New Materials Based on Cationic Porphyrins Conjugated to Chitosan or Titanium Dioxide: Synthesis, Characterization and Antimicrobial Efficacy.

The post-functionalization of 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide, known as a highly efficient photosensitizer (PS) for antimicrobial photodynamic therapy (aPDT), in the presence of 3- or 4-mercaptobenzoic acid, afforded two new tricationic porphyrins with adequate carboxylic pending groups to be immobilized on chitosan or titanium oxide. The structural characterization of the newly obtained materials confirmed the success of the porphyrin immobilization on the solid supports. The photophysical properties and the antimicrobial photodynamic efficacy of the non-immobilized porphyrins and of the new conjugates were evaluated. The results showed that the position of the carboxyl group in the mercapto units or the absence of these substituents in the porphyrin core could modulate the action of the photosensitizer towards the bioluminescent Gram-negative Escherichia coli bacterium. The antimicrobial activity was also influenced by the interaction between the photosensitizer and the type of support (chitosan or titanium dioxide). The new cationic porphyrins and some of the materials were shown to be very stable in PBS and effective in the photoinactivation of E. coli bacterium. The physicochemical properties of TiO2 allowed the interaction of the PS with its surface, increasing the absorption profile of TiO2, which enables the use of visible light, inactivating the bacteria more efficiently than the corresponding PS immobilized on chitosan.

Recent Advances in Catalyzed Sequential Reactions and the Potential Use of Tetrapyrrolic Macrocycles as Catalysts.

Complexes of porphyrins and of other similar tetrapyrrolic macrocycles are extensively explored as catalysts for different chemical processes, and the development of solid catalysts for heterogeneous processes using molecules with the ability to act as multifunctional catalysts in one-pot reactions is increasing and can lead to the wider use of this class of molecules as catalysts. This mini review focuses on the application of this class of complexes as catalysts in a variety of sequential one-pot reactions.

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 (CO3(2-) 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.

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.

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.

Introduction to the RSC Advances Emerging Investigators Series 2022.

Dr Fabienne Dumoulin and Professor Shirley Nakagaki are delighted to introduce the RSC Advances Emerging Investigators Series, which highlights some of the very best work of early career researchers.

Comparison of the Photodynamic Action of Porphyrin, Chlorin, and Isobacteriochlorin Derivatives toward a Melanotic Cell Line.

Melanoma is the most dangerous form of skin cancer, with an abrupt growth of its incidence over the last years. It is extremely resistant to traditional treatments such as chemotherapy and radiotherapy, but therapies for this cancer are gaining attention. Photodynamic therapy (PDT) is considered an effective modality to treat several types of skin cancers and can offer the possibility to treat one of the most aggressive ones: melanoma. In this work, the effect of PDT on a melanotic cell line (B16F10 cells) was assessed by exposing cultured cells to 5,10,15-tris(pentafluorophenyl)-20-(4-pyridyl)porphyrin (PS1) and to its chlorin (PS2) and isobacteriochlorin (PS3) corresponding derivatives and red LED light (λ = 660 ± 20 nm). The PDT effect in the cells' viability was measured using the MTT assay. The cell apoptosis was quantified by flow cytometry, and the subcellular localization of the photosensitizer was determined by fluorescence microscopy. In addition, the ability of PS2 to generate superoxide radicals was qualitatively assessed by tyrosine nitration. The results show that the efficiency of the PDT process is dependent on the structure of the PS and on their ability to produce singlet oxygen. Besides that, the photoactivation efficiency is highly dependent on the cellular sublocalization of the PS and on its cellular uptake and singlet oxygen production. We also found that the resistant cell line B16F10 has distinctive chlorin, isobacteriochlorin, or porphyrin-specific resistance profiles. Furthermore, it is shown that the highly fluorescent chlorin derivative PS2 can also be considered in imaging diagnostics.

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.

Copper-phthalocyanine coordination polymer as a reusable catechol oxidase biomimetic catalyst.

The development of selective, efficient, and recoverable/reusable catalysts for oxidation reactions has become one of the main challenges of modern chemistry. Considering our interest in efficient catalytic systems based on porphyrin (Por) and phthalocyanine (Pc) coordination polymers, we report here the synthesis, characterization and catalytic activity of a new Pc coordination polymer (coined hereafter as Cu4CuPcSPy). The new Pc material was obtained in excellent yield, from the reaction of H2PcSPy with an excess amount of copper(ii) acetate. The catalytic efficiency of Cu4CuPcSPy was evaluated in the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in the presence of molecular oxygen from air, with or without the addition of aqueous 30% hydrogen peroxide. The comparison between the homogeneous (CuPcSPy) and the heterogeneous (Cu4CuPcSPy) catalytic systems showed a better performance for the Cu4CuPcSPy material, that can be recovered by filtration and reused, maintaining its activity roughly unchanged during three catalytic cycles. An increment of approximately 30% was also verified in the catalytic activity of the homogeneous and heterogeneous systems by adding aqueous hydrogen peroxide to the catalytic reactions.

