Iron Porphyrin Research Articles

Dynamic Correlation on the Adaptive Sampling Configuration Interaction (ASCI) Reference Function: ASCI-DSRG-MRPT2.

A balanced description of static and dynamic electron correlations is at the heart of quantum chemical methods. To obtain accurate results in strongly correlated systems using wave-function-based methods, a large active space is necessary to ensure correct descriptions of static correlations. Correcting the results for dynamic correlations is also necessary. In this work, we present implementations of second-order perturbation theory for dynamic correlations based on the adaptive sampling configuration interaction self-consistent field (ASCI-SCF) method. In particular, we implemented spin-free driven similarity renormalization group second-order multireference perturbation theory (DSRG-MRPT2). The extrapolation of the ASCI + PT2 energy based on the relaxed Hamiltonian in DSRG-MRPT2 gives a reasonable approximation of DSRG-MRPT2 based on CASSCF. We demonstrate the application of the ASCI-DSRG-MRPT2 method in evaluations of the spin-state energy gaps in iron porphyrins, polyacenes, and periacenes along with the reaction energies of methane oxidation by FeO+ and electrocyclic ring formation in cethrene.

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.

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.

MOF-On-MOF Dual Enzyme-Mimic Nanozyme with Enhanced Cascade Catalysis for Colorimetric/Chemiluminescent Dual-Mode Aptasensing.

A novel metal-organic framework (MOF)-on-MOF dual enzyme-mimic nanozyme was designed as enhanced cascade signal amplification for the colorimetric and chemiluminescent (CL) dual-mode aptasensing. The MOF-on-MOF hybrid is composed of MOF-818 with catechol oxidase-like activity and iron porphyrin MOF [PMOF(Fe)] with peroxidase-like activity, called MOF-818@PMOF(Fe). MOF-818 can catalyze the 3,5-di-tert-butylcatechol substrate and produce H2O2 in situ. Subsequently, PMOF(Fe) catalyzes H2O2 to produce reactive oxygen species, which oxidize 3,3',5,5'-tetramethylbenzidine or luminol to produce color or luminescence. Thanks to the nano-proximity effect and the confinement effect, the efficiency of the biomimetic cascade catalysis is greatly improved, which in turn generates enhanced colorimetric and CL signals. Taking the detection of chlopyrifos as an example, the prepared dual enzyme-mimic MOF nanozyme is combined with the aptamer with specific recognition ability to develop a colorimetric/CL dual-mode aptasensor for highly sensitive and selective detection of chlorpyrifos. The proposed MOF-on-MOF dual nanozyme-enhanced cascade system may provide a new pathway for the further development of a biomimetic cascade sensing platform.

The construction of Fe-porphyrin nanozymes with peroxidase-like activity for colorimetric detection of glucose

As a type of nanomaterials with enzyme-mimetic catalytic properties, nanozymes have attracted wide concern in biological detection. H2O2 was the characteristic product of diverse biological reactions, and the quantitative analysis for H2O2 was an important way to detect disease biomarkers, such as acetylcholine, cholesterol, uric acid and glucose. Therefore, there is of great significance for developing a simple and sensitive nanozyme to detect H2O2 and disease biomarkers by combining with corresponding enzyme. In this work, Fe-TCPP MOFs were successfully prepared by the coordination between iron ions and porphyrin ligands (TCPP). In addition, the peroxidase (POD) activity of Fe-TCPP was proved, in detail, Fe-TCPP could catalyze H2O2 to produce ·OH. Herein, glucose oxidase (GOx) was chosen as the model to build cascade reaction by combining Fe-TCPP to detect glucose. The results indicated glucose could be detected by this cascade system selectively and sensitively, and the limit of detection of glucose was achieved to 0.12 μM. Furthermore, a portable hydrogel (Fe-TCPP@GEL) was further established, which encapsulated Fe-TCPP MOFs, GOx and TMB in one system. This functional hydrogel could be applied for colorimetric detection of glucose by coupling with a smartphone easily.

