada and Hitoshi Tamiaki
Photochemical & Photobiological Sciences 2008 vol. 7(Issue 4) pp:492-497
Publication Date(Web):13 Mar 2008
DOI:10.1039/B719272J
Recently we isolated the purple photosynthetic bacterium, Rhodopseudomonas sp. Rits, which was phylogenetically related to Rhodopseudomonas (Rps.) palustris. In this study, the light-dependent and time-dependent changes in the carotenoid composition were investigated by HPLC analysis of extracts from the cultures. All seven carotenoids in the biosynthetic pathway from lycopene to spirilloxanthin were detected. Especially, 3,4-didehydrorhodopin, having twelve conjugated double bonds as well as one terminal hydroxy group, was isolated in a remarkably large amount and fully characterized for the first time. The biosynthetic intermediate was commonly found in the Rps. palustris strains (CGA009, Morita and NBRC100419).
Co-reporter:Hitoshi Tamiaki, Tomotaka Michitsuji and Reiko Shibata
Photochemical & Photobiological Sciences 2008 vol. 7(Issue 10) pp:1225-1230
Publication Date(Web):04 Jun 2008
DOI:10.1039/B802359J
Zinc 31-demethyl-bacteriopheophorbides-d possessing various 17-propionate residue (172-COOCH2–) were prepared as models of light-harvesting pigments in major photosynthetic antennae of green bacteria. The synthetic compounds were monomeric in polar organic solvents to give the same visible absorption spectra, but self-aggregated in non-polar organic solvents to afford large oligomers with broadened and red-shifted absorption bands. The peak positions were identical for all the self-aggregates but the widths of the redmost (Qy) bands were dependent upon the substituents. More hydrophobic and less sterically hindered hydrocarbon moieties as the esterifying group sharpened oligomeric Qy bands, giving less inhomogeneous supramolecular structures due to stabilization of the self-aggregates. In the reverse esters (172-CH2OCO–) structurally isomeric to the above compounds, the same optical behavior was observed. Movement of the oxo group from the 173- to 175-position (172-COOCH2– → 172-CH2OCO–) slightly increased the widths of self-aggregated Qy bands without change of the peak positions, where minor less self-aggregated components would enhance in the solution due to a little more stabilization of such species by the 174-carbonyl group.
Co-reporter:Hitoshi Tamiaki, Kazuhiro Fukai, Hideki Shimazu, Katsunori Nishide, Yutaka Shibata, Shigeru Itoh and Michio Kunieda
Photochemical & Photobiological Sciences 2008 vol. 7(Issue 10) pp:1231-1237
Publication Date(Web):04 Jun 2008
DOI:10.1039/B802353K
A heterodimer, where zinc pyropheophorbide-a was linked with zinc pyropheophorbide-d through ethylene glycol diester, was prepared, as well as the corresponding homodimers. The synthetic dimers were complexed with methanol in benzene to give folded dimers by mutual Zn⋯O(Me)–H⋯OC131 bonding. Such complexes had furthest red (Qy) absorption bands at longer wavelengths than the monomeric species. These red-shifts were ascribable to excitonic coupling of the Qy transition states in the chlorin π–π stacking conformer. In the heterodimeric system, a minor band was observed at the shorter wavelength side of the main Qy band. This observation can be explained by an additional contribution of Qy vibronic state to the exciton-coupled states. Based on the experimental results, a pair of chlorophyll(Chl)-d with Chl-a as well as a Chl-d homopair were proposed as dimers in reaction centers of Chl-d dominating cyanobacteria.
Co-reporter:Tadashi Mizoguchi, Tae-Yeun Kim, Seiji Sawamura and Hitoshi Tamiaki
The Journal of Physical Chemistry B 2008 Volume 112(Issue 51) pp:16759-16765
Publication Date(Web):November 26, 2008
DOI:10.1021/jp804990f
When pressure was applied to the main light-harvesting apparatus (chlorosomes) isolated from several green photosynthetic bacteria (up to 128 MPa), the Qy-absorption band in an aqueous solution was shifted to longer wavelengths. The shift, Δν, was completely reversible for (de)compression and also showed a linear relation as a function of the applied pressure. The pressure-sensitivity in the Δν was dependent upon the bacterial species. The pressure coefficient, Δν/ΔP, was −565 to −535 cm−1GPa−1 for the chlorosomes from several green sulfur bacteria (Chlorobium species), which have several bacteriochlorophyll(BChl) homologues at the 8- and 12-positions as the antenna pigments. In contrast, a smaller value (−445 cm−1 GPa−1) was estimated for the chlorosomes from the green nonsulfur bacterium (Chloroflexus aurantiacus), which has a single homologue with 8-ethyl and 12-methyl groups. These results were confirmed by the similar pressure dependency of in vitro self-aggregates of isolated BChls-c having various alkyl substituents at the 8- and 12-positions. The present pressurization study enables us to discuss a physiological meaning of a variety of antenna pigments in green photosynthetic bacteria.
