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Photosynthetic organisms provide, directly or indirectly, the energy that sustains life on earth by harvesting light from the sun. The amount of light impinging on the surface of the earth vastly surpasses the energy needs of life including man. Harvesting the sun is, therefore, an option for a sustainable energy source: directly by improving biomass production, indirectly by coupling it to the production of hydrogen for fuel or, conceptually, by using photosynthetic strategies for technological solutions based on non-biological or hybrid materials. In this review, we summarize the various light climates on earth, the primary reactions responsible for light harvesting and transduction to chemical energy in photosynthesis, and the mechanisms of competitively adapting the photosynthetic apparatus to the ever-changing light conditions. The focus is on oxygenic photosynthesis, its adaptation to the various light-climates by specialized pigments and on the extension of its limits by the evolution of red-shifted chlorophylls. The implications for potential technical solutions are briefly discussed.

As naturally occurring bacteriochlorophyll-$d$ models, zinc methyl (3¹R)-bacteriopheophorbides-$d$ possessing ethyl, vinyl, and ethynyl groups at the 3²-position were prepared by chemically modifying chlorophyll-$a$. The synthetic molecules self-aggregated in an aqueous Triton X-100 micelle solution similarly as in the major light-harvesting antenna of photosynthetic green bacteria to give supramolecularly ordered large oligomers with red-shifted and broadened visible absorption bands, compared with the monomeric bands. The sequential hydrogenation of the 3²-ethynyl to ethyl group via the vinyl group gradually suppressed the chlorosomal self-aggregation ability. The successive elongation of the 3¹-alkyl chain from a methyl to propyl group via an ethyl group also diminished the $J$-aggregation ability. These decreases in the self-aggregation were ascribable to the steric enhancement of the 3²-substituents near the 3¹-hydroxy group requisite for the $J$-aggregation.

Chlorins provide many ideal features for use as red-region fluorophores but require molecular tailoring for solubilization in aqueous solution. A chlorin building-block bearing 18,18-dimethyl, 15-bromo and 10-[2,4,6-tris(propargyloxy)phenyl] substituents has been transformed via click chemistry with CH₃(OCH₂CH${}_2{)}_{12}$-N₃ followed by Suzuki coupling with 3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)propanoic acid, thereby installing a water-solubilization motif and a bioconjugatable handle, respectively. In toluene, $N,N$-dimethylformamide (DMF) or water, the resulting facially encumbered free base chlorin exhibits characteristic chlorin absorption (${\lambda }_{\mathrm{\text{abs}}}$$\sim$412, 643 nm) and fluorescence (${\lambda }_{\mathrm{\text{em}}}$$\sim$645 nm) spectra with only modest variation in fluorescence quantum yield (${\mathrm{\Phi }}_{\text{f}})$ values (0.24, 0.25 and 0.19, respectively). The zinc chlorin derived therefrom exhibits similar spectral constancy (${\lambda }_{\mathrm{\text{abs}}}$$\sim$414 and 613 nm, ${\lambda }_{\mathrm{\text{em}}}$$\sim$616 nm) and ${\mathrm{\Phi }}_{\mathrm{\text{f}}}=$ 0.094, 0.10 and 0.086 in the three solvents. The results together indicate the viability of the molecular design and synthetic methodology to create red-region fluorophores for use in diverse applications.

