Complementary face-to-face dimer formation from meso-aryl subporphyrins bearing a 2-carboxyphenyl group

meso-Aryl-substituted subporphyrins bearing a 2-carboxyphenyl group were prepared and shown to form complementary face-to-face dimers upon azeotropic removal of methanol.     

Efficient promotion of phosphate diester cleavage by a face-to-face cyclodextrin dimer without metal

An organic face-to-face cyclodextrin dimer promotes the cleavage of bis(4-nitrophenyl) phosphate efficiently in neutral pH without the addition of metal. Both of the phosphate diester bonds can be cleaved.     

Investigation of unsubstituted porphyrazine by proton NMR and the structure of porphyrazine ligands

The proton NMR spectra of unsubstituted porphyrazine (tetraazaporphine) and of its Zn complex in pyridine-D₅ and in CF₃COOD have been obtained for the first time. The observed strong deshielding of the pyrrole hydrogen atoms of these compounds compared with porphyrins indicates the existence of strong intramolecular hydrogen bonds with neighboring pyrrolenic nitrogen atoms. An unsymmetrical bridge structure is proposed for the reaction center of unsubstituted porphyrazine with significantly ionized N?H bonds. It is suggested that a symmetrical bridge structure almost completely ionized, may exist only in the presence of such strong electron-accepting substituents as halogen in the pyrrole rings of the porphyrazine macrocycle.     

Serendipitous synthesis of trimetallic porphyrazine triads

We report the synthesis and characterization of structurally unusual porphyrazine triads with three macrocycles bound to a central pyrazine core. These trimacrocyclic complexes were accidentally discovered during studies on the peripheral metallation of porphyrazinediamines. The crystal structure of the tri-zinc porphyrazine triad is described and the spectroscopic properties including electronic absorption spectra of this complex and the corresponding magnesium, free-base, and copper derivatives are reported.     

Acid-base properties of thianaphthene-annulated porphyrazine and tetra(pyrazino)porphyrazine complexes with aluminum group metals

Acid-base properties of Al(III), Ga(III), and In(III) complexes with tert-butyl-substituted thianaphthene-annulated porphyrazine and tetra(2,3-pyrazino)porphyrazine in proton-donor medium (CH₂Cl₂-CF₃COOH) were studied by spectrophotometric titration. The concentration stability constants of the singly protonated complexes were determined. The effects of the metal nature and aromatic heterocyclic fragment on the basicity of meso-nitrogen atoms were analyzed. Negative inductive effect of the sulfur atom in the thianaphthene fragment reduces the basicity of the meso-nitrogen atoms as compared to analogous porphyrazine and phthalocyanine complexes. Acid-base transformations of the thianaphthene-annulated tetra(2,3-pyrazino)porphyrazine involve both meso-nitrogen atoms and those in the pyrazine rings.     

Highly conductive electrostatically assembled porphyrazine films

The electrochemical and photoelectrochemical response of molecular films formed by (3,4-pyridyl)porphyrazine coordinated to four peripheral [Ru(bipy)₂Cl]⁺ groups (TRPz) has been investigated, in comparison with the corresponding electrostatic assembled bilayer films generated in the presence of the tetrasulfonate phthalocyaninatecopper(II) complex (CuTSPc). Both types of films are redox conductors, but an additional electron conduction mechanism through the stacked rings π system has been observed in the bilayer films, based on impedance spectroscopy. Their combined action promotes an enhanced photoaction response for the bilayer films in the presence of dissolved dioxygen.     

The symmetrical porphyrazine with annulated six membered rings

Tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) with annulated six membered rings has been prepared by two different methods. In Method A: cyclotetramerization of 2,3-dicyano-5,6-cyclohexanopyrazine (1) in the presence of Mg(OPr)₂ in n-propanol afforded the tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) (2). In Method B: selenodiazole rings on the periphery of tetrakis(selenodiazole)porphyrazinato magnesium(II) were opened by the action of H₂S to yield the vicinal diamino functionalities. The ring closure of the vicinal diamino groups with 1,2-cyclohexanedione afforded the tetrakis(cyclohexylpyrazino) porphyrazinato magnesium(II) (2).     

