Iron porphyrin-modified electrodes: influence of the method of modification on the stability and electroactivity in oxidation of sulfite or hydrogensulfite in ethanol–water solutions

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the electrode to sulfite or hydrogensulfite were observed. The behavior of the polymer-modified electrode is different in water compared to ethanol–water.     

高分子/石墨复合材料的制备与导电性能的研究进展

介绍了近年来高分子/石墨复合材料制备方法和导电机理的研究进展。通过氧化、插层以及插层后加热可以在石墨碳层上引入极性基团,提高其比表面积,有利于高分子进行插层。用处理后比表面积高的石墨制备复合材料可以降低材料的渗滤值,提高材料的导电性能。复合材料的导电机理可以用渗滤理论来解释。     

金属卟啉催化的过氧化氢选择氧化烃类反应机理研究

本文综合介绍了近年来采用过氧化氢为氧化剂,金属铁卟啉和锰卟啉模拟酶体系催化烯烃环氧化和烷烃氧化的反应机理。总结了采用不同手段促进过氧化氢的异裂,以有效形成金属卟啉活性中间体的反应过程。     

Manganese porphyrins/mesoporous amberlyst 15 nanocomposites: Robust biomimetic catalysts for aqueous oxidation of olefins

In this study, the manganese complexes of N-methylated meso-tetra(2-, 3-, or 4 pyridyl)porphyrins, immobilized into the pores of the sodium salt of mesoporous amberlyst 15 nanoparticles (nanoAmbSO₃Na), nanoAmbSO₃@MnT(2-MePy)P (OAc), nanoAmbSO₃@MnT(3-MePy)P (OAc), and nanoAmbSO₃@MnT(4-MePy)P (OAc), were synthesized and characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), thermal gravimetric analysis (TGA), nitrogen adsorption/desorption porosimetry analysis, and diffuse reflectance UV–vis spectroscopy. FESEM images revealed a particle size less than ~40 nm for the nanocomposites. The results of BET are in accord with the occupation of the larger pores of the polymer matrix in the case of MnT(2-MePy)P (OAc) as the most sterically demanding metalloporphyrin of the series, and the smaller pores in the case of the other ones. The immobilized manganese porphyrins were used as catalysts for the oxidation of olefins with sodium periodate in the presence of imidazole (ImH) as the co-catalyst. The negligible oxidative destructions of the immobilized manganese porphyrins under the oxidative conditions allowed the comparison of the inherent catalytic activity of the metalloporphyrins, decreased as nanoAmbSO₃@MnT(4-MePy)P (OAc) > nanoAmbSO₃@MnT(3-MePy)P (OAc) ≫ nanoAmbSO₃@MnT(2-MePy)P (OAc). Contrary to the general belief that electron-deficient metalloporphyrins are more efficient catalysts than the electron-rich ones, the most electron-deficient metalloporphyrin of the series, that is, nanoAmbSO₃@MnT(2-MePy)P (OAc), showed the lowest catalytic activity. Due to the high oxidative stability of the immobilized manganese porphyrins, ring opening of epoxide competes with the epoxidation reaction to decrease the yield of epoxide at longer reaction times than the optimized one.     

Poly(N-isopropylmethacrylamide-co-4-acrylamidobenzo-18-crown-6) microgels with expanded networks for excellent adsorption of lead(II) ions

Lead(II) (Pb²⁺) ions are toxic heavy metal ions that can accumulate in the human body through water and cause severe health problems, including neurotoxicity, nephrotoxicity, hematological toxicity and even genotoxicity effects. To remove Pb²⁺ selectively and effectively from aqueous solutions, we develop a novel type of Pb²⁺-recognizable microgels with excellent adsorption capacity to Pb²⁺, which are fabricated from 4-acrylamidobenzo-18-crown-6 (B18C6Am) and N-isopropylmethacrylamide (NIPMAM) monomers by precipitation copolymerization method. The prepared poly(N-isopropylmethacrylamide-co-4-acrylamidobenzo-18-crown-6) (PNMB) microgels exhibit expanded structures, because the electron-donating methyl groups at α-carbon could descend the polarity of CO in the NIPMAM monomers and thus weaken the polymer segment···segment interactions. The expanded structures of PNMB microgels are beneficial for adsorption of Pb²⁺ due to the low steric hindrance in the polymeric networks. The Pb²⁺ adsorption isotherms of PNMB microgels are consistent with the Langmuir model for monolayer adsorption. The results indicate that the prepared Pb²⁺-recognizable PNMB microgels are highly promising for the selective removal of lead(II) ions from aqueous solutions.     

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes

The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,β′-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6 , bispalladium(II) dioxo-di-p-pyrirubyrin 9 , and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting ( 9 ) the wavelength of Yb-based fiber lasers. The incorporation of an α,β′-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules.     

Protonated Porphyrins: Bifunctional Catalysts for the Metal-Free Synthesis of N-Alkyl-Oxazolidinones

The protonation of commercially available porphyrin ligands yields a class of bifunctional catalysts able to promote the synthesis of N-alkyl oxazolidinones by CO₂ cycloaddition to corresponding aziridines. The catalytic system does not require the presence of any Lewis base or additive, and shows interesting features both in terms of cost effectiveness and eco-compatibility. The metal-free methodology is active even with a low catalytic loading of 1 % mol, and the chemical stability of the protonated porphyrin allowed it to be recycled three times without any decrease in performance. In addition, a DFT study was performed in order to suggest how a simple protonated porphyrin can mediate CO₂ cycloaddition to aziridines to yield oxazolidinones.     

Electrocatalytic Behavior of Manganese and Cobalt Porphyrins Attached to Graphene Quantum Dots: Applied in the Oxidation of Hydrazine

Manganese and cobalt metalated 5, 10, 15-tris(aminophenyl)-20-(4-carboxyphenyl) porphyrins (ClMnTA₃CPP and CoTA₃CPP) were synthesized and attached to graphene quantum dots (GQDs) via π-π interaction and electrostatic interaction. The electrochemical oxidation of hydrazine was performed via cyclic voltammetry and chronoamperometry. The CoTA₃CPP showed good electrocatalytic activity towards the oxidation of hydrazine in terms of catalytic rate constants and limits of detection (LoD). ClMnTA₃CPP showed lower overpotential 0.60 V. The introduction of GQDs improved the electrocatalytic ability when combined with CoTA₃CPP and ClMnTA₃CPP with the lowest LoD (0.0025 mM CoTA₃CPP–GQDs) followed by ClMnTA₃CPP–GQDs with 0.0033 mM.