An Efficient Intercalation Supramolecular Structure for Photocatalytic CO2 Reduction to Ethylene Under Visible Light

AbstractPhotocatalytic CO2 reduction (CO2PR) into multi‐carbon products (especially C2H4) is a highly attractive route for global carbon cycle, however, which is seriously limited by sluggish C‐C coupling kinetics and competitive hydrogen evolution reaction (HER) and so on. Herein, the fabrication of a novel supramolecular assembly of NiAl‐Fe‐TCPP is reported by intercalating iron porphyrin (Fe‐TCPP) into NiAl‐layered double hydroxide (NiAl‐LDH), and the resultant NiAl‐Fe‐TCPP exhibit superior catalytic performance on CO2PR to C2H4 under visible light irradiation in presence of photosensitizer. A high C2H4 selectivity up to 93.4% in the carbon‐containing products with the production rate as high as 24.7 µmol h−1 can be achieved over NiAl‐Fe‐TCPP. The ex/in situ X–ray absorption spectoscopy (XAS) indicates that the electron transfer between NiAl‐LDH and Fe‐TCPP can promote the generation of low‐valence of Fe sites, resulting in the efficient production of C2H4. The spin‐polarized density functional theory (DFT) calculations find that the synergistic mechanism that CO2 molecules are activated to CO on NiAl‐LDH and then spilled to Fe‐TCPP and coupled to COCHO#, which is further reduced to C2H4, are feasible in the perspective of Gibbs free energy. Moreover, the strong host‐guest interactions between NiAl‐LDH and Fe‐TCPP lead to the promoted photocatalytic activity and superior cycle stability.

Potential Induced Protonation of the Second Coordination Sphere in a Hangman-type Iron Porphyrin Complex Promotes HER: Insights via in Situ Raman Spectroelectrochemistry.

The iron-based porphyrin complex containing a bispyridine-based hanging unit termed Py2XPFe was previously used as an effective catalyst for the reduction of protons to molecular hydrogen in solution. Here, the molecular compound was immobilized on a modified gold electrode surface and investigated by spectroelectrochemical methods under catalytic conditions. Immobilization of the Py2XPFe was facilitated using a pyridine-based amine linker molecule grafted to the gold electrode by electrochemical amine oxidation. The linker molecule denoted in this report as Pyr-1 allows for effective coordination of the iron porphyrin compound to the modified gold surface through axial coordination of the pyridine component to the Fe center. Resonance Raman spectroelectrochemistry was performed on the immobilized catalyst in pH 7 buffer at increasing cathodic potentials. This facilitates the electrochemical hydrogen evolution reaction (HER) while concurrently allowing for the observation of the v4, v3, and v2 porphyrin marker bands, which are sensitive to oxidation and spin state changes at the metal center. The observed changes in these bands at decreasing potential indicate that the immobilized Py2XPFe exists in the formal high-spin FeIII state before being reduced to the low-spin FeII state resulting from axial interaction with the linker moiety. This FeII state likely acts as the precatalyst for the HER reaction. Surfaced enhanced Raman spectroelectrochemistry was also conducted on the system as the gold electrode provides a sufficient surface enhancement effect so as to observe the bonding nature of the pyridine substituents within the second coordination sphere. As the potential is lowered cathodically, the pyridine ring breathing modes at 999 cm-1 are shown to increase in intensity due to protonation, which reach an intensity saturated limit whereat HER is conducted. This suggests that in pH 7 buffer, the increase in cathodic potentials facilitates protonation of the pyridine-based second coordination sphere. The extent to which protonation occurs can be viewed as a function of decreasing potential due to an increase in proton flux at the immobilized catalyst which, at the required onset potential for catalysis, aids in the reduction of protons to molecular hydrogen.

Two-dimensional iron porphyrin nanozyme mimics cytochrome P450 activity for cancer proliferation inhibition

Two-dimensional materials have excellent performance in energy catalysis and biomedicine due to their unique advantages in surface and interfacial properties. Taking into account the unique advantages of the surface interface and catalysis of two-dimensional materials, it is a very feasible way to construct two-dimensional materials with clear atomic structure to break the redox balance in tumor cells, so as to achieve efficient anti-tumor effects. Based on this, we selected the porphyrin ligands that widely exist in nature, equipped with iron metal active centers, and constructed a two-dimensional iron porphyrin nanozyme with a clear atomic structure, which simulated the redox activity of cytochrome P450 enzymes. The experimental results show that by carrying a rotatable pyridine group on the porphyrin ring, the iron porphyrin monomers can be effectively connected and expanded into a two-dimensional iron porphyrin microstructure. Enough iron centers are exposed on the surface of two-dimensional iron porphyrins as catalytic sites. In the presence of oxidants, two-dimensional iron porphyrins can efficiently catalyze the oxidation of small organic molecules, and have good P450-like enzymatic activity. At the same time, the two-dimensional iron porphyrin nanomaterial was used for anti-tumor, and it was found that it has an efficient ability to inhibit tumor proliferation, which may be due to the catalytic oxidation of various organic small molecules in tumor cells by the high concentration of hydrogen peroxide in tumor cells. At the same time, we found that the two-dimensional iron porphyrin nanozyme may have a good drug loading capacity due to the many exposed iron sites on its surface, which provides a possible option for drug loading to achieve combined high-efficiency tumor therapy.

