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An N‐centered epimeric mixture of chlorophyll‐a derivatives methylated at the inner nitrogen atom was separated by reverse‐phase high‐performance liquid chromatography. Circular dichroism (CD) spectroscopic analyses of the epimerically pure N22‐methyl‐chlorins revealed that the minor first‐eluted and major second‐eluted stereoisomers were (22S)‐ and (22R)‐configurations, respectively. Their visible absorption and CD spectra in solution were dependent on the N22‐stereochemistry. The epimer‐dependent spectral changes were independent of the substituents at the peripheral 3‐position of the core chlorin chromophore. [ABSTRACT FROM AUTHOR]

Zinc methyl 3‐hydroxymethyl‐pyropheophorbides‐a possessing an acylhydrazinylidene group at the 131‐position were prepared by chemically modifying chlorophyll‐a, which were models of bacteriochlorophyll‐d as one of the light‐harvesting pigments in photosynthetic green bacteria. Similar to the self‐aggregation of natural bacteriochlorophyll‐d in the antenna systems called chlorosomes, some of the synthetic models self‐aggregated in an aqueous Triton X‐100 solution to give red‐shifted and broadened visible absorption bands. The newly appeared oligomeric bands were ascribable to the exciton coupling of the chlorin π‐systems along the molecular y‐axis, leading to intense circular dichroism bands in the red‐shifted Qy and Soret regions. The self‐aggregation in the aqueous micelle was dependent on the steric size of the terminal substituent at the 13‐acylhydrazone moiety. An increase in the length of the oligomethylene chain as the terminal moved the red‐shifted Qy maxima to shorter wavelengths, and branched alkyl and benzyl substitutes afforded no more self‐aggregates to leave monomeric species in the hydrophobic environment inside the micelle. These results indicated that the acyl groups on the 13‐hydrazone as the alternative of the natural 13‐ketone regulated the chlorosome‐like self‐aggregation. [ABSTRACT FROM AUTHOR]

Additive‐assisted donor and acceptor domain regulation is regarded as an effective strategy to further release the potential photovoltaic performance of the existing organic solar cells (OSCs). Meanwhile, it is also critical to find high‐efficient, stable, non‐toxic, and low‐cost biological materials as bio‐additives to replace the traditional toxic halogen‐based additives. In this study, bio‐additives derived from a natural chlorophyll pigment named as ZnChl and H2Chl are employed to optimize the morphology and molecular stack of the PM6:Y6 active layer. The eutectic molecular stack of the blends is more ordered and tighter after introducing the bio‐additive chlorophyll derivatives to the system compared to the pristine PM6:Y6 blends. Owing to such a fine‐tuned donor‐acceptor microstructure network, the photovoltaic performance of the H2Chl bio‐additive‐based OSC achieves a 17.30% PCE and ZnChl‐based device obtains an efficiency of 16.61%, which is much higher than that of the control device with a 15.97% PCE. The result proves the feasibility of introducing environmental‐ and eco‐friendly chlorophyll derivatives as bio‐additives to further improve the photovoltaic performance of the OSCs. [ABSTRACT FROM AUTHOR]

Methyl pyropheophorbides‐a possessing an o/m‐(methoxycarbonyl)phenyl group at the 3‐position were prepared by Diels–Alder reaction of 3‐(trans‐1,3‐butadienyl)chlorin with methyl propiolate and successive didehydrogenation of the resulting 1,4‐cyclohexadienes. The 3‐arylated chlorin bearing the sterically demanding o‐COOMe group as the major product was a 1:1 mixture of high‐performance liquid chromatography‐separable rotational isomers around the C3–C31 bond, while the minor product with the m‐COOMe was less sterically hindered to exhibit rapid atropisomerization at room temperature. The 3‐aryl group of the major product was nearly perpendicular to the chlorin π‐system and less conjugated with the chlorin moiety than that of the minor product wherein more π‐conjugation occurred to give slightly red‐shifted Qy bands. Although both the atropisomers of the o‐substitute in dichloromethane showed similar visible absorption bands and fluorescence emission data, their circular dichroism bands in the ultraviolet‐C light region were dependent on the stereochemistry. [ABSTRACT FROM AUTHOR]

The catalytic organic‐hydride transfer to CO2 was first achieved through the photoinduced two‐electron reduction of the [Ru(bpy)2(pbn)]2+/[Ru(bpy)2(pbnHH)]2+ (bpy=2,2'‐bipyridine, pbn=2‐(pyridin‐2‐yl)benzo[b]‐1,5‐naphthyridine, and pbnHH=2‐(pyridin‐2‐yl)‐5,10‐dihydrobenzo[b]‐1,5‐naphthyridine) redox couple in the presence of 1,3‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[d]imidazole (BIH). The active species for the catalytic hydride transfer to carbon dioxide giving formate is [Ru(bpy)(bpy⋅−)(pbnHH)]+ formed by one‐electron reduction of [Ru(bpy)2(pbnHH)]2+ with BI⋅. [ABSTRACT FROM AUTHOR]

