M. Graça P. M. S. Neves

Oxidation of alkylaromatics with hydrogen peroxide catalysed by manganese(III) porphyrins in the presence of ammonium acetate

The oxidation of toluene (1), ethylbenzene (2) and cumene (3) with hydrogen peroxide, in the presence of several manganese(III) porphyrins with electron-withdrawing substituents, was studied using ammonium acetate as a co-catalyst. All products were characterised and their formation was justified by studying the oxidation of primary precursors, under the same conditions. The formation of the nitrate compounds was shown to be dependent on the presence of ammonium acetate. The oxidation of cumene and ethylbenzene afford products resulting from dehydrogenation reactions.

Corroles as anion chemosensors: exploiting their fluorescence behaviour from solution to solid-supported devices

The reactivity of the new gallium(III) complex of 3-vinyl-5,10,15-tris(pentafluorophenyl)corrole 4, as a diene in Diels–Alder reactions was studied using 1,4-benzoquinone and 1,4-naphthoquinone as dienophiles. In these reactions only the dehydrogenated adducts 5 and 6 were isolated. All the new corrole derivatives 4–6 were fully characterized by elemental analysis, 1H-NMR, 13C-NMR, 19F-NMR, MALDI-TOF-MS, UV-Vis absorption and emission spectroscopy. The sensing ability of compounds 4–6 and of their precursors 1–3 was studied in solution towards the spherical halide ions F−, Cl−, Br−, I−, the linear anion CN− and the bulky anions CH3COO− and H2PO4−. This study was also realized in gas-phase with the anions F− and CN−. A red-shift in the absorption spectra and an enhancement in the emission intensity were observed, with compounds 1, 3 and 5 being strongly sensitive to fluoride. The highest association constant was obtained for 1 with F−, being able to quantify 0.69 ppm of this anion. On the other hand, compounds 1 and 2 present a high sensitivity towards cyanide anions, producing a red-shift in the absorption and emission spectra and an increase in the emission intensity, being able to quantify a minimal amount of 1.43 ppm. Moreover, compounds 1 and 5 were used to prepare two low-cost solid polymers, based on polymethylmethacrylate (PMMA) and polyacrylamide, the last one being very promising since it is able to detect ca. 70.0 ppb of CN− in water. Compounds 2a and 5 were also tested in the presence of 4,4′-bipyridine, caffeine and nicotine and compound 2a proved to be very sensitive to 4,4′-bipyridine, while compound 5 was really effective for detecting caffeine and nicotine.

Strategies for Corrole Functionalization

This review covers the functionalization reactions of meso-arylcorroles, both at the inner core, as well as the peripheral positions of the macrocycle. Experimental details for the synthesis of all known metallocorrole types and for the N-alkylation reactions are presented. Key peripheral functionalization reactions such as halogenation, formylation, carboxylation, nitration, sulfonation, and others are discussed in detail, particularly the nucleophilic aromatic substitution and the participation of corroles in cycloaddition reactions as 2π or 4π components (covering Diels-Alder and 1,3-dipolar cycloadditions). Other functionalizations of corroles include a large diversity of reactions, namely Wittig reactions, reactions with methylene active compounds, formation of amines, amides, and imines, and metal catalyzed reactions. At the final section, the reactions involving oxidation and ring expansion of the corrole macrocycle are described comprehensively.

Corrole and corrole functionalized silica nanoparticles as new metal ion chemosensors: a case of silver satellite nanoparticles formation.

Corrole macrocycles are very appealing dyes for incorporation into light harvesting devices. This work shows the sensorial ability of 5,10,15-tris(pentafluorophenyl)corrole 1 and its monoanionic species toward Na(+), Ca(2+), Cu(2+), Cd(2+), Pb(2+), Hg(2+), Ag(+), and Al(3+) metal ions in toluene and acetonitrile. The photophysical studies toward metal ions were carried out by absorption and emission spectroscopy. From all metal ions studied, corrole 1 shows to be colorimetric for Hg(2+) allowing a naked-eye detection of Hg(2+) through a change of color from purple to blue in acetonitrile and from green to yellow in toluene. In addition a new β-imine corrole 4 was successful synthesized and further functionalized with 3-isocyanatopropyl-trimethoxysilane resulting in an alkoxysilane derivative 5. The grafting of alkoxysilane derivative 5 with optically transparent silica nanoparticles (SiNPs) was achieved succesfully. The new-coated silica nanoparticles with corrole 5 were studied in the presence of Cu(2+), Hg(2+), and Ag(+) as metal ion probes. Interestingly, upon addition of Ag(+), groups of satellite AgNPs were formed around the SiNPs and were checked by transmission electron microscopy (TEM). At same time, a change of color from green to yellow was observed.

Synthesis, Spectroscopy Studies, and Theoretical Calculations of New Fluorescent Probes Based on Pyrazole Containing Porphyrins for Zn(II), Cd(II), and Hg(II) Optical Detection

New pyrazole-porphyrin conjugates were successfully prepared from a reaction of β-porphyrin-chalcone derivatives with phenylhydrazine in acetic acid followed by an oxidative step. This fast and efficient synthetic approach provided the expected compounds in yields up to 82%. The sensing ability of the new porphyrin-pyrazole derivatives to detect the metal ions Ag(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Cr(3+) was studied by spectrophotometric and spectrofluorimetric titrations. In the presence of Zn(2+), the conjugates exhibit changes in the emission spectra that are desired for a ratiometric-type fluoroionophoric detection probe. The studies were extended to gas phase, where the pyrazole-porphyrin conjugates show ability to sense metal ions with high selectivity toward Cu(2+) and Ag(+), and in poly(methyl methacrylate) doped films with promising results for Zn(2+) detection.

An efficient approach for aromatic epoxidation using hydrogen peroxide and Mn(III) porphyrins

Efficient epoxidation, in very high conversions and selectivities, of aromatic hydrocarbons with hydrogen peroxide, in the presence of Mn(III) porphyrins [Mn(TDCPP)Cl, Mn(beta NO(2)TDCPP)Cl, Mn(TPFPP)Cl] as catalysts is described; naphthalene and anthracene afford the anti-1,2:3,4-arene dioxides whereas with phenanthrene the 9,10-oxide is obtained.

Homogeneous catalytic oxidation of styrene and styrene derivatives with hydrogen peroxide in the presence of transition metal-substituted polyoxotungstates

The tetrabutylammonium (TBA) salts of the Keggin-type polyoxotungstates with general formula [XW11M(H2O)O39](n−m)−, where X = P, B or Si and M = Mn, Fe or Co, were evaluated as catalysts in the oxidation of styrene, α-methylstyrene, p-methylstyrene, α,p-dimethylstyrene, p-chlorostyrene, p-nitrostyrene, and p-methoxystyrene under mild conditions, using aqueous H2O2 as an eco-sustainable oxidant. In this study, the influence of the catalysts and of the different styrene substituents on the oxidation reaction profile was evaluated in terms of conversion and selectivity. For all the performed catalytic studies, the main product results from the oxidative cleavage of the vinyl double bond, except in the case of the oxidation of p-methoxystyrene catalysed by BW11Mn, for which p-methoxyphenol is the main product. The catalysts BW11Mn and SiW11Co give rise to 100% conversion for almost all of the substrates, excluding p-methoxystyrene and p-nitrostyrene for both catalysts and α,p-dimethylstyrene only in the case of BW11Mn. The selectivity for CC cleavage products resulting from the oxidative cleavage of the vinyl double bond can be as high as 98%, reaching 98% conversion for p-nitrostyrene when SiW11Co was used as a catalyst. Possible pathways are discussed and the oxidation of a few presumed intermediates was carried out. The systematic study of several substituted styrene derivatives suggests a possible reactivity order for these compounds in the catalytic system considered.

Mimicking P 450 processes and the use of metalloporphyrins

Metalloporphyrins (MPs) are known to catalyze in vitro a broad range of cytochrome P450-mediated reactions occurring in vivo. Most of the biomimetic research using MPs in oxidative catalysis has been directed towards the oxidation of organic compounds presenting significant reactivity features in one functional group. Much less effort has been made to imitate the oxidation of more complex molecules, with a range of functionalities, such as drugs or other xenobiotics. By varying the structure of the porphyrin, the metal ion, the oxidant, and the reaction conditions, it is possible to modulate the regioselectivity of the oxidation reactions. Recently, and along with studies on the synthesis and reactivity of porphyrins, chlorins, and phthalocyanines, our group was able to develop an interesting line of research in the field of biomimetic oxidation of organic compounds using environmentally benign hydrogen peroxide as oxidant and Mn(III) or Fe(III) porphyrin complexes as catalysts. The more up to date results obtained in such work are reviewed here.

Corrole-silica hybrid particles: synthesis and effects on singlet oxygen generation

The present study describes the first example of hybrid particles composed of amorphous silica and corrole. The hybrid particles were obtained by covalent linking of the gallium(III)(pyridine) complex of 5,10,15-tris(pentafluorophenyl)corrole (GaPFC) at the surface of functionalized silica spheres. The functionalization step was achieved by a nucleophilic substitution reaction between corrole and 3-aminopropyltriethoxysilane previously grafted at the silica surfaces. The hybrids were morphologically and chemically characterized and the results have confirmed covalent linkages between corrole molecules and the silica particles. Preliminary studies on the capacity of corrole and hybrid particles to generate singlet oxygen was evaluated by a chemical method in which 1,3-diphenylisobenzofuran was used to trap singlet oxygen. The new corrole-silica hybrid particles have shown lower efficiency to generate singlet oxygen as compared to the pure corrole precursor. This effect was interpreted as a consequence of interparticle interactions mediated by the corrole molecules grafted at the silica surfaces that result in their clustering. Taken together, these findings demonstrate that despite lower efficiency in terms of singlet oxygen generation, the hybrid materials offer an alternative route to develop new platforms with potential for photodynamic therapy.

Do charge-remote fragmentations occur under matrix-assisted laser desorption ionization post-source decompositions and matrix-assisted laser desorption ionization collisionally activated decompositions?

The precursor ions of tetraphenylporphyrins that are substituted with fatty acids can be introduced into the gas phase by matrix-assisted laser desorption ionization (MALDI) and undergo post-source and collisionally activated decompositions (CAD) in a time-of-flight mass spectrometer. The goal of the research is to obtain a better understanding of post-source decompositions (PSD); specifically, we asked the question of whether ions undergoing PSD have sufficient energy to give charge-remote fragmentations along an alkyl chain. We chose the porphyrin macrocycle because we expected it to act as an inert “support,” allowing the molecule to be desorbed by MALDI and to be amenable to charge-remote fragmentation. MALDI-PSD and MALDI-CAD spectra are similar to high-energy CAD spectra and considerably more informative than low-energy CAD spectra, showing that charge-remote fragmentations of the fatty acid moieties do occur upon MALDI-PSD and MALDI-CAD.