First syntheses and X-ray structures of a meso-alkyl-substituted corrole and its Ga(III) complex

The solvent-free condensation of heptafluorobutanal and pyrrole leads to the corresponding meso-alkyl-substituted corrole, which was metallated by gallium chloride to provide the first first-row non-transition-metal corrole. Both the ligand and the complex were characterized by X-ray crystallography.     

High-valent corrole metal complexes

This commentary concentrates on corrole complexes with the three metal ions that are most relevant to oxidation catalysis: chromium, manganese, and iron. Particular emphasis is devoted to the only recently introduced meso-triarylcorroles and a comparison with the traditionally investigated beta-pyrrole-substituted corroles. Based on a combination of spectroscopic methods, electrochemistry, and X-ray crystallography, it is concluded that in most high-valent metallocorroles the corrole is not oxidized. Both experimental (for (oxo)chromium(V) corrole) and computational (for (oxo)manganese(V) corrole) evidence indicate that the stabilization of high-valent metal ions by corroles originates from a combination of short metal-nitrogen bonds and large metal out-of-plane displacements in the corrole, which lead to quite unexpected interactions of the oxo-metal pi* orbitals with the in-plane orbitals of the corrole.     

High-valent transition metal centers versus noninnocent ligands in metallocorroles: insights from electrochemistry and implications for high-valent heme protein intermediates

For relatively electron-rich corrole ligands, the halfwave potentials for oxidation of Cu(III), Sn(IV)Ph, Fe(IV)Ph, and Fe(IV)-O-Fe(IV) complexes are significantly lower than those of Sn(IV)Cl, Fe(IV)Cl, Mn(IV)Cl, and Cr(V)(O) complexes, suggesting that the corrole ligand is relatively electron-rich or 'innocent' in the former group of complexes and that it is relatively electron-deficient or 'noninnocent' in the latter group. Both the formal charge of the central metal ion and the nature of the axial ligand, if any, appear to be key determinants of the electronic character of the corrole ligand in metallocorrole complexes, a theme that has interesting resonances with recent findings on high-valent heme protein intermediates. However, for very strongly electron-deficient ligands such as meso-tris(pentafluorophenyl)corrole (TPFPC) and beta-octabromo-meso-tris(pentafluorophenyl)corrole (Br(8)TPFPC), which cannot sustain significant radical character, the various metal complexes all exhibit comparable halfwave potentials for oxidation and the ligand may be considered to be relatively innocent.     

DNA/HSA interaction and nuclease activity of an iron(III) amphiphilic sulfonated corrole

The DNA binding of amphiphilic iron(III) 2,17‐bis(sulfonato)‐5,10,15‐tris(pentafluorophenyl)corrole complex (Fe–SC) was studied using spectroscopic methods and viscosity measurements. Its nuclease‐like activity was examined by using pBR322 DNA as a target. The interaction of Fe–SC with human serum albumin (HSA) in vitro was also examined using multispectroscopic techniques. Experimental results revealed that Fe–SC binds to ct‐DNA via an outside binding mode with a binding constant of 1.25 × 10⁴ M^–1. This iron corrole also displays good activity during oxidative DNA cleavage by hydrogen peroxide or tert‐butyl hydroperoxide oxidants, and high‐valent (oxo)iron(V,VI) corrole intermediates may play an important role in DNA cleavage. Fe–SC exhibits much stronger binding affinity to site II than site I of HSA, indicating a selective binding tendency to HSA site II. The HSA conformational change induced by Fe–SC was confirmed by UV/Vis and CD spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopy and density functional theoretical calculations of manganese corroles. A parallelism between high-valent metallocorroles and metalloporphyrins, relevant to horseradish peroxidase and chloroperoxidase compound I and II intermediates.