Novel iron(III) porphyrazine complex. Complex speciation and reactions with NO and H2O2

The complex [iron(III) (octaphenylsulfonato)porphyrazine] (5-), Fe (III)(Pz), was synthesized. The p K a values of the axially coordinated water molecules were determined spectrophotometrically and found to be p K a 1 = 7.50 +/- 0.02 and p K a 2 = 11.16 +/- 0.06. The water exchange reaction studied by (17)O NMR as a function of the pH was fast at pH = 1, k ex = (9.8 +/- 0.6) x 10 (6) s (-1) at 25 degrees C, and too fast to be measured at pH = 10, whereas at pH = 13, no water exchange reaction occurred. The equilibrium between mono- and diaqua Fe (III)(Pz) complexes was studied at acidic pH as a function of the temperature and pressure. Complex-formation equilibria with different nucleophiles (Br (-) and pyrazole) were studied in order to distinguish between a five- (in the case of Br (-)) or six-coordinate (in the case of pyrazole) iron(III) center. The kinetics of the reaction of Fe (III)(Pz) with NO was studied as a model ligand substitution reaction at various pH values. The mechanism observed is analogous to the one observed for iron(III) porphyrins and follows an I d mechanism. The product is (Pz)Fe (II)NO (+), and subsequent reductive nitrosylation usually takes place when other nucleophiles like OH (-) or buffer ions are present in solution. Fe (III)(Pz) also activates hydrogen peroxide. Kinetic data for the direct reaction of hydrogen peroxide with the complex clearly indicate the occurrence of more than one reaction step. Kinetic data for the catalytic decomposition of the dye Orange II by H 2O 2 in the presence of Fe (III)(Pz) imply that a catalytic oxidation cycle is initiated. The peroxide molecule first coordinates to the iron(III) center to produce the active catalytic species, which immediately oxidizes the substrate. The influence of the catalyst, oxidant, and substrate concentrations on the reaction rate was studied in detail as a function of the pH. The rate increases with increasing catalyst and peroxide concentrations but decreases with increasing substrate concentration. At low pH, the oxidation of the substrate is not complete because of catalyst decomposition. The observed kinetic traces at pH = 10 and 12 for the catalytic cycle could be simulated on the basis of the obtained kinetic data and the proposed reaction cycle. The experimental results are in good agreement with the simulated ones.     

Novel four-hydrogen-bond assembled oligoamide dimer with pyrazoline moieties and its photoluminescent properties

In this paper,the synthesis and characterization of a triarylpyrazoline modified four-H-bonded molecular duplex are described. Its molecular structure has been confirmed by ~1H NMR and ESI-MS.The duplex emits strong pure blue light peaking at 448 and 452 nm under UV photoexcitation in solution and solid state,respectively,and its relative photoluminescence quantum efficiency in solution is determined as 0.778 using quinine sulfate as reference.In concentration of>40 mmol/L,the duplex can gelate DMSO, and...     

New porphyrazine macrocycles with high viscosity-sensitive fluorescence parameters

New tetraaryltetracyanoporphyrazines have been obtained in the form of metal complexes and free bases via template assembly of a variety of aryltricyanoethylenes as structural units of the macrocycle, and photophysical properties of the products have been studied. The unique high sensitivity of the fluorescent properties to viscosity has been demonstrated. This property opens the possibility of application of the said compounds as sensors of local viscosity. The prepared macrocycles exhibit significant photocytotoxicity, and can be thus used as sensitizers of photodynamic therapy.     

Novel phenolic glycoside dimer and trimer from the whole herb of Pyrola rotundifolia

From the water-soluble constituents of the whole herb of Pyrola rotundifolia (Pyrolaceae), one novel phenolic glycoside dimer, pyrolaside A (1), and one novel phenolic glycoside trimer, pyrolaside B (2), together with two known phenolic glycosides homoarbutin (3) and isohomoarbutin (4), were isolated. The structures were elucidated by spectroscopic analysis and confirmed with chemical degradation. In vitro tests for antimicrobial activity showed pyrolaside B (2) to possess significant activity against two Gram-positive organisms, Staphylococcus aureus and Micrococcus luteus.     

