Immobilization of anionic metalloporphyrins on zinc hydroxide nitrate and study of an unusual catalytic activity

Structural Analysis of Selenium Coordination Compounds and Mesoporous TiO2-Based Photocatalysts for Hydrogen Generation

This study reports the synthesis of ten coordination compounds (1-10) derived from the ligand bis((3-aminopyridin-2-yl)selanyl)methane (L) and different metal centers (CoII, CuI, CuII, ZnII, and AgI). Single crystals of the complexes were obtained via slow diffusion from overlaid solutions of ligand L and the corresponding metal. Their crystalline structures were determined by single-crystal X-ray diffraction (SCXRD) and further characterized using spectroscopic, spectrometric, and voltammetric techniques. Complexes 1-5, 7, and 10 were evaluated as cocatalysts of mesoporous titanium dioxide (m-TiO2) for photocatalytic hydrogen production via water photolysis under solar light simulation, using triethanolamine (TEOA) as the sacrificial agent. The results showed that complexes 4, 5, 7, and 10 enhanced m-TiO2 photocatalytic activity, achieving hydrogen evolution rates at least four times higher than standard m-TiO2 and P25. Among these, the photocatalyst m-TiO2-7 (7 = [Cu2(μ-SO4)2L2]) exhibited the highest hydrogen production, reaching approximately 7800 μmol/g over a 6-h experiment-nearly 26 times greater than pure m-TiO2 (300 μmol/g). These findings highlight the potential of organoselenium metal complexes for the development of novel photocatalytic materials based on nonprecious metals.

Atomic scale insight into the decomposition of nanocrystalline zinc hydroxynitrate toward ZnO using Mn2+ paramagnetic probes

Layered zinc hydroxynitrate (ZHN), with the chemical formula Zn5 (OH)8 (NO3)2·2H2O, exhibits a range of special properties such as anion-exchange and intercalation capacity, as well as biocompatibility, making it attractive for a large variety of applications in fields from nanotechnology to healthcare and agriculture. In this study nanocrystalline ZHN doped with 1,000 ppm Mn2+ was prepared by two synthesis methods (coprecipitation and solid state reaction) using similar environment-friendly precursors. The complex morpho-structural [X-ray diffraction, scanning and transmission electron microscopy, textural analysis] and spectroscopic [Fourier transform infrared and electron paramagnetic resonance (EPR)] characterization of the two ZHN nanopowders showed similar crystalline structures with Mn2+ ions localized in the nanocrystals volume, but with differences in their morphological and textural characteristics, as well as in the doping efficiency. ZHN obtained by coprecipitation consists of larger nanoplatelets with more than two times larger specific surface area and pore volume, as well as a dopant concentration than in the ZHN sample obtained by solid state reaction. The thermal stability and the on-set of the structural phase transformation have been investigated at atomic scale with high accuracy by EPR, using Mn2+ as paramagnetic probes. The on-set of the ZHN structural phase transformation toward ZnO was observed by EPR to take place at 110°C and 130°C for the samples prepared by coprecipitation and solid state reaction, respectively, evidencing a manganese induced local decrease of the transformation temperature. Our results contribute to the selection of the most appropriate ZHN synthesis method for specific applications and in the development of new green, cost-effective synthesis routes for Mn2+ doped nano-ZnO.

Hybrid Materials Based on Imidazo[4,5-b]porphyrins for Catalytic Oxidation of Sulfides

Heterogenized metalloporphyrin catalysts for oxidation reactions are extensively explored to improve chemical production. In this work, manganese meso-tetraarylporphyrins were immobilized on hydrated mesoporous titanium dioxide (SBET = 705 m2 g−1) through carboxylate or phosphonate anchoring groups separated from the macrocycle by the 2-arylimidazole linker fused across one of the pyrrolic rings of the macrocycle. The element composition of two mesoporous hybrid materials thus obtained were investigated and the integrity of the immobilized complexes was shown by different physicochemical methods. Finally, the catalytic efficiency of the more stable material Mn(TMPIP)/TiO2 with the phosphonate anchor was evaluated in the selective oxidation of sulfides to sulfoxides by molecular oxygen in the presence of isobutyraldehyde (IBA). The heterogenized complex has shown excellent catalytic activity exhibiting a turnover (TON) of ~1100 in a single catalytic run of the sulfoxidation of thioanisole. The catalyst was successfully reused in seven consecutive catalytic cycles.

