Iron Porphyrin Research Articles

Phenoxazine‐Sensitized CO2‐to‐CO Reduction with an Iron Porphyrin Catalyst: A Redox Properties‐Catalytic Performance Study

AbstractWe have evaluated six phenoxazine derivatives as visible light photosensitizers for the photochemical reduction of CO2 to CO with an iron porphyrin catalyst in organic media. The phenoxazine core was functionalized with electron‐donating or ‐withdrawing groups to modify the photophysical properties. Both singlet and triplet excited state potentials of the sensitizers spanned several hundred mV range and the ground state oxidation potentials spanned 250 mV. We observed that no correlation can be established between the production of CO and the excited state potential of the phenoxazine, which determines the driving force for electron transfer to the catalyst. On the contrary, a clear correlation can be made between the oxidation potentials of the phenoxazine and the production of CO. This observation indicates that the process was limited by photosensitizer regeneration and highlights the fact that electron transfers not directly related to the catalyst activation could play a key role in homogeneous photocatalytic systems.

Stability of Fe(III) and Sn(IV) Metalloporphyrins Adsorbed on Cation-Exchanged Montmorillonite

The iron(III)tetraphenylporphyrin chloride Fe(III)TPPCl, iron(III)tetra-naphthylporphyrin Fe(III)TNPCl, μ-oxo-bis[tetraphenylporphyriniron(III)] [(Fe(III)TPP)2O], μ-oxo-bis[tetranaphthylporphyriniron(III)] [(Fe(III)TNP)2O], tin(IV)tetraphenylporphyrin chloride Sn(IV)TPPCl2 and tin(IV)tetra-naphthylporphyrin Sn(IV)TNPCl2 complexes were all found to be adsorbed onto the montmorillonite MMT clay without demetallation. The evidence from the visible absorption and diffuse reflectance spectra all showed that the species present on the montmorillonite are the metallated form. Also the evidence from Mossbauer spectroscopy confirm these findings. The only process that occurs is that the dimeric form of the iron complexes underwent transformation to the monomeric form. The clay-complex systems were characterized using visible absorption spectra, diffuse reflectance spectra, X-ray diffraction, Mossbauer spectra and Electron microscopy.
 HIGHLIGHTS
 
 Fe(III)TPPCl, Fe(III)TNPCl, Sn(IV)TPPCl2, and Sn(IV)TNPCl2 porphyrin complexes adsorbed onto the montmorillonite clay without demetallation
 The dimeric forms of iron porphyrin complexes [(Fe(III)TPP)2O] and [(Fe(III)TNP)2O are converted to the monomeric form when adsorbed on montmorillonite clay
 The weak acidity of montmorillonite clay does not have the ability to cause demetallation of the metallo complexes of porphyrin

Cover Picture: Dissection of Light‐Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction (Angew. Chem. Int. Ed. 14/2022)

Unravelling the mechanism of charge accumulation and utilization in the light-driven carbon dioxide reduction using iron porphyrins bearing hydrogen bonding scaffolds revealed unprecedented puzzle pieces about its rate limiting step. While the formal Fe(0) redox state has been widely accepted as the catalytically active species, Zakaria Halime, Ally Aukauloo et al. show in their Communication (e202117530) that the Fe(I) species is already involved in the substrate activation of the photocatalytic cycle.

Titelbild: Dissection of Light‐Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction (Angew. Chem. 14/2022)

Die Entschlüsselung des Mechanismus der Ladungsakkumulation bei der lichtgetriebenen Kohlendioxidreduktion unter Verwendung von wasserstoffverbrückten Eisenporphyrinen liefert neue Einblicke in den geschwindigkeitsbegrenzenden Schritt. Während der formale Fe(0)-Redoxzustand weithin als die katalytisch aktive Spezies galt, zeigen Zakaria Halime, Ally Aukauloo et al. in ihrer Zuschrift (DOI: 10.1002/ange.202117530), dass die Fe(I)-Spezies bereits an der Substrataktivierung des photokatalytischen Zyklus beteiligt ist.

