Porphyrin Complexes Research Articles

Preparation and quality control of a new porphyrin complex labeled with 45Ti for PET imaging

This study aims to produce and quality control of a new porphyrin complex labeled with 45Ti for PET imaging, so at the first step, the cross-section of 45Sc(p,n)45Ti was investigated by TALYS-1.6 and the optimal target thickness and theoretical yield were calculated by SRIM code. The purified 45Ti was labeled with the anticancer agent of tetrakis (pentafluorophenyl) porphyrin (TFPP). The radiochemical purity and the percentage of labeling were evaluated by radiation layer chromatography then the division coefficient of [45Ti]-TFPP was calculated. The dual coincidence imaging system was used for imaging 1 and 2 h after injection [45Ti]-TFPP to rats. Immediately after imaging, the mean percent injected dose per gram and specific activity of different tissues including blood, heart, lungs, stomach, liver, bone, kidney, spleen, intestine, muscle, feces, and skin were measured. The yield of 45Ti production was measured 468 MBq/μAh and the labeling rate was observed more than 98%. The highest activity was observed in the liver (%ID/g = 2.27%, 1 h) and spleen (2.2%, 1 h), respectively, because of the high lipophilic of 45Ti-TFPP. SPECT images showed a significant uptake of radiopharmaceuticals in the abdomen. The labeling rate of 45Ti-TFPP was high and this compound has the potential for clinical application in different ways than PSMA, it can be joined with photodynamic therapy (Severin et al., 2015).

Substituent Effects in Iron Porphyrin Catalysts for the Hydrogen Evolution Reaction.

For a future hydrogen economy, non-precious metal catalysts for the water splitting reactions are needed that can be implemented on a global scale. Metal-nitrogen-carbon (MNC) catalysts with active sites constituting a metal center with fourfold coordination of nitrogen (MN4 ) show promising performance, but an optimization rooted in structure-property relationships has been hampered by their low structural definition. Porphyrin model complexes are studied to transfer insights from well-defined molecules to MNC systems. This work combines experiment and theory to evaluate the influence of porphyrin substituents on the electronic and electrocatalytic properties of MN4 centers with respect to the hydrogen evolution reaction (HER) in aqueous electrolyte. We found that the choice of substituent affects their utilization on the carbon support and their electrocatalytic performance. We propose an HER mechanism for supported iron porphyrin complexes involving a [FeII (P⋅)]- radical anion intermediate, in which a porphinic nitrogen atom acts as an internal base. While this work focuses on the HER, the limited influence of a simultaneous interaction with the support and an aqueous electrolyte will likely be transferrable to other catalytic applications.

Efficient degradation of 4-nitrophenol using VO(TPP) impregnated TiO2 photocatalyst: Insight into kinetics and mechanism

Heterogeneous composites of metalloporphyrins with TiO2 possess exceptional photosensitizing properties, which works efficiently in degradation of organic pollutants. Herein, vanadium porphyrin complex {VO(TPP)} was loaded on TiO2 photocatalyst {VO(TPP)–TiO2} by the wet impregnation method. The as-prepared catalysts were characterized to analyze physicochemical properties and the photocatalytic degradation of 4-nitrophenol (4-NP) was investigated to assess their catalytic efficiency. XRD results revealed that VO(TPP)–TiO2 is dual-phase anatase/rutile with high crystallinity. The UV-DRS study showed that the loading of {VO(TPP)} on TiO2 caused a red-shift in the absorption spectrum and decreased the band-gap as well. The surface area has increased significantly after impregnation as confirmed by BET isotherm. The degradation of 4-NP follows pseudo-first-order kinetics, and the VO(TPP)–TiO2 showed higher degradation (99%) of 4-NP as compared to pure TiO2 (87%). The degradation mechanism of 4-NP and its pathway was also discussed using UV–Vis spectroscopy and electrospray mass spectrometry analysis.Graphical abstract

Luminescent iridium(III) porphyrin complexes as near-infrared-emissive biological probes.

We report herein the design, synthesis and characterisation of a series of luminescent iridium(III) porphyrin complexes [Ir(ttp)(CH2CH2OH)] (H2ttp = 5,10,15,20-tetra-4-tolylporphyrin) (1), [Ir(tpp-Ph-NO2)(CO)Cl] (H2tpp-Ph-NO2 = 5-(4-((4-nitrophenoxy)carbonyloxymethyl)phenyl)-10,15,20-triphenylporphyrin) (2), [Ir(tpp-COOMe)(Py)2](Cl) (H2tpp-COOMe = 5-(4-methoxycarbonylphenyl)-10,15,20-triphenylporphyrin; Py = pyridine) (3) and [Ir(tpp-COOH)(Py)2](Cl) (H2tpp-COOH = 5-(4-carboxylphenyl)-10,15,20-triphenylporphyrin) (4). All the complexes displayed long-lived near-infrared (NIR) emission attributed to an excited state of mixed triplet intraligand (3IL) (π → π*) (porphyrin) and triplet metal-to-ligand charge transfer (3MLCT) (dπ(Ir) → π*(porphyrin)) character. The cytotoxicity of the complexes toward HeLa cells was examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cationic complexes 3 and 4 exhibited higher cytotoxic activity toward HeLa cells than their neutral counterparts 1 and 2. Cellular uptake studies by inductively coupled plasma-mass spectrometry (ICP-MS) and laser-scanning confocal microscopy (LSCM) indicated that complexes 3 and 4 showed higher cellular uptake efficiencies than complexes 1 and 2 due to their cationic charge, and they were enriched in the perinuclear region of the cells with negligible nuclear uptake. Additionally, the carboxyl complex 4 was used to label a model protein bovine serum albumin (BSA) via an amidation reaction. The resultant luminescent protein conjugate 4-BSA displayed similar photophysical properties and intracellular localisation behaviour to its parent complex. The results of this work will contribute to the development of luminescent iridium(III) porphyrin complexes and related bioconjugates as NIR-emissive probes for bioimaging applications.