Co-reporter:Jiro Harada;Tadashi Mizoguchi;Sayaka Yoshida;Megumi Isaji
Photosynthesis Research 2008 Volume 95( Issue 2-3) pp:213-221
Publication Date(Web):2008 February
DOI:10.1007/s11120-007-9254-1
Rhodopseudomonas sp. Rits is a recently isolated new species of photosynthetic bacteria and found to accumulate a significantly high amount of bacteriochlorophyll (BChl) a intermediates possessing non-, di- and tetra-hydrogenated geranylgeranyl groups at the 17-propionate as well as normal phytylated BChl a (Mizoguchi T et al. (2006) FEBS Lett 580:137–143). A phylogenetic analysis showed that this bacterium was closely related to Rhodopseudomonas palustris. The strain Rits synthesizes light-harvesting complexes 2 and 4 (LH2/4), as peripheral antennas, as well as the reaction center and light-harvesting 1 core complex (RC-LH1 core). The amounts of these complexes were dependent upon the incident light intensities, which was also a typical behavior of Rhodopseudomonas palustris. HPLC analyses of extracted pigments indicated that all four BChls a were associated with the purified photosynthetic pigment–protein, as complexes described above. The results suggested that this bacterium could use these pigments as functional molecules within the LH2/4 and RC-LH1 core. Pigment compositional analyses in several purple photosynthetic bacteria showed that such BChl a intermediates were always detected and were more widely distributed than expected. Long chains in the propionate moiety of BChl a would be one of the important factors for assembly of LH systems in purple photosynthetic bacteria.
Co-reporter:Hitoshi Tamiaki;Hideaki Yoshimura;Yasuhide Shimamura
Photosynthesis Research 2008 Volume 95( Issue 2-3) pp:223-228
Publication Date(Web):2008 February
DOI:10.1007/s11120-007-9247-0
Zinc complexes of 3-hydroxymethyl-13/15-carbonyl-chlorins having a six-membered lactone as the E-ring were prepared by modifying purpurin-18 as models of bacteriochlorophyll-d, one of the chlorophyllous pigments in the main light-harvesting antenna systems (chlorosomes) of green photosynthetic bacteria. The synthetic 13-carbonylated compound self-aggregated in 1%(v/v) tetrahydrofuran and hexane to give large oligomers possessing red-shifted and broadened electronic absorption bands and intense circular dichroism bands at the shifted Qy region, indicating that the supramolecular structure of the resulting self-aggregate was similar to those of natural and artificial chlorosomal aggregates. The red-shift value observed here was smaller than the reported values in chlorosomal pigments having a five-membered keto-ring, which was ascribable to a weaker intermolecular hydrogen-bonding of 13-C=O with 31-OH in a supramolecule of the former self-aggregate and suppression of the π–π interaction among the composite chlorins. On the other hand, the isomeric 15-carbonylated molecule was monomeric even in the nonpolar organic solvent, confirming the reported proposal that the linear orientation of three interactive moieties, OH, C=O and Zn, in a molecule is requisite for its chlorosomal self-aggregation.
Co-reporter:Hitoshi Tamiaki;Reiko Shibata;Tadashi Mizoguchi
Photochemistry and Photobiology 2007 Volume 83(Issue 1) pp:152-162
Publication Date(Web):26 FEB 2007
DOI:10.1562/2006-02-27-IR-819
Molecular structures of (bacterio)chlorophylls [=(B)Chls] in photosynthetic apparatus are surveyed, and a diversity of the ester groups of the 17-propionate substituent is particularly focused on in this review. In oxygenic photosynthetic species including green plants and algae, the ester of Chl molecules is limited to a phytyl group. Geranylgeranyl and farnesyl groups in addition to phytyl are observed in (B)Chl molecules inside photosynthetic proteins of anoxygenic bacteria. In main light-harvesting antennas of green bacteria (chlorosomes), a greater variety of ester groups including long straight chains are used in the composite BChl molecules. This diversity is ascribable to the fact that chlorosomal BChls self-aggregate to form a core part of chlorosomes without any specific interaction of oligopeptides. Biological significance of the long chains is discussed in photosynthetic apparatus, especially in chlorosomes.
Co-reporter:Reiko Shibata, Tadashi Mizoguchi, Toshiyuki Inazu and Hitoshi Tamiaki
Photochemical & Photobiological Sciences 2007 vol. 6(Issue 7) pp:749-757
Publication Date(Web):08 May 2007
DOI:10.1039/B702866K
Zinc 31-hydroxy-131-oxo-chlorins possessing two, three, four and six perfluorooctyl chains were synthesized from naturally occurring chlorophyll-a. Only the synthetic zinc chlorin possessing six perfluorooctyl chains was directly dissolved in perfluorinated solvents due to its high fluorine content in molecular weight (over 50%). In this solution, visible absorption spectra gave a red-shifted Qy band at 723 nm (compared to 648 nm in THF) and showed the formation of well-ordered self-aggregates. No monomeric form was observed in the solution from any fluorescence emission spectra from visible absorption spectra. In the aggregate solution, no precipitation occurred during either standing for a long period or heating at 70 °C. This showed that the supramolecular structure was stabilized by F–F interactions on its surface among the perfluorooctyl chains on the 17-position and perfluorinated solvents. The core part of the supramolecular structure was constructed by a special intramolecular bond of Zn⋯O32-H⋯OC131, which was confirmed from resonance Raman spectral analysis.
Co-reporter:Hitoshi Tamiaki;Takuya Watanabe;Michio Kunieda
Research on Chemical Intermediates 2007 Volume 33( Issue 1-2) pp:161-168
Publication Date(Web):2007 January
DOI:10.1163/156856707779160915
Zinc methyl 31-demethyl-17,18-cis-bacteriopheophorbide-d was prepared as a model of naturally occurring bacteriochlorophyll-d. From the absorption spectral analysis, the synthetic cis-chlorin self-aggregated in a non-polar organic solvent to give an oligomer possessing red-shifted and broadened peaks, compared to the non-aggregated form. The red-shifted values by self-aggregation were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of the cis-isomer took on more disordered supramolecular structures than those of the trans-isomer.