Synthesis of novel hexamolybdenum cluster-functionalized copper hydroxide nanocomposites and its catalytic activity for organic molecule degradation

A novel heterogeneous catalytic nanomaterial based on a molybdenum cluster-based halide (MC) and a single-layered copper hydroxynitrate (CHN) was first prepared by colloidal processing under ambient conditions. The results of the elemental composition and crystalline pattern indicated that CHN was comprehensively synthesized with the support of the MC compound. The absorbing characteristic in the ultraviolet and near-infrared regions was promoted by both of the ingredients. The proper chemical interaction between the materials is a crucial reason to modify the structure of the MCs and only a small decrease in the magnetic susceptibility of CHN. The heterogeneous catalytic activity of the obtained MC@CHN material was found to have a high efficiency and excellent reuse when it is activated by hydrogen peroxide (H₂O₂) for the degrading reaction of the organic pollutant at room temperature. A reasonable catalytic mechanism was proposed to explain the distinct role of the copper compound, Mo₆ compound, and H₂O₂ in the production of the radical hydroxyl ion. This novel nanomaterial will be an environmentally promising candidate for dye removal.

Applications of Fluorous Porphyrinoids: An Update†

Porphyrins and related macrocycles have been studied broadly for their applications in medicine and materials because of their tunable physicochemical, optoelectronic and magnetic properties. In this review article, we focused on the applications of fluorinated porphyrinoids and their supramolecular systems and summarized the reports published on these chromophores in the past 5-6 years. The commercially available fluorinated porphyrinoids: meso-perfluorophenylporphyrin (TPPF₂₀ ) perfluorophthalocyanine (PcF₁₆ ) and meso-perfluorophenylcorrole (CorF₁₅ ) have increased photo and oxidative stability due to the presence of fluoro groups. Because of their tunable properties and robustness toward oxidative damage these porphyrinoid-based chromophores continue to gain attention of researchers developing advanced functional materials for applications such as sensors, photonic devices, component for solar cells, biomedical imaging, theranostics and catalysts.

Zn(ferulate)-LSH Systems as Multifunctional Filters

Excessive UV solar radiation exposure causes human health risks; therefore, the study of multifunctional filters is important to skin UV protective ability and also to other beneficial activities to the human organism, such as reduction of reactive oxygen species (ROS) responsible for cellular damages. Potential multifunctional filters were obtained by intercalating of ferulate anions into layered simple metal hydroxides (LSH) through anion exchange and precipitation at constant pH methods. Ultrasound treatment was used in order to investigate the structural changes in LSH-ferulate materials. Structural and spectroscopic analyses show the formation of layered materials composed by a mixture of LSH intercalated with ferulate anions, where carboxylate groups of ferulate species interact with LSH layers. UV-VIS absorption spectra and in vitro SPF measurements indicate that LSH-ferulate systems have UV shielding capacity, mainly UVB protection. The results of reactive species assays show the ability of layered compounds in capture DPPH^•, ABTS^•+, ROO^•, and HOCl/OCl⁻ reactive species. LSH-ferulate materials exhibit antioxidant activity and singular optical properties that enable their use as multifunctional filters.