Interactions of N-hydroxyamphetamine with an iron porphyrin: A unique intramolecular H-bond probed by DFT calculations

Hydroxylamine (NH2OH) and its N-substituted derivatives (RNHOH) are important biological intermediates in the global N cycle. Heme plays a central role in the binding and activation of these hydroxylamines. We report the crystal structures of N-hydroxyamphetamine (AmphNHOH) in complex with Fe and Co heme models. We demonstrate a previously unrecognized internal H-bond interaction between a hydroxylamine RNHO–H group and a porphyrin N-atom. We utilize density functional theoretical (DFT) calculations to show that the conformations with the internal H-bond represent global minima along the potential energy surfaces for both the Fe and Co heme models. A natural bond orbital (NBO) analysis reveals a donor π (porN=C) to acceptor σ* (O-H) interaction of 3.04 kcal/mol for Fe, accounting for 11% of the total heme–AmphNHOH interaction energy. Our DFT calculations with the parent Fe–NH2OH suggests that the presence of internal H-bonds between hydroxylamine (R/H)NHOH moieties and heme N-atoms may be more common than previously recognized.

Analisis Aktivitas Fisik Ringan dan Berat Terhadap Kadar Hemoglobin

Physical activity is all body movements caused by skeletal muscles with the need for energy expenditure. Physical activity is divided into 3 categories. Light, moderate and heavy physical activity. Heavy physical activity will increase metabolic activity, the acid produced in the form of hydrogen ions and lactic acid will increase a lot, this will cause a decrease in pH and intravascular hemolysis. The affinity between oxygen and hemoglobin will decrease when the blood pH is low. Hemoglobin is a tetrameric protein of erythrocytes that binds to non-protein molecules, namely iron porphyrin compounds called heme. This study aims to determine the effect of light and heavy physical activity on hemoglobin levels in students of the Faculty of Science and Technology IKest Muhammadiyah Palembang. This type of research is carried out in the form of experiments which are analyzed descriptively quantitatively and presented in the form of simple tables and diagrams. The sample was examined using a Hematology Analyzer with the Alfa Swelab Plus brand, the Pothomertic method. The results showed that the average hemoglobin level for light physical activity was 15.01g/dL and heavy physical activity was 15.2 g/dL with the One Way Anova test, the value = 0.689. The conclusion of the study showed that there was no effect between light and heavy physical activity on hemoglobin levels in students of the Faculty of Science and Technology IKest Muhammadiyah Palembang.

Lignin peroxidase-catalyzed direct oxidation of trace organic pollutants through a long-range electron transfer mechanism: Using propranolol as an example

In this work, lignin peroxidase (LiP) was extracted for the in vitro degradation of a persistent compound (propranolol, PPN). The results showed that 94.2% of PPN was degraded at 30 U L−1 LiP activity and 10 mg L−1 PPN. The PPN degradation rate increased from 33.5% to 94.2% when the veratryl alcohol (VA) concentration varied from 0 to 180 µM, but decreased to 73.1% with further VA addition. This phenomenon confirmed that VA was indispensable, however, it also acted as a competitive inhibitor of PPN oxidation. Computational analysis revealed that the Trp171…iron porphyrin (TRP-FeP) path was responsible for specific substrate (e.g., VA) transformation, and another long-range electron transfer (LRET) path through His–Asp…FeP (HSP-FeP) was discovered for non-specific substrate (e.g., PPN) degradation. These two electron-transfer routes shared one catalytic center, and VA protected the enzyme from H2O2-dependent inactivation. The HSP-FeP path transformed PPN through single electron transfer or H abstraction mechanisms. In addition, hydroxyl radicals generated in the LiP/H2O2 system were involved in the hydroxylation of the PPN intermediates. Possible degradation pathways were deduced using these degradation mechanisms and mass-spectrometry analysis. The multipath degradation mechanism endowed LiP with a remarkable capacity for removing various recalcitrant pollutants in environmental remediation.

Dissection of Light-Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction.