Co-reporter:Michio Kunieda, Emi Nakato, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 185(2–3) pp:321-330
Publication Date(Web):25 January 2007
DOI:10.1016/j.jphotochem.2006.06.027
By modifying β-octaethylporphyrin we prepared 131-oxo- and deoxo-porphyrins 1 and 3 possessing an exo-five-membered E-ring, which is a structural requirement of naturally occurring chlorophyllous pigments, and also 131-oxo- and deoxo-porphyrins 2 and 4 lacking the E-ring as reference compounds. Visible absorption spectra of 131-deoxo-porphyrins 3/4 bearing/lacking the E-ring and their zinc complexes showed a relatively small difference, indicating that geometry of the tetrapyrrole unit in 3 was altered by formation of the E-ring but its contribution to the visible spectrum was limited. In contrast, a spectral difference between 131-oxo-porphyrins 1/2 bearing/lacking the E-ring (as well as their zinc complexes) was clearly observed; fixation of 131-oxo group by the E-ring as in 1 resulted in its red-shifted absorption spectrum (ca. 10 nm for each band). These results indicated that introduction of the E-ring to a porphyrin macrocycle slightly affected its optical properties and that a larger effect was observed by fixation of 131-oxo group to a porphyrin π-conjugate system.
Co-reporter:Michio Kunieda
European Journal of Organic Chemistry 2006 Volume 2006(Issue 10) pp:
Publication Date(Web):13 MAR 2006
DOI:10.1002/ejoc.200500909
We have synthesized zinc 31-hydroxychlorins 1–4 possessing a methoxycarbonyl group at the 13-position by modifying naturally occurring chlorophyll-a. Synthetic zinc chlorins 1–4 have three specific substituents, namely 31-OH, central Zn and 13-C=O moieties, along the Qy axis, and 1–3 self-aggregate in an aqueous medium containing Triton X-100, as do natural bacteriochlorophylls in the main light-harvesting antennas (chlorosome) of green photosynthetic bacteria. The 13-methoxycarbonyl group in 1–3 is a prerequisite for such self-aggregation, while the other methoxycarbonyl groups at the 151- and/or 172-positions are not. This indicates that such a linear situation of these substituents is significant for chlorosomal self-aggregation of chlorophyllous pigments and also that the 13-methoxycarbonyl group is an alternative to the 13-keto-carbonyl group in natural pigments. Furthermore, the resulting oligomers of 1–3 have fluorescence emission peaks at less than 700 nm, which are considerably more blue-shifted than previously prepared self-aggregates of chlorins possessing the 13-keto-carbonyl group fixed onto an exo five-membered ring, and are a new class of artificial light-harvesting systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Co-reporter:Tadashi Mizoguchi, Ayumi Shoji, Michio Kunieda, Hideaki Miyashita, Tohru Tsuchiya, Mamoru Mimuro and Hitoshi Tamiaki
Photochemical & Photobiological Sciences 2006 vol. 5(Issue 3) pp:291-299
Publication Date(Web):16 Dec 2005
DOI:10.1039/B514088A
Acaryochloris marina is a unique photosynthetic prokaryote containing chlorophyll(Chl)-d as a major photoactive pigment (over 95%). The molecular structure of Chl-d is proposed as the 3-formyl analog of Chl-a. However, the stereochemistry of Chl-d at the 132-, 17- and 18-positions has not yet been established unambiguously. In the first part of this paper, we describe the determination of their stereochemistries to be 132-(R)-, 17-(S)- and 18-(S)-configurations by using 1H-1H NOE correlations in 1H-NMR and circular dichroism spectra as well as chemical modification of Chl-a to produce stereochemically defined Chl derivatives. In the second part of the paper, we report a facile synthesis of a self-aggregative Chl by modifying isolated Chl-d. Since Chl-d was characterized by its reactive 3-formyl group, the formyl group was reduced with t-BuNH2BH3 to afford the desirable Chl, 3-deformyl-3-hydroxymethyl-pyrochlorophyll-d (31-OH-pyroChl-d). The synthetic 31-OH-pyroChl-d molecules spontaneously self-organized to form well-ordered aggregates in a non-polar organic solvent. The self-aggregates are a good model of major light-harvesting antenna systems of green photosynthetic bacteria, chlorosomes, in terms of the following three findings. (1) Both the red-shifted electronic absorption band above 750 nm and its induced reverse S-shape CD signal around 750 nm were observed in 0.5% (v/v) THF–cyclohexane. (2) The stretching mode of the 13-carbonyl group was downshifted by about 35 cm−1 from the wavenumber of its free carbonyl. (3) The self-aggregates were quite stable on titration of pyridine to the suspension, in comparison with those of natural chlorosomal bacteriochlorophyll-d possessing the 3-(1-hydroxyethyl) group.