Oxidation catalyst obtained by the immobilization of layered double hydroxide/Mn(iii) porphyrin on monodispersed silica spheres.

Several functional hybrid materials have been reported as immobilized porphyrin derivatives in various organic and inorganic host materials (polymers, mineral clays, silica, etc.), with potential applications in various fields, such as photochemistry, electrochemistry and heterogeneous catalysis. Layered double hydroxides (LDHs), commonly known as hydrotalcite-like materials, have also been analyzed for use as supports for metallocomplexes. Recently, nanocomposite materials with a core-shell structure produced by combining two kinds of nanometer-size materials have received considerable attention, since the use of these materials is a promising strategy to prevent the aggregation and self-oxidation of molecules, reducing the catalytic activity. In this study, monodispersed hierarchical layered double hydroxides on silica spheres (LDH@SiO2) with core-shell structures were developed for metalloporphyrin immobilization and the materials were used as the oxidant catalysts of different substrates.

Nanofibrous and nanotubular supports for the immobilization of metalloporphyrins as oxidation catalysts.

Nanofibrous and nanotubular materials, natural and synthetic, are important alternative matrices for the immobilization of metallocomplexes, especially metalloporphyrins, as oxidation catalysts. The process permits a regular and controllable distribution of the active phase at the outer and/or inner surfaces of the tubes, promoting a special environment for the approximation of a substrate to the catalytic active species. The immobilization also prevents the molecular aggregation and bimolecular self-destruction reactions, facilitates the recovery and reuse of the catalyst, reduce de cost of material preparation and environmental concerns. A variety of nanofibrous and nanotubular structures are presented and specific examples of immobilization of iron porphyrins in different supports and their oxidation catalytic activities are presented and discussed.

Selective oxidation catalysts obtained by immobilization of iron(III) porphyrins on thiosalicylic acid-modified Mg-Al layered double hydroxides.

Nitrate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and exfoliated in formamide. Reaction of the single layer suspension with thiosalicylic acid under different conditions afforded two types of solids: LDHA1, in which the outer surface was modified with the anion thiosalicylate, and LDHA2, which contained the anion thiosalicylate intercalated between the LDH layers. LDHA1 and LDHA2 were used as supports to immobilize neutral (FeP1 and FeP2) and anionic (FeP3) iron(III) porphyrins. For comparison purposes, the iron(III) porphyrins (FePs) were also immobilized on LDH intercalated with nitrate anions obtained by the co-precipitation method. Chemical modification of LDH facilitated immobilization of the FePs through interaction of the functionalizing groups in LDH with the peripheral substituents on the porphyrin ring. The resulting FePx-LDHAy solids were characterized by X-ray diffraction (powder) and UV-Vis and EPR spectroscopies and were investigated as catalysts in the oxidation of cyclooctene and cyclohexane. The immobilized neutral FePs and their homogeneous counterparts gave similar product yields in the oxidation of cyclooctene, suggesting that immobilization of the FePs on the thiosalicylate-modified LDHs only supported the catalyst species without interfering in the catalytic outcome. On the other hand, in the oxidation of cyclohexane, the thiosalicylate anions on the outer surface of LDHA1 or intercalated between the LDHA2 layers influenced the catalytic activity of FePx-LDHAy, leading to different efficiency and selectivity results. FeP1-LDHA2 performed the best (29.6% alcohol yield) due to changes in the polarity of the surface of the support and the presence of FeP1. Interestingly, FeP1 also performed better in solution as compared to the other FePs. Finally, it was possible to recycle FeP1-LDHA2 at least three times.

First insight into catalytic activity of anionic iron porphyrins immobilized on exfoliated layered double hydroxides.

Mg-Al layered double hydroxide (LDH) intercalated with glycinate anions was synthesized through co-precipitation and exfoliated in formamide and the single-layer suspension was reacted with aqueous iron porphyrin solutions (Fe(TDFSPP) and Fe(TCFSPP)). The obtained materials were characterized by X-ray powder diffraction, UV-vis, and electron paramagnetic resonance and investigated in the oxidation reaction of cyclooctene and cyclohexane using iodosylbenzene as oxidant. The iron porphyrin seems to be immobilized at the surface of the glycinate intercalated LDH. The catalytic activities obtained in heterogeneous media for iron porphyrin, Fe(TDFSPP), was superior to the results obtained under homogeneous conditions, but the opposite effect was observed on the Fe(TCFSPP), indicating that, instead of the structural similarity of both iron porphyrins (second-generation porphyrins), the immobilization of each one produced different catalysts. The best catalytic activity of the Fe(TDFSPP)/Gly-LDH, compared to Fe(TCFSPP)/Gly-LDH, can be explained by the easy access of the oxidant and the substrate to the catalytic sites in the former, probably located at the surface of the layered double hydroxide pillared with glycinate anions. A model for the immobilization and a mechanism for the oxidation reaction will be discussed.

Manganese chlorins immobilized on silica as oxidation reaction catalysts.