Enhancing Charge Separation through Oxygen Vacancy-Mediated Reverse Regulation Strategy Using Porphyrins as Model Molecules

Highly efficient charge separation has been demonstrated as one of the most significant steps playing decisive roles in enhancing the overall efficiency of photoelectrochemical (PEC) processes. In this study, by employing 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin-Ni (NiTCPP) as a prototype, an oxygen vacancy (Vo)-mediated reverse regulation strategy is proposed for tuning hole transfer, which in turn can accelerate the transport of electrons and thus enhancing charge separation. The optimal NiO/NiTCPP system exhibits much higher (≈40 times) photocurrent and longer (≈13 times) lifetime of charge carriers compared with those of pure NiTCPP. Furthermore, the electron transfer kinetic rate constant (K_eff ) is quantitatively determined by an efficient scanning photoelectrochemical microscopy (SPECM). The K_eff of the optimal system has a 5.7-fold improvement. In addition, the similar enhancement in charge separation from other semiconductors (CoTCPP and FeTCPP) are also observed, indicating that the Vo-mediated reverse regulation strategy is a promising pathway for tuning the properties of light harvesters in solar energy conversion.

Comparison between catalytic activities of two zinc layered hydroxide salts in brilliant green organic dye bleaching

This paper reports the use of two layered hydroxide salts (LHS) (zinc hydroxide nitrate - ZHN - Zn₅(OH)₈(NO₃)₂·2H₂O, and zinc hydroxide chloride - ZHC - Zn₅(OH)₈Cl₂·H₂O) as catalysts for brilliant green (BG) organic dye bleaching, using hydrogen peroxide as oxidant. The LHS were prepared by precipitation reaction between an aqueous solution of zinc salts and an aqueous ammonia solution. The solids were characterized by powder X-ray diffraction (XRD), electron paramagnetic resonance (EPR), ultraviolet-visible electronic spectroscopy (UV-Vis) and Fourier-transform infrared spectroscopy (FTIR). The catalytic activity of the solids was investigated at temperatures of 25, 35 and 45 °C, using different molar ratios of oxidant:dye:Zn²⁺ ions (present in the catalyst), in the absence and presence of ambient light. The kinetic aspect of the reaction was investigated considering that the reaction showed pseudo-first order behavior in relation to BG dye concentration. We propose a mechanism where superoxide radicals account for most of the bleaching taking place. The catalytic results obtained, along with the low cost and low toxicity of zinc compounds, establish ZHN and ZHC as novel catalysts for dye wastewater treatment, an area with constant demand for new methods and materials given its relationship with environmental equilibrium and human health.

Practicably efficient ethylbenzene oxidation catalyzed by manganese tetrakis(4-sulfonatophenyl)porphyrin grafted to powdered chitosan

Manganese tetrakis(4-sulfonatophenyl)porphyrin chloride was grafted onto powdered chitosan via an acid–base reaction and ligation. The grafted catalyst was characterized by transmission electron microscopy, ultraviolet and visible spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and thermogravimetry. Ethylbenzene oxidation with O[Formula: see text] by the catalyst in the absence of additives and solvents can achieve moderate yields (approximately 30%) of acetophenone and phenethyl alcohol. The grafted catalyst can be reused four times for oxidation reactions. The results indicate that the catalytic activity of manganese tetrakis(4-sulfonatophenyl)porphyrin chloride is promoted by the ligation and grafting function of the amino groups in the powdered chitosan.

Catalytic activity of biomimetic model of cytochrome P450 in oxidation of dopamine

The introduction of electron-withdrawing group into porphyrin molecule as cytochrome P450 model can tune the energy level and have an effect on the electronic structure. In this work, linking with the strong electron-withdrawing fluorine atoms, a starburst dendritic molecule, 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin iron (III) chloride (FeTFPP), containing a saddle-shaped porphyrin as the central core and four pentafluorophenyl rings as the peripheral functional groups was successfully synthesized. Subsequently, the macrocyclic conjugate polymer film of FeTFPP was achieved via a low-cost electrochemical method and exploited as an efficient mimetic enzyme. Furthermore, a biomimetic sensor was constructed by the poly(FeTFPP) film and graphene (rGO) sheet (rGO-poly(FeTFPP)) for selective and sensitive detection of dopamine (DA). Here, the FeTFPP polymer performs three functions: electrochemical recognition (owing to the hydrogen bonding between the strongly electronegative fluorine atoms and DA), biomimetic microenvironment (owing to interaction between porphyrin core and DA), electrocatalysis (owing to remarkable catalytic ability of iron (III) ion). Under optimum conditions, the response to DA was linear in the concentration range between 0.05 to 300μM, and the detection limit was 0.023μM. In addition, we applied the rGO-poly(FeTFPP) film to detect DA in real samples and the results implied its feasibility for practical application. As a result, it is believed that the rGO-poly(FeTFPP) film is one of the promising biomimetic catalysts for electrocatalysis and relevant fields.