Soret-excited resonance Raman (RR) spectra are reported for the Mn(III) and Mn(IV)Cl derivatives of meso-tris(p-(trifluoromethyl)phenyl)corrole, H(3)T(p-CF(3)-P)Cor, and the Mn(III) derivative of beta-octabromo-meso-tris(p-(trifluoromethyl)phenyl)corrole, H(3)Br(8)T(p-CF(3)-P)Cor. Three high-frequency bands in the RR spectrum of Mn(III)[T(p-CF(3)-P)Cor] at 1465, 1524 and 1615 cm(-1) appear to upshift to 1486, 1528 and 1620 cm(-1) for Mn(IV)[T(p-CF(3)-P)Cor]Cl. This suggests that the electronic character of the corrole ligand is significantly different for these two compounds, which is consistent with electrochemical evidence for partial radical character of the corrole ligand for Mn(IV)[T(p-CF(3)-P)Cor]Cl but not for Mn(III)[T(p-CF(3)-P)Cor]. The observed upshifts are also consistent with DFT calculations showing a shortening of some of the relevant bonds in the Mn(IV)Cl derivative relative to the Mn(III) derivative. The results raise the possibility of an extensive parallelism between the electronic structures of high-valent metallocorroles and metalloporphyrins. Three high-frequency bands in the RR spectrum of Mn(III)[T(p-CF(3)-P)Cor] at 1331, 1465 and 1545 cm(-1) appear to downshift to 1320, 1457 and 1537 cm(-1) for Mn(III)[Br(8)T(p-CF(3)-P)Cor]. This is consistent with the suspected longer carbon-carbon bond lengths in the brominated corrole macrocycle.     

Enzymatic ring opening of an iron corrole by plant-type heme oxygenases: unexpected substrate and protein selectivities

Heme oxygenases are widely distributed enzymes involved in the oxidative cleavage of the heme macrocycle that yields the open-chain tetrapyrrole biliverdin IX, CO, and iron. For the first time, two regioisomeric iron corroles [α-CH- and γ-CH-Fe(cor)] have been utilized as artificial substrate and cofactor analogues to mammalian, plant, cyanobacterial, and bacterial heme oxygenases. The non-natural enzymatic cleavage of γ-CH-Fe(cor), catalyzed by plant-type heme oxygenases from Arabidopsis thaliana and Synechocystis sp., happens selectively at the unexpected bipyrrolic position and yields a biomimetic biliverdin-like product. The reaction is selective for this corrole regioisomer and for plant-type heme oxygenases and is the first report of an enzymatic corrole ring opening.     

Formation of stable and metastable porphyrin- and corrole-iron(IV) complexes and isomerizations to iron(III) macrocycle radical cations

Oxidations of three porphyrin-iron(III) complexes (1) with ferric perchlorate, Fe(ClO₄)₃, in acetonitrile solutions at −40 °C gave metastable porphyrin-iron(IV) diperchlorate complexes (2) that isomerized to known iron(III) diperchlorate porphyrin radical cations (3) when the solutions were warmed to room temperature. The 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetramesitylporphyrin (TMP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) systems were studied by UV-visible spectroscopy. Low temperature NMR spectroscopy and effective magnetic moment measurements were possible with the TPP and TMP iron(IV) complexes. Reactions of two corrole systems, 5,10,15-tris(pentafluorophenyl)corrole (TPFC) and 5,15-bis(pentafluorophenyl)-10-p-methoxyphenylcorrole (BPFMC), also were studied. The corrole-iron(IV) chlorides reacted with silver salts to give corrole-iron(IV) complexes. The corrole-iron(IV) nitrate complexes were stable at room temperature. (TPFC)-iron(IV) toslyate, (TPFC)-iron(IV) chlorate, and (BPFMC)-iron(IV) chlorate were metastable and rearranged to their electronic isomers iron(III) corrole radical cations at room temperature. (TPFC)-iron(III) perchlorate corrole radical cation was the only product observed from reaction of the corrole-iron(IV) chloride with silver perchlorate. For the metastable iron(IV) species, the rates of isomerizations to the iron(III) macrocycle radical cation electronic isomers in dilute acetonitrile solutions were relatively insensitive to electron demands of the macrocyclic ligand but reflected the binding strength of the ligand to iron. Kinetic studies at varying temperatures and concentrations indicated that the mechanisms of the isomerization reactions are complex, involving mixed order reactivity.     