Synthetic strategies that comply with the principles of green chemistry represent a challenge: they will enable chemists to conduct reactions that maximize the yield of products with commercial interest while minimizing by-products formation. The search for catalysts that promote the selective oxidation of organic compounds under mild and environmentally friendly conditions constitutes one of the most important quests of organic chemistry. In this context, metalloporphyrins and analogues are excellent catalysts for oxidative transformations under mild conditions. In fact, their reduced derivatives chlorins are also able to catalyze organic compounds oxidation effectively, although they have been still little explored. In this study, we synthesized two chlorins through porphyrin cycloaddition reactions with 1.3-dipoles and prepared the corresponding manganese chlorins (MnCHL) using adequate manganese(II) salts. These MnCHL were posteriorly immobilized on silica by following the sol-gel process and the resulting solids were characterized by powder X-ray diffraction (PXRD), UVVIS spectroscopy, FTIR, XPS, and EDS. The catalytic activity of the immobilized MnCHL was investigated in the oxidation of cyclooctene, cyclohexene and cyclohexane and the results were compared with the ones obtained under homogeneous conditions.

Encapsulation of Fe(III) and Cu(II) complexes in NaY zeolite.

The use of nonporphyrin complexes encapsulated in zeolites as catalysts for oxidation reactions has been improved in the past decades by the discovery of increasing numbers of nonheme monoxygenases. The zeolite lattice can change the oxidative chemistry of the metallocomplexes, resulting in a catalytic effect different from those observed in homogeneous reactions. We report the encapsulation of iron and copper metallocomplexes with the ligand (2-hydroxybenzyl)(2-methylpyridyl)amine, Hbpa, and iron complexes with the ligand N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl) ethylenediamine, H(2)bbpen. The zeolite-encapsulated metallocomplexes were prepared by diffusion of the ligands through the pores of the zeolites, already exchanged with the respective metal. The syntheses were performed in methanol and toluene solutions. Elemental analysis of solids with the Hbpa ligand have indicated better complexation for synthesis in toluene, where 74% of the iron atoms were coordinated by the ligand, against 37% for the synthesis in methanol. For the immobilization with the H(2)bbpen ligand in toluene it was observed that 46% of the iron atoms are coordinated, showing that the diffusion of the small ligand Hbpa through the zeolite cage was facilitated. The EPR spectra of the solids show signals at g = 2.0, which was attributed to an Fe-Fe interaction from the noncoordinated atoms, and g = 4.3 attributed to iron (III) in a rhombic geometry.

Study of the catalytic behavior of montmorillonite/iron(III) and Mn(III) cationic porphyrins.

Two samples of montmorillonite (one of Brazilian origin, BNC1 clay, and the other STX-1, supplied by the Clay Mineral Society Repository (University of Missouri, USA) were allowed to react with biomimetic metalloporphyrins of Fe(III) and Mn(III) in cationic form. The compounds were characterized by several techniques, showing that the metalloporphyrins molecules were adsorbed at the surface of the clay platelet crystals. The catalytic activities of the intercalated complexes for the oxidation of alkane were dependent upon the concentration of the porphyrin immobilized in the clay and factors such as the metal ion species in the porphyrins, choice of solvent, and concentration of the iodosylbenzene oxidant. Good selectivity to cyclohexanol instead of cyclohexanone was observed for the catalytic oxidation of cyclohexane by iodosylbenzene.

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.

Porphyrin-kaolinite as efficient catalyst for oxidation reactions.

The preparation, characterization, and application in oxidation reactions of new biomimetic catalysts are reported. Brazilian Sao Simao kaolinite clay has been functionalized with [meso-tetrakis(pentafluorophenyl)porphinato]iron(III), Fe(TPFPP). To obtain the functionalized clay, the natural clay was purified by dispersion-sedimentation, expanded by insertion of dimethyl sulfoxide (DMSO), and functionalized with amino groups by substitution of DMSO with ethanolamine. These previous steps allowed clay functionalization with Fe(TPFPP), leading to a layered material with a basal spacing of 10.73 A. Clay functionalization with the porphyrin was confirmed by formation of the secondary amine, as demonstrated by FTIR bands at 3500-3700 cm(-1). UV-vis spectroscopy revealed a red shift in the Soret band of the iron porphyrin in the functionalized material as compared to the parent iron porphyrin catalyst in solution, indicating Fe(III)P --> Fe(II)P reduction. The catalytic performance of the functionalized clay was evaluated in the epoxidation of cyclooctene, with complete selectivity for the epoxide (100% epoxide yield), and ketonization of cyclohexane, cyclohexanone being the major product. The novel catalyst was also evaluated in the Baeyer-Villiger (BV) oxidation of cyclohexanone, with 85% conversion of cyclohexanone in epsilon-caprolactone, with total selectivity to epsilon-caprolactone.

Microporous porphyrin solids.

Metalloporphyrins are exceedingly useful building blocks for the design and synthesis of molecularly based solids. The use of hydrogen bonding or metal ion coordination provides a wide range of framework solids. Using various polyfunctionalized porphyrins, we have created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates. Their pore dimensions are comparable to zeolites, and they show shape and size selectivity in sorption of guest molecules and in epoxidation of alkenes.