Recent Advances in Solid Catalysts Obtained by Metalloporphyrins Immobilization on Layered Anionic Exchangers: A Short Review and Some New Catalytic Results

Layered materials are a very interesting class of compounds obtained by stacking of two-dimensional layers along the basal axis. A remarkable property of these materials is their capacity to interact with a variety of chemical species, irrespective of their charge (neutral, cationic or anionic). These species can be grafted onto the surface of the layered materials or intercalated between the layers, to expand or contract the interlayer distance. Metalloporphyrins, which are typically soluble oxidation catalysts, are examples of molecules that can interact with layered materials. This work presents a short review of the studies involving metalloporphyrin immobilization on two different anionic exchangers, Layered Double Hydroxides (LDHs) and Layered Hydroxide Salts (LHSs), published over the past year. After immobilization of anionic porphyrins, the resulting solids behave as reusable catalysts for heterogeneous oxidation processes. Although a large number of publications involving metalloporphyrin immobilization on LDHs exist, only a few papers have dealt with LHSs as supports, so metalloporphyrins immobilized on LHSs represent a new and promising research field. This work also describes new results on an anionic manganese porphyrin (MnP) immobilized on Mg/Al-LDH solids with different nominal Mg/Al molar ratios (2:1, 3:1 and 4:1) and intercalated with different anions (CO₃²⁻ or NO₃⁻). The influence of the support composition on the MnP immobilization rates and the catalytic performance of the resulting solid in cyclooctene oxidation reactions will be reported.

Oxygen oxidation of ethylbenzene over manganese porphyrin is promoted by the axial nitrogen coordination in powdered chitosan

A less wasteful production method of oxidation ethylbenzene to acetophenone and phenethyl alcohol was adviced. It revealed an important role in tuning catalytic reactivity of metalloporphyrins by the axial ligand for oxidation of hydrocarbon.

Galactodendritic porphyrinic conjugates as new biomimetic catalysts for oxidation reactions

This work employed [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin] ([H2(TPPF20)], H2P1) as the platform to prepare a tetrasubstituted galactodendritic conjugate porphyrin (H2P3). After metalation with excess copper(II) acetate, H2P3 afforded a new solid porphyrin material, Cu4CuP3S. This work also assessed the ability of the copper(II) complex (CuP3) of H2P3 to coordinate with zinc(II) acetate, to yield the new material Zn4CuP3S. UV-visible, Fourier transform infrared, and electron paramagnetic resonance spectroscopies aided full characterization of the synthesized solids. (Z)-Cyclooctene epoxidation under heterogeneous conditions helped to evaluate the catalytic activity of Cu4CuP3S and Zn4CuP3S. The efficiency of Cu4CuP3S in the oxidation of another organic substrate, catechol, was also investigated. According to the results obtained in the heterogeneous process, Cu4CuP3S mimicked the activity of cytochrome P-450 and catecholase. In addition, Cu4CuP3S was reusable after recovery and reactivation. The data obtained herein were compared with the results achieved for the copper complex (CuP1) of [H2(TPPF20)] and for CuP3 under homogeneous conditions.

Synthesis, characterization, and atropisomerism of iron complexes containing the tetrakis(2-chloro-6-fluorophenyl)porphyrinate ligand

The synthesis of iron complexes containing the 5,10,15,20-tetrakis(2-chloro-6-fluorophenyl)porphyrin ligand is presented and the factors surrounding the observed atropisomerism are investigated.

A zinc sulfide-supported iron tetrakis (4-carboxyl phenyl) porphyrin catalyst for aerobic oxidation of cyclohexane

Fe TCPP/ZnS catalyst, which possessed much higher catalytic activity than Fe TCPP, was conveniently prepared and was easily recovered by simple isolation from the reaction mixture, and it was a promising catalyst in industrial applications.