Iron porphyrins are among the best molecular catalysts for the electrocatalytic CO2 reduction reaction. Powering these catalysts with the help of photosensitizers comes along with a couple of unsolved challenges that need to be addressed with much vigor. We have designed an iron porphyrin catalyst decorated with urea functions (UrFe) acting as a multipoint hydrogen bonding scaffold towards the CO2 substrate. We found a spectacular photocatalytic activity reaching unreported TONs and TOFs as high as 7270 and 3720 h-1 , respectively. While the Fe0 redox state has been widely accepted as the catalytically active species, we show here that the FeI species is already involved in the CO2 activation, which represents the rate-determining step in the photocatalytic cycle. The urea functions help to dock the CO2 upon photocatalysis. DFT calculations bring support to our experimental findings that constitute a new paradigm in the catalytic reduction of CO2 .

Dissection of Light‐Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction

AbstractIron porphyrins are among the best molecular catalysts for the electrocatalytic CO2 reduction reaction. Powering these catalysts with the help of photosensitizers comes along with a couple of unsolved challenges that need to be addressed with much vigor. We have designed an iron porphyrin catalyst decorated with urea functions (UrFe) acting as a multipoint hydrogen bonding scaffold towards the CO2 substrate. We found a spectacular photocatalytic activity reaching unreported TONs and TOFs as high as 7270 and 3720 h−1, respectively. While the Fe0 redox state has been widely accepted as the catalytically active species, we show here that the FeI species is already involved in the CO2 activation, which represents the rate‐determining step in the photocatalytic cycle. The urea functions help to dock the CO2 upon photocatalysis. DFT calculations bring support to our experimental findings that constitute a new paradigm in the catalytic reduction of CO2.

An iron-porphyrin grafted metal–organic framework as a heterogeneous catalyst for the photochemical reduction of CO2

Photocatalytic reduction of carbon dioxide (CO2) into value-added carbon products is a promising strategy for dealing with carbon emission. Selected metal–organic frameworks (MOFs) have been shown promise in photocatalytic CO2 reduction owing to their photochemical activity and structural modularity. Here, we take advantage of displaceable nonstructural ligands on the nodes of a pyrene-based MOF, NU-1000, to graft a molecular catalyst, tetra(4-carboxyphenyl) porphyrin iron (III) chloride (Fe-TCPP). The pyrene linkers in the MOF absorb photons and transfer electrons to the porphyrin catalyst, resulting in a self-contained photocatalyst. The obtained Fe-TCPP@NU-1000 heterogeneous catalysts exhibit activity for CO2 photoreduction under illumination at 390 nm, with a TON for CO of 22 in 2 h. Molecular hydrogen is co-evolved. Leaching of the grafted catalyst from the MOF ultimately limits performance.

Acid-Degradable Hydrogen-Generating Metal-Organic Framework for Overcoming Cancer Resistance/Metastasis and Off-Target Side Effects.

The development of stimuli‐responsively degradable porous carriers for both controlled drug release and high biosafety is vitally important to their clinical translation, but still challenging at present. A new type of porphyrin–iron metal organic framework (Fe‐MOF) nanocrystals is engineered here as acid‐degradable drug carrier and hydrogen donor by the coordination between porphyrin and zero‐valence Fe atom. Fe‐MOF nanocrystals exhibit excellent acid‐responsive degradation for H2 generation and simultaneous release of the loaded drug for combined hydrogen‐chemotherapy of cancer multidrug resistance (MDR) and metastasis and for local hydrogen eradication of the off‐target induced toxic side effects of the drug to normal cells/tissues. Mechanistically, released H2 assists chemotherapeutic drug to efficiently inhibit cancer metastasis by immunoactivating intratumoral M1‐phenotype macrophages and consequently downregulating the expression of metastasis‐related matrix metalloproteinase‐2 (MMP‐2) and can also downregulate the expressions of both P‐glycoprotein (P‐gp) protein and adenosine triphosphate (ATP) in MDR cancer cells to sensitize chemotherapeutic drug for enhanced damage to mitochondria and DNA. High anti‐MDR/antimetastasis efficacies and high biocompatibility endow Fe‐MOF nanocrystals and the Fe‐MOF‐based nanomedicine with high potential for clinical translation.

