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Understanding the crystal-packing patterns of tetrapyrroles underpins a number of objectives in materials sciences. Here, the zinc chelate of 3,13-diacetyl-10-(pentafluorophenyl)-18,18-dimethylchlorin was prepared, crystallized in the presence of tetrahydrofuran (THF), and analyzed by single-crystal x-ray diffraction (SCXRD). The zinc chlorin (Zn1) afforded a herringbone pattern of parallel columnar stacks of chlorins rotated by 67.41${}^{\circ }$ with respect to each other. The chlorins within a column are stacked in pairs having interplanar distances of 3.289 Å within a pair and 4.407 Å between pairs. The chlorins in a pair are aligned in a “head-to-head” arrangement with cofacial $\pi$–$\pi$ overlap chiefly only of the respective ring A units; the overall composition is thus of columnar stacks of slipped-stacked pairs of chlorins. Each chlorin is enantiomeric due to the coordination at the Zn(II) center of a single THF molecule; the juxtaposition of chlorin $\alpha$–$\beta$ faces opposite the apically ligated THF molecules affords a racemate. All chlorins in a column face in the same direction, with 3,13-acetyl groups essentially coplanar with the macrocycle and oriented toward the respective 5,15-positions (affording an O$\cdot \cdot \cdot$H–C contact of 2.33 or 2.39 Å), and with interdigitation of alternating pentafluorophenyl groups in adjacent columns. A large number of SCXRD analyses of synthetic chlorins will likely be required to understand the relationship between structure and assembly patterns.

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.

Recent developments in the synthesis and transformation of porphyrins and their derivatives are presented. In connection with the Fifth International Conference on Porphyrins and Phthalocyanines (ICPP-5) a survey of current method developments and reactivity studies is made. The review focuses on synthetic advances in porphyrin chemistry. A brief survey of important developments covers selectively the literature from 2004 to late 2007.

Ferrochelatase (also known as PPIX ferrochelatase; Enzyme Commission number 4.9.9.1.1) catalyzes the insertion of ferrous iron into PPIX to form heme. This reaction unites the biochemically synchronized pathways of porphyrin synthesis and iron transport in nearly all living organisms. The ferrochelatases are an evolutionarily diverse family of enzymes with no more than six active site residues known to be perfectly conserved. The availability of over thirty different crystal structures, including many with bound metal ions or porphyrins, has added tremendously to our understanding of ferrochelatase structure and function. It is generally believed that ferrous iron is directly channeled to ferrochelatase in vivo, but the identity of the suspected chaperone remains uncertain despite much recent progress in this area. Identification of a conserved metal ion binding site at the base of the active site cleft may be an important clue as to how ferrochelatases acquire iron, and catalyze desolvation during transport to the catalytic site to complete heme synthesis.

Ferrochelatase, the terminal enzyme of the heme biosynthetic pathway, catalyzes the insertion of ferrous iron into protoporphyrin IX to give heme. Resonance Raman spectroscopy has been instrumental in defining the distortion (mode and extent) of the porphyrin substrate, which is a critical step in the catalytic mechanism of ferrochelatase. Saddling is the predominant porphyrin out-of-plane deformation induced upon binding to ferrochelatase. Our analysis demonstrated that the intensity of the γ₁₅ line, which is assigned to an out-of-plane porphyrin vibration, in resonance Raman spectra obtained for wild-type- and variant ferrochelatase-bound porphyrin, correlates with the saddling deformation undergone by the porphyrin substrate. Further analysis of the three dimensional X-ray structures of bacterial, human and yeast ferrochelatases and the type and extent of distortion of the protein-bound porphyrin substrate and inhibitors using normal structure decomposition, support the view that ferrochelatase catalysis involves binding of a distorted porphyrin substrate and releasing of a flatter, metalated porphyrin.

The review aims at being an exhaustive summary of the use of Huisgen azide-alkyne dipolar addition in the synthesis of tetrapyrrolic compounds, mainly porphyrins, phthalocyanines, chlorins and bacteriochlorins.

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.

A series of chlorophyll derivatives possessing a carboxy group were synthesized aiming at their application as sensing materials and to dye-sensitized solar cells (DSSCs). Their absorption and fluorescence responses to amine concentrations in THF and photovoltaic performance of DSSCs on TiO₂ films were investigated.

Cavitands and porphyrinoids are two major groups of molecules. If cyclodextrins are maybe the most famous type of cavitands, the properties of resorcinarenes are now well known and rise rapidly increasing attention. This mini-review aims at detailing all the combinations of resorcinarenes with porphyrinoids reported so far, evidencing the bright future of such combos. In addition, two newly synthesized porphyrins-resorcinarene hybrids are reported.