Co-reporter:Hitoshi Tamiaki, Yasuo Azefu, Reiko Shibata, Reiko Sato, Kazunori Toma
Colloids and Surfaces B: Biointerfaces 2006 Volume 53(Issue 1) pp:87-93
Publication Date(Web):1 November 2006
DOI:10.1016/j.colsurfb.2006.08.001
As models of naturally occurring glycolipids, structurally well-determined amphiphilic compounds were prepared. The synthetic molecules have β-d-galactopyranosyl or α-d-mannopyranosyl and two dodecyl groups as terminal hydrophilic sugar and hydrophobic hydrocarbon moieties, respectively. The two long alkyl chains are connected by 3,5-dioxybenzamide through ether linkages to give a lipid analog purified easily due to its absorbance of ultraviolet light. In the synthetic glycolipids, the glycoside and lipid parts are covalently bound via an oligomethylene spacer. The glycolipids could be easily incorporated into liposomes of l-α-phosphatidylcholine. The monoglycosyl moiety of the synthetic glycolipids possessing a hexamethylene spacer was present on the surface of the liposomes and interacted specifically with a lectin to give liposomal assemblies. Such agglutination of these liposomes induced by lectins was determined by analyses of turbidity and particle size based on dynamic light scattering and laser diffraction methods. The other liposomes possessing a shorter ethylene or longer decamethylene linker gave few lectin-induced agglutinates, indicating that these spacers were not effective for the presentation of the galacto-terminal on the liposomal surfaces. Similar spacer-dependent recognition of ricin with a galactolipid-incorporated phospholipid monolayer was confirmed by surface plasmon resonance technique on a substrate.
Co-reporter:Hiroki Hirabayashi, Masaaki Amakawa, Yasumaro Kamimura, Yayoi Shino, Hiroyuki Satoh, Shigeru Itoh, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology A: Chemistry 2006 Volume 183(1–2) pp:121-125
Publication Date(Web):30 September 2006
DOI:10.1016/j.jphotochem.2006.03.003
A water-soluble chlorophyll (Chl) protein complex isolated from Chenopodium album is converted to another form of the pigment protein (CP740) containing bacteriochlorin type pigments by irradiation with visible light in an aqueous aerated solution. In order to investigate the photoconverted pigments in CP740, all the chlorophyllous pigments were extracted with organic solvents from CP740 and were analyzed by high-performance liquid chromatography and mass spectrometry. Two separated products were mono-oxygen adducts to Chl a at the B-ring. Their visible spectral analysis combined with model calculation supported that they would be 8-oxo- (P700) and 7,8-epoxy-derivatives (P726). During extraction, covalent bonds of pigments with proteins in CP740 would be cleaved to produce the above mono-oxygenated Chls a. Based on the molecular structures of P700 and P726, bacteriochlorophyll type pigments in CP740 were proposed.
Co-reporter:Yoshitaka Saga, Hitoshi Tamiaki, Yutaka Shibata, Shigeru Itoh
Chemical Physics Letters 2005 Volume 409(1–3) pp:34-37
Publication Date(Web):20 June 2005
DOI:10.1016/j.cplett.2005.04.080
Abstract
The excitation energy transfer from bacteriochlorophyll(BChl)-c self-aggregates to energy-accepting BChl-a in proteins (baseplates) in an individual photosynthetic light-harvesting complex (chlorosome) of a green filamentous photosynthetic bacterium Chloroflexus aurantiacus was successfully observed at cryogenic temperature. The ratio of intensity of the fluorescence peak of BChl-a to that of BChl-c self-aggregates in individual chlorosomes, which demonstrated relative efficiency of the excitation energy transfer, was heterogeneous between 0.09 and 0.72. This suggests that excitonic interaction between BChl-c self-aggregates and BChl-a in baseplates was heterogeneous among individual chlorosomes.
Co-reporter:Hitoshi Tamiaki
Photochemical & Photobiological Sciences 2005 vol. 4(Issue 9) pp:675-680
Publication Date(Web):30 Jun 2005
DOI:10.1039/B416360E
Extramembranous light-harvesting antennae called ‘chlorosomes’ are the main sunlight-absorbing and energy-migrating systems in photosynthetic green bacteria. In a chlorosome, specific chlorophyllous pigments self-aggregate in hydrophobic environments surrounded by a lipid monolayer to form large oligomers. The self-aggregates of chlorosomal chlorophylls possessing a chlorin π-system absorb sunlight and can emit near-infrared light, which is transferred to a bacteriochlorin pigment situated in the chlorosomal surface membrane. In vivo and in vitro self-aggregates of natural chlorosomal chlorophylls and their models have been investigated by electronic absorption analysis. Here their self-aggregation is reviewed from the viewpoint of substituent effect on the pyrrolic B-ring. Substituents at the 7- and 8-positions did not disturb the formation of their self-aggregates but affected their absorption bands.
Co-reporter:Hirozo Oh-oka;Tadashi Mizoguchi
Photochemistry and Photobiology 2005 Volume 81(Issue 3) pp:666-673
Publication Date(Web):30 APR 2007
DOI:10.1111/j.1751-1097.2005.tb00242.x
The reaction center complex of heliobacteria contains three kinds of chlorophyll pigments, bacteriochlorophyll gF (BChl gF), its 132-epimer BChl g′F and 81-hydroxy-chlorophyll aF (81-OH-Chl aF). Because the full stereochemistry of these naturally occurring chlorophyllous pigments has remained unknown, we determined the stereochemistry of both BChl gF and 81-OH-Chl aF extracted from Heliobacterium modesticaldum. The configurations of the specific functional groups at ring-B as well as those at ring-D and -E were investigated by use of nuclear Overhauser effect correlations in their 1H-NMR spectra and circular dichroism spectra, as well as by modified Mosher's method in their chemical modification: (1) E-configuration was confirmed for the 8-ethylidene group at ring-B in BChl gF, (2) R-configuration was identified for the 1-hydroxyethyl group at ring-B in 81-OH-Chl aF and (3) 132-(R)-, 17-(S)- and 18-(S)-configurations at ring-D and -E in both BChl gF and 81-OH-Chl aF were confirmed. These stereo-chemistries enabled us to discuss their biosynthesis and to propose possible routes for preparation of ethylidene and 1-hydroxyethyl groups at the 8-position.