Synthesis and Electrocatalytic CO2 Reduction Activity of an Iron Porphyrin Complex Bearing a Hydroquinone Moiety

Abstract An iron porphyrin complex bearing a hydroquinone moiety at the meso position was newly designed and synthesized. Electrochemical analysis revealed that it catalyzes CO2 reduction at a lower overpotential compared with an iron complex without a hydroquinone moiety. Experimental and theoretical investigation suggested that a hydroquinone moiety at the meso position stabilizes the coordination bond between the metal center and CO2 via a hydrogen bond interaction with the latter in the secondary coordination sphere.

Selectivity in Electrochemical CO2 Reduction.

The electrocatalytic CO2 reduction reaction (CO2RR) to generate fixed forms of carbons that have commercial value is a lucrative avenue to ameliorate the growing concerns about the detrimental effect of CO2 emissions as well as to generate carbon-based feed chemicals, which are generally obtained from the petrochemical industry. The area of electrochemical CO2RR has seen substantial activity in the past decade, and several good catalysts have been reported. While the focus was initially on the rate and overpotential of electrocatalysis, it is gradually shifting toward the more chemically challenging issue of selectivity. CO2 can be partially reduced to produce several C1 products like CO, HCOOH, CH3OH, etc. before its complete 8e-/8H+ reduction to CH4. In addition to that, the low-valent electron-rich metal centers deployed to activate CO2, a Lewis acid, are prone to reduce protons, which are a substrate for CO2RR, leading to competing hydrogen evolution reaction (HER). Similarly, the low-valent metal is prone to oxidation by atmospheric O2 (i.e., it can catalyze the oxygen reduction reaction, ORR), necessitating strictly anaerobic conditions for CO2RR. Not only is the requirement of O2-free reaction conditions impractical, but it also leads to the release of partially reduced O2 species such as O2-, H2O2, etc., which are reactive and result in oxidative degradation of the catalyst.In this Account, mechanistic investigations of CO2RR by detecting and, often, chemically trapping and characterizing reaction intermediates are used to understand the factors that determine the selectivity in CO2RR. The spectroscopic data obtained from different intermediates have been identified in different CO2RR catalysts to develop an electronic structure selectivity relationship that is deemed to be important for deciding the selectivity of 2e-/2H+ CO2RR. The roles played by the spin state, hydrogen bonding, and heterogenization in determining the rate and selectivity of CO2RR (producing only CO, only HCOOH, or only CH4) are discussed using examples of both iron porphyrin and non-heme bioinspired artificial mimics. In addition, strategies are demonstrated where the competition between CO2RR and HER as well as CO2RR and ORR could be skewed overwhelmingly in favor of CO2RR in both cases.

H2S/Thiols, NO•, and NO-/HNO: Interactions with Iron Porphyrins.

In the past decade, gasotransmitters NO• and H2S have been thoroughly studied in biological contexts, as their biosynthesis and physiological effects became known. Moreover, an additional intricate crosstalk reaction scheme between these compounds and related species is thought to exist as part of the cascade signaling processes in physiological conditions. In this context, heme enzymes, as modeled by iron porphyrins, play a central role in catalyzing the key interconversions involved. In this work, iron porphyrin interactions with sulfide and nitric-oxide-related species are described. The stability and reactivity of mixed ternary systems are also described, and future perspectives are discussed.

Effect of Support on Oxygen Reduction Reaction Activity of Supported Iron Porphyrins

Effect of Support on Oxygen Reduction Reaction Activity of Supported Iron Porphyrins

Sandwiching Phosphorene with Iron Porphyrin Monolayer for High Stability and Its Biomimetic Sensor to Sensitively Detect Living Cell Released NO.

Instability of 2D phosphorene material is the major obstacle for its broad applications. Herein phosphorene is sandwiched with self‐assembled iron porphyrin monolayers on both sides (I‐Phene) to significantly enhance stability. Iron porphyrin has strong interaction with phosphorene through formation of P—Fe bonds. The sandwich structure offers excellent stability of phosphorene by both‐sided monolayer protections for an intact phosphorene structure more than 40 days under ambient conditions. Meanwhile, the electron transfer between iron porphyrin and phosphorene result in a high oxidation state of Fe, making I‐Phene biomimetic sensitivity toward oxidation of nitric oxide (NO) for 2.5 and 4.0 times higher than phosphorene and iron‐porphyrin alone, respectively. Moreover, I‐Phene exhibits excellent selectivity, a wide detection range, and a low detection limit at a low oxidation potential of 0.82 V, which is comparable with the reported noble metal based biomimetic sensors while ranking the best among all non‐noble biomimetic ones. I‐Phene is further used for real‐time monitoring NO released from cells. This work provides effective approach against phosphorene degrading for outstanding stability, which has universal significance for its various important applications, and holds a great promise for a highly sensitive biomimetic sensor in live‐cell assays.