Cobalt(IV) corroles as catalysts for the electroreduction of O2: reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin

A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O(2) to H(2)O and/or H(2)O(2) when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1M HClO(4). The examined compounds are represented as (PCY)M(III)ClCo(IV)Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H(2)Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co(2) which were shown to efficiently electrocatalyze the four electron reduction of O(2) at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co(2), (PCY)H(2)Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O(2) electroreduction at potentials more positive by an average 110mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E(1/2) values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co(2) and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H(2)Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co(2) contains a Co(II) porphyrin and a Co(IV) corrole.     

Synthesis, spectroscopy, and structures of new rhodium(I) and rhodium(III) corroles and catalysis thereby

The syntheses and molecular structures of six- and five-coordinated rhodium(III) corroles (by pyridines and a chiral amine, respectively) and the rhodium(I) complex of a chiral corrole are described, together with some interesting features in the NMR spectra of the complexes and their utilization as carbene-transfer catalysts.     

Photophysical properties of a new, stable corrole-porphyrin dyad

The synthesis of a new stable corrole-porphyrin dyad, made up of a free-base corrole and a free-base porphyrin connected by an amide linker is presented and the characterization of the photoinduced processes taking place in the array is described. The dyad was synthesized from meso-substituted trans-A₂B-corrole bearing acid chloride functionality and meso-substituted A₃B-porphyrin possessing one free NH₂ group. The structure of the dyad was carefully designed and optimized to ensure stability of the molecule. The preparation of the amine component was achieved via phthalimide protection strategy which occurred to be more efficient than the traditional nitro group reduction. Results obtained from time resolved and steady state spectroscopy experiments indicate the existence of an equilibrium between the two lowest singlet excited states of the dyad, one localized on the corrole and the other on the porphyrin unit, which are nearly iso-energetic (ΔG = −0.01 eV). Independently of the excited component, energy transfer occurs in both directions (very likely with a Förster mechanism) and an equilibrium with K_eq close to 1 is rapidly set with back and forward rates of the order of 10⁹ s⁻¹. Both states decay with a common lifetime (6.2 ns) that is longer compared to the corrole model (3.9 ns) and shorter with respect to the porphyrin reference (9.9 ns). The longer lived excited state localized on porphyrin acts as a reservoir for the excited state localized on corrole. At 77 K the equilibration does not take place during the lifetime of the excited states, and the decay of the two species occurs independently.     

Amphiphilic corroles bind tightly to human serum albumin

Amphiphilic 2,17-bis-sulfonato-5,10,15(trispentafluorophenyl)corrole (2) and its Ga and Mn complexes (2-Ga and 2-Mn) form tightly bound noncovalent conjugates with human serum albumin (HSA). Protein-induced changes in the electronic absorption, emission, and circular dichroism spectra of these corroles, as well as results obtained from HPLC profiles of the conjugates and selective fluorescence quenching of the single HSA tryptophan, are interpreted in terms of multiple corrole:HSA binding sites. High-affinity binding sites, close to the unique tryptophan, are fully occupied at very low concentrations. At biologically relevant HSA concentrations (2-3 orders of magnitude larger than those employed in our studies), all corroles (2, 2-Ga, and 2-Mn) may be considered as fully conjugated.     

Aluminum corrolin, a novel chlorophyll analogue

A corrole-based chlorophyll analogue has been prepared, based on the notation that the major differences between the prosthetic groups of chlorophylls and hemes are the presence of a non-transition metal (Mg vs. Fe) and one reduced double bond in the porphyrin ligand. As corroles act as tri- rather than dianionic ligands, the analogy requires the insertion of aluminum into the macrocycle and the reduction of one of its double bonds, two reactions that have not been previously reported with any corrole. The aluminum complexes of both the corrole and the corrolin (the dihydrocorrole) display fluorescence quantum yield that are much larger than of chlorophyll and of all other previously reported synthetic analogues. The results suggest that the light metal atom ion is responsible for low intersystem crossing probability to the triplet excited state and the structural rigidity of the hexa-coordinated complexes for reducing the probability of internal conversion.     