Chlorophyll(Chl)‐a derivatives containing some rigid linkers in the C20 substituents, which were inserted between a hydroxymethyl group and the chlorin π‐skeleton, were synthesized and their self‐aggregation abilities were investigated. Measurements of electronic absorption, circular dichroism and infrared absorption spectra revealed that the zinc complex of a Chl‐a derivative bearing a (p‐ethynyl)benzyl alcoholic moiety at the C20‐position gave its J‐aggregates in an aqueous micellar solution through the hydrogen and coordination bonding. These results exhibited the potential of Chl‐a derivatives bearing a hydroxyl group in the C20 substituents as the model compounds for chlorosomal light‐harvesting antennas. [ABSTRACT FROM AUTHOR]

According to the previous study, a bilayer organic photovoltaic with unconventional energy‐level alignment has been studied. Unlike the donor–acceptor system, this kind of structure has the potential to produce a high open‐circuit voltage (VOC) device and provides another method to realize high‐power conversion efficiency in organic solar cells. However, the VOC of the device is not high enough, and there is no direct observation of the Z‐characteristic. Herein, the device performance is improved according to the strategy provided in the latest report. With ethylenediamine regulating the interface, the VOC and short‐circuit current are improved from 0.59 to 0.77 V and 0.9 to 1.9 mA cm−2, respectively. The overall efficiency increases by 280%. The enhancement and direct observation of Z‐characteristics are observed. Considering the efficiency improvement brought by Z‐characteristic enhancement in this work, combined with the previous work, the theoretical efficiency limitation is 22.5% under a low light intensity and 30% under a high light intensity. This article supports the previous work, shows that the Z‐characteristic device has very broad optimization potential, provides a method for the fabrication of high efficiency and high VOC devices, and also provides a reference for other semiconductor optoelectronic devices. [ABSTRACT FROM AUTHOR]

Hydrogen energy is an abundant, clean, sustainable and environmentally friendly renewable energy source. Therefore, the production of hydrogen by photocatalytically splitting water on semiconductors has been considered in recent years as a promising and sustainable strategy for converting solar energy into chemical energy to replace conventional energy sources and to solve the growing problem of environmental pollution and the global energy crisis. However, highly efficient solar‐driven photocatalytic hydrogen production remains a huge challenge due to the poor visible light response of available photocatalytic materials and the low efficiency of separation and transfer of photogenerated electron‐hole pairs. In the present work, organic heterojunction structures based on bacteriochlorophyll (BChl) and chlorophyll (Chl) molecules were introduced and used for solar‐driven photocatalytic hydrogen production from water under visible light. Also, noble metal‐free photocatalyst was successfully constructed on Ti3C2Tx nanosheets by simple successive deposition of Chl and BChl, which was used for the photocatalytic splitting water to hydrogen evolution reaction (HER). The results show that the optimal BChl@Chl@Ti3C2Tx composite has a high HER performance with 114 μmol/h/gcat, which is much higher than the BChl@Ti3C2Tx and Chl@Ti3C2Tx composites. [ABSTRACT FROM AUTHOR]

Chlorophyll‐a derivatives possessing a substituted methylene group at the 132‐position were prepared by the mixed aldol condensation of methyl 3‐hydroxymethyl‐pyropheophorbide‐a with aldehydes bearing a methyl, p‐nitro/cyanophenyl, or pentafluorophenyl group. Their electronic absorption spectra were dependent on the substituents at the methylene terminal. The Soret bands were broadened by increasing the group electronegativity of the substituents, which was ascribable to the charge transfer from the core chlorin to the peripheral substituent in a molecule. Although their Qy absorption and fluorescence emission bands resembled each other, the emission intensities decreased with an increase in the electronegativity because of intramolecular electron transfer quenching. Some of their zinc complexes self‐aggregated in a less polar organic solvent to give red‐shifted and broadened absorption bands with intense circular dichroism couplets, which were similar to those of bacteriochlorophyll‐c/d aggregates in natural chlorosomes as the main light‐harvesting antennas of green photosynthetic bacteria and their models. The J‐aggregation was suppressed with an enhancement in the size of the 132‐substituents. [ABSTRACT FROM AUTHOR]

Composites composed of a chlorophyll‐a derivative and Ti3C2Tx MXene recently showed promising results as photocatalysts for the hydrogen evolution reaction. Herein, this type of composites is prepared by using a layered Ti3C2Tx material via an HCl@LiF etching technique, instead of the previously adopted HF etching technique. The performance of H2 evolution, therefore, showed a fourfold increase in this photocatalytic system, compared with the reported data in our previous works. The underlying reason for such a large improvement of the chlorophyll‐MXene photocatalyst performance would be attributed to a more suitable surface chemistry, higher conductivity, fewer defects, higher surface area, and larger interlayer space of Ti3C2Tx introduced by the Li+ ions from LiF in the etching process. Herein, it is revealed that the preparation method of MXenes used as the cocatalysts is key to improve the H2 evolution efficiency in photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

The Z‐scheme process is a photoinduced electron‐transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z‐scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl‐1 and Chl‐2, on the surface of Ti3C2Tx MXene with two‐dimensional accordion‐like morphology, forming Chl‐1@Chl‐2@Ti3C2Tx composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl‐1 and Chl‐2, sublayer Chl‐1 is a simulation of PSI, whereas upper layer Chl‐2 is equivalent to PSII, and the resultant electron transport can take place from Chl‐2 to Chl‐1. Under the illumination of visible light (>420 nm), the HER performance of Chl‐1@Chl‐2@Ti3C2Tx photocatalyst was found to be as high as 143 μmol h−1 gcat−1, which was substantially higher than that of photocatalysts of either Chl‐1@Ti3C2Tx (20 μmol h−1 g−1) or Chl‐2@Ti3C2Tx (15 μmol h−1 g−1). [ABSTRACT FROM AUTHOR]

