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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.

A method has been proposed to reason the choice among the known optimized models for methods for estimating chlorophyll (Chl) concentration in the seawater according to the information-logarithmic criterion, which provides a comparison of theoretical models by the SeaWiFS data. It has been shown that the most appropriate means is to determine the Chl concentration, since the concentration of Chl in seawater is systematically investigated by marine ships or remote sensing. All optimized models of the optical properties of seawater can be verified by checking the simulated and measured Chl concentration data.

The influence of photodegradation on the optical limiting process of chloroform solutions of chlorophyll A is investigated. Optical limitation experiments were carried out with a frequency-doubled, 10 ns Nd:YAG laser at a 5 Hz repetition rate, as a function of sample degradation. Optical limitation becomes less effective in photodegraded samples, which may be explained by the decrease in the concentration of chlorophyll A molecules. It is concluded that the optical limiting process is mainly related to the reverse saturated absorption mechanism, and contributions from light scattering due to photodegradation and the cavity bubbles appear irrelevant.

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.

The SeO₂ oxidation of chlorophyll (Chl) a in deaerated pyridine solution under argon, produced, after 4 hours of refluxing, work-up and chromatographic purifications on a sucrose column, 13²(S/R)-hydroxy-Chl a (20%), 13²(S/R), P4(S/R)-dihydroxy-Chl a (19%) and P4(S/R)-hydroxy-13²-demethoxycarbonyl-13²-oxo-Chl a (10%). The major products were characterized by ¹H and ¹³C NMR spectra, electronic absorption spectra (UV-vis) and FAB-MS. The C-13² oxidation of the enolizable isocyclic ring was found to be faster than the allylic C-P4 oxidation of the phytyl chain. Essential features of the mechanisms proposed for the C-P4 allylic oxidation and the C-13² oxidation of Chla are the ene-reaction and the [2,3]-sigmatropic rearrangement. In the C-13² oxidation, the ene-reaction affords the selenite ester of the Chl enol as the first intermediate, which is then converted by [2,3]-sigmatropic rearrangement to the hydrolyzable Chl selenoxylate ester intermediate. However, in pyridine, we regard the attack of the nucleophilic oxygen atom of the Chl enol or enolate to the electrophilic Se-atom of SeO₂ as a likely alternative for the ene-reaction of the Chl isocyclic ring. The C-P4 hydroxylation of the phytyl chain exhibited very little diastereoselectivity, whereas the C-13² hydroxylation reaction showed moderate diastereoselectivity, producing 80% of 13²(R)-HO-Chl a (de = 60%) and 20% of 13²(S)-HO-Chl a. Kinetic or thermodynamic control of the [2,3]-sigmatropic rearrangement was considered as a possible factor underlying the diastereoselectivity observed for the C-13² hydroxylation.

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.

Demetalation kinetics of zinc chlorophyll derivative 1 possessing two formyl groups directly linked to the A- and B-rings of the chlorin macrocycle, which was synthesized from chlorophyll b, was examined under acidic conditions and compared with those of Zn chlorins 2 and 3 possessing a single formyl group in the A- and B-ring, respectively, as well as Zn chlorin 4 lacking any formyl group to unravel the substitution effects on demetalation properties of chlorophyllous pigments. Demetalation kinetics of diformylated Zn chlorin 1 was slower than those of monoformylated Zn chlorins 2 and 3, indicating that the effect of the electron-withdrawing formyl group on demetalation kinetics was amplified by introduction of two formyl groups to the chlorin macrocycle. High correlations were observed between demetalation rate constants of Zn chlorins 1–4 and the sum of Hammett σ parameters of the 3- and 7-substituents on the chlorin macrocycle, indicating that the combination of electron-withdrawing abilities of the substituents linked directly to the cyclic tetrapyrrole was responsible for demetalation properties of zinc chlorophyll derivatives.

Reactions of thiol with the C3-vinyl group of various chlorophyll (Chl) derivatives were examined. The reactions resemble thiol-olefin co-oxidation, except that the vinyl C=C double bond was cleaved to afford a formyl group without any transition metal catalyst, and that the simple anti-Markovnikov adduct of thiol to olefin was obtained as a minor product. Peripheral substituents of Chl derivatives little affected the reaction, while the central metal atom of the chlorin macrocycle influenced the composition of the products. Oxygen and acid dissolved in the reaction mixture can facilitate the oxidation. Sufficiently mild conditions in this regioselective oxidation at the C3¹-position are significant in bioorganic chemistry.

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.

The vibrational properties of metal complexes of monoformylated and diformylated chlorophyll derivatives were compared with those of the corresponding free-base chlorins to unravel the effects of the central metal on the carbonyl stretching vibration modes of the peripheral oxygen functional groups in the chlorin macrocycle by means of FTIR spectroscopy. The 3-C=O stretching vibrational bands of a 3-formyl group were shifted to lower wavenumbers by insertion of Zn and Cu into the center of the 3-formyl free-base chlorin. In contrast, the 7- and 8-C=O stretching vibrational bands of the formyl groups linked to the B-ring of the chlorin macrocycle were barely shifted even if 7- and 8-formyl free-base chlorins were metalated. The down-shifts of the 3-C=O and few shifts of the 7-/8-C=O vibrational stretching bands were in line with the results of DFT calculations. The difference in the effects of the central metal on the vibrational properties between the formyl group in the A-ring and those in the B-ring is ascribable to the different conjugation manners with the adjacent π-system: the 3-formyl group was connected to the chlorin 18π-system, whereas the 7-/8-formyl groups were conjugated to the rather isolated C7–C8 double bond. The 13-C=O stretching vibrational bands were shifted to lower wavenumbers by metalation. These down-shifts can also be rationalized by invoking the conjugation of the 13-keto group with the chlorin 18π-system.

Advances in chlorin synthetic chemistry now enable the de novo preparation of diverse chlorin-containing molecular architectures. Five distinct molecular designs have been explored here, including hydrophobic bioconjugatable (oxo)chlorins; a hydrophilic bioconjugatable chlorin; a trans-ethynyl/iodochlorin building block; a set of chlorins bearing electron-rich (methoxy, dimethylamino, methylthio) groups at the 3-position; and a set of ten 3,13-disubstituted chlorins chiefly bearing groups with extended π-moieties. Altogether 23 new chlorins (17 targets, 6 intermediates) have been prepared. The challenge associated with molecular designs that encompass the combination of "hydrophilic, bioconjugatable and wavelength-tunable" chiefly resides in the nature of the hydrophilic unit.

Major photosynthetic pigments chlorophyll(Chl)s have a cyclic tetrapyrrole with a five-membered exocyclic E-ring as photofunctional moieties. Its transformation is one promising methodology to develop functional pigments based on Chl chemistry. This paper report a facile conversion from Chl derivatives lacking the 13²-methoxycarbonyl moiety to the corresponding chlorophyllous pigments, whose exocyclic E-ring had two oxo groups at the 13¹- and 13²-positions, by contact with the TiO₂ particles in the presence of molecular oxygen in the dark. The conversion proceeded under mild conditions without hydrolysis of the ester group in the 17-propionate residue. This is in sharp contrast to the inevitable ester cleavage in the conventional synthesis of Chl derivatives that possess α-diketone in the E-ring. The reaction properties in the present method allowed us to perform a one-step conversion of Chl derivatives esterified with a natural isoprenoid alcohol phytol to the corresponding 13²-oxo-pigments. No removal of central Zn from the chlorin macrocycle occurred in the present conversions using Zn pyropheophytin a as a starting material.

Following extraction from photosynthetic organisms, chlorophylls are prone to reactions including demetalation, dephytylation and specific oxidations of the exocyclic ring E, termed allomerizations. Allomerization of chlorophylls has been well-characterized in methanol and to a lesser extent in aqueous solution. Here we detail novel allomerization-like reactions of chlorophyll a and chlorophyll b. In the presence of heme, detergent-solubilized chlorophyll a is hydroxylated at its C13² position in ring E and, surprisingly, the C18 position in ring D. Two major oxidation products are synthesized — a C13²-OH and a C13²-OH, C18-OH derivative of chlorophyll a. We track the origin of the oxygen atoms added in these hydroxylated chlorophylls using ¹⁸O₂ labeling and demonstrate that the additional oxygen atoms are derived from molecular oxygen. A similar heme-catalyzed reaction is also observed using chlorophyll b as a substrate. These results highlight the need for care when dealing with extracted chlorophylls and demonstrate an unusual hydroxylation of the C18 position of chlorophylls in the presence of heme.

“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.

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.

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.

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.

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.