DIFFERENCES IN HEMOGLOBIN LEVELS BEFORE AND AFTER HEAVY PHYSICAL ACTIVITY

Introduction: Hemoglobin is an erythrocyte tetrameric protein that binds to a non-protein molecule, the Iron porphyrin compound called heme. The most important function of hemoglobin is transporting oxygen (O2) from the lungs to the peripheral tissues and transporting carbon dioxide (CO2) from the tissues to the lungs for exhalation to the outside. Factors that affect hemoglobin levels one of physical activity. Strenuous physical activity that releases a lot of sweat such as aerobics, cycling (19 – 22 km/h), swimming, tennis and running. The study aimed to determine the difference in hemoglobin levels before and after heavy physical activity in the form of running for 5 minutes with a heart rate frequency > 145 times/minute. Method: data analysis using Paired Sample T-Test SPSS. This research was conducted at the Muhammadiyah Institute of Health Sciences and Technology Palembang in March 2021 with a total of 32 respondent. Results: the average hemoglobin levels before physical activity is 15,1 g/dL while hemoglobin levels after heavy physical activity is 15,3 g/dL, based on the Test Paired Sample t-Test get p > 0.05 that is no difference between the two. Discussion: there was no difference between hemoglobin levels before and after heavy physical activity.

Probing the spin states of tetra‐coordinated iron(II) porphyrins by their vibrational and pre K‐edge x‐ray absorption spectra

AbstractTetra‐coordinated iron(II) porphyrins are observed in triplet (intermediate spin, IS) ground state with low‐lying quintet (high spin, HS) and singlet (low spin, LS) excited states. It is well known in the literature that the bond distances are dependent on the spin state such that the distances are larger for HS compared to the LS/IS states. This implies the existence of strong magneto‐structural correlations. Herein, the possibility to obtain the spin‐state information for a series of tetra‐coordinated square planar iron(II) porphyrin complexes have been explored by exploiting the magneto‐structural correlations obtained from first principle calculations. The spin‐state dependent nature of the chemical bonds and spin polarization on the N‐atoms play a crucial role in the vibrational dynamics of the central Fe‐atom. Theoretical nuclear resonance vibrational spectroscopy (NRVS) is adopted to investigate the vibrational dynamics and the Fe‐atom associated spectral peaks and their spin‐dependent features. We find that NRVS studies along with iron pre‐K‐edge x‐ray absorption analysis convincingly provide the information on the spin state, which could be utilized to identify the spin states without adopting any magnetic probes.

Diversifying the functions of heme proteins with non-porphyrin cofactors

Heme proteins perform diverse biochemical functions using a single iron porphyrin cofactor. This versatility makes them attractive platforms for the development of new functional proteins. While directed evolution and metal substitution have expanded the properties, reactivity, and applications of heme proteins, the incorporation of porphyrin analogs remains an underexplored approach. This review discusses the replacement of heme with non-porphyrin cofactors, such as porphycene, corrole, tetradehydrocorrin, phthalocyanine, and salophen, and the attendant properties of these conjugates. While structurally similar, each ligand exhibits distinct optical and redox properties, as well as unique chemical reactivity. These hybrids serve as model systems to elucidate the effects of the protein environment on the electronic structure, redox potentials, optical properties, or other features of the porphyrin analog. Protein encapsulation can confer distinct chemical reactivity or selectivity of artificial metalloenzymes that cannot be achieved with the small molecule catalyst alone. Additionally, these conjugates can interfere with heme acquisition and uptake in pathogenic bacteria, providing an inroad to innovative antibiotic strategies. Together, these examples illustrate the diverse functionality that can be achieved by cofactor substitution. The further expansion of this approach will access unexplored chemical space, enabling the development of superior catalysts and the creation of heme proteins with emergent properties.

Hydrogen-Bonding Secondary Coordination Sphere Effect on CO2 Reduction

Great efforts of the scientific community are focused on the development of catalysts for the reduction of carbon dioxide (CO2) to useful molecules such as carbon monoxide, formic acid, methanol, ethanol, methane, ethylene, or acetate. Various metal porphyrin complexes were synthesized and studied to develop highly active and selective catalysts. While the substituents on the porphyrin core (the primary coordination sphere) determine the reactivity of the metal, the introduction of the secondary coordination is important for the binding and activation of CO2. In this review, selected examples of iron porphyrin catalysts with a secondary coordination sphere capable of stabilizing intermediates of the CO2 reduction process by hydrogen bonding are presented.

Investigation of Iron(III) Tetraphenylporphyrin as a Redox Flow Battery Anolyte: Unexpected Side Reactivity with the Electrolyte.

Redox flow batteries (RFBs) present an opportunity to bridge the gap between the intermittent availability of green energy sources and the need for on-demand grid level energy storage. While aqueous vanadium-based redox flow batteries have been commercialized, they are limited by the constraints of using water as an electrochemical solvent. Nonaqueous redox flow battery systems can be used to produce high voltage batteries due to the larger electrochemical window in nonaqueous solvents and the ability to tune the redox properties of active materials through functionalization. Iron porphyrins, a class of organometallic macrocycles, have been the subject of many studies for their photocatalytic and electrocatalytic properties in nonaqueous solvents. Often, iron porphyrins can undergo multiple redox events making them interesting candidates for use as anolytes in asymmetrical redox flow batteries or as both catholyte and anolyte in symmetrical redox flow battery systems. Here the electrochemical properties of Fe(III)TPP species relevant to redox flow battery electrolytes are investigated including solubility, electrochemical properties, and charge/discharge cycling. Commonly used support electrolyte salts can have reactivities that are often overlooked beyond their conductivity properties in nonaqueous solvents. Parasitic reactions with the cations of common support electrolytes are highlighted herein, which underscore the careful balance required to fully assess the potential of novel RFB electrolytes.

Green Aromatic Epoxidation with an Iron Porphyrin Catalyst for One-Pot Functionalization of Renewable Xylene, Quinoline, and Acridine.

Sustainable functionalization of renewable aromatics is a key step to supply our present needs for specialty chemicals and pursuing the transition to a circular, fossil-free economy. In the present work, three typically stable aromatic compounds, representative of products abundantly obtainable from biomass or recycling processes, were functionalized in one-pot oxidation reactions at room temperature, using H2O2 as a green oxidant and ethanol as a green solvent in the presence of a highly electron withdrawing iron porphyrin catalyst. The results show unusual initial epoxidation of the aromatic ring by the green catalytic system. The epoxides were isolated or evolved through rearrangement, ring opening by nucleophiles, and oxidation. Acridine was oxidized to mono- and di-oxides in the peripheral ring: 1:2-epoxy-1,2-dihydroacridine and anti-1:2,3:4-diepoxy-1,2,3,4-tetrahydroacridine, with TON of 285. o-Xylene was oxidized to 4-hydroxy-3,4-dimethylcyclohexa-2,5-dienone, an attractive building block for synthesis, and 3,4-dimethylphenol as an intermediate, with TON of 237. Quinoline was directly functionalized to 4-quinolone or 3-substituted-4-quinolones (3-ethoxy-4-quinolone or 3-hydroxy-4-quinolone) and corresponding hydroxy-tautomers, with TON of 61.

Peroxymonosulfate activated by natural porphyrin derivatives for rapid degradation of organic pollutants via singlet oxygen and high-valent iron-oxo species

The activation of peroxymonosulfate (PMS) by sodium ferric chlorophyllin (SFC), a natural porphyrin derivative extracted from chlorophyll-rich substances, was systematically investigated for facile degradation of bisphenol A (BPA). SFC/PMS is capable of degrading 97.5% of BPA in the first 10 min with the initial BPA concentration of 20 mg/L and pH = 3, whereas conventional Fe2+/PMS could only remove 22.6% of BPA under identical conditions. It demonstrates a prominent flexibility to a broad pH range of 3–11 with complete pollutant degradation. A remarkable tolerance toward concomitant high concentration of inorganic anions (100 mM) was also observed, among which (bi)carbonates can even accelerate the degradation. The nonradical oxidation species, including high-valent iron-oxo porphyrin species and 1O2, are identified as dominant species. Particularly, the generation and participation of 1O2 in the reaction is evidenced by experimental and theoretical methods, which is vastly different from the previous study. The specific activation mechanism is unveiled by density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The results shed light on effective PMS activation by iron (III) porphyrin and the proposed natural porphyrin derivative would be a promising candidate for efficient abatement of recalcitrant pollutants toward complicated aqueous media in wastewater treatment.

Bimetallic Cooperativity and Hydrogen Bonding Allow Efficient Reduction of CO2

AbstractReducing CO2 selectively to one of the several C1 products is challenging, as the thermodynamic reduction potentials for the different n e−/n H+ reductions of CO2 are similar and so is the reduction potential for H+ reduction. Recently, Halime, Aukauloo, and co‐workers have taken inspiration from the active site of nickel CO dehydrogenase (Ni‐CODH) to design bimetallic iron porphyrins bridged by a urea moiety. These complexes show fast and selective reduction of CO2 to CO and the results suggest a Ni‐CODH type mechanism at play where one of the two metals binds and reduces the CO2 while the other stabilizes the reduced species by forming a bridged complex, facilitating the C−O bond cleavage.

Bimetallic Cooperativity and Hydrogen Bonding Allow Efficient Reduction of CO2.

Reducing CO2 selectively to one of the several C1 products is challenging, as the thermodynamic reduction potentials for the different n e- /n H+ reductions of CO2 are similar and so is the reduction potential for H+ reduction. Recently, Halime, Aukauloo, and co-workers have taken inspiration from the active site of nickel CO dehydrogenase (Ni-CODH) to design bimetallic iron porphyrins bridged by a urea moiety. These complexes show fast and selective reduction of CO2 to CO and the results suggest a Ni-CODH type mechanism at play where one of the two metals binds and reduces the CO2 while the other stabilizes the reduced species by forming a bridged complex, facilitating the C-O bond cleavage.

Spectroscopic fingerprints of iron-coordinated cobalt and iron porphyrin layers on graphene

Spectroscopic fingerprints of iron-coordinated cobalt and iron porphyrin layers on graphene

Comparison of the Performance of Density Functional Methods for the Description of Spin States and Binding Energies of Porphyrins.

This work analyzes the performance of 250 electronic structure theory methods (including 240 density functional approximations) for the description of spin states and the binding properties of iron, manganese, and cobalt porphyrins. The assessment employs the Por21 database of high-level computational data (CASPT2 reference energies taken from the literature). Results show that current approximations fail to achieve the "chemical accuracy" target of 1.0 kcal/mol by a long margin. The best-performing methods achieve a mean unsigned error (MUE) <15.0 kcal/mol, but the errors are at least twice as large for most methods. Semilocal functionals and global hybrid functionals with a low percentage of exact exchange are found to be the least problematic for spin states and binding energies, in agreement with the general knowledge in transition metal computational chemistry. Approximations with high percentages of exact exchange (including range-separated and double-hybrid functionals) can lead to catastrophic failures. More modern approximations usually perform better than older functionals. An accurate statistical analysis of the results also casts doubts on some of the reference energies calculated using multireference methods. Suggestions and general guidelines for users are provided in the conclusions. These results hopefully stimulate advances for both the wave function and the density functional side of electronic structure calculations.

Fabrication of FeTCPP@CNNS for Efficient Photocatalytic Performance of p-Nitrophenol under Visible Light

A photocatalyst of iron–porphyrin tetra-carboxylate (FeTCPP)-sensitized g-C3N4 nanosheet composites (FeTCPP@CNNS) based on g-C3N4 nanosheet (CNNS) and FeTCPP have been fabricated by in situ hydrothermal self-assembly. FeTCPP is uniformly introduced to the surface of CNNS. Only a small amount of FeTCPP is introduced, and the stacked lamellar structure is displayed in the composite. As compared with pure CNNS, the FeTCPP@CNNS composites exhibit significantly improved photocatalytic performance by the photodegradation of p-nitrophenol (4-NP). At the optimum content of FeTCPP to CNNS (3 wt%), the photodegradation activity of the FeTCPP@CNNS photocatalyst can reach 92.4% within 1 h. The degradation rate constant for the 3% FeTCPP@CNNS composite is 0.037 min−1 (4-NP), which is five times that of CNNS (0.0064 min−1). The results of recycling experiments show that 3% FeTCPP@CNNS photocatalyst has excellent photocatalytic stability. A possible photocatalytic reaction mechanism of FeTCPP@CNNS composite for photocatalytic degradation of 4-NP has been proposed. It is shown that superoxide radical anions played the major part in the degradation of 4-NP. The appropriate content of FeTCPP can enhance the charge transfer efficiency. The FeTCPP@CNNS composites can provide more active sites and accelerate the transport and separation efficiency of photogenerated carriers, thus further enhancing the photocatalytic performance.