Natural bacteriochlorophyll‐a was converted to chemically stable free‐base derivatives with different substituents along the y‐axis. Compared to the natural type compound methyl pyrobacteriopheophorbide‐a possessing the C3‐acetyl and C13‐keto‐carbonyl groups, its deoxo‐bacteriochlorin lacking the C3‐ and C13‐carbonyl groups showed a blue‐shift of the Qy peak. On the other hand, introduction of the dicyanomethylene group(s) at the 31‐ and/or 131‐position(s) caused an opposite effect due to its electron‐withdrawing ability as well as the expansion of the π‐conjugation system along the y‐axis, and the Qy peak maxima were red‐shifted to around 780 nm. These semi‐synthetic bacteriochlorins in an aerated solvent could generate singlet oxygen upon illumination with far‐red light, which was evaluated by mouse B16 melanoma cells to be applicable as photosensitizers. Besides this, it was demonstrated that they could be utilized as electron‐donating materials combined with fullerene derivatives to fabricate bulk‐heterojunction organic solar cells. [ABSTRACT FROM AUTHOR]

Pheophytin(Pheo)‐a as the free base of chlorophyll(Chl)‐a, was fluorinated at the 20‐position using N‐fluorobenzenesulfonimide, followed by insertion of a magnesium cation at the central position to afford 20‐fluoro‐Chl‐a. On the other hand, 32,32‐difluoro‐Chl‐a was obtained from Pheo‐d possessing the 3‐formyl group by the Wittig reaction using (triphenylphosphonio)difluoroacetate and the successive magnesium insertion. The synthetic 20‐fluoro‐ and 32,32‐difluoro‐Chls‐a showed similar optical properties and enzymatic hydrolysis of the phytyl ester to original (intact) Chl‐a. By contrast, their 132‐stereochemical inversion (epimerization) occurred more rapidly, and the removal of their central magnesium (pheophytinization) was more tolerant than Chl‐a due to the electronic effect of the fluorine atom(s) through the chlorin π‐system in a molecule. Since a fluorine atom is comparable in the size to a hydrogen atom, these chemically stable fluorinated Chls‐a are promising as the synthetic alternatives to naturally occurring Chl‐a, and are useful for the structural and functional investigation in oxygenic phototrophs. [ABSTRACT FROM AUTHOR]

Accurately mimicking structure and function of natural chlorophyll (Chl) assemblies is very challenging. Herein, we report the synthesis of a fullerene‐appended Chl dimer being capable of intramolecular photoinduced charge separation (CS) with a unique structure reminiscent of reaction centers (RCs) in phototrophs. Structural analyses revealed that the Chl dimer adopts a bird‐like structure in which two Chl components overlapped partially with one of the four pyrrole rings in a Chl ring similar to in a Chl pair in the natural RC complexes. A comparative study including voltammetry and spectrometric analyses using the Chl dimer and its corresponding monomer with and without a fullerene moiety was performed to gain insight into the effect of Chl pairing on (photo)redox properties. Our results suggest that the present dimer motif that closely resemble the Chl pair in natural RCs lead to more facile oxidation and lower energy of the CS state of the Chl dimer than those of the Chl monomer, resulting in its photoredox behavior different from that of the monomer Chl. [ABSTRACT FROM AUTHOR]

The lead‐free double perovskite, Cs2AgBiBr6, has received keen attention as photovoltaic absorber with nontoxicity and highly stabilities. However, the large bandgap (2.1 eV) and low optical absorption property of Cs2AgBiBr6 have limited its power conversion efficiency (PCE) in perovskite solar cells (PSCs) to low values around 2% due to the lack in short‐circuit current density (Jsc). Herein, Cs2AgBiBr6 perovskite is combined with a photoactive zinc chlorophyll derivative (Zn‐Chl) as a hole‐transporting layer (HTL) that is capable of sensitizing the perovskite absorber. The Zn‐Chl‐sensitized Cs2AgBiBr6 device exhibits a PCE up to 2.79%, the highest value for double perovskite‐based solar cells to date, with a Jsc of 3.83 mA cm−2, which is 22–27% higher than that of the devices with conventional nonphotoactive HTLs such as 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD), poly(3‐hexylthiophene) (P3HT), and poly(triarylamine) (PTAA). Through photophysical investigation, it is found that the Zn‐Chl not only plays the role of an HTL but also the role of a photoactive layer in the PSC devices. Moreover, the Zn‐Chl‐based device shows a much higher extinction coefficient than those based on Spiro‐OMeTAD, P3HT, and PTAA. This work demonstrates promise toward the realization and application of environmentally friendly solar cells. [ABSTRACT FROM AUTHOR]