The degradation of the green pigment chlorophyll in plants is known to yield phyllobilins as highly abundant linear tetrapyrroles. Recently, a split path of the degradation pathway has been discovered, leading to so-called dioxobilin-type (or type-II) phyllobilins. The first characterized type-II phyllobilin was colorless featuring four deconjugated pyrrole units. Similar to the type-I branch, for which yellow oxidation products of the colorless phyllobilins – the type-I phylloxanthobilins – are known, a type-II phylloxanthobilin has recently been characterized from senescent leaves of grapevine. Type-I phylloxanthobilins appear to be actively produced in the plant, are known to possess interesting chemical properties, and were shown to act as potent antioxidants that can protect cells from oxidative stress. Here we report the isolation and structural characterization of a type-II phylloxanthobilin from de-greened leaves of savoy cabbage, which turned out to be structurally closely related to bilirubin. Bilirubin is known to possess high antioxidative activity; in addition, savoy cabbage is considered to promote health benefits due to its high content in antioxidants. We therefore investigated the in vitro antioxidative potential of the newly identified type-II phylloxanthobilin using two different approaches, both of which revealed an even higher antioxidative activity for the type-II phylloxanthobilin from savoy cabbage compared to bilirubin.

Chlorophyll (Chl) and bacteriochlorophyll (BChl) pigments, which are crucial cyclic tetrapyrroles in photosynthesis, generally have a chiral center in their exo-cyclic five-membered E-ring. Although $S$-epimers (primed-type) of (B)Chl pigments are rarely present in photosynthetic organisms, they play key roles in photosynthetic reaction center complexes. The epimerization mechanism of (B)Chl pigments in vivo has not been unraveled. The structural effects on the physicochemical properties of (B)Chl epimerization reactions provide useful information to tackle this question. We analyzed epimerization of three pigments, BChl $a$, Chl $a$, and 3-acetyl Chl $a$, to elucidate the structural factors that are responsible for epimerization reactions. We compared the epimerization kinetics of the three pigments and concluded that the bacteriochlorin skeleton (7,8,17,18-tetrahydroporphyrin) significantly retarded the epimerization kinetics. Thus, BChl $a$ exhibited slower epimerization kinetics than Chl $a$ in spite of the presence of the electron-withdrawing 3-acetyl group that accelerates epimerization. In contrast to the large structural effects of (B)Chl molecules on epimerization kinetics, the thermodynamic properties at equilibrium in the epimerization of the three pigments were barely influenced by their molecular structures. This study also demonstrates that a semi-synthetic pigment, 3-acetyl Chl $a$, is appropriate for comparative analyses of the structural effects of BChl $a$ and Chl $a$ on their physicochemical properties.

Methyl protopyropheophorbides-a/d were prepared by modification of readily available chlorophyll-a. The key step was oxidation of 13¹-oxo-chlorin to the corresponding porphyrin, and 2,3-dichloro-5,6-dicyano-p-benzoquinone was effective for 17,18-dehydrogenation. A reduction in oxidation potential of the chlorin was necessary for the oxidation. Facile oxidation was achieved by insertion of zinc as the central metal, reduction of the 13-carbonyl group and/or aggregation by high concentration. The synthetic 13¹-oxo-porphyrins had vinyl and formyl groups at the 3-position. These groups were very reactive in the molecule and selectively converted to other functional groups.

Regioselective bromination of methyl pyropheophorbide a at the C3²-position of the terminal double bond has been carried out as a one-pot two-step addition/elimination process. The elimination occurs with 100% stereoselectivity and bromovinyl 4 has E-configuration of the C3-double bond. The reactivity of unsaturated bromide 4 has been evaluated in the series of the Pd-catalyzed coupling reactions.

Tolyporphins are unusual tetrapyrrole macrocycles produced by the filamentous cyanobacterium–microbial community HT-58-2, the only known source to date. Numerous cyanobacterial samples have been collected worldwide but most have not been screened for secondary metabolites. Identification of tolyporphins typically has entailed lipophilic extraction followed by chromatographic fractionation and spectroscopic and/or mass spectrometric analysis. For quantitation, lengthy lipophilic extraction, sample processing and HPLC separation are needed. Examination by MALDI-TOF-MS (with the matrix 1,5-diaminonaphthalene) of lipophilic crude extracts of small-scale HT-58-2 samples (2 mL) without chromatographic fractionation enabled semi-quantitation of tolyporphin A over a 41-day growth period. Screening for tolyporphin A in intact or slightly sheared and vortexed HT-58-2 samples (no lipophilic extraction), and confirmation of identity by tandem MS, were carried out by IR-MALDESI-FTMS. Tolyporphin A was identified by the molecular ion and four characteristic fragments. The molecular ion of chlorophyll $a$ also was observed. The sheared and vortexed sample contained substantial numbers of intact cells as demonstrated by regrowth of the filamentous cyanobacterium–microbial culture. The semi-quantitative and rapid qualitative methods developed herein should facilitate examination of other tolyporphin-producing organisms among the vast worldwide strains of cyanobacteria as well as investigation of the biosynthesis of tolyporphins.

Various chlorophyll and bacteriochlorophyll derivatives possessing a magnesium or zinc atom at the central position and a free carboxylic acid group at the C17${}^{\mathrm{\text{2}}}$-position, also known as (bacterio)chlorophyllides, were synthesized through a combination of organic synthesis techniques and enzymatic steps. The semi-synthetic (bacterio)chlorophyllides were purified and analyzed using reversed-phase high-performance liquid chromatography with UV-vis spectroscopy and mass spectrometry. These free propionic acid-containing chlorophyllous pigments can be useful research materials for the study of (bacterio)chlorophyll metabolisms.

This study investigates the effect of copper on the germination and growth of watermelon plants. It was found that copper only inhibited the germination and growth of watermelon plants when its concentrations were high. Copper concentrations of either 50 or 100μM increased chlorophyll content in the plants slightly while copper concentrations over 100μM led to an obvious decrease in chlorophyll contents. It is concluded that excess copper significantly affects the germination and growth of watermelon.

We studied soybean leaves of the main soybean cultivars and their mutants from Shanxi Province, China, using multifractal spectrum analysis of transmission scanned gray scale images of excised leaves. We demonstrate that the parameters of multifractal spectra correlate with the biological status of the plant. The width $\mathrm{\Delta }\alpha$ of the multifractal spectrum, a parameter of the transmission scanned gray scale image, is a good indicator of the metabolic state and growth rate of a soybean leaf. In general, the larger the value of $\mathrm{\Delta }\alpha$, the more exuberant the metabolism and the faster the growth rate of the leaf. ${\alpha }_{min}$ is a parameter related with the distribution of chlorophyll in leaf, it reflects the concentration degree of chlorophyll; the smaller the value of ${\alpha }_{min}$, the higher the concentration degree of chlorophyll in the leaf. ${\alpha }_{max}$ is a parameter related with the distribution of water in the leaf, it reflects the concentration degree of water; the larger the value of ${\alpha }_{max}$, the higher the concentration degree of water in the leaf. In order to reduce the impact of errors in the calculation of $\mathrm{\Delta }\alpha$, ${\alpha }_{min}$ and ${\alpha }_{max}$, we introduced three new parameters — the characteristic width $\mathrm{\Delta }{\alpha }_C$, the characteristic ${\alpha }_S$ and the characteristic ${\alpha }_L$. We compare the values of $\mathrm{\Delta }\alpha$, ${\alpha }_{min}$ and ${\alpha }_{max}$ among the different leaves qualitatively by replacing $\mathrm{\Delta }\alpha$, ${\alpha }_{min}$ and ${\alpha }_{max}$ with $\mathrm{\Delta }{\alpha }_C$, ${\alpha }_S$ and ${\alpha }_L$, respectively. In research of soybean leaf growth, stress resistance of soybean cultivars and the breeding of excellent varietals, $\mathrm{\Delta }{\alpha }_C$ is shown here to be a new and useful indicator for analysis.