Development of drug delivery systems based on layered hydroxides for nanomedicine

Layered hydroxides (LHs) have recently fascinated researchers due to their wide application in various fields. These inorganic nanoparticles, with excellent features as nanocarriers in drug delivery systems, have the potential to play an important role in healthcare. Owing to their outstanding ion-exchange capacity, many organic pharmaceutical drugs have been intercalated into the interlayer galleries of LHs and, consequently, novel nanodrugs or smart drugs may revolutionize in the treatment of diseases. Layered hydroxides, as green nanoreservoirs with sustained drug release and cell targeting properties hold great promise of improving health and prolonging life.

Chemical reactions catalyzed by metalloporphyrin-based metal-organic frameworks

The synthetic versatility and the potential application of metalloporphyrins (MP) in different fields have aroused researchers' interest in studying these complexes, in an attempt to mimic biological systems such as cytochrome P-450. Over the last 40 years, synthetic MPs have been mainly used as catalysts for homogeneous or heterogeneous chemical reactions. To employ them in heterogeneous catalysis, chemists have prepared new MP-based solids by immobilizing MP onto rigid inorganic supports, a strategy that affords hybrid inorganic-organic materials. More recently, materials obtained by supramolecular assembly processes and containing MPs as building blocks have been applied in a variety of areas, like gas storage, photonic devices, separation, molecular sensing, magnets, and heterogeneous catalysis, among others. These coordination polymers, known as metal-organic frameworks (MOFs), contain organic ligands or complexes connected by metal ions or clusters, which give rise to a 1-, 2- or 3-D network. These kinds of materials presents large surface areas, Brønsted or redox sites, and high porosity, all of which are desirable features in catalysts with potential use in heterogeneous phases. Building MOFs based on MP is a good way to obtain solid catalysts that offer the advantages of bioinspired systems and zeolitic materials. In this mini review, we will adopt a historical approach to present the most relevant MP-based MOFs applicable to catalytic reactions such as oxidation, reduction, insertion of functional groups, and exchange of organic functions.

Immobilization of anionic iron(III) porphyrins onto in situ obtained zinc oxide

A family of anionic iron(III) porphyrins (FePor) was immobilized onto zinc oxide (ZnO) obtained by the in situ hydrothermal decomposition of zinc hydroxide nitrate, a layered hydroxide salt. The immobilization probably occurred via the interaction between the anionic charges on the porphyrins and the positively charged surface of the ZnO, in slightly acidic to neutral pH. The resulting solids were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRDP), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and ultraviolet-visible spectroscopy (UV-Vis) (solid samples), which confirmed the formation of ZnO and the immobilization of the FePor. The prepared materials were employed as catalysts for the heterogeneous catalytic oxidation of cyclooctene, cyclohexane, and n-heptane, using iodosylbenzene as the oxygen donor. Good catalytic results were achieved for all the substrates, and selectivity for the alcohol was verified during the oxidation of alkanes. The reuse capacity of the solid catalyst was also investigated.

Catalysts for heterogeneous oxidation reaction based on metalloporphyrins immobilized on kaolinite modified with triethanolamine

Raw kaolinite was modified with triethanolamine (TEA), in an attempt to create a new support for the immobilization of metalloporphyrins. Anionic metalloporphyrins containing Fe(3+) or Mn(3+) as metallic centers were immobilized on the prepared support, and the obtained solids were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), thermal analysis (thermogravimetric and differential thermal analyses--TGA/DTA), and scanning electron microscopy (SEM). The solids were used in heterogeneous oxidation catalysis of cyclooctene and cyclohexane. The yields from the oxidation of cyclooctene depended on the amount of TEA and/or water present in the solids. Good reaction yields were obtained for the oxidation of cyclohexane, with selectivity for the alcohol. In one specific case, a possible co-catalytic activity was verified for TEA during the oxidation of cyclohexane.