Ionic Manganese Porphyrins with S-containing Counter Anions: Mimicking Cytochrome P450 Activity for Alkene Epoxidation

The ionic manganese porphyrins, composed of trimethylbenzylammonium cations and S-containing anions, were designed to mimic cytochrome P450. S-containing anions could function as the stoichiometric axial ligands and counterions dually. Such ionic catalysts showed good catalytic performance in alkene epoxidation as compared with their neutral counterparts, in terms of activity, epoxide selectivity, and recyclability.     

Comparative in vitro Studies of the Topoisomerase I Inhibition and Anticancer Activities of Metallated N-Confused Porphyrins and Metallated Porphyrins

Using the original approach, a series of metallated N-confused porphyrins and metallated porphyrins have been synthesized and characterized. For all the synthesized porphyrins, in vitro studies of cytotoxic activity against K562, U937, HL-60, Jurkat, A549 and HeLa cancer cell lines, the ability to induce apoptosis and effects on the cell cycle as well as the kinetics of proliferative activity of porphyrins and their respective metallated complexes in real time have been developed. The inhibitory activity of metallated porphyrins against human topoisomerase I and the possible mechanism of inhibition have been carried out by modelling using molecular docking.     

Characterization of Several Metalloporphyrins in Unusual Oxidation States. The Effect of Axial and Equatorial Ligands

The effect of axial and equatorial ligands on the generation of unusual oxidation states in metalloporphyrins is discussed. Selected examples have been taken from the literature. These include the generation of Ni(III) and Ru(III) porphyrins from Ni(II) and Ru(II) complexes containing specific axial and equatorial ligands as well as the generatoin of a Cu(I) metalloporphyrin dianion which is produced upon the overall three-electron reduction of Cu(II) tetracyanoporphyrin. Special emphasis is placed on the oxidation and reduction of σ bonded iron phenyl porphyrins. These complexes, which are stable as Fe(III), may be oxidized by a single electron to yield unstable compounds characterized as containing a great deal of Fe(IV) character, or reduced by a single electron to produce stable species which resemble, in part, radical anions of Fe(III). This singly deduced species may be described by a resonance equilibria between an Fe(III) porphyrin anion radical and an Fe(II) porphyrin anion. Likewise, the singly oxidized complex may be described by a resonance equilibria between an Fe(IV) porphyrin cation and an Fe(III) cation radical.     

A comparison of the change from inhibiting to enhancing anions in the electrochemical oxidations of ethylene glycol and formaldehyde

Techniques dealing with inhibiting anions have previously been employed to measure their properties. The present approach is to change the behavior of inhibiting anions. Anions, which have long been considered to inhibit reactions, are shown to enhance some electrochemical reaction rates. Fluoroborate, nitrate, and (hydrogen) sulfate are separately shown to increase the current response of the electrochemical oxidation of formaldehyde. The reaction rate of the oxidation of ethylene glycol is increased but for a restrictive set of conditions. Experimental data, as well as theoretical considerations lead to the conclusion that adsorption of the added anions is the slow step of the process that increases the reaction rate. The differences in the response of ethylene glycol and formaldehyde follow well-documented changes of surface CO. These observations are consistent with general properties of the step in the part of the mechanism on the electrode surface that enhances the reaction rate.     

Exfoliation and dispersion of micrometer-sized LDH particles in poly(ethylene terephthalate) and their nanocomposite thermal stability

Effect of surface modification on exfoliation and dispersion of micrometer-sized layered double hydroxide (LDH) in poly(ethylene terephthalate) (PET) and the thermal stability of the resultant PET/LDH nanocomposites or composite have been studied. First, large micrometer-sized LDH with carbonate anions was prepared by urea hydrolysis method. Then, various anions including nitrate (NO₃⁻), dodecyl sulfate (DS⁻) or dodecyl benzene sulphonate (DBS⁻) were intercalated into the interlayer space via anion exchange reaction. By solution intercalation process, PET/LDH_DS and PET/LDH_DBS nanocomposites were successfully obtained, while the LDH_NO₃ could not be exfoliated enough in the PET matrix. Finally, the thermal stabilities of the PET/LDH nanocomposites or composite were investigated.     

Potential controlled anion absorption in a novel high surface area composite of Cladophora cellulose and polypyrrole

The electrochemical properties of a novel composite paper material of high surface area consisting of polypyrrole (PPy) deposited on cellulose derived from Cladophora sp. algae have been investigated in electrolytes containing different concentrations of nitrate, chloride and p-toluene sulfonate, as well as in solutions containing both p-toluene sulfonate and chloride. The oxidation mechanism and the dependence of the oxidation behavior of the polypyrrole, which was obtained by oxidation of pyrrole with iron(III) chloride, on the anion type and concentration have been studied. Current nucleation maxima, appearing at different times depending on the anion concentration, were obtained during the oxidation of the reduced polymers as a result of the combined action of the formation and growth of conducting polymer strands and anion diffusion. No loss of capacity was seen during repeated oxidation and reduction of the polymer indicating that trapping of anions in the reduced polymer did not limit the electroactivity of the present material. The latter can be explained by the thin polymer layer present on the cellulose substrate. During the oxidation of the polymer, the anions most likely first cover most of the surface of the composite before diffusing into the bulk of the polymer. The estimated distance between these surface sites was also found to match the size of the anions. For electrolytes containing a mixture of anions, the oxidation charge depends on the concentration and size of the different anions.The combination of the thin polymer coating and the large specific surface area of the composite give rise to a high ion absorption capacity even for large anions. Hence, the investigated material should be well-suited for use in biotechnological applications involving, e.g., desalting and extraction of proteins and DNA from biological samples.     

Interaction of vanadium and nickel porphyrins with catalysts, relevance to catalytic demetallisation

The binding of vanadium and nickel porphyrins to γ-Al₂O₃, SiO₂-Al₂O₃ MoO₃/Al₂O₃, NiO/Al₂O₃, and to Co- and Ni-Mo/Al₂O₃ catalysts in their oxide and sulfide forms, and their subsequent decomposition reactions when heated in nitrogen or exposed to hydrogen and thiophene in catalytic hydrodesulfurisation, have been studied by electron spin resonance. We wished to discover which part of the porphyrin molecule became bound to the catalyst and to which surface sites. Our main conclusions are that the porphyrins are bound to the catalyst by a donor-acceptor interaction,, the delocalised π-system of the porphyrin ring being the electron donor, and the Bronsted and/or Lewis acid function of the catalyst being the acceptor. Depending on the conditions, oxidation or hydrogenation of the porphyrin ring at the meso carbons is the initial stage in the decomposition of the bound porphyrins.     

Quantum dot based turn-on fluorescent probes for anion sensing

The design of fluorescent probes for turn-on sensing of anions has been especially significant because it can effectively enhance sensing sensitivity by decreasing the background interference. In the present work, we have systematically studied the potential applications of fluorescent quantum dots (QDs) in turn-on anion sensing. The fluorescence of QDs are firstly quenched by three different mechanisms, i.e. fluorescence resonance energy transfer, electron transfer and surface states modulated fluorescence. The fluorescence of the pre-quenched QDs can then be recovered by various anions due to the modulating effects of added anions on the interaction between QDs and QDs, the interaction between QDs and quenchers, and the surface chemistry of the quenched QDs, respectively. The results described here indicate that turn-on sensing of various anions by QDs-based systems can be achieved by rationally choosing fluorescence modulating strategies, demonstrating the versatility of QDs in the corresponding applications.     

Porphyrin polymers and organic frameworks

The versatility of porphyrins as optoelectronic or catalytic units makes them attractive elements for inclusion in functional materials. Polymers that include porphyrins have been created with a wide variety of structures and used in a wide range of applications. This review covers recent developments in the synthesis, characterization and applications of polymeric materials in which porphyrins are key components of the repeat units, including the rapidly growing area of metal–organic frameworks and related covalent organic frameworks. © 2015 Society of Chemical Industry     

An inelastic electron tunnelling spectroscopy (IETS) study of poly(vinylacetate) poly(methyl methacrylate) and poly(vinylalcohol) adsorbed on aluminium oxide

IETS is used to investigate the adsorption of poly(vinylacetate) (PVA), poly(methylmethacrylate) (PMMA), and poly(vinylalcohol) (PVOH) on aluminium oxide. These polymers are of interest in the field of adhesion science, and until now synthetic macromolecules have not been studied in this way. Both commercially available polymers and those synthesized in our laboratory have been used. On the basis of IET spectra presented here, and existing i.r. spectra it is believed that PMMA and PVA undergo ester cleavage at the oxide surface leading to their subsequent adsorption. For PMMA this is thought to be via carboxylate anions generated on the polymer side groups, while PVA is expected to be adsorbed as PVOH. Bonding of PVOH to the oxide is not fully understood, but may occur by the formation of an AlOC bridge. Another possibility for the above polymers, that of intermolecular hydrogen bonding between polar polymer side groups, and adsorbed hydroxyl species present on the oxide surface, cannot be ruled out.     

Oxidation of polycyclic aromatic hydrocarbons with hydrogen peroxide catalyzed by Iron(III)porphyrins

A variety of iron-metallated functional porphyrins have been synthesized and their catalytic activity to oxidize polycyclic aromatic hydrocarbons, (PAHs) using hydrogen peroxide as oxidant was investigated. It was found that iron-metallated porphyrins bearing strong electronegative groups at β-pyrrolic positions show an exceptionally high catalytic efficiency.     

Light-induced electron spin polarization in the ground state of water-soluble copper porphyrins

Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed.     

Structural diversity in expanded porphyrins

Inspired by the chemistry of porphyrins, in the last decade, a new research area where porphyrin analogues such as expanded, isomeric, and contracted porphyrins have been synthesized, and their chemistry has been exploited extensively. Expanded porphyrins are macrocyclic compounds where pyrrole or heterocyclic rings are connected to each other through meso carbon bridges. Depending on the number of pyrrole rings in conjugation or the number of double bonds linking the four pyrrole rings expanded porphyrins containing up to 64 pi electrons are reported in the literature. The interest in these systems lies in their potential applications as anion binding agents, as photosensitizers for photodynamic therapy (PDT), in antisensing applications, as MRI contrasting agents, and more recently, as material for nonlinear optical application. Expanded porphyrins containing more than four pyrrole or heterocyclic rings, such as sapphyrin (five pyrrole), rubyrin (six pyrrole), heptaphyrin (seven pyrrole), and octaphyrin (eight pyrrole), are reported in the literature. Furthermore, substituents on expanded porphyrins can be attached either at the meso carbons or at beta-pyrrole positions. beta-substituted expanded porphyrins generally adopt normal structure where all the pyrrole nitrogens point inward in the cavity 1, while the meso-substituted expanded porphyrins exhibit normal 2, inverted 3, fused 4, confused 5, and figure eight 6 conformations. The conformation of expanded porphyrin is dependent on the nature of the linkage of the heterocyclic rings, the nature and the number of the heteroatoms present in the cavity, and the state of protonation. It is possible to change one conformation to another by varying temperature or by simple chemical modification, such as protonation by acids. An understanding of the structure-function correlation in expanded porphyrins is an important step for designing these molecules for their potential applications. In this context, even though several meso aryl expanded porphyrins are reported in literature, there is no comprehensive understanding of structural diversity exhibited by them. In this Account, an attempt has been made to provide a systematic understanding of the conditions and circumstances that lead to various conformations and structures. Specifically, the structural diversities exhibited by five pyrrolic macrocycles to ten pyrrolic macrocycles are covered in this Account. In pentapyrrolic systems, sapphyrins, N-fused, and N-confused pentaphyrins are described. It has been shown that the positions of the heteroatom affect the conformation and in turn the aromaticity. In hexapyrrolic systems, rubyrins and hexaphyrins are covered. The conformation of core-modified rubyrins was found to be dependent on the number and nature of the heteroatom present inside the core. Further, in the hexapyrrolic systems, an increase in the number of meso carbons from four (rubyrin) to six (hexaphyrin) increases the conformational flexibility, where different types of conformations are observed upon going from free base to protonated form. Heptapyrrolic and octapyrrolic expanded porphyrins also exhibit rich structural diversity. Octaphyrins are known to exhibit figure eight conformation, where the macrocycle experiences a twist at the meso carbon, losing aromatic character. By suitable chemical modification, it is possible to avoid the twist, and planar 34 pi core-modified octaphyrins have been reported that show aromatic character and obey the (4 n + 2) Hückel rule. The structural diversity exhibited by nine pyrrolic macrocycles (nonaphyrins) and ten pyrrolic macrocycles (decaphyrins) are also described.     

Reverse osmosis separation of inorganic salts using polyvinylalcohol membranes

Permeabilities and fluxes of fifty-four mono-, divalent anions and cations of sodium and chloride salts have been tested under experimental conditions of 50 bar and room temperature through asymmetric polyvinylalcohol membranes crosslinked with formaldehyde. The following percent rejections among these salts are given: sodium salts of divalent anions (70–80%), chloride salts of divalent cations (30–40%), H₂ SO₄ (30%), sodium salts of monovalent monoatomic anions, chloride salts of monovalent cations (15– 30%) and HCl, HNO₃, NaOH, KOH (10–20%). Sodium salts of monovalent polyatomic anions gave higher rejections than those of monovalent monoatomic anions. Higher rejection of divalent anions than that of divalent cations of chloride salts suggests that the membrane surface is negatively charged.     