Plenty of thin‐film solar cell technologies using organic materials have been developed to alleviate energy shortages. As developing devices for solar energy applications, artificial photosynthesis is a trend inspired from natural photosynthesis. Although the sophisticated system that exists in nature is fascinating, the development of photovoltaic devices focusing on the usage of natural chlorophylls has been quite limited, compared with the application of other counterparts such as artificial porphyrins or phthalocyanines. Herein, the development of semisynthetic chlorophyll derivatives as functional materials for solar cells are focused on. (Bacterio)chlorins possessing a carboxylic acid moiety as a binding site to semiconductors are synthesized to improve the efficiencies of dye‐sensitized solar cells, which are now leading to another application: photocatalysts for hydrogen evolution. In contrast, derivatives without a carboxy group can be applied to organic solar cells. As for the application for perovskite solar cells, self‐assembling aggregates of a kind of derivatives are proven to be suitable as hole‐transporting materials. In addition, a new type of solid‐state biosolar cells is proposed, in which chlorophyll derivatives act solely as the photoactive materials. This Report can enlarge the scope of advanced functional materials in the field of solar energy applications. [ABSTRACT FROM AUTHOR]

Chlorophyll(Chl)‐a derivatives containing some rigid linkers in the C3‐substituent, inserted between a hydroxymethyl group and a zinc 131‐oxo‐chlorin moiety, were synthesized as models of bacteriochlorophyll‐c/d/e molecules in the main light‐harvesting antennae (chlorosomes) of photosynthetic green bacteria. These model compounds were synthesized from a C3‐ethynylated Chl‐a derivative via several coupling reactions, and the lengths of the linkers were controlled by ethynylene and p‐phenylene groups. In less polar organic solvents or an aqueous micellar solution, some derivatives self‐aggregated in a J‐type fashion similar to that observed in natural chlorosomes, which was confirmed with UV/Vis absorption and CD spectroscopies. Their self‐aggregation abilities were dependent on the length of the inserted linkers and the conformation of the propargylic/benzylic alcoholic hydroxy groups. [ABSTRACT FROM AUTHOR]

Efficient photocatalytic hydrogen evolution reaction (HER) in the visible‐to‐near infrared region at a low cost remains a challenging issue. This work demonstrates the fabrication of organic‐inorganic composites by deposition of supramolecular aggregates of a chlorophyll derivative, namely, zinc methyl 3‐devinyl‐3‐hydroxymethyl‐pyropheophorbide a (Chl) on the surface of Ti3C2Tx MXene with 2D accordion‐like morphology. This composite material is employed as noble metal‐free catalyst in photocatalytic HER under the white light illumination, where Chl serves as a small molecule organic semiconductor component instead of ordinary inorganic and polymer organic semiconductors such as TiO2 and g‐C3N4, and Ti3C2Tx serves as a co‐catalyst. Different composition ratios of Chl/Ti3C2Tx are compared for their light‐harvesting ability, morphology, charge transfer efficiency, and photocatalytic performance. The best HER performance is found to be as high as 52 ± 5 µmol h−1 gcat−1 after optimization. Such a large HER activity is attributed to the efficient light harvesting followed by exciton transfer in Chl aggregates and the resultant charge separation at the interface of Chl/Ti3C2Tx. [ABSTRACT FROM AUTHOR]

Fine‐tuning the electronic absorption properties of chlorophylls is important for their use as light‐absorbing pigments. By oxidative coupling, a cationic pyridinium group was selectively introduced at the peripheral vinyl group of three types of synthetic chlorophylls with different degrees of π‐conjugation of the cyclic tetrapyrroles (bacteriochlorin, chlorin, and porphyrin). The substitution with the electron‐withdrawing pyridinium group moved redmost electronic absorption and main fluorescence emission maxima to longer wavelengths. This substitution effect depended on the core π‐system and decreased with increasing the degree of dehydrogenation of the cyclic tetrapyrrole (bacteriochlorin > chlorin > porphyrin). Moreover, fluorescence quenching was observed as a consequence of the introduction of the pyridinium group. The electrochemical measurements and theoretical model calculations showed that the quenching is ascribed to an intramolecular electron transfer from the core π‐skeleton to the peripheral cationic pyridinium group. [ABSTRACT FROM AUTHOR]

C3‐(Trans‐2‐arylethenyl)carbonylated chlorophyll derivatives possessing a bacteriochlorin or chlorin π‐system were synthesized by cross‐aldol (Claisen–Schmidt) condensation of methyl pyrobacteriopheophorbide‐a or 3‐acetyl‐3‐devinyl‐pyropheophorbide‐a bearing the C3‐acetyl group with p‐(un)substituted benzaldehydes under basic conditions. The corresponding porphyrin‐type chlorophyll derivatives were prepared by the oxidation (17,18‐didehydrogenation) of the chlorin‐type. Their Qy absorption and fluorescence emission maxima in dichloromethane correlated well with Hammett substituent constants of the p‐substituents. Several electron‐withdrawing p‐substituents suppressed the emission due to photoinduced electron transfer quenching in a molecule. The substitution sensitivities for their maxima and fluorescence quantum yields decreased in the order of bacteriochlorin‐, chlorin‐ and porphyrin‐type derivatives. [ABSTRACT FROM AUTHOR]

We report the in vitro activity of recombinant BchC oxidoreductase involved in bacteriochlorophyll a biosynthesis. BchC of Rhodobacter capsulatus preferentially oxidizes 31R‐3‐(1‐hydroxyethyl)‐chlorophyllide a and 31R‐3‐(1‐hydroxyethyl)‐bacteriochlorophyllide a in the presence of NAD+ to 3‐acetyl‐chlorophyllide a and bacteriochlorophyllide a, respectively, leaving the unreacted 31S‐epimers. In the reverse reaction, BchC with NADH predominately produces 31R‐epimeric alcohols from the 3‐acetyl‐(bacterio)chlorins. BchC of Chlorobaculum tepidum demonstrates the same 31R‐selectivity, suggesting that utilization of 31R‐epimers in BchC‐catalyzed reductions may be conserved across different phyla of photosynthetic bacteria. Additionally, the presence of BchC accelerates the 3‐vinyl hydration by BchF hydratase of Chlorobaculum tepidum during conversion of chlorophyllide a to 3‐acetyl‐chlorophyllide a through 3‐(1‐hydroxyethyl)‐chlorophyllide a, indicating that these enzymes work cooperatively to promote efficient bacteriochlorophyll a biosynthesis. [ABSTRACT FROM AUTHOR]

ABSTRACT: Two types of poly(ethylene glycol) (PEG)‐based amphiphiles were synthesized: a diblock‐type amphiphile (PEG1) with a hydrophobic moiety on one terminal of PEG (PEG with the molecular weight of 2000), and a triblock‐type amphiphile (PEG2) with hydrophobic moieties on both terminals of PEG. The hydrophobic moiety consisted of hydrophobic C14 alkyl tails covalently linked through a gallamide component. The sol–gel transitions of the aqueous solution of PEG1 and PEG2 were studied. At the PEG amphiphile concentration of 15 wt %, PEG1 gave a clear solution over a wide temperature range from 20 to 80 °C, while PEG2 was partially soluble in water. However, the aqueous blend solution of PEG1 and PEG2 exhibited a hydrogel depending on the blend ratio and temperature. It was considered that the composition of PEG1 and PEG2 governed the sol–gel transition, and that the dynamic moduli could be effectively controlled by changing the mixing ratios of the PEG amphiphiles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45402. [ABSTRACT FROM AUTHOR]

We have successfully demonstrated solar water splitting using a newly fabricated photoelectrochemical system with a Pt-loaded SiC photocathode, a CoO x-loaded BiVO4 photoanode, and a perovskite solar cell. Detection of the evolved H2 and O2 with a 100 % Faradaic efficiency indicates that the observed photocurrent was used for water splitting. The solar-to-hydrogen (STH) efficiency was 0.55 % under no additional bias conditions. [ABSTRACT FROM AUTHOR]

Solid-state chlorophyll solar cells (CSCs) employing a carboxylated chlorophyll derivative, methyl trans-32-carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO2, on which four zinc hydroxylated chlorophyll derivatives were spin-coated for hole transporter chlorophylls (HTCs), are described. Key parameters, including the effective carrier mobility of the HTC films, as determined by the space charge-limited current method, and the frontier molecular orbitals of these DSCs and HTCs, as estimated from cyclic voltammetry and electronic absorption spectra, suggest that both charge separation and carrier transport are favorable. The power conversion efficiencies (PCEs) of the present CSCs with fluorine-doped tin oxide (FTO)/TiO2/DSC/HTCs/Ag were determined to follow the order of HTC-1>HTC-2>HTC-3>HTC-4, which coincided perfectly with the order of their hole mobilities. The maximum PCE achieved was 0.86 % with HTC-1. The photovoltaic devices studied herein with two types of chlorophyll derivatives as dye sensitizers and hole transporters provide a unique solution for the utilization of solar energy with a view to truly realizing 'green energy'. [ABSTRACT FROM AUTHOR]

Zinc chlorophyll derivatives Zn-1- 3 possessing a tertiary amino group at the C31 position have been synthesized through reductive amination of methyl pyropheophorbide- d obtained from naturally occurring chlorophyll- a. In a dilute CH2Cl2 solution as well as in a dilute 10 %(v/v) CH2Cl2/hexane solution, Zn-1 possessing a dimethylamino group at the C31 position showed red-shifted UV/Vis absorption and intensified exciton-coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 31-N atom of the dimethylamino group. However, Zn-2/3 bearing 31-ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, where an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and 1H NMR spectroscopic analyses including DOSY measurements revealed that Zn-1 formed closed-type dimers via an opened dimer by single-to-double axial coordination with an increase in concentration and a temperature decrease in CH2Cl2, while Zn-2/3 gave open and flexible dimers in a concentrated CH2Cl2 solution at low temperature. The supramolecular closed dimer structures of Zn-1 were estimated by molecular modelling calculations, which showed these structures were promising models for the chlorophyll dimer in a photosynthetic reaction center. [ABSTRACT FROM AUTHOR]

Chlorophylls (Chls) are abundant, naturally occurring pigments that play key roles in light-harvesting and electron/energy transfer in natural photosynthetic apparatus. To demonstrate the idea that Chls are suitable hole transporters, we employed two Chl derivatives, Chl-1 and Chl-2, which self-assembled readily into π-stacking aggregates through a simple spincasting process, in perovskite solar cells (PSCs). The Chl aggregate films exhibit an ultra-smooth film surface, high hole mobility, appropriate energy levels, and efficient hole injection efficiencies that are all key characteristics for efficient hole transporters in PSCs. CH3NH3PbI3− xCl x-based PSCs with these Chls as hole transporters were fabricated and compared with P3HT as a standard hole transporter. PSCs based on Chl-1 and Chl-2 without the use of typical additives, such as 4- tert-butylpyridine and lithium bis(trifluoromethanesulfinyl)imide, gave power conversion efficiencies of 11.44 and 8.06 %, respectively. This research provides a unique way to incorporate low-cost and environmentally friendly natural photosynthetic materials in the development of highly efficient photovoltaic devices. [ABSTRACT FROM AUTHOR]