Co-reporter:Tomohiro Miyatake, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2005 Volume 6(2–3) pp:89-107
Publication Date(Web):October 2005
DOI:10.1016/j.jphotochemrev.2005.06.001
Green photosynthetic bacteria possess light-harvesting antenna systems, called chlorosomes, in which a number of bacteriochlorophyll(BChl)-c/d/e molecules self-aggregate to form rod-shaped oligomers. All BChls-c/d/e have a 1-hydroxyethyl group at the 31-position and are 31-epimeric mixtures at various ratios. These stereoisomers were isolated and structurally determined by several experimental techniques. In vitro studies on their self-aggregation indicated that the 31-stereochemistry affected the supramolecular structures of the chlorosomal assemblies. Some recent reports suggested that both stereoisomers are required for making rod-shaped chlorosome-type aggregates, i.e., the 31R/S-stereoisomers co-operate in the construction of the antenna system. The synthetic models of BChls possessing a chiral secondary alcoholic group also exhibited stereochemical control of the self-aggregation. In this review, we will discuss the unique stereochemical control on the chlorosomal BChl self-aggregates.
Co-reporter:Nobuo Kosaka
European Journal of Organic Chemistry 2004 Volume 2004(Issue 11) pp:
Publication Date(Web):26 APR 2004
DOI:10.1002/ejoc.200400027
A covalently doubly linked cyclic chlorophyll hetero-dyad was stereospecifically prepared as a model for naturally stacked chlorophyll suprastructures. In the synthetic dyad, two composite macrocycles are situated very close to each other such that the Qy transition dipole moments intramolecularly interact to give intense circular dichroism peaks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Co-reporter:Tomohiro Miyatake, Hitoshi Tamiaki, Manabu Fujiwara, Takayuki Matsushita
Bioorganic & Medicinal Chemistry 2004 Volume 12(Issue 9) pp:2173-2178
Publication Date(Web):1 May 2004
DOI:10.1016/j.bmc.2004.02.021
Aqueous assemblies of zinc chlorins possessing a nonionic (oligo)oxyethylene, a cationic quaternary ammonium or an anionic sulfonate group were prepared in the presence of a synthetic surfactant. The nonionic zinc chlorin formed aggregates when admixed with a nonionic surfactant such as Triton X-100 to give a highly ordered oligomeric J-aggregate similarly as natural bacteriochlorophyll-c or d does in a chlorosome. In addition, the coassemblies of the cationic zinc chlorin with an anionic surfactant and of the anionic zinc chlorin with a cationic surfactant gave large oligomers of these chlorophyllous pigments. The structures of hydrophilic groups in both the zinc chlorin and surfactant molecules controlled their aqueous coassemblies.Graphic
Co-reporter:Nobuo Kosaka
European Journal of Organic Chemistry 2004 Volume 2004(Issue 11) pp:
Publication Date(Web):12 MAY 2004
DOI:10.1002/ejoc.200490022
The cover picture shows the molecular structure of a synthetic doubly-linked cyclic chlorophyll “hetero”-dyad (left) and its symbolic image using natural leaves (right). Two chlorophyllous κ-systems are stereospecifically and covalently bonded with two different linkers and close to each other in a nearly parallel fashion. The present synthetic strategy has great potential for the systematic preparation of various cyclic chlorophyll hetero-dyads. Details of the synthesis and characterization are described in the article by N. Kosaka and H. Tamiaki on p. 2325 ff.
Co-reporter:Yoshitaka Saga, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology B: Biology 2004 Volume 73(1–2) pp:29-34
Publication Date(Web):23 January 2004
DOI:10.1016/j.jphotobiol.2003.10.001
A chlorophyll analog forming self-assembled monolayers (SAMs) on a gold surface was synthesized for the first time. 132-(Demethoxycarbonyl)pheophorbide-a, which was converted from naturally occurring chlorophyll-a, was condensed with 2-hydroxyethyl disulfide to give a chlorin dyad linked by a disulfide bond. The chlorin analog was spontaneously immobilized on a gold substrate by soaking in an acetone solution of the dyad for 24 h. The resulting gold plate exhibited a visible absorption spectrum with about 420- and 675-nm maxima as the Soret and Qy peaks, respectively, indicating that chlorin π-conjugates were modified on the gold substrate through Au–S bonding. Both visible absorption and fluorescence emission bands of the chlorin chromophores on the gold substrate were red-shifted compared with those of the synthesized chlorin dyad in a homogeneous acetone solution. The measured absorbance at the Soret maximum suggests that the chlorin chromophores on the gold plate were densely packed on a gold surface to form a SAM. Cathodic photocurrents were generated from SAMs of the chlorins on a gold substrate with irradiation of visible-lights above 400 nm. Photoinduced electron transfer from chlorins on the gold substrate to oxygen molecules in an electrolyte solution were attributed to the cathodic photocurrent generation.