O2 reduction by iron porphyrins with electron withdrawing groups: to scale or not to scale.

Iron porphyrins are synthesized by systematically introducing electron withdrawing groups (EWGs) on pyrroles to evaluate the relationship between rate (k) and overpotential (η). The results indicate that while EWGs lead to a rise in the thermodynamic FeIII/II reduction potential (E0), the potential of the O2 reduction reaction (ORR) does not scale with E0. More importantly, the iron porphyrins with higher E0 show an order of magnitude higher rate of ORR than unsubstituted iron tetraphenyl porphyrin. This contests the scaling relationship often offered to predict rates of ORR by iron porphyrins based on their E0. Mechanistic investigations reveal that the rate-determining step (rds) of ORR change between these iron porphyrins with EWG's, as the pKa and E0 of several key intermediate species likely change on altering the macrocycle. These results suggest that linear dependence of log(rate) on E0 or η may only be valid for complexes where the rds of ORR remains the same.

Iron and zinc porphyrin linked MoO(dithiolene) complexes in relevance to electron transfer between Mo-cofactor and cytochrome b5 in sulfite oxidase.

Oxo-molybdenum (dithiolene) complexes covalently linked individually to iron and zinc porphyrin have been synthesized to show an electron transfer between the two metal centres in relevance to electron transfer from Mo-cofactor to cytochrome b5 domains in the oxidative half of the catalytic cycle of native sulfite oxidase. This association has been investigated by electrochemical, EPR measurement and X-ray absorbance spectroscopy techniques.

Synergism between iron porphyrin and dicationic ionic liquids: tandem CO2 electroreduction-carbonylation reactions.

Here, we report a simple procedure that drastically reduces the electrochemical E(FeI/Fe0) and E0cat of the commercially available iron(III) tetraphenylporphyrin chloride (FeIIITPP·Cl) catalyst via a synergetic effect with the imidazolium dications of the ionic liquid electrolyte. This procedure enhanced the performance of catalytic systems in the electrochemical production of CO and enabled us to perform different tandem CO2 reduction-carbonylation reactions under mild conditions.

Tandem electrocatalytic CO2 reduction with Fe-porphyrins and Cu nanocubes enhances ethylene production.

Copper-based tandem schemes have emerged as promising strategies to promote the formation of multi-carbon products in the electrocatalytic CO2 reduction reaction. In such approaches, the CO-generating component of the tandem catalyst increases the local concentration of CO and thereby enhances the intrinsic carbon-carbon (C-C) coupling on copper. However, the optimal characteristics of the CO-generating catalyst for maximizing the C2 production are currently unknown. In this work, we developed tunable tandem catalysts comprising iron porphyrin (Fe-Por), as the CO-generating component, and Cu nanocubes (Cucub) to understand how the turnover frequency for CO (TOFCO) of the molecular catalysts impacts the C-C coupling on the Cu surface. First, we tuned the TOFCO of the Fe-Por by varying the number of orbitals involved in the π-system. Then, we coupled these molecular catalysts with the Cucub and assessed the current densities and faradaic efficiencies. We discovered that all of the designed Fe-Por boost ethylene production. The most efficient Cucub/Fe-Por tandem catalyst was the one including the Fe-Por with the highest TOFCO and exhibited a nearly 22-fold increase in the ethylene selectivity and 100 mV positive shift of the onset potential with respect to the pristine Cucub. These results reveal that coupling the TOFCO tunability of molecular catalysts with copper nanocatalysts opens up new possibilities towards the development of Cu-based catalysts with enhanced selectivity for multi-carbon product generation at low overpotential.