“Non-fluorescent” chlorophyll catabolites (NCCs) were named “rusty pigments” originally, as they easily oxidized to yellow chlorophyll catabolites (YCCs) and other colored natural “phyllobilins.” In the present work, binding of Zn(II)-ions by YCC and its methyl ester YCC-Me, and structural investigations of the resulting Zn(II)-complexes are reported. Binding of Zn-ions to the weakly luminescent YCC or YCC-Me in DMSO produces orange-yellow complexes that exhibit strong green emission. The Zn-complex of YCC-Me was isolated and characterized by UV-vis-, fluorescence-, mass- and NMR-spectra. The data revealed a 2:1 complex, Zn(YCC-Me)${}_2$, in which YCC-Me serves as bidentate ligand. The Zn(II)-center in Zn(YCC-Me)${}_2$ is, thereby, deduced to be coordinated in a pseudo tetrahedral fashion. Formation of Zn(YCC-Me)${}_2$ (and of Zn(YCC)${}_2)$ is compatible with an isomerization of the lactam form of ring D to the corresponding lactim tautomer in these neutral Zn(II)-complexes.

Using the sterically hindered base, 1,8-diazabicyclo[5.4.0]undec-7-ene, for enolization and tert-butyldimethylsilyl-trifluoromethanesulfonate for silylation, chlorophyll (Chl) $a$ produced after 15 min at 0 $°$C in deaerated pyridine solution under argon, after work-up and chromatographic purification on a sucrose column, tert-butyldimethylsilyl-enol ether of Chl $a$ in a yield of 77%. The 13¹-deoxo-13¹,13²-didehydro-chlorophyll $a$, was obtained in a yield of 23% through a reaction sequence, where Chl $a$ was first reduced with sodium borohydride to 13${}^1(R,S)$-hydroxy-Chl $a$, which via demetalation yielded 13${}^1(R,S)$-hydroxypheophytin $a$. In the presence of the sterically hindered base, 1,8-bis(dimethylamino)naphthalene, trifluoroacetylimidazole dehydrated 13${}^1(R,S)$-hydroxypheophytin $a$ to 13¹-deoxo-13¹,13²-didehydro-pheophytin $a$, which after metalation yielded 13¹-deoxo-13¹,13²-didehydro-Chl $a$. Using 1,8-bis(dimethylamino)naphthalene and trifluoroacetylimidazole, the straight conversion of 13${}^1(R,S)$-hydroxy-Chl $a$ to 13¹-deoxo-13¹,13²-didehydro-Chl $a$ was found unsuccessful. The major products were characterized by electronic absorption spectra (UV-vis) and practically completely assigned ¹H and ${}^{13}$C NMR spectra. Some intermediates of the syntheses were also characterized by ESI-TOF mass spectra. Compared with Chl $a$, the macrocyclic ring-current in the synthesized Chl $a$ enol derivatives was found weakened by the expansion of the $\pi$-system to include the isocyclic ring E. Nevertheless, these enol derivatives were still considered to be diamagnetic and aromatic. The possibility of the functional role of the enol derivatives of chlorophyll in photosynthesis is discussed.

C13²-$S$-epimers of chlorophyll (Chl) molecules are important cofactors in the photosystem I reaction centers in oxygenic photosynthetic organisms; however, their production mechanism is still unclear. The reaction properties of Chl epimerization are helpful for a better understanding of the molecular mechanism of the in vivo formation of Chl C13²-$S$-epimers. We report herein the kinetic properties of the epimerization of formylated Chl molecules, Chl $b$ and Chl $d$, by use of triethylamine. Both Chl $b$ and Chl $d$ performed faster epimerization kinetics than Chl $a$, indicating that the electron-withdrawing ability of the formyl groups directly linked to the chlorin macrocycle is responsible for acceleration of the epimerization. Comparing the rate constants of the two mono-formylated Chl molecules indicated that the epimerization of Chl $b$ was faster than that of Chl $d$. This difference is rationalized by invoking a combination of the inductive effects of the C3- and C7-substituents in Chls; the sums of Hammett $\sigma$ parameters of the C3- and C7-substituents exhibited high correlations with the epimerization rate constants of Chls $b$, $d$, and $a$.