Co-reporter:Yoshitaka Saga, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology B: Biology 2004 Volume 75(1–2) pp:89-97
Publication Date(Web):19 July 2004
DOI:10.1016/j.jphotobiol.2004.05.012
Chlorosomes containing bacteriochlorophyll(BChl)-c and those containing BChl-d were isolated from two substrains of Chlorobium vibrioforme f. sp. thiosulfatophilum NCIB 8327, respectively. The two types of chlorosomes were investigated from the following aspect, what kinds of effects the molecular structure of chlorosomal BChls had on structural and spectroscopic properties of in vivo self-aggregates in chlorosomes without alteration of the other components such as chlorosomal proteins and lipids; both chlorosomes were expected to have the same components except for light-harvesting BChls. In their visible absorption spectra, the differences of Soret and Qy peak positions between BChl-c containing and BChl-d containing chlorosomes were similar to the differences between monomeric BChl-c and d. An inverse S-shaped CD signal in the Qy region of BChl-d containing chlorosomes was 1.4 times larger than that of BChl-c containing chlorosomes, when the Qy absorbance of the two chlorosomes was almost the same. This implies that the excitonic interaction of BChl-d is larger than that of BChl-c in natural chlorosomes. Resonance Raman spectroscopy showed that BChl self-assemblies in both chlorosomes were essentially formed by the same local structural interaction among 31-hydroxy group, 13-keto group, and central magnesium. BChl-d self-aggregates in chlorosomes were more tolerant of 1-hexanol than in vivo BChl-c aggregates, suggesting that the molecular structure of BChl-d provided more stable self-assemblies than BChl-c in natural chlorosomes.
Co-reporter:Tadashi Mizoguchi, Yoshitaka Saga and Hitoshi Tamiaki
Photochemical & Photobiological Sciences 2002 vol. 1(Issue 10) pp:780-787
Publication Date(Web):23 Aug 2002
DOI:10.1039/B202466G
Eight bacteriochlorophyll (BChl)-d homologs and epimers were isolated from a strain of the green sulfur bacterium Chlorobium vibrioforme. By a combination of mass spectrometry and 1H-NMR spectroscopy using the chemical shifts of meso- and 31-protons and 1H–1H NOE correlations, the molecular structures were determined as (31R)-8-ethyl-12-methyl, (31R)-8-ethyl-12-ethyl, (31R)-8-propyl-12-methyl, (31S)-8-propyl-12-methyl, (31R)-8-propyl-12-ethyl, (31S)-8-propyl-12-ethyl, (31S)-8-isobutyl-12-methyl and (31S)-8-isobutyl-12-ethyl. The aggregation behavior of the epimerically pure BChls-d in hydrophobic organic solvents was examined to investigate the absolute configuration of the 3-(1-hydroxyethyl) group as well as the bulkiness of the C8 and C12 side-chains by using electronic-absorption and fluorescence-emission spectroscopies. At high concentration of the BChls-d in CH2Cl2, the absolute configuration of the 3-(1-hydroxyethyl) group governed the formation of a subunit as a building block for the subsequent higher assembly. Upon dilution of the resulting subunit with hexane, the bulkiness of the C8 and C12 side-chains were found to affect the association of the subunits differently: the bulkiness of the C8 side-chain acted as a promoter for the association due to a stabilized hydrophobic interaction among the relevant larger side-chain, whereas the bulkiness of the C12 side-chain acted as an inhibitor for that association due to introduction of a particular steric-hindrance around the side-chain in the aggregates.
Co-reporter:Yoshitaka Saga;Tetsuichi Wazawa;Tadashi Mizoguchi;Yoshiharu Ishii;Toshio Yanagida
Photochemistry and Photobiology 2002 Volume 75(Issue 4) pp:433-436
Publication Date(Web):1 MAY 2007
DOI:10.1562/0031-8655(2002)0750433SHISLH2.0.CO2
The fluorescence emission properties of single chlorosomes from the green sulfur photosynthetic bacterium Chlorobium (Chl.) tepidum are studied for the first time, using a total internal reflection fluorescence microscope. The fluorescence peak positions of bacteriochlorophyll (BChl)-c self-aggregates in a single chlorosome of Chl. tepidum were widely distributed in the wavelength region between 750 and 768 nm, and the standard deviation (s.d. = 4.1 nm, n = 51) was larger than that of single chlorosomes of Chloroflexus (Cfl.) (s.d. = 1.9 nm, n = 50). The spectral heterogeneity among single chlorosomes from Chl. tepidum was in sharp contrast to those from Cfl. aurantiacus. The difference of chlorosomal spectral properties between Chl. tepidum and Cfl. aurantiacus at the single-unit level would be ascribed to the homolog composition of BChl-c—chlorosomes of Chl. tepidum have BChl substituted with various alkyl groups at both the 8- and 12-positions, whereas light-harvesting BChl-c molecules in Cfl. chlorosomes have the same substituents at the 8- (ethyl group) and 12- (methyl group) positions.
Co-reporter:Yasuhiko Kureishi, Haruki Shiraishi, Hitoshi Tamiaki
Journal of Electroanalytical Chemistry 2001 Volume 496(1–2) pp:13-20
Publication Date(Web):19 January 2001
DOI:10.1016/S0022-0728(00)00262-X
To investigate a dye-based solar cell, a naturally occurring chlorophyll analogue (chlorin 1) modified electrode was prepared. Synthetic zinc chlorin 1 easily self-aggregated to form supramolecules (1)n in non-polar organic solvents as well as in the thin film. The photocurrent of the electrode modified with self-aggregated chlorin (1)n (CE1) was measured in the range from −300 to 300 mV (vs. Ag ∣ Ag+) by irradiation with >510 nm light. Below 100 mV of the bias potential, cathodic photocurrents of CE1 were observed in an aqueous solution of 0.1 M 2-(N-morpholino)ethanesulfonic acid+0.1 M Na2SO4 at pH 6.7. The photocurrent action spectrum of CE1 was similar to the visible absorption spectrum of (1)n on a Pyrex plate, indicating that the photoexcited state of zinc chlorin aggregates (1)n* played a role as a photosensitizer on CE1 with a wide band of longer wavelength light. An oxygen molecule dissolved in an aqueous solution was an electron acceptor; electron transfer from (1)n* to O2 at the interface between the carbon paste electrode and the aqueous solution yielded the cathodic photocurrent. The quantum yield for CE1 was estimated to be 0.09% (730 nm). The value was larger than the quantum yield for the carbon paste electrode modified with monomeric zinc chlorin 3 (CE3), 0.01% (660 nm). These results indicate that self-aggregation of zinc chlorin (1)n made an efficient photosensitizer of solar cells and utilized up to 800 nm light.
