Tetrapyrrolic Macrocycles Research Articles

Design and Construction of a Porphyrin-Based Samarium(III)-Metal-Organic Framework for Antibiotic Detection.

Porphyrins bearing the unique 18π electron tetrapyrrolic macrocycles exhibit interesting photophysical and photochemical properties and have been considered as promising ligands for the construction of functionalized metal-organic frameworks (MOFs). The combination of porphyrin-type ligands with lanthanide metals featured with diverse coordination environments to realize the novel functions as well as the diversity of the MOF is thus attractive but challenging. Herein, an unprecedented porphyrin-based samarium MOF (Sm-BCPP) composed of a 5,10-bis(4-carboxyphenyl)-10,20-diphenyl porphyrin (H2BCPP) ligand and samarium-formed one-dimensional clusters has been constructed via a solvothermal approach, and the synthesized Sm-BCPP has excellent chemical stabilities, exhibiting red luminescence. Interestingly, Sm-BCPP demonstrated excellent fluorescence quenching against commonly used antibiotics, showing an ultrahigh fluorescence quenching constant (KSV) and ultralow detection limit (LOD), among which the detection limit of rifampicin (LOD = 0.33 nM) and nitrofurazone (LOD = 0.24 nM) was found to be lower than most reported MOF materials. Encouragingly, the Sm-BCPP MOF exhibited excellent stability in aqueous solutions at different pH environments, and the detection capability in the natural water environment indicated its practical application potential. The in-depth studies suggested that the mechanism of the fluorescence quenching against antibiotics involved internal filtration effect and photoinduced electron transfer.

Novel Chlorin with a HYNIC: Synthesis, 99mTc-Radiolabeling, and Initial Preclinical Evaluation

The use of radiopharmaceuticals for diagnostics in oncology allows for the detection of the disease at an early stage. Among diagnostic radionuclides, 99mTc is a promising isotope that has been used to create several drugs for clinical use. One of the most effective 99mTc chelators is 6-hydrazinylnicotinic acid (HYNIC), which, when combined with various vector molecules, can be used for targeted delivery of radionuclides to tumor tissues. At the same time, it is known that tetrapyrrole macrocycles are capable of selective accumulation in tumors, and thus can be used to target radiopharmaceuticals with 99mTc. In this work, the conjugate of natural chlorin and HYNIC was obtained, and preliminary preclinical studies were carried out on its radiocomplex with 99mTc.

Metal (M = Cr, Mo, W, Re) carbonyl complexes with porphyrin and carborane isocyanide ligands: light-induced oxidation and carbon oxide release for antitumor efficacy.

The tetrapyrrolic macrocycle as a scaffold for various chemical modifications provides broad opportunities for the preparation of complex multifunctional conjugates suitable for binary antitumor therapies. Typically, illumination with monochromatic light triggers the photochemical generation of reactive oxygen species (ROS) (photodynamic effect). However, more therapeutically valuable effects can be achieved upon photoactivation of tetrapyrrole derivatives. Herein we report the novel porphyrin-based complexes of transition metals with isocyanide and carbonyl ligands. Synthesis of complexes presumed the use of 5-(p-isocyanophenyl)-10,15,20-triphenylporphyrin as a ligand in reactions with metal carbonyl complexes, M(CO)6 (M = Cr, Mo, W), Re2(CO)10 and Re(CO)5Cl. Based on these complexes and isocyanocarborane, the heteroleptic carbonyl complexes with porphyrin and carborane isocyanide ligands were prepared. In cell-free systems, the new compounds retained photochemical characteristics of the parental porphyrin derivative, such as triplet state formation and ROS generation, upon light-induced activation. In the cell culture, the carborane-containing derivatives demonstrated a more pronounced intracellular accumulation than their nonboronated counterparts. As expected, illumination at the Soret band (405 nm) of cells loaded with the new complexes caused photodynamic cell damage. In contrast, illumination at 530 nm instead initiated the release of carbon oxide (CO) followed by cell death independently of the photodynamic effect. Light-induced CO release was analyzed using second derivatives of UV-Vis spectra and our originally developed Spectrophotometric elimiNAtion of Photoinduced Side reactions (SNAPS) method. The yield of CO release decreased in the raw depending on metals in the carbonyl moiety: Mo ≥ Cr > W > Re ≥ Re2. Overall, our novel metal carbonyl complexes with porphyrin and carborane isocyanide ligands emerge as potent bi-functional conjugates for combined photodynamic and photoinducible CO-releasing antitumor agents.

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts.

This review provides an overview of recent progress made in the field of catalysis using metal-free tetrapyrrolic macrocycles, focusing on calix[4]pyrroles, porphyrins and corroles, which are structurally related to porphyrins. Calix[4]pyrroles are versatile receptors in supramolecular chemistry while porphyrins are considered as 'pigment of life' due to their role in vital biological processes. Beyond their natural functions, synthetic porphyrins have been applied in various fields, including organometallic catalysis, dye-sensitized solar cells, sensing, artificial olfactory systems, photodynamic therapy (PDT), anticancer drugs, biochemical probes, and electrochemical devices. Relevant examples of these two pyrrolic macrocycles as metal-free organocatalysts, photocatalysts, and electrocatalysts are presented here. The effect of macrocyclic structural modifications such as their functionalization with different substituents, distortion from planarity, conformational flexibility and rigidity towards catalytic activity are presented, highlighting the potential of these two macrocycles as metal-free catalysts.

Fluorenyl-corroles: Characterization, photophysical, photobiological, and DNA/BSA-binding properties of novel examples

In this study, it was evaluated the photophysical, electrochemical, photobiological, and DNA/BSA-binding properties of fluorenyl corrole derivatives H3MFluCor and H3TFluCor. Absorption and emission analyses were corroborated by theoretical calculations performed using time-dependent density functional theory, which revealed natural transition orbitals densities concentrated around the tetrapyrrolic macrocycle in all cases. The experimental studies indicated that the corroles H3MFluCor and H3TFluCor are stable in solution and exhibited photostability primarily in DMSO(5%)/Tris-HCl (pH 7.4) buffer. The generation of reactive oxygen species (ROS) and log POW values highlight their potential application in photobiological methods, as these corroles effectively generate ROS with more lipophilic characteristics. Furthermore, their binding capacity towards double-stranded DNA and bovine serum albumin (BSA) was also evaluated by spectroscopic techniques and molecular docking calculations. The interactive profile with biomolecules indicates that the corrole derivatives H3MFluCor and H3TFluCor tend to binding into the minor grooves of DNA through secondary forces, which are particularly pronounced at site III of the BSA, likely due to the static interactions.

Tetrapyrrolic macrocycles self-organization into floating layers and sensory properties of their Langmuir-Schaefer films

The influence of the chemical structure of the 5,10,15,20-tetraphenylporphyrin (I) and 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (II) on their supramolecular organization in floating layers at the air/water interface and sensor properties in Langmuir-Schaefer films has been investigated. It was shown that a minor change in the macrocycle structure (namely, the replacement of a single nitrogen atom from the center to the periphery of macrocycle) has a considerable effect on the surface properties and hysteresis processes of the floating layers. Using the Bruster angle microscopy, it was established that both porphyrins aggregate even before the compression of their floating layers begins. The aggregation is more pronounced in porphyrin I. The analysis of hysteresis loops showed that the formation of a floating layer by the modified porphyrin II requires approximately 100 times more energy than for the unmodified porphyrin I. Using the Langmuir-Schaefer (LS) method, the floating layers were transferred onto solid substrates and the resulting thin films were analyzed by atomic force microscopy, scanning electron microscopy, polarization optical microscopy, and spectrophotometry. The combination of these methods revealed a general tendency of the porphyrins to form 3D structures on the surface of LS-films. The study of the basic properties of the porphyrin's LS-films showed that both porphyrins are diprotonated. The protonation process in porphyrin II occurs at a concentration of HClO4 that is 1000 times lower than that observed in porphyrin I. The greater tendency to protonation of porphyrin II is caused by the availability of both nitrogen atoms (the external nitrogen atom located at the macrocycle periphery and the internal nitrogen atom, which becomes more assesible to interactions due to the distortion of the macrocycle). As for the sensor properties of LS-films for iodide ion in aqueous solutions, it was observed that the diprotonated form of porphyrin I exhibited higher sensitivity due to a more developed film surface because of the presence of a greater number of 3D aggregates. The data obtained can be used in the development of efficient pH-controlled thin-film sensor materials for halide ions.