SYMMETRICAL SYNTHESIS AND CHARACTERIZATION OF FIVE-COORDINATE In(III) PORPHYRINS WITH SALICYLIC ACID DERIVATIVES

Investigations of the In(III)porphyrin complexes with substituted salicylates(X) as axial ligands have been carried out using electronic and biological studies. Electronic spectra of the complexes are accompanied by shifting of wavelength towards hypsochromic/blue-shift or bathochromic/red-shift along with 'ƒ' values decided by the nature of the functional groups attached to the salicylate ligand. IR frequencies appear at 550cm-1–400cm−1 for In–N(Por) and at 650cm−1–700cm−1 for In–OSA. 1HNMR spectra reveal the merging of the salicylate ring with that of the protons of the macrocyclic ring. The 13CNMR studies confirm the resonance of the meso-carbon tetraphenyl porphyrin ring between 130ppm to 160ppm and the salicylate ring carbons in the region of 110ppm to 165ppm. Thermal analysis confirms the presence of indium nitride (In-N) in an argon atmosphere from 0oC to 900oC. Cyclic voltammetry(CV) revealed the reduced or oxidized properties of these complexes lead to the generation of π-anion or cation radicals by two one-electron transfer reactions. In(III)porphyrin complexes with substituted salicylates were also screened for in-vitro antifungal activity(%inhibition) against the microbe "Acremonium fusidoides spp." using the PDA method, which shows that the percentage inhibition is inverse to the diameter of the colony. The freeradical scavenging or antiradical activity (%RSA) by the DPPH method reveals that these complexes were absorbance and concentration-dependent.

Catalytic reduction of dinitrogen to ammonia using molybdenum porphyrin complexes.

Porphyrin complexes are well-known in O2 and CO2 reduction, but their application to N2 reduction is less developed. Here, we show that oxo and nitrido complexes of molybdenum supported by tetramesitylporphyrin (TMP) are effective precatalysts for catalytic N2 reduction to ammonia, verified by 15N2 labeling studies and other control experiments. Spectroscopic and electrochemical studies illuminate some relevant thermodynamic parameters, including the N-H bond dissociation free energy of (TMP)MoNH (43 ± 2 kcal mol-1). We place these results in the context of other work on homogeneous N2 reduction catalysis.

Homo- and hetero-halogen interaction based molecular associations in wheel–axle topology derived Sn(iv) porphyrin complexes: an experimental and theoretical analysis

In-depth structural and packing features of homo- and hetero-halogen interactions in hexa-coordinated metalloporphyrins with the aid of X-ray crystallography, DFT and NCI-RDG analyses are described.

Significance of the connecting position between Zn(ii) porphyrin and Re(i) bipyridine tricarbonyl complex units in dyads for room-temperature phosphorescence and photocatalytic CO2 reduction: unexpected enhancement by triethanolamine in catalytic activity.

We synthesized three new dyads composed of a Zn porphyrin and fac-Re(bpy)(CO)3Br (bpy = 2,2'-bipyridine) units, ZnP-nBpy[double bond, length as m-dash]ReBr (n = 4, 5, and 6), in which the porphyrin is directly connected at the meso-position through the 4-, 5-, or 6-position of the bpy. We investigated the relationships between the connecting positions and the photophysical properties as well as catalytic activity in the CO2 reduction reaction. The dyad connected through the 6-position, ZnP-6Bpy[double bond, length as m-dash]ReBr, showed obvious phosphorescence with a lifetime of 280 μs at room temperature, in N,N-dimethylacetamide (DMA), whereas the other two dyads showed almost no phosphorescence under the same conditions. The photocatalytic CO2 reduction reactions in DMA using 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the electron donor and the three dyads ZnP-nBpy[double bond, length as m-dash]ReBr selectively produced CO with similar initial rates, but the durabilities were low. The addition of triethanolamine (TEOA) suppressed the decomposition of dyads, improving their durabilities and reaction efficiencies. In particular, ZnP-5Bpy[double bond, length as m-dash]ReBr was remarkably improved-it gave the highest durability and reaction efficiency among the three dyads; the reaction quantum yield reached 24%. The reason for this significant activity is no accumulation of electrons on the Zn porphyrin in ZnP-5Bpy[double bond, length as m-dash]ReