Porphyrin Complexes Research Articles

Proton Activation in the Presence of a Weak Acid Facilitated by Second Coordination Sphere Effects in Iron Porphyrins**

AbstractThe catalytic activity of two iron‐based porphyrin complexes containing pyridine‐functionalized second coordination spheres, referred to as Py2XPFe and CuPy2XPFe, have been investigated for the hydrogen evolution reaction (HER) and compared with the unsubstituted analog TMPFe in acetonitrile. The CuPy2XPFe incorporates a second metal center within the pyridine residues and represents a heterodinuclear system, while the structurally analogous Py2XPFe lacks an additional metal in the second coordination sphere. Both the Py2XFe and CuPy2XPFe complexes are observed to activate the weak acid, acetic acid (AcOH) at the FeII/I couple rather than at the more energy intensive FeI/0 couple observed for the unfunctionalized TMPFe complex at low acid concentrations. The ability of the monometallic Py2XPFe to activate the weak proton source at the FeII/I couple manifests as an ECEC(E)′ type electrochemical mechanism, rather than an EECC(E)′ type mechanism as observed for TMPFe. The CuPy2XPFe displays improved reactivity compared with the Py2XPFe and TMPFe under the same substrate conditions, however the mechanistic nuances into bimetallic CuPy2XPFe system are currently unclear. The concentration of AcOH was incrementally increased and the rate constants of the initial protonation step i. e. formation of a hydridic species (k1,app), as well as of the protonation of the hydridic species to produce dihydrogen (kglobal) were calculated using the Foot‐of‐the‐wave and plateau current rate equation methodologies, respectively. The kinetic analysis indicates that the activation of protons through the ECEC(E)′ type mechanism for the Py2XPFe results in a system in which k1,app< kglobal. As both the monometallic Py2XPFe and bimetallic CuPy2XPFe activate the AcOH at less cathodic potentials than TMPFe under identical conditions, the overpotentials (ηTOF/2) for these complexes are thus dramatically lower. The reactivity difference of the Py2XPFe when compared to non‐substituted iron porphyrin analogs is due to the hanging group's influence, which is believed to either act as hydrogen bond promoters for the active site or aids to stabilize a catalytic intermediate species during catalysis.

Modulation of optical oxygen sensitivity of H2(TPP) by using Eu3+, Gd3+ and Yb3+ ions doped silicate-based bioactive glass powders immersed in simulated body fluid

Improving the performance of optical oxygen sensors can be accomplished by adding additives to the composition comprising an oxygen-sensitive probe encapsulated in a polymeric matrix. In this study, to advance the oxygen sensing ability, free meso-tetraphenyl porphyrin (H2(TPP)) was chosen as a luminophore. The sol-gel based 13–93 bioactive glass powders (BG) co-doped with ytterbium (Yb3+), gadolinium (Gd3+), and europium (Eu3+) and immersed in simulated body fluids (SBF) were also used as additives. After being immersed in SBF, bioactive glasses containing Eu3+, Gd3+, and Yb3+ were found to be able to convert hydroxyapatite corresponding to in vitro bioactivity tests. The optimum additive concentration for all glass samples is 3 wt%, based on photoluminescence-based properties. The luminescence dye was incorporated into poly(trimethylsilylpropyne) [poly(TMSP)] matrices in the form of a thin film along with bioactive glass additives to improve oxygen sensitivity. Emission-based intensity values of all porphyrin complexes have been followed as a signal drop during oxygen sensing measurements. The H2(TPP) along with the additive of BG:Eu3+ showed a 6.88 fold of I0/I ratio compared to the undoped and Gd3+ and Yb3+-doped BG forms in terms of the relative signal change. Large Stoke's shift (Ksv) values, high luminescence abilities, and linear spectral response make them promising candidates as oxygen sensing agents. It was concluded that prepared bioactive glass powders are suitable to use as additive materials for improving the oxygen sensitivity of meso-tetraphenyl porphyrin dye.

Structural and functional alterations of polydopamine-coated hemoglobin: New insights for the development of successful oxygen carriers

One of the major factors that is currently hindering the development of hemoglobin (Hb)-based oxygen carriers (HBOCs) is the autoxidation of Hb into nonfunctional methemoglobin. Modification with polydopamine (PDA), which is a biocompatible free radical scavenger has shown the ability to protect Hb against oxidation. Due to its tremendous potential in the development of successful HBOCs, herein, we conduct a thorough evaluation of the effect of PDA on the stability, aggregation, structure and function of the underlying Hb. By UV–vis spectrometry we show that PDA can prevent Hb's aggregation while thermal denaturation studies indicate that, although PDA coating resulted in a lower midpoint transition temperature, it was also able to protect the protein from full denaturation. These results are further corroborated by differential scanning calorimetry. Circular dichroism reveals that PDA can promote changes in Hb's secondary structure while, by UV–vis spectroscopy, we show that PDA also interacts with the porphyrin complex located in Hb's hydrophobic pocket. Last but not least, affinity studies show that PDA-coated Hb has a higher capability for oxygen release. Such an effect is further enhanced at lower pH. Importantly, through molecular docking simulations we provide a plausible explanation for the observed experimental results.

A π‐Conjugated Porphyrin Complex as Cathode Material Allows Fast and Stable Energy Storage in Calcium Batteries

AbstractRechargeable calcium batteries (RCB) are prospective candidates for sustainable energy storage, as they hold the promise of the high energy density of lithium‐ion batteries (LIBs) while simultaneously combining it with highly abundant raw materials. However, for long time, calcium batteries have faced severe issues with regard to cycling stability, until recently developments demonstrated improved battery cycle life when employing CaSn alloy anodes with fluorinated alkoxyborate electrolytes. These findings opened up the possibility to study cathode materials for RCBs not only in a more comparable manner, but also in a practical full cell design. As representative of emerging organic electrode materials (OEMs), we investigated tetrakis(4‐pyridyl) porphyrin as both free ligand (H2TPyP) and in the form of its copper MOF complex (CuTPyP−MOF) as active cathode species in RCBs. The cells demonstrated high capacities and excellent cycling stability at the same time. Even at elevated current densities of e. g., 2000 mA/g the full cells delivered stable capacities of ~90 mAh/g proving its excellent rate capability. This study explores the electrochemical performance of porphyrin active materials in calcium batteries and represents a significant step forward in the progress toward organic electrodes for multivalent energy storage systems.

Synergistic effect of two metal porphyrins in a polymer catalyst for oxygen electroreduction

This work considers the formation and catalytic properties of films of individual hydroxyphenyl porphyrin complexes with manganese (manganese(III) acetate 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (MnAc(4-OHPh)P)) and iron (iron(III) chloride 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (FeCl(4-OHPh)P)) and their composites. The films of individual metalloporphyrins and bimetallic composites were obtained by superoxide-assisted electrochemical deposition in dimethylsulfoxide solutions. The formation of the bimetallic (Mn + Fe) porphyrin composite was confirmed by spectral methods. An analysis of the atomic-force microscopy results showed that the composite films consisted of larger globules and were rougher than those of individual porphyrins. The electroactive surface areas of the individual porphyrin films and the composite were significantly different from each other. The mechanism and kinetics of the oxygen electroreduction reaction (ORR) on the films of individual porphyrins and bimetallic composite were evaluated using a rotating disk electrode. The kinetic current density of the Tafel slope and the position of the ORR current wave on the surface of the poly-(MnAc(4-OHPh)P + FeCl(4-OHPh)P) composite indicate smaller kinetic limitations and lower overvoltage on this material than on carbositall and films of individual porphyrins. The smaller kinetic limitations and better energy characteristics can be explained by the synergistic effect produced by the combined action of the Mn- and Fe- catalytically active centers during ORR on the composite film.

Synthesis, crystal structure and spectroscopic characterization of the Co(II) bis(pyridine) “picket fence” porphyrin complex. Potential application as antibacterial agent

In this work, we describe the synthesis, spectroscopic and structural properties of the new compound bis(pyridine)(α, β, α, β-tetrakis (o-pivalamidophenyl) porphyrinato) cobalt (II) [CoII(TpivPP)(py)2] (I). The molecular structure determined by X-rays of the compound shows that this species is a six-coordinate cobalt (II) metalloporphyrin. The UV–visible spectrum of (I) shows that the value of the Soret band (415 nm) is shifted towards the green with respect to the free base H2TpivPP while the λmax values of the Q band are 530 and 563 nm. The proton NMR spectrum of (I) clearly indicated that these derivatives are cobalt(II) paramagnetic porphyrin complexes. Zones of inhibition are studied against the bacterial strains Escherichia coli, Streptococcus pneumoniae and the fungal strains Aspergillus niger, Aspergillus fumigatus. The reported results show that cobalt porphyrin has better antibacterial and antifungal efficacy against gram-positive and gram-negative strains of bacteria as well as fungal strains.

Iron(III) porphyrin complexes as metalloradical catalysts.

Iron(III) porphyrin complexes as metalloradical catalysts.

Selective Electrocatalytic Reduction of Nitrous Oxide to Dinitrogen with an Iron Porphyrin Complex

Selective Electrocatalytic Reduction of Nitrous Oxide to Dinitrogen with an Iron Porphyrin Complex

Supramolecular Self-Assembly of the Zwitterionic Sn(IV)-Porphyrin Complex

[Sn(OSO3)2(TPyHP)](HSO4)2∙8H2O (1), an ionic Sn(IV)-porphyrin complex, was prepared by reacting [Sn(OH2)2TPyP] with dilute sulfuric acid. X-ray structural analysis revealed that the zwitterionic [Sn(OSO3)2TPyHP]2+ species consists of two anionic axial Sn–O–SO3 units and four peripheral pyridinium moieties, with an overall dicationic charge balanced by two hydrogen sulfate (HSO4−) counter-anions. Ionic hydrogen bonding between the oxygen atoms of axial sulfato ligands and the peripheral pyridinium groups of adjacent Sn(IV)-porphyrin cations led to the formation of a 1D channel filled with counter-anions and water molecules. The supramolecular self-assembly of 1 was further characterized using various spectroscopic techniques, including 1H NMR spectroscopy, elemental analysis, ESI-mass spectrometry, UV-vis spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy, thermogravimetric analysis (TGA), and powder X-ray diffractometry. The zwitterionic [Sn(OSO3)2TPyHP]2+ complex is a structurally well-defined complementary scaffold involved in supramolecular self-assembly. This novel class of ion-assembled metalloporphyrin is a potential functional porphyrin material used in ion exchange applications.

Iron(III)-based metalloradical catalysis for asymmetric cyclopropanation via a stepwise radical mechanism.

Metalloradical catalysis (MRC) exploits the metal-centred radicals present in open-shell metal complexes as one-electron catalysts for the generation of metal-stabilized organic radicals-key intermediates that control subsequent one-electron homolytic reactions. Cobalt(II) complexes of porphyrins, as stable 15e-metalloradicals with a well-defined low-spin d7 configuration, have dominated the ongoing development of MRC. Here, to broaden MRC beyond the use of Co(II)-based metalloradical catalysts, we describe systematic studies that establish the operation of Fe(III)-based MRC and demonstrate an initial application for asymmetric radical transformations. Specifically, we report that five-coordinate iron(III) complexes of porphyrins with an axial ligand, which represent another family of stable 15e-metalloradicals with a d5 configuration, are potent metalloradical catalysts for olefin cyclopropanation with different classes of diazo compounds via a stepwise radical mechanism. This work lays a foundation and mechanistic blueprint for future exploration of Fe(III)-based MRC towards the discovery of diverse stereoselective radical reactions.