Ferrochelatase catalyzes the insertion of ferrous iron into protoporphyrin IX to generate heme. Despite recent research on the reaction mechanism of ferrochelatase, the precise roles and localization of individual active site residues in catalysis, particularly those involved in the insertion of the ferrous iron into the protoporphyrin IX substrate, remain controversial. One outstanding question is from which side of the macrocycle of the bound porphyin substrate is the ferrous iron substrate inserted. Pre-steady state kinetic experiments done under single-turnover conditions conclusively demonstrate that metal ion insertion is pH-dependent, and that the conserved active site His-Glu pair coordinately catalyzes the metal ion insertion reaction. Further, p$K_a$ calculations and molecular dynamic simulations indicate that the active site His is deprotonated and the protonation state of the Glu relates to the conformational state of ferrochelatase. Specifically, the conserved Glu in the open conformation of ferrochelatase is deprotonated, while it remains protonated in the closed conformation. These findings support not only the role of the His-Glu pair in catalyzing metal ion insertion, as these residues need to be deprotonated to bind the incoming metal ion, but also the importance of the relationship between the protonation state of the Glu residue and the conformation of ferrochelatase. Finally, the results of this study are consistent with our previous proposal that the unwinding of the $\pi$-helix, the major structural determinant of the closed to open conformational transition in ferrochelatase, is associated with the Glu residue binding the Fe${}^{2+}$ substrate from a mitochondrial Fe${}^{2+}$ donor.

A series of (bacterio)chlorophyll derivatives covalently linked with fullerenes were synthesized to explore their potential as donor–acceptor conjugates to organic solar cells (OSCs). Their physical properties and photovoltaic performances were investigated and compared with (bacterio)chlorins without fullerenes. A weak intramolecular interaction between the (bacterio)chlorin chromophore and the fullerene unit(s) was observed in their electronic absorption spectra in solution, and efficient fluorescence quenching occurred in their monomeric states. All the (bacterio)chlorin-fullerene conjugates worked as components for single material OSCs and the best power conversion efficiency of 0.62% with $J_{\mathrm{\text{sc}}}=1.59$ mA cm${}^{-2}$, $V_{\mathrm{\text{oc}}}=0.81$ V, and $\mathrm{\text{FF}}=0.48$ was achieved for chlorin-C3-methyl phenyl-C${}_{61}$-butylate, DA-2.

Tetrapyrrolic systems largely inspired by nature have attracted much attention in organic electronics and biomedical applications owing to their planar structure and extended $\pi$-conjugated double bonds. As a result, delocalization of $\pi$-electron cloud leads the excellent optical absorption and fluorescent properties. Nonetheless, the utilization of non-covalent interactions result in the self-assembled nanostructures providing applications in bioimaging and electronics. In this review, it is demonstrated that the recent reports on the self-assembly in tetrapyrrolic systems via supramolecular interactions lead to well-defined nanoarchitectures. Moreover, the importance of porphyrin based derivatives in nanoelectronics and chemotherapeutic applications is reported. Therefore, the inclination of tetrapyrroles towards the design and development of novel supramolecular nanostructures are considered the hallmark for nanorobotics, shape memory polymers and bionic arms.

The replacement of cobalt in vitamin B${}_{12}$ derivatives by other transition metals is a formal path to non-natural corrins. Here, we describe nibinamide (Nibi), the novel Ni(II)-analogue of the natural B${}_{12}$-derivative cobinamide (Cbi), and its synthesis from the metal-free ligand of Cbi, hydrogenobinamide (Hbi), both isolated as tetrafluoroborate salts. Aqueous solutions of the metal-free corrin Hbi are strongly fluorescent, whereas its Ni(II)-complex Nibi is non-luminescent. The solution structures of Hbi and of Nibi were characterized by hetero-nuclear NMR-spectroscopy. The Ni(II)-corrin Nibi was deduced to be roughly iso-structural to cob(I)inamide (Cbi${}^I)$ and to house a diamagnetic d⁸-metal-ioniso-electronic to Co${}^I$ in Cbi${}^I$. The chemically robust Nibi is, thus, a structural mimic of enzyme-activated and reduced biosynthetic precursors of vitamin B${}_{12}$ and a B${}_{12}$-antimetabolite potentially functioning as a specific inhibitor of B${}_{12}$-biosynthesis.