The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1,3-diketonate group at the C3 position were synthesized from methyl pyropheophorbide-d through Barbier acylmethylation of the C3-formyl moiety, oxidation of the C3-carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ=400-500 nm, with a Qy band shifted to a longer wavelength of λ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C33-position of the conjugate afforded an additional charge-transfer band over λ=500 nm, producing a pigment that bridged the green gap in standard chlorophylls. [ABSTRACT FROM AUTHOR]

Zinc bacteriochlorophyll- d analogs possessing an amino group instead of the original hydroxy group at the C31 position were prepared by chemical modification of naturally occurring chlorophyll- a. The synthetic 31-epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C31-center in the separated amines was determined by NMR analysis of their diastereomeric amides as well as by their asymmetric synthesis from authentic stereoisomers. Both the epimers were monomeric in tetrahydrofuran to give sharp electronic absorption bands, while they self-aggregated to form chlorosomal oligomers with the redshifted bands in an aqueous Triton X-100 micelle solution ( pH = 6.9). The resulting oligomers deaggregated by addition of p-toluenesulfonic acid to give monomeric N-protonated ammonium species. The aggregation and deaggregation were dependent on the 31-stereochemistry, indicating that each epimer produced supramolecularly different self-aggregates. [ABSTRACT FROM AUTHOR]

Photosynthetic green sulfur bacteria inhabit anaerobic environments with very low-light conditions. To adapt to such environments, these bacteria have evolved efficient light-harvesting antenna complexes called as chlorosomes, which comprise self-aggregated bacteriochlorophyll c in the model green sulfur, bacterium Chlorobaculum tepidum. The pigment possess a hydroxy group at the C31 position that produces a chiral center with R- or S-stereochemistry and the C31-hydroxy group serves as a connecting moiety for the self-aggregation. Chlorobaculum tepidum carries the two possible homologous genes for C3-vinyl hydratase, bchF and bchV. In the present study, we constructed deletion mutants of each of these genes. Pigment analyses of the bchFinactivated mutant, which still has BchV as a sole hydratase, showed higher ratios of S-epimeric bacteriochlorophyll c than the wild-type strain. The heightened prevalence of S-stereoisomers in the mutant was more remarkable at lower light intensities and caused a red shift of the chlorosomal Qy absorption band leading to advantages for light-energy transfer. In contrast, the bchV-mutant possessing only BchF showed a significant decrease of the S-epimers and accumulations of C3-vinyl BChl c species. As transcriptional level of bchV was upregulated at lower light intensity, the Chlorobaculum tepidum adapted to low-light environments by control of the bchV transcription. [ABSTRACT FROM AUTHOR]

The supramolecular organogelation of bacteriochlorophyll(BChl)-c carrying an isobutyl substituent at the 8-position was observed in carbon tetrachloride at a concentration of about 10 mM at room temperature. The BChl-c gel was evaluated by several spectroscopic measurements: the electronic absorption spectrum exhibited a far-red shift of the Qy-absorption from 660 to 748 nm and the FTIR spectrum showed a shorter frequency shift of the 13-C=O stretching from 1683 to 1643 cm-1 compared to the shifts of the corresponding monomer solution in tetrahydrofuran. These observations strongly indicate that the gelating BChl-c molecules form self-aggregates that are reminiscent of light-harvesting chlorosomes of green photosynthetic bacteria. The present supramolecular organogel prepared from natural chlorophylls is promising for the creation of an intelligent soft material involving artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Methyl 131-(di)cyanomethylene-pyropheophorbides were synthesized by Knoevenagel reactions of the corresponding 131-oxo-chlorins prepared from modifying chlorophyll- a with malononitrile or cyanoacetic acid. Alternatively, methyl 131-cyanomethylene-pyropheophorbides were produced by Wittig reactions of 131-oxo-chlorins with Ph3P= CHCN. Self-aggregation of zinc complexes of the semi-synthetic chlorophyll derivatives possessing a hydroxy or methoxy group at the 31-position was examined in 1%(v/v) tetrahydrofuran or dichloromethane and hexane by electronic absorption and circular dichroism spectroscopy. Although intermolecular hydrogen-bonding between the 31-hydroxy and 131-oxo groups of bacteriochlorophylls- c/ d/ e/ f was essential for their self-aggregation in natural light-harvesting antenna systems (=chlorosomes), zinc 31-hydroxy-131-di/monocyanomethylene-chlorins self-aggregated in the less/lesser polar organic solvents to form chlorosome-like large oligomers in spite of lacking the 131-oxo moiety as the hydrogen-bonding acceptor. Zinc 31-methoxy-131-dicyanomethylene-chlorin gave similar self-aggregates regardless of lack of both the 31-hydroxy and 131-oxo groups. The present self-aggregation was ascribable to stronger coordination of the 31-oxygen atom to the central zinc than the conventional systems, where the electron-withdrawing cyano group(s) increased the coordinative ability of the central zinc through the chlorin π-system. [ABSTRACT FROM AUTHOR]

Bacteriochlorophyll ( BChl) e was coassembled with BChl c in Triton X-100 micelles in aqueous solutions. The Qy absorption bands of the coaggregates were positioned between those of aggregates consisting solely of BChl c or e. The electronic absorption spectra of the coaggregates could not be reproduced by linear combinations of the spectra of the aggregates consisting solely of each pigment, but they were in line with the simulated spectra for the self-aggregates in which both BChls were randomly distributed. These suggest that BChls c and e are not spatially separated; they are homogenously distributed over the self-aggregates to give electronic spectra that are different from those of the aggregate consisting solely of each pigment. Deaggregation of the scrambled self-aggregates by excess Triton X-100 did not produce any spectral components assigned to an aggregate consisting solely of either BChl c or e. Acid-induced decomposition of the scrambled aggregates showed different kinetics from those of the aggregates consisting solely of each pigment. These also support the homogeneous distribution of BChls c and e in the scrambled self-aggregates. These results will be useful to investigate the major light-harvesting antenna systems of green photosynthetic bacteria that contain two kinds of chlorosomal BChls. [ABSTRACT FROM AUTHOR]

Zinc complex of pyropheophorbide- b, a derivative of chlorophyll- b, was covalently dimerized through ethylene glycol diester. The synthetic homo-dyad was axially ligated with two methanol molecules from the β-face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto-carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, 1H NMR and IR spectra. All the synthetic zinc chlorin homo- and hetero-dyads consisting of pyropheophorbides- a, b and/or d took the above methanol-locked and π- π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo-dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo-dyads partially took such supramolecules. The J-type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel chlorophyll b (Chl-b) derivative was found from phycophagic protists. [•] The derivative was identified as 132,173-cyclopheophorbide b enol (cPPB-bE). [•] cPPB-bE co-occurred with Chl-a-derived cPPB-aE by preying on Chl-a/b algae. [•] cPPB-bE is likely to be a de-phototoxicified catabolite of Chl-b, similarly as cPPB-aE. [•] Chl-b is directly catabolized along protistan phycophagic processes, unlike in land plants. [ABSTRACT FROM AUTHOR]

Developing new strategies for controlling polymer conformations through precise molecular recognition can potentially generate a machine-like motion that is dependent on molecular information-an important process for the preparation of new intelligent nanomaterials (e.g., polymer-based nanomachines) in the field bordering between polymer chemistry and conventional supramolecular sciences. Herein, we propose a strategy to endow a helical polymer chain with dynamic spring-like (contraction/expansion) motion through the one-dimensional self-assembly (aggregation/disaggregation) of peripheral amphiphilic molecules. In this developing system, we employed a semi-artificial helical polysaccharide presenting peripheral amphiphilic chlorophyll units as a power device that undergoes contractive motion in aqueous media, driven by strong π-π interactions of its chlorophyll units or by cooperative molecular recognition of bipyridyl-type ligands through pairs of chlorophyll units, thereby converting molecular information into the regulated motion of a spring. In addition, this system also undergoes expansive motion through coordination of pyridine. We anticipate that this strategy will be applicable (when combined with the established wrapping chemistry of the helical polysaccharide) to the development of, for example, drug carriers (e.g., nano-syringes), actuators (stimuli-responsive films), and directional transporters (nano-railways), thereby extending the frontiers of supramolecular science. [ABSTRACT FROM AUTHOR]

Demetalation of chlorophyll ( Chl) a and its analogs is an important reaction in oxygenic photosynthetic organisms, which produces the primary electron acceptors in photosystem II reaction centers and is crucial in the Chl degradation. From these viewpoints, demetalation reactions of four Chl a analogs, 3,8-divinyl- Chl a ( DV- Chl a), 3-devinyl-3-ethyl- Chl a (meso Chl a), 132-demethoxycarbonyl- Chl a (pyro Chl a) and protochlorophyll a ( PChl a), were kinetically analyzed under weakly acidic conditions, and were compared with that of Chl a. DV- Chl a exhibited slower demetalation kinetics than did Chl a, whereas demetalation of meso Chl a was faster than that of Chl a. The difference in demetalation kinetics of the three chlorophyllous pigments originates from the electron-withdrawing ability of the vinyl group as the peripheral substituent compared with the ethyl group. Removal of the electron-withdrawing and homoconjugating 132-methoxycarbonyl group in Chl a ( Chl a → pyro Chl a) accelerated demetalation kinetics by two-fold. PChl a possessing the porphyrin-type skeleton exhibited slower demetalation kinetics than Chl a. The structure-dependent demetalation properties of Chl a analogs will be useful for understanding in vivo Chl demetalation reactions in oxygenic photosynthetic organisms. [ABSTRACT FROM AUTHOR]