Co-reporter:Shiki Yagai;Tomohiro Miyatake;Yoshiyuki Shimono
Photochemistry and Photobiology 2001 Volume 73(Issue 2) pp:153-163
Publication Date(Web):1 MAY 2007
DOI:10.1562/0031-8655(2001)0730153SSOSAS2.0.CO2
Zinc-chlorin 3 (see Fig. 2 in text) possessing a tertiary 31-hydroxyl group and a 13-keto group was synthesized as a model for the antenna chlorophylls of green bacteria. Self-aggregation of 3 in nonpolar organic media was examined and compared to 1 and 2 possessing a primary and secondary 31-hydroxyl group, respectively. Zinc-chlorin 3 self-aggregated in 1 vol% CH2Cl2–hexane to form oligomers and showed a red-shifted Qy maximum at 704 nm compared to the monomer (648 nm in CH2Cl2). This red-shift is larger than that of 2S (648 697 nm) and comparable to that of 2R (648 705 nm), but smaller than that of 1 (648 740 nm), indicating that while a single 31-methyl group (prim-OH sec-OH) suppressed close and/or higher aggregation, the additional 31-methyl group (sec-OH tert-OH) did not further suppress aggregation. The relative stability of the aggregates was in the order 1 > 2R∼ 3 > 2S as determined by visible spectral analyses. Molecular modeling calculations on dodecamers of zinc-chlorins 1, 2R and 3 gave similar well-ordered energy-minimized structures, while 1 stacked more tightly than 2R and 3. In contrast, 2S gave a relatively disordered (twisted) structure. The calculated dodecameric structures could explain the visible spectral data of 1–3 in nonpolar organic media.
Co-reporter:Yoshitaka Saga;Katsumi Matsuura
Photochemistry and Photobiology 2001 Volume 74(Issue 1) pp:72-80
Publication Date(Web):1 MAY 2007
DOI:10.1562/0031-8655(2001)0740072SSOSAO2.0.CO2
Self-aggregation of naturally occurring bacteriochlorophyll (BChl)-e in nonpolar organic solvents was investigated by visible absorption, fluorescence emission and circular dichroism spectra. Cultured brown-colored photosynthetic bacteria have several BChl-e as light-harvesting antenna pigments. Three major BChl-e homologs were separated from the extracts of the culture by reverse-phase high-performance liquid chromatography (HPLC) and characterized by 1H-NMR and fast-atom bombardment mass spectroscopy: 8-ethyl-12-ethyl ([E,E])-, 8-propyl-12-ethyl- and 8-isobutyl-12-ethyl-BChl-e farnesyl esters. All the homologs consisted of a mixture of the 31-epimers, and epimerically pure BChl-e were also given by HPLC separation. All the separated BChl-e epimers, the epimeric mixtures and the homologous mixtures formed self-aggregates in 2% dichloromethane/hexane, giving visible absorption spectra similar to that of the whole cells, which showed two peaks (or shoulders) around 430–450 and 520 nm at the Soret region as well as a red-shifted Qy band relative to the monomeric. The spectral properties of the Soret band were basically unchanged among the epimers or epimeric/homologous mixtures. In contrast, the Qy band of aggregates of epimeric mixtures (except [E,E]) and homologous mixtures red-shifted and broadened compared with the epimerically pure. The red-shift and broadening of the Qy band are advantageous for efficient energy transfer from BChl-e aggregates to BChl-a in a baseplate in chlorosomes because their spectral overlap increases.
Co-reporter:Tomohiro Miyatake Dr.;Toru Oba Dr. Dr.
ChemBioChem 2001 Volume 2(Issue 5) pp:
Publication Date(Web):2 MAY 2001
DOI:10.1002/1439-7633(20010504)2:5<335::AID-CBIC335>3.0.CO;2-Y
Zinc analogues of bacteriochlorophylls c and d self-assembled in aqueous media with phospholipids. A methanol solution of zinc chlorin and α-lecithin was put in a cellulose tube and the inner methanol solvent was gradually replaced with water by dialysis to form the self-assembled oligomers. Visible absorption spectra of the aqueous solution showed that zinc chlorins formed J-aggregates within the hydrophobic core of α-lecithin assemblies and that the supramolecular structure of the aggregates depended upon the stereochemistry at the 31-position and the alkyl substituents at the 8-, 12-, and 174-positions of the zinc chlorin. When the aqueous aggregates were prepared with a mixture of 31-epimers and/or 8-, 12-, or 174-homologues of zinc 31-hydroxy-131-oxochlorins, the structurally distinct components coaggregated to make scrambled oligomers. However, during the dialysis, zinc 31-hydroxy- and 71-hydroxy-131-oxochlorins slowly individually aggregated to give two structurally different oligomer units in the cellulose tube. In contrast, if the two zinc chlorin components rapidly self-assembled in an aqueous medium, these components coaggregated to form scrambled oligomers. The present study shows that both the molecular structure of the pigments and the speed of the oligomerization determine the molecular arrangement in chlorosome-type self-assembled oligomers.