Porphyrin complexes of transition metals with a large dipole moment as active components of new film electret materials

Porphyrin complexes of transition metals with a large dipole moment as active components of new film electret materials

Porphyrins: ‘‘Smart Catalysts’’ for the Synthesis of High-Added Value Compounds

The chemical industry needs to develop clean, efficient and selective procedures to synthesize high added-value fine chemicals and catalytic processes provide powerful tools to reach this goal. The key point to perform sustainable transformations is the choice of catalytic systems that show selectivity, activity and stability, resulting in high TOF (turnover frequency) and TON (turnover number), not to mention an efficient catalyst must be easily recovered and recycled. Based on these concepts, the employment of metal porphyrin complexes in catalysis is constantly growing due to the enormous potential of this class of molecules. Metal porphyrins are robust and their chemo-physical properties can easily be fine-tuned by varying their molecular structure to allow the use of these catalysts to selectively promote a large number of organic transformations.We have studied in depth the employment of metal porphyrin complexes to create new C-N and C-C bonds by using organic azides[1] and diazo compounds[2] and more recently we have focused our interest also on the synthesis of high-added value fine chemicals by using waste, such as CO2, as starting material by applying 100% atom economic procedures.[3] We will present different synthetic protocols which will also be discussed from a mechanistic point of view based on spectroscopic and theoretical studies and the identification of active intermediates. It is important to point out that mechanistic speculations are fundamental to optimize the catalytic performance of porphyrin complexes and spread out their applications in other fields of homogeneous catalysis References [1] Damiano, C.; Sonzini, P.; Caselli, A.; Gallo, E. Adv. Organom. Chem. 2021, 76, 145 [2] Damiano, C.; Sonzini, P.; Gallo, E. Chem. Soc. Rev. 2020 , 49, 4867[3] a) Sonzini, P.; Damiano, C.; Intrieri, D.; Manca, G.; Gallo, E. Adv. Synth. Catal. 2020, 362, 2961. b) Damiano, C.; Sonzini, P.; Manca, G.; Gallo, E. Eur. J. Org. Chem. 2021, 2807. c) M. Cavalleri, C. Damiano, G. Manca, E. Gallo, Chem. Eur. J. 2022, e202202729. d) P. Sonzini, N. Berthet, C. Damiano, V. Dufaud, E. Gallo J. Catalysis 2022, 414, 143–154

Electrochemical Investigations of Ru(L)(NO)(OPh) and Related Derivatives (L = Porphyrin or Bis(salicyl)Diiminate Ligand)

A set of porphyrin and non-porphyrin complexes Ru(por)(NO)(OAr) and Ru(sal)(NO)(OAr’) complex have been prepared and studied by electrochemical and spectroelectrochemical methods (por = octaethylporphyrin, Ar = Ph, C6H4-2-NHC(=O)CF3; C6H3-2,6-(NHC(=O)CF3)2, sal = racemic (R,R/S,S)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediamine, N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminobenzene; Ar’ = OPh, p-C6H4CF3). The consequence of 1-electron oxidation is loss of the aryloxide ligand, however the mechanism of that loss depends on the specific aryloxide ligand present in the complex. This conclusion is supported by cyclic voltammetry, DigiElch simulations, chemical oxidation studies, EPR spectroelectrochemistry and in-situ fiber-optic infrared spectroelectrochemistry measurements.

Preparation, Characterizations and Theoretical Calculations of a Mg(II) Porphyrin Complex with Axial O-bonded 4-Pyrrolidinopyridine

We hereby report the synthesis of a new hexacoordinated magnesium(II) metalloporphyrin with the formula [Mg(TBrPP)(4-pypo-κO)2] (1) where TBrPP is the meso-tetra(para-bromophenyl)porphyrinate and (4-pypo-κO) is the O-bonded 4-pyrrolidinopyridine axial ligand. This Mg(II) coordination is considered the linking isomer of the already known N-bonded 4-pyrrolidinopyridine (4-pypo-κN) with the formula [Mg(TTP)(4-pypo-κN)2] where TTP is the meso-tetra(p-tolyl)porphyrinate. Complex 1 was characterized by elemental analysis, IR, 1H NMR, UV/Vis and fluorescence spectrometric techniques, cyclic voltammetry measurements as well as single-crystal X-ray diffraction analysis. The Wingx supported program PLATON and the Hirshfeld surface analysis were both used to elucidate the intermolecular interactions in the crystal lattice of complex 1.Computational studies at DFI/B3LYP-D3/6-31G(d,p)-LanL2DZ level of DFT were used to elucidate the minimum energy geometry, the HOMO and LUMO molecular orbitals characteristics and the reactivity of complex 1. The molecular electrostatic potential (MEP) calculations on complex 1 have been made to determine the electrophilic-nucleophilic character of our new Mg(II) metalloporphyrin. Furthermore, the quantum theory atom in molecule (QTAIM) calculations were performed to get more insights into the type of interactions between the [Mg(TBrPP)] moiety and the two 4-pyrrolidinopyridine axial ligands of complex 1.

Optical Dual Gas Sensor for Simultaneous Detection of Nitric Oxide and Oxygen

This work presents a new optical dual sensor based on PtTFPP-containing electrospun fibers and CsPbBr3 perovskite quantum dots (PQDs) for simultaneous detection of oxygen (O2) and nitric oxide (NO) gases, wherein PtTFPP-containing electrospun fibers for O2 sensing was based on electrospinning process fabricated by platinum(II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) complex immobilized in cellulose acetate (CA) matrix. CsPbBr3 PQDs were used as NO-sensitive material and coated on the surface of PtTFPP-containing electrospun fibers. Both materials were excited by a UV LED with a central wavelength of 380 nm, and the fluorescence intensities of sensing materials were recorded and analyzed with a spectrometer. The experiment results show that the optical NO and O2 sensors have linear Stern–Volmer plots, and the sensitivities are around 2.7 and 10.7, respectively. The response and recovery times of the optical NO sensor are 71 and 109 s, respectively. For optical O2, response and recovery times are 60 and 65 s, respectively. The optical dual sensor with a new method based on fluorescent dye containing electrospun fibers and coated with CsPbBr3 PQDs has been successfully developed to detect NO and O2 gases simultaneously. The optical dual gas sensor provides great potential for practical applications with low cost and ease of fabrication.

Magnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N-Confused Core.

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and -s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.

An Insight on the Potential of Manganese Porphyrins in Cancer Treatment

Abstract: Porphyrin ligands are recognized for their exclusive tendency to form metal porphyrin complexes of pronounced value. Such metal porphyrin complexes display their inimitable roles as catalysts in various fields viz. conversion reactions, oxidation reactions, organic synthesis, pharmaceutical areas, biological and environmental fields, and many more. Out of different metal porphyrins; manganese porphyrins are one of the appreciated metal porphyrins due to their prodigious catalytic performance and potential in cancer treatment. In this perspective, the proficient participation of manganese porphyrins in the treatment of cancer along with operative discussions on molecular pathways have been briefly but effectively assessed based on the recent scientific literatures available.

Distortion effect on the ligation of imidazoles to water-insoluble iron(III) porphyrin