Chlorosomes are one of the most unique natural light-harvesting antennas and their supramolecular nanostructures are still under debate. Chlorosomes contain bacteriochlorophyll (BChl)- c, d and e molecules and these pigments self-aggregate under a hydrophobic environment inside a chlorosome. The self-aggregates are mainly constructed by the following three interactions: hydrogen bonding, coordination bonding and π-π stacking. Supramolecular nanostructures of self-aggregated BChls have been widely investigated by spectroscopic and microscopic techniques. Model compounds of such chlorosomal BChl molecules have been synthesized and the effects of esterified long alkyl chains at the 17-propionate residue for their self-aggregation have been studied. Structurally simple zinc chlorophyll derivatives possessing an oligomethylene chain as the esterifying group at the 17-propionate residue were prepared as chlorosomal BChl models. The synthetic zinc BChls self-aggregated in nonpolar organic solvents to give precipitates. The resulting insoluble self-aggregated solids were investigated on a variety of substrates, including hydrophobic, neutral and hydrophilic substrates, by visible absorption, circular dichroism and polarized light absorption spectroscopies, as well as atomic force, transmission electron and scanning electron microscopies. The self-aggregates of synthetic Zn-BChls formed rods with an approximately 5 nm diameter and wires with further elongated growth of the rods (aspect ratio >200). The diameter size was consistent with that estimated for natural chlorosomal rods in a filamentous anoxygenic phototroph, Chloroflexus aurantiacus. The supramolecular formation and stability of the rod on the examined substrates depended on the length of an oligomethylene chain at the 17-propionate residue as well as on the surface properties. Especially, the number of the 5 nm rods on the substrates increased with an elongation of the chain. [ABSTRACT FROM AUTHOR]

Abstract: Chlorophyll-a (Chl-a) was readily converted into Chl-d under mild conditions without any enzymes. Treatment of Chl-a dissolved in dry tetrahydrofuran (THF) with thiophenol and acetic acid at room temperature successfully produced Chl-d in 31% yield. During the acidic oxidation, removal of the central magnesium, pheophytinization, was sufficiently suppressed. This mild pathway can give insights into the yet unidentified Chl-d biosynthesis. [Copyright &y& Elsevier]

Summary The Arabidopsis ACCELERATED CELL DEATH 2 (ACD2) protein protects cells from programmed cell death (PCD) caused by endogenous porphyrin-related molecules like red chlorophyll catabolite or exogenous protoporphyrin IX. We previously found that during bacterial infection, ACD2, a chlorophyll breakdown enzyme, localizes to both chloroplasts and mitochondria in leaves. Additionally, acd2 cells show mitochondrial dysfunction. In plants with acd2 and ACD2 + sectors, ACD2 functions cell autonomously, implicating a pro-death ACD2 substrate as being cell non-autonomous in promoting the spread of PCD. ACD2 targeted solely to mitochondria can reduce the accumulation of an ACD2 substrate that originates in chloroplasts, indicating that ACD2 substrate molecules are likely to be mobile within cells. Two different light-dependent reactive oxygen bursts in mitochondria play prominent and causal roles in the acd2 PCD phenotype. Finally, ACD2 can complement acd2 when targeted to mitochondria or chloroplasts, respectively, as long as it is catalytically active: the ability to bind substrate is not sufficient for ACD2 to function in vitro or in vivo. Together, the data suggest that ACD2 localizes dynamically during infection to protect cells from pro-death mobile substrate molecules, some of which may originate in chloroplasts, but have major effects on mitochondria. [ABSTRACT FROM AUTHOR]

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 (132 R)- and (132 S)-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 (132 R)-forms, which are generally found in photosynthetically active chlorophyllous pigments. [ABSTRACT FROM AUTHOR]

Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d, which had a methyl group at this position. The activation energy of demetalation of 31 R-8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 31 R-[E,E]-BChl c. 15N-labeled 31 R-[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15NH4Cl, and their 15N NMR spectra were measured. The chemical shifts of N21, N22 and N23 atoms of 31 R-[E,E]-BChl e were lower-field shifted than those of 31 R-[E,E]-BChl c, respectively, and especially the difference in chemical shifts of N22 was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d. [ABSTRACT FROM AUTHOR]

Abstract: Substituent-dependent demetalation kinetics of natural bacteriochlorophyll (BChl) c and e homologs purified from two green sulfur photosynthetic bacteria was first studied. Separated BChl e homologs, which possessed a formyl group at the 7-position of their chlorin macrocycles, exhibited a significantly slow removal of central magnesium to free-base bacteriopheophytins in acidic aqueous acetone compared with the corresponding BChl c homologs, which possessed a methyl group at the 7-position. Additional methyl groups at the 82-position of both BChl c and e molecules had little effect on the demetalation kinetics. [Copyright &y& Elsevier]

During anaerobic cobalamin (vitamin B12) biosynthesis, CbiL catalyzes methylation at the C-20 position of a cyclic tetrapyrrole ring using S-adenosylmethionine as a methyl group source. This methylation is a key modification for the ring contraction process, by which a porphyrin-type tetrapyrrole ring is converted to a corrin ring through elimination of the modified C-20 and direct bonding of C-1 to C-19. We have determined the crystal structures of Chlorobium tepidum CbiL and CbiL in complex with S-adenosylhomocysteine (the S-demethyl form of S-adenosylmethionine). CbiL forms a dimer in the crystal, and each subunit consists of N-terminal and C-terminal domains. S-Adenosylhomocysteine binds to a cleft between the two domains, where it is specifically recognized by extensive hydrogen bonding and van der Waals interactions. The orientation of the cobalt-factor II substrate was modeled by simulation, and the predicted model suggests that the hydroxy group of Tyr226 is located in close proximity to the C-20 atom as well as the C-1 and C-19 atoms of the tetrapyrrole ring. These configurations allow us to propose a catalytic mechanism: the conserved Tyr226 residue in CbiL catalyzes the direct transfer of a methyl group from S-adenosylmethionine to the substrate through an S N2-like mechanism. Furthermore, the structural model of CbiL binding to its substrate suggests the axial residue coordinated to the central cobalt of cobalt-factor II. [ABSTRACT FROM AUTHOR]