Co-reporter:Hitoshi Tamiaki;Yasushi Nagata;Seiichi Tsudzuki
European Journal of Organic Chemistry 1999 Volume 1999(Issue 10) pp:
Publication Date(Web):19 OCT 1999
DOI:10.1002/(SICI)1099-0690(199910)1999:10<2471::AID-EJOC2471>3.0.CO;2-Y
Reaction of zinc 5,15-bis(3,5-di-tert-butylphenyl)porphyrin with S-(trifluoromethyl)-3,7-dinitrobenzothiophene trifluoromethanesulfonate in tetrahydrofuran gave the 10-trifluoromethylated compound as the major product and 2-CF3- and 10,20-di-CF3-porphyrins as the minor products. The direct trifluoromethylation is effective for preparation of longer-wavelength absorbing meso-trifluoromethylated porphyrins and chlorins.
Co-reporter:Shiki Yagai, Tomohiro Miyatake, Hitoshi Tamiaki
Journal of Photochemistry and Photobiology B: Biology 1999 Volume 52(1–3) pp:74-85
Publication Date(Web):30 October 1999
DOI:10.1016/S1011-1344(99)00105-0
The aggregation behavior of synthetic zinc-81-hydroxy-chlorins in nonpolar organic media and in solid thin film has been compared with that of zinc-31-hydroxy-chlorin, a model of bacteriochlorophyll-d in the chlorosomes of green photosynthetic bacteria. Zinc-81-hydroxy-131-oxo- and 31,131-dioxo-chlorins 1a and 3a self-aggregate in nonpolar organic solvents and in solid thin films. They show less red-shifted and wider visible absorption bands at the Soret and Qy regions and also more intense circular dichroism (CD) signals at the Soret region than self-aggregates of zinc-31-hydroxy-131-oxo-chlorin 5a. The 1H-NMR spectroscopic data indicate that the hydroxyl group at the 81-position of 1a coordinates with the central zinc of an adjacent molecule in the supramolecule. From the infrared spectra, we can deduce that the interactions of the functional groups of 1a in the aggregates are unspecific or weak. For this reason, the supramolecular structures are partially amorphous. Visible absorption and CD spectra establish that the lack of one of the three interactive moieties (81-hydroxy, 13-keto groups and central zinc) suppresses the aggregation ability of chlorins. Furthermore, zinc-3-acetyl-81-hydroxy-chlorin 2a does not self-aggregate in nonpolar organic solvents because both the hydroxyl and keto groups take various configurations. However, additional substitution of keto carbonyl group at the 3-position (1a→3a) affects the aggregation ability. It is concluded that the fixation of either the OH or CO group to the chlorin moiety possessing an exo-five-membered ring, as well as both the presence of OH, CO and central metal in the molecule and the linear location of the three interactive moieties are necessary for the formation of well-ordered self-aggregates of chlorophyll analogues, which are seen in native chlorosomes.
Co-reporter:Tadashi Mizoguchi, Yuki Kimura, Taichi Yoshitomi, Hitoshi Tamiaki
Biochimica et Biophysica Acta (BBA) - Bioenergetics (November 2011) Volume 1807(Issue 11) pp:1467-1473
Publication Date(Web):November 2011
DOI:10.1016/j.bbabio.2011.07.008
Co-reporter:Tadashi Mizoguchi, Megumi Isaji, Jiro Harada, Hitoshi Tamiaki
Biochimica et Biophysica Acta (BBA) - Bioenergetics (March 2012) Volume 1817(Issue 3) pp:395-400
Publication Date(Web):March 2012
DOI:10.1016/j.bbabio.2011.12.001
Co-reporter:Tadashi Mizoguchi, Chihiro Nagai, Michio Kunieda, Yuki Kimura, Atsushi Okamura and Hitoshi Tamiaki
Organic & Biomolecular Chemistry 2009 - vol. 7(Issue 10) pp:NaN2126-2126
Publication Date(Web):2009/03/18
DOI:10.1039/B900802K
Chlorophyll (Chl)-c1 and Chl-c2 were extracted from a commercially available diatom Chaetoseros calcitrans, and the former (8-ethyl) and the latter (8-vinyl) were efficiently separated by reverse-phase HPLC using a polymeric octadecylsilyl column to afford analytically pure compounds in an amount adequate for further chemical modification. The conformation of the unique acrylate moiety at the 17-position of isolated Chls-c in THF was unambiguously determined to be “cisoid” around the C17–C171 bond using 1H-1H NOE correlations: C171C172 was on the same side as C17C18. Interestingly, correlations originating from the “transoid” conformer could not be observed under the present NMR conditions, indicating that the rotation of the acrylate was considerably restricted. To elucidate the function of the rigid acrylate in Chls-c, we examined their electronic absorption properties using two synthetic types of esters possessing a porphyrin π-system: acrylate-type (17-CHCH–COOR) prepared by esterification of natural Chl-c1 and Chl-c2, and propionate-type (17-CH2–CH2–COOR) by 17,18-oxidation of natural Chl-a and its 8-vinyl analog. The Soret absorption bands at around 450 nm of the acrylate-type were red-shifted and broadened more than those of the propionate-type. Consequently, the unique acrylate in Chls-c serves as an aid for expanding the absorption region around 400–500 nm in order to capture intense irradiation from the sun for photosynthesis.
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