Axial ligands control the various chemical reactions triggered by heme proteins. Thus, studies on the reaction of iron porphyrin with ligands are important for understanding their functions. Here, a spectroscopic investigation was performed to clarify the distortion effect of the porphyrin ring on the ligation of imidazoles (imidazole (Im), 1-methyl- and 2-methylimidazole (1-MeIm and 2-MeIm)) to iron(III) porphyrin. The overall stability constant ([Formula: see text] was found to have increased, while [Formula: see text] decreased with increasing distortion of the porphyrin core. However, the [Formula: see text] of the tetraphenyl-substituted complex, which is considered the least distorted, was not minimal, while the [Formula: see text] was not maximal. These results suggest that the stability of bis-ligand iron(III) porphyrin complexes depends on the increase in the saddle-type distortion of the porphyrin, the type of distortion, and the steric hindrance at the surrounding substituents. Furthermore, the ligation of 1-MeIm to iron(III) porphyrin hydroxo complexes with the porphyrin ring distortion was investigated. The ligation of 1-MeIm to the iron(III) dodecaphenylporphyrin hydroxo complex (DPPFeOH) suggests that a reaction mechanism different from the general reaction mechanism may occur simultaneously, i.e., a simultaneous reaction. In addition, the [Formula: see text] of DPPFeOH was found to be approximately 15 times smaller than that of the chloride complex. The relationship between the distortion and stability of bis-ligands iron(III) porphyrin complexes obtained in this study is expected to assist in the elucidation of the model reaction of heme proteins.

Porphyrin and phthalocyanine heavy metal removal: overview of theoretical investigation for heterojunction organic solar cell applications.

Heavy metals are highly noxious, and their presence can cause diverse effects on living organisms and the environment. Crown ether porphyrins and phthalocyanines are known to effectively extract these pollutants and are also used in photovoltaic devices. This study aims to evaluate various factors that govern intramolecular charge transfer (ICT) and photo-injection processes, including maximum absorption wavelength (λmax), density of states (DOS), charge transfer dipole (μCT), light harvesting efficiency (LHE), open-circuit voltage (Voc), and free energy change of electron injection (ΔGinj) in order to investigate the performance of different compounds designed from metalloporphyrins for bulk-heterojunction organic solar cell (BHJ-OSC) applications. The porphyrin complex showed the best optoelectronic properties, with remarkable LHE values and CT amounts compared to phthalocyanine derivatives. The central metal played a significant role in optimizing the optical properties of the materials for use in solar cells. HgPr4O and CdPr4O were found to have optimal Voc values, resulting in effective injection, high electron, and hole mobilities, making them ideal materials for highly efficient BHJ-OSC devices. Density functional theory (DFT) approach was employed with the B3LYP functional and the def2TZVP basis set as implemented in the Gaussian 16 revision C.01 program to investigate the designed complexes and to compute geometrical parameters, frontier molecular orbitals (FMOs), and natural bond orbital (NBO). Furthermore, the time-dependent density functional theory (TD-DFT) method was used to analyze the optical properties and photovoltaic characteristics of selected metalloporphyrins by examining the UV-Vis spectra. In summary, the study presents a thorough description of the structural and electronic properties of the investigated complexes and provides insights into their potential use in photovoltaic applications.

Catalytic Degradation of Triphenylmethane Dyes with an Iron Porphyrin Complex as a Cytochrome P450 Model.

The organic dyes used in printing and dyeing wastewater have complex components, diverse structures and strong chemical stability, which make them not suitable for treatment and difficult to degrade in the environment. Porphyrins are macromolecules with 18 π electrons formed by four pyrrole molecules connected with a methylene bridge that has a stable structure. Porphyrin combines with iron to form an active intermediate with a structure similar to the cytochrome P450 enzyme, so they are widely used in the biomimetic field. In the current study, 5,10,15,20-tetra (4-carboxyphenyl) porphine ferric chloride (III) (Fe(III)TCPP) was used as a catalyst and iodosobenzene was used as an oxidant to explore the catalytic degradation of triphenylmethane dyes, such as rhodamine B (RhB) and malachite green (MG). The results of UV-Vis spectral analysis have shown that the conversion rate of the rhodamine B was over 90% when the amount of Fe(III)TCPP was 0.027 mM and the amount of iodosobenzene was eight equivalents. When the catalyst was 0.00681 mM and the amount of the oxidant was five equivalents, the conversion rate of the malachite green reached over 95%. This work provides a feasible method for the degradation of triphenylmethane dyes.