Cobalt(II) porphyrazine catalysed reduction of nitrite

Studies on the catalytic reduction of nitrite on carbon electrodes modified with Co(II) tetra-2,3-pyridinoporphyrazine (CoTppa, 1), N,N′,N′′,N′′′-tetramethyltetra-2,3-pyridinoporphyrazine ([CoTm-2,3-tppa]⁴⁺, 2) and Co(II) N,N′,N′′,N′′′-tetramethyltetra-3,4-pyridinoporphyrazine ([CoTm-3,4-tppa]⁴⁺, 3) are reported. There is a close correspondence between the proximity of the methyl groups to the porphyrazine ring and the catalytic activity of the porphyrazine complexes. Bulk electrolysis gave ammonia and hydroxylamine as some of the products. The catalytic activity of the cationic complex, 3, towards the detection of low concentrations of nitrite (<10⁻⁹ M) in water containing sodium sulfate, was compared with the activities of the anionic cobalt(II) tetrasulfophthalocyanine ([CoTSPc]⁴⁻, 4) and the mixed [Co^IITm-3,4-tppa]⁴⁺·[CoTSPc]⁴⁻ (5) complexes. Complex 5 showed the best catalytic activity of the three in that large currents were obtained for very low concentrations of nitrite.     

Electronic structure and optical properties of a tin-encapsulated nickel porphyrazine compound

The recently synthesized metal-encapsulated porphyrazine compound, [Sn(t-Bu)₂]₄-star-Ni(porphyrazine)-S₈, shows very interesting structural and optical absorption features compared with other metal-centered porphyrazines, e.g., metal phthalocyanines (Pc). Using self-consistent-field local density theory, we studied the ground-state and excited-state electronic structure of this molecule and compared it with its metal phthalocyanine analog NiPc. The theoretical optical spectra including oscillator strengths are in good agreement with experimental absorption and show that the characteristic transitions at the so-called Soret band in NiPc are red-shifted in the new compound. © 1994 John Wiley & Sons, Inc.     

Identification of randomers of tetra(tert-butyl)porphyrazine

Randomers of tetra(tert-butyl)porphyrazine, the assignment of which was made on the basis of data from mass spectrometry and high-resolution PMR spectroscopy, were isolated by high-performance liquid column chromatography.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1261–1263, September, 1988.     

Nanoaggregates of copper porphyrazine in floating layers and Langmuir-Schaefer films

Aggregation behavior of unsubstituted copper porphyrazine (CuPaz) on the water surface was studied by analysis of compression curves, Brewster angle microscopy (BAM), and optical spectroscopy. The structure and stability of the CuPaz aqua aggregates in the floating layers are determined by hydration degree that depends on initial surface concentration and surface pressure. Langmuir-Schaefer (LS) films of CuPaz were prepared by deposition of the variously structured floating layers and studied by X-ray scattering technique and optical spectroscopy. Stable and labile structures were detected and compared with the floating CuPaz aqua aggregates. Conditions of formation of the stable four-stacked nanoaggregates in LS films were determined. A model comprising both nucleation of CuPaz on the water surface and structural transformations in the solid films is proposed.     

Photophysical insights on quantum dots-zinc porphyrazine system studied in solution

The present study reports spontaneous interaction of a quantum dots, namely, CdS_xSe_1-x/ZnS (QD) with zinc porphyrazine (1) in toluene. It is observed from steady state fluorescence measurements that photoluminescence of QD suffers quenching by 1. Time resolved fluorescence measurements reveal small change in the lifetime of QD (16.10 ns) following it interaction with 1 (15.77 ns). The magnitude of k_q for QD-1 system, i.e., k_q ​= ​5.25 ​× ​10¹² ​L⋅mol⁻¹⋅sec⁻¹ (evaluated from the stern-volmer plot) establishes that photoexcited QD undergoes decay by 1 according to static quenching mechanism. The results emerging from above study confirm that QD-1 system may be judiciously applied as an energy storage material in near future.     

Novel discotic liquid crystal oligomers: 1,3,5-triazine-based triphenylene dimer and trimer with wide mesophase

Series of novel 1,3,5-triazine-based triphenylene oligomers 7, 10 and 12 with large bridging polyaromatic core were designed and synthesised by simple procedures in high yields. Their structures were confirmed by FTIR, ¹H NMR, ESI-MS and elemental analyses. Their mesomorphic behaviours were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. 1,3,5-triazine-based triphenylene monomer 7 has no mesomorphic property, but 1,3,5-triazine-based triphenylene dimer 10 and 1,3,5-triazine-based triphenylene trimer 12 possess excellent mesomorphic properties. The mesomorphic temperature range of compound 12 was as wide as 180°C. These studies indicated that the mesomorphic properties were determined by the numbers of triphenylene units. More units of triphenylene in the oligomers resulted in better mesomorphic properties.