Cobalt Complex of an N-Linked Carbacorrole Analog: Axial Ligand Effect on Electronic Structure

Corrole, recognized as a contracted tetrapyrrolic macrocycle featuring an α,α'-linked bipyrrole moiety, has garnered attention for its unique trianionic N4 donor environment at the inner core. This characteristic has prompted the exploration of various high-valent metal species for potential catalytic applications. In our pursuit of uncovering new reactivity in metallo-corroles, we have previously synthesized a distinct carbacorrole ligand known as N-confused/N-linked corrole analogs.[1] The former variant incorporates an inverted pyrrole moiety connected at the α and β’-linking positions, while the latter exhibits a unique linkage between the α-pyrrole ring and the pyrrolic N site. The resulting [NNNC] coordination environment of carbacorroles stabilizes distinctive organometallic species, particularly with copper(III) ions.[2]In this study, we synthesized novel cobalt complexes featuring an N-linked carbacorrole analog with a benzo annulation, referred to as benzonorrole. The electronic structure of the ensuing complex is notably influenced by the axial ligands. The monodentate pyridine axial coordination to the cobalt norrole complex revealed unique reactivity, resulting in an oxygenated product at the inner carbon site. The oxygenated cobalt norrole complex can be characterized as a singlet Co(II) ligand radical at the ground state, as evidenced by various spectroscopic methods and magnetic susceptibility measurements. Upon substitution with a triphenylphosphine ligand, the resulting five-coordinated cobalt norrole complex was found to be stable and considered a diamagnetic cobalt(III) species, devoid of redox noninnocent character. This talk will delve into the detailed structure and electrochemical properties of these intriguing complexes.[1] Fujino, K.; Hirata, Y.; Kawabe, Y.; Morimoto, T.; Srinivasan, A.; Toganoh, M.; Miseki, Y.; Kudo, A.; Furuta, H. Angew. Chem. Int. Ed. 2011, 50, 6855-6859; Toganoh, M.; Kawabe, Y.; Uno, H.; Furuta, H. Angew. Chem. Int. Ed. 2012, 51, 8753-8756.[2] Maurya, Y.; Noda, K.; Yamasumi, K.; Mori, S.; Uchiyama, T.; Kamitani, K.; Hirai, T.; Ninomiya, K.; Nishibori, M.; Hori, Y.; Shiota, Y.; Yoshizawa, K.; Ishida, M.; Furuta, H. J. Am. Chem. Soc. 2018, 140, 6883-6892.

Electrocatalytic Properties of meso‐ Perfluorinated Metallo Corroles for the Reduction of CO2

Corrole, a contracted tetrapyrrolic macrocycle has been also used to design molecular for the CO2 reduction. The electrochemical activity towards CO2 reduction can rival those of their porphyrin analogues. However, the catalytic activity of the metallocorrole is initiated at the corresponding MII/I couple. Accordingly, a catalytic current in presence of CO2 with cobalt corrole appears when the CoI species is generated. We have designed an electron deficient A2B corrole holding two ‐CF3 groups and a benzonitrile in the meso positions and its cobalt complex (1). We reasoned that these groups could shuffle the redox potentials to reach the M(I) oxidation states at more positive values thereby lowering the overpotential for the catalytic CO2 reduction. Our results clearly show that catalyst 1 when adsorbed on a carbon electrode, shows the most favourable catalytic performance for CO production, achieving an efficiency of 85% with a current density of ‐1.5 mA cm‐2 at ‐1.0 V vs NHE. The current densities of controlled potential electrolysis with increasing amount of KHCO3, were found to increase more than one order of magnitude with the formation of MeOH.

The photophysical, photobiological, and DNA/HSA-binding properties of corroles containing carbazole and phenothiazine moieties

This study characterized four corrole derivatives, namely Cbz-Cor, MetCbz-Cor, PTz-Cor, and PTzEt-Cor, examining their photophysical, electrochemical, photobiological, and biomolecule-binding properties. Experimental photophysical data of absorption and emission elements correlated with a theoretical analysis obtained through time-dependent density functional theory (TD-DFT). As for the photophysical properties, we observed lower fluorescence quantum yields and discernible differences between the excited and ground states, as indicated by Stokes shift values. Natural Transition Orbit (NTO) plots presented high occupied molecular orbital - low unoccupied molecular orbital (HOMO-LUMO) densities around the tetrapyrrolic macrocycle in all examples. Our findings demonstrate that corroles maintain stability in solution and offer photostability (<20 %), predominantly in DMSO(5 %)/Tris-HCl (pH 7.4) buffer solution. Furthermore, the singlet oxygen (1O2) quantum yield and log POW values underscore their potential application in photoinactivation approaches, as these corroles serve as effective ROS generators with more lipophilic features. We also evaluated their biomolecular binding capacity towards salmon sperm DNA and human serum albumin using spectroscopic techniques and molecular docking analysis for sustenance. Concerning biomolecule interaction profiles, the corrole derivatives showed a propensity for interacting in the minor grooves of the double helix DNA due to secondary forces, which were more pronounced in site III of the human serum protein.

Characterization of the iron-sulfur clusters in the nitrogenase-like reductase CfbC/D required for coenzyme F430 biosynthesis.

Coenzyme F430 is a nickel-containing tetrapyrrole, serving as the prosthetic group of methyl-coenzyme M reductase in methanogenic and methanotrophic archaea. During coenzyme F430 biosynthesis, the tetrapyrrole macrocycle is reduced by the nitrogenase-like CfbC/D system consisting of the reductase component CfbC and the catalytic component CfbD. Both components are homodimeric proteins, each carrying a [4Fe-4S] cluster. Here, the ligands of the [4Fe-4S] clusters of CfbC2 and CfbD2 were identified revealing an all cysteine ligation of both clusters. Moreover, the midpoint potentials of the [4Fe-4S] clusters were determined to be -256 mV for CfbC2 and -407 mV for CfbD2. These midpoint potentials indicate that the consecutive thermodynamically unfavorable 6 individual "up-hill" electron transfers to the organic moiety of the Ni2+-sirohydrochlorin a,c-diamide substrate require an intricate interplay of ATP-binding, hydrolysis, protein complex formation and release to drive product formation, which is a common theme in nitrogenase-like systems.

Coordination reaction of manganese(III)porphyrins with pyridine as model to obtain the donor-acceptor dyads with fullerene acceptors

In connection with the use of the pyridyl group as the bridge in the coordination of metalloporphyrins with fullerene acceptors to obtain the photoinduced electron transfer donor-acceptor systems, the study of coordination of unsubstituted pyridine molecules and the determination of the chemical structure, spectral properties, and stability of the obtained complexes becomes relevant. The coordination of pyridine molecules by manganese(III)porphyrins depending on their structure was studied in this work. In all cases, coordination ends with the formation of 1 : 1 complexes in toluene, the structure of which was established using the data of MALDI-TOF mass spectrometry and 1H NMR spectroscopy. The numerical values of the stability constants of the coordination complexes were determined; they change from 0.16 to 104 L/mol depending on the nature of the axial anion in the manganese(III)porphyrin, the structure of the tetrapyrrole macrocycle, and the functional substitution in it. The obtained data facilitate the choice of structures in the creation of hybrid materials based on metalloporphyrins by the immobilization and supramolecular chemistry methods.