Corroles that bind with high affinity to both apo and holo transferrin

The interactions of transferrin (Tf) with the water soluble corrole 1 and with its gallium (1-Ga) and manganese (1-Mn) complexes were studied to establish the possible utilization of corrole-transferrin conjugates for targeting these corroles to cells that express the transferrin receptor. The protein, in both its iron-free apo form (apoTf) and the iron-bound holo form (holoTf), was found to spontaneously bind all three derivatives. This conclusion was reached from titrations followed by several spectroscopic methods and dilution experiments measured by fluorescence. The such elucidated very small dissociation constant of 2 x 10(-7) M and 3 x 10(-8) M for 1-Ga with apoTf and holoTf, respectively and <10(-9) M for 1 with both protein forms are clearly relevant for the physiological concentration of transferrin in serum.     

Phosphorus(V) corrole: DNA binding,photonuclease activity and cytotoxicity toward tumor cells

A new phosphorus(V) corrole, 10-(4-hydroxylphenyl)-5,15-bis(pentafluorophenyl)corrolato (trans-dihydroxo)phosphorus(V) 1-P, was synthesized and characterized. The interaction of 1-P with calf thymus DNA (CT-DNA) was studied by multi-spectroscopic methods. The photonuclease activity of this complex was examined by agarose gel electrophoresis. 1-P may bind to CT-DNA via an outside binding mode and display good photonuclease activity. 1-P displayed low dark toxicity but high photocytotoxic activity against H460 and A549 tumor cell lines.     

DNA interaction and photodynamic antitumor activity of transition metal mono-hydroxyl corrole

A series of iron(III), manganese(III) and copper(III) mono-hydroxyl corrole complexes had been prepared and well characterized by UV–vis, ¹H NMR, ¹⁹F NMR and HR-MS. These metallocorroles may bind to CT-DNA through external binding mode. Metallocorrole Fe-2c exhibited significant phototoxicity and low toxicity toward A549 tumor cells. While manganese (III) and copper (III) corroles showed hypotoxicity to A549, MCF-7 and HepG-2 tumor cells, whether under dark or illumination conditions. All tested metallocorroles exhibited non-toxicity to human normal cells (GES-1) with or without irradiation at 625 nm. Cell cycle analysis indicated that metallocorrole Fe-2c arrested the cell cycle at G2/M phase and increased the Sub-G1 phase in A549 cell lines. It was mainly localized at mitochondria and could significantly reduce mitochondrial membrane potential after photodynamic treatment, which would further induce tumor cell apoptosis.     

High-valent transition metal corrolazines

High-valent metalloporphyrin intermediates have been implicated as key players in numerous mechanistic proposals for both biological (e.g., heme protein) and synthetic porphyrin mediated transformations. However, the direct observation of these species is quite challenging because of the inherently short lifetimes of many of these metalloporphyrin intermediates. This review focuses on our own efforts to synthesize and study a new class of porphyrinoid compounds called corrolazines, which are designed to stabilize high-valent species for direct analysis. These compounds are related to corroles, which also exhibit the unusual ability to stabilize high oxidation states, and the reactivity and physical properties of relevant corrole and porphyrin analogs are compared with the appropriate corrolazines. The chemistry of Cu, Co, V, and Mn are highlighted, with a particular emphasis on the reactivity of high-valent manganese-oxo complexes.     

Synthesis, X-structure and solvent induced electronic states tuning of meso-tris(4-nitrophenyl)corrolato-copper complex

Copper(II) ion insertion into the coordination core of meso-tris(p-nitrophenyl)corrole (1), in air showed the formation of meso-tris(p-nitrophenyl)corrolatoCu(III) (2), with the generation of superoxide radical as the side product of the reaction. Single-crystal X-ray diffraction analysis revealed that 2 exhibits weak π-π stacking interaction. Among the two electronic states, diamagnetic Cu(III)-corrole³⁻ exits in DCM solution and in contrast is paramagnetic Cu(II)-corrole²⁻ cationic radical in DMF solution. This difference in electronic behavior in solution is due to the small energy gap between HOMO and LUMO that is readily influenced by solvent interaction.     

Coordination behavior of amine bases to the axial site of a (dibenzo[b,i][1,4,8,11]tetraazacyclotetradecinato)cobalt(II)

The mutual interaction of various amine bases with the (dibenzo[b,i][1,4,8,11] tetraazacyclotetradecinato)cobalt(II) (Co(II)-1) was investigated by measuring electronic spectra in methyl benzoate. The Co(II)-1 became the pentacoordinated complex by taking up an amine base in the axile site: Co(II)-1 + B ? BCo(II)-1. For the mutual interaction of substituted pyridines with the Co(II)-1, the general behavior of the equilibrium constants was explained on the basis of the amine basicity and the Hammett equation by reference to the corresponding behavior of the porphyrin, corrin and corrole complexes. Moreover, there exists a systematic correlation between log K and the chemical shift of the corresponding 4-position in the ¹³C-NMR spectra of substituted pyridines. The isoequilibrium temperature obtained from a plot of ΔH against ΔS was 260 K. The equilibrium is primarily controlled by entropy at the usual temperature. The weaker coordination tendency of some hindered pyridine such as 2-methyl- and 2,6-dimethylpyridine toward Co(II)-1 was attributed to the steric effect between the in-plane ligand of Co(II)-1 and the 2- and/or 6-methyl groups of substituted pyridines in the coordination process.     

Fluorescence detection of hydrazine in an aqueous environment by a corrole derivative

Broadly, the industrial applications of hydrazine cause environmental pollution and damage to living organisms because of the high toxicity of hydrazine. Therefore, monitoring hydrazine in the environmental system is of great significance to human health. Here, a new fluorescent probe PC-N ₂ H ₄ based on corrole dye was developed for the detection of hydrazine that had excellent specificity, low limit of detection (LOD: 88 nM), and a wide pH range (6–12). Upon addition of hydrazine into the probe solution, the strong red fluorescence was ‘turned on’ centred at 653 nm with a 127-fold fluorescence intensity enhancement. The detection mechanism was proved using ESI-MS, ¹H NMR, and density functional theoretical calculations. Importantly, the probe was utilized to fabricate a ready-to-use test strip to realize the visual inspection of hydrazine. Furthermore, PC-N ₂ H ₄ was successfully applied for practical detection of hydrazine in water samples with satisfactory recoveries ranging from 96.2% to 105.0%, and indicating that the designed PC-N ₂ H ₄ is highly promising for hydrazine detection in an aqueous environment. Considering the diverse toxicological functions of hydrazine, PC-N ₂ H ₄ was also successfully used to image exogenous hydrazine in HeLa cells and zebrafish.     

壳聚糖酶的克隆表达与壳寡糖的制备分析

目的:克隆壳聚糖酶基因于大肠杆菌中实现高表达,制备壳寡糖。方法:以枯草芽孢杆菌总DNA为模板扩增壳聚糖酶基因(CSN),克隆至载体pET23a(+)上,转化菌株BL21(DE3)。重组子经0.5 mmol/L IPTG诱导后,SDS-PAGE和质谱检测与鉴定重组酶。酶纯化后水解壳聚糖,薄层色谱分析其水解产物。结果:质谱证明壳聚糖酶(31.5kDa)成功表达,表达量占菌体总蛋白的45%左右。纯化后重组酶浓度为900 mg/L,纯度95%、回收率85%,酶活力为10 000 U/mg。壳聚糖降解产物为壳二糖至壳四糖。结论:原核表达载体pET23a(+)-CSN构建正确,壳聚糖酶表达量与活性高,适用于水解壳聚糖制备壳寡糖。