Electrochemical synthesis of novel π-extended phenoxazine derivatives of porphyrincatecholes

Three new functionalized phenoxazine-catechol porphyrins 7a–c have been synthesized by a green one-pot method and structurally characterized by spectroscopic analysis. The electro-oxidation of 5,10,15,20-tetrakis(2,3-dihydroxyphenyl) porphyrins(1a–c) with four catechol units in the presence of 2-aminophenol 8 as bidentate nucleophile has been done and phenoxazine rings have been formed by intermolecular and intramolecular Michael addition reactions. Spectroscopic characterization and voltammetry results have allowed us to propose four independent ECEC mechanisms for the electrochemical oxidation pathway. The functionalization of the porphyrins affected their photophysical properties. Expansion of the UV–vis spectrum range and the decrease of the fluorescence intensity of the products would support the energy transfer between the porphyrin core excited states to the four substitutions as the electron acceptor subunits. SEM images indicate that this method produces regularly shaped manganese porphyrin nano-particles 7c that possess a cubic nano structure.     

Poly(3,4-ethylenedioxythiophene)/Au-nanoparticles composite as electrode coating suitable for electrocatalytic oxidation

Composite materials consisting of poly(3,4-ethylenedioxythiophene) including Au nanoparticles, encapsulated by citrate anions, have been firmly deposited on an electrode surface through a simple method, taking advantage of the interaction between Au metal and thiophene polymeric backbone. A series of similar electrode coatings, also including different amounts of nanoparticles inside, has been characterised in terms of thickness and surface morphology, through different microscopic techniques. The electrocatalytic properties have been studied with respect to the oxidation of glucose in alkaline media, which is prevented from occurring on the pure organic material.     

Molecular Pincers Using a Combination of N-H and C-H Donors for Anion Binding

A naphthalene imide (1) and a naphthalene (2) bearing two pyrrole units have been synthesized, respectively, as anion receptors. It was revealed by ¹H NMR spectral studies carried out in CD₃CN that receptors 1 and 2 bind various anions via hydrogen bonds using both C-H and N-H donors. Compared with receptor 2, receptor 1 shows higher affinity for the test anions because of the enhanced acidity of its pyrrole NH and naphthalene CH hydrogens by the electron-withdrawing imide substituent. Molecular mechanics computations demonstrate that the receptors contact the halide anions via only one of the two respective available N-H and C-H donors whereas they use all four donors for binding of the oxyanions such as dihydrogen phosphate and hydrogen pyrophosphate. Receptor 1, a push-pull conjugated system, displays a strong fluorescence centered at 625 nm, while receptor 2 exhibits an emission with a maximum peak at 408 nm. In contrast, upon exposure of receptors 1 and 2 to the anions in question, their fluorescence was noticeably quenched particularly with relatively basic anions including F⁻, H₂PO₄⁻, HP₂O₇³⁻, and HCO₃⁻.     

Characterization of network morphology in anion binding hydrogels used for wastewater remediation

This work reports on morphological features of hydrogels, which have been used for the ultimate removal and recovery of nutrient and toxic anions from wastewater effluents. The sorbent used was crosslinked polyamine (PAA·HCl) polymeric hydrogels. The surface topography and morphology of these hydrogels were characterized by tapping mode atomic force microscopy. The change of the gel surface in response to the degree of crosslinking was observed via phase imaging. The crosslinker amount affects both the crosslink density and uniformity. Phase images were recorded at moderate to hard tapping conditions (A_sp/A₀=0.3-0.6) and related to surface stiffness variations associated with Young's modulus (E) change. Bright ellipse and sponge-like domains of submicrometer scale were found on irregularly crosslinked gels, while the gel topography was uniform in gels that were prepared with a more regular distribution of crosslinks. The observed AFM domain size was strongly affected by the gel's degree of crosslinking.     

Porphyrins and metalloporphyrins: potential hypoxic agents

Synthetic water-soluble porphyrins and their metalloporphyrin derivatives with Co(III), Cu(II), Ru(II) and Pt(II), containing various functional groups within the meso-positions of the porphyrin, were synthesised and evaluated as hypoxic agents, especially as cytotoxins and radiosensitisers. Cobalt complexes of the porphyrins containing positively charged methylpyridinium groups showed selective toxicity toward hypoxic Chinese Hamster Ovary (CHO) cells. The Co(III) complexes of the cationic and the anionic porphyrins are all weak radiosensitisers toward hypoxic cells, the highest sensitisation enhancement ratio (SER = 1.22, at 50 muM) being with a porphyrin complex containing a cis-arrangement of two nitro and two methylpyridinium meso-substituents. A copper complex of a tetracationic porphyrin showed slight radiosensitisation activity with an SER value of about 1.1. The other metalloporphyrins showed no hypoxic selectivity or radiosensitisation activity. In total, over 50 porphyrin free bases have been synthesised, of which half are water-soluble and have been metallated; thus, the chemistry is now in place for further development of water-soluble hypoxic agents.     

手性硅宁—卟啉配体的合成与表征

首次合成了３种新的手性硅宁－卟啉配体。它们的结构分别用紫外可见光谱、核磁共振谱、红外光谱和质谱进行了表征。