Porphyrinoid framework embedded with polycyclic aromatic hydrocarbons: new synthetic marvels.

The highly conjugated tetrapyrrolic porphyrin macrocycle and its contracted and expanded congeners have been extensively used for a wide range of applications across diverse research domains because of their captivating and intriguing features. Over the years, the porphyrin framework and electronic properties of porphyrinoids have been modified and tuned by replacing one or more pyrrole ring(s) with five- and six-membered heterocycles/carbacycles, and their resulting properties have been explored. In recent times, polycyclic aromatic hydrocarbons (PAHs), such as biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, fluorene, pyrene and dibenzo[g,p]chrysene, have been used to replace one or more pyrrole rings of porphyrinoids, and resulting polycyclic-aromatic-embedded porphyrinoids show unique features that differ from those of other modified porphyrinoids. The polycyclic aromatic hydrocarbons in the porphyrinoid macrocyclic framework induce different π-conjugation pathways in macrocycles, exhibit variable degrees of aromaticity from nonaromatic to aromatic and antiaromatic and provide a unique ligand environment to form stable coordination and organometallic complexes in which metals show uncommon oxidation states and unusual reactivity. This review presents an overview of the synthesis, coordination chemistry, structure and properties of various porphyrinoids with an embedded PAH that have been reported to date.

Synthesis of chiral hexynones for use as precursors to native photosynthetic hydroporphyrins

A planned total synthesis of photosynthetic tetrapyrrole macrocycles installs essential stereochemical features in early precursors via established asymmetric methodology.

A Heteroatom-Containing Functional Poly(Silylenevinylene): Synthesis, Anion Binding, and Sensing of Anion Extraction Processes.

Catalytic hydrosilylation is one of the important synthetic approaches to prepare functional organosilicon polymers. Herein, a functional silicon copolymer is constructed by polyhydrosilylation reaction between a novel 3,7-bis(dimethyl silane)-10-(2-ethylhexyl)-10H-phenothiazine monomer and a neutral tetrapyrrolic macrocycle, namely, 5,5,10,15,15,20-hexamethyl-10α, 20α-bis(4-[ethynylphenyl]) calix[4]pyrrole. The as-constructed copolymer (Mn =9609, PDI=2.2) is investigated as an extractant for organic anions as their tetrabutylammonium salts under interfacial aqueous-organic (water-chloroform) conditions. In this context, a distinctive naked-eye colorimetric as well as fluorescence detection method is developed based on anion-directed hydrogen-bonding interactions. This kind of color/fluorescence monitoring serves as a handy tool for rapid screening of anion extraction processes. The copolymer exhibits high selectivity toward extraction of chloride anion. This study augments the field of polycarbosilanes, poly(silylenevinylene)s in particular, allowing access to a new application window that can be further advanced with good grace in near future.

The prospects for the use of vitamin B12 derivatives in pharmacology

Background. The structure of corrin tetrapyrrole macrocycles (compounds similar in structure to vitamin B12) is a kind of universal chemical template for targeted drug delivery, and the development of chemical sensors and antidotes.Objective: systematization of information on targeted modulation of certain corrins’ properties through chemical modifications.Material and methods. Literature analysis using modern methods of topological and metric data analysis was carried out. All relevant publications (n=863) were extracted from the PubMed/MEDLINE database on request “(cobalamin OR Cobyrinic OR vitamin B12) AND (Molecular Conformation [MeSH Terms] OR Vitamin B 12/*analogs &amp; derivatives/*chemistry [MeSH Terms] OR Vitamin B 12/*chemistry [MeSH Terms] OR Structure-Activity Relationship [MeSH Terms])”.Results. Information was systematized on how it is possible to regulate the properties of vitamin B12 (cobalamin) derivatives by introducing specific substitutions of groups in the corrin ring, on chemical modifications of cobalamin derivatives, biosynthetic approaches to the synthesis of cobalamin derivatives, and the effects of interactions of these modified corrins with “small” inorganic and organic molecules.Conclusion. The results obtained by systematic computer analysis of publications on corrins make it possible to reasonably form samples of candidate molecules for corrin studies in silico, in vitro, and in vivo.

Tying a knot between crown ethers and porphyrins.

Porphyrins and crown ether hybrids have emerged as a promising class of molecules composed of elements of a tetrapyrrole macrocycle and an oligo(ethylene glycol) segment. These hybrid systems constitute a broad group of compounds, including crowned porphyrins, crownphyrins, and calixpyrrole-crown ether systems forming Pacman complexes with transition metals. Their unique nature accustoms them as excellent ligands and hosts capable of binding guest molecules/ions, but also to undergo unusual transformations, such as metal-induced expansion/contraction. Depending on the design of the particular hybrid, they present unique features involving intriguing redox chemistry, interesting optical properties, and reactivity towards transition metals. In this perspective article, the overview of both the early designs of porphyrin-crown ether hybrids, as well as the most recent advances in the synthesis and characterisation of this remarkable group of macrocyclic systems, are addressed. The discussion covers the strategies employed in synthesising these systems, including cyclisation reactions, self-assembly, and their remarkable reactivity. The potential applications of porphyrin-crown ether hybrids are also highlighted. Moreover, the discussion identifies the challenges associated with synthesising and characterising hybrids, outlining the possible future directions.

Calix[3]Pyrrole and Related Macrocycles: Synthesis and Properties

Calix[4]pyrrole is a porphyrinogen-like macrocycle in which four pyrrole units are linked by four sp3-hybridized carbon atoms at the α-positions. While such tetrapyrrolic macrocycles are readily synthesized by acid-catalyzed condensation reactions of pyrrole monomer and carbonyl compound, analogous macrocycles composed of three pyrrole units are always not observed. Calix[3]pyrrole is a ring-contracted analogue of calix[4]pyrrole, and has been missing in porphyrin-related chemistry. In this presentation, the first synthesis of calix[3]pyrrole and its furan-embedded analogues is reported, and their unique reactivity derived from their macrocyclic ring strain will be discussed.Synthesis of calix[3]pyrrole started with a linear trimer of 3,3-dimethylpentane-2,5-dione. Intramolecular cyclization of the linear hexaketone was accomplished in 5 steps to give a cyclic hexaketone precursor. Paal–Knorr type pyrrole formation reaction of cyclic hexaketone gave calix[3]pyrrole in 41% yield (Scheme 1). Using similar strategies, analogous calix[3]-type macrocycles, namely, calix[1]furan[2]pyrrole, calix[2]furan[1]pyrrole, and calix[3]furan, were successfully synthesized. Single crystal X-ray diffraction analysis of calix[3]pyrrole revealed its strained structure, and the theoretical calculations showed the strain energy of calix[3]pyrrole is 22.1 kcal/mol per unit higher than that of calix[4]pyrrole. Such strain energy tends to decrease as the number of pyrrole unit decreased.Calix[3]pyrrole exhibited unique reactivity derived from macrocyclic ring strain under acidic (Rothemund–Lindsey) conditions that are frequently used for porphyrin synthesis. When calix[3]pyrrole was dissolved in 10 mM solution of trifluoroacetic acid in dichloromethane, calix[6]pyrrole was quantitatively formed within 30 seconds (Scheme 1). Similar strain-induced ring expansion was observed for calix[1]furan[2]pyrrole, but full conversion took approximately 5 minutes. On the other hand, calix[2]furan[1]pyrrole and calix[3]furan did not show ring expansion. Detailed mechanistic analysis revealed that protonation at a pyrrole unit in calix[3]pyrrole triggers irreversible ring-cleavage to give a linear tripyrrane moiety which undergoes cyclodimerization under acidic conditions.The strain-induced ring expansion reaction of calix[3]pyrrole solved a long-standing question in porphyrin-related chemistry. Tripyrrolic macrocycles such as calix[3]pyrrole are, even formed, not isolable from pyrrole condensation reaction using acid, because the strain-induced conversion to calix[6]pyrrole is too fast. Besides, this reaction provided a novel approach to ring-expanded calix-type macrocycles. Figure 1

Synthesis and Electrochemical Properties of Hydrogenated Porphyrins: Chlorinphlorin and Tetrahydrocorrin

Synthesis and Electrochemical Properties of Hydrogenated Porphyrins: Chlorinphlorin and TetrahydrocorrinSynthetic tetrapyrrolic compounds have been extensively examined including the hydrogenated forms and their metalated derivatives. The suite of compounds includes porphyrins, chlorins, bacteriochlorins, isobacteriochlorins, and corroles. Nonetheless, a host of new macrocyclic structures await discovery, and their chemistry to be explored. This talk will focus on two rare hydrogenated forms of porphyrin: tetrahydrocorrins (TDC) and a chorinphlorin. The monoanionic tetrapyrrolic macrocycle B,C-tetradehydrocorrin (TDC) resides at the 4e− and 4H+ midpoint between corroles and corrins. This chemical space remains largely unexplored due to a lack of reliable synthetic strategies. We now report the preparation and characterization of Co(II)- and Ni(II)-metalated TDC derivatives ([Co-TDC]+ and [Ni-TDC]+ , respectively) with a combination of crystallographic, electrochemical, computational, and spectroscopic techniques. The chlorinphlorin is an especially rare compound, and consequently, its formation and chemistry have eluded characterization. The rational and reproducible synthesis of the chlorinphlorin will be reported together with its characterization, including the compound’s X-ray crystal structure and redox properties. The talk highlights, despite the extensive chemistry of porphyrins and their related macrocycles, new frontiers await exploration.

Tolyporphins-Exotic Tetrapyrrole Pigments in a Cyanobacterium-A Review.

Tolyporphins were discovered some 30 years ago as part of a global search for antineoplastic compounds from cyanobacteria. To date, the culture HT-58-2, comprised of a cyanobacterium-microbial consortium, is the sole known producer of tolyporphins. Eighteen tolyporphins are now known-each is a free base tetrapyrrole macrocycle with a dioxobacteriochlorin (14), oxochlorin (3), or porphyrin (1) chromophore. Each compound displays two, three, or four open β-pyrrole positions and two, one, or zero appended C-glycoside (or -OH or -OAc) groups, respectively; the appended groups form part of a geminal disubstitution motif flanking the oxo moiety in the pyrroline ring. The distinct structures and repertoire of tolyporphins stand alone in the large pigments-of-life family. Efforts to understand the cyanobacterial origin, biosynthetic pathways, structural diversity, physiological roles, and potential pharmacological properties of tolyporphins have attracted a broad spectrum of researchers from diverse scientific areas. The identification of putative biosynthetic gene clusters in the HT-58-2 cyanobacterial genome and accompanying studies suggest a new biosynthetic paradigm in the tetrapyrrole arena. The present review provides a comprehensive treatment of the rich science concerning tolyporphins.

Metal exchange kinetics of asymmetrically substituted cd(II)- tetraarylporphyrins with cobalt and zinc chlorides in dmf

The metal exchange reactions of Cd(II)-5-(4-nitrophenyl)-10,15,20-triphenylporphyrin and Cd(II)-5,10,15-tri-(4-nitrophenyl)-20-phenylporphyrin with cobalt and zinc chlorides in dimethylformamide were studied by the spectrophotometric method. The kinetic parameters of metal exchange were calculated and a possible stoichiometric mechanism of the process is established. The influence of the nature of the solvate salt and the chemical modification of the tetrapyrrole macrocycle on the kinetic parameters of the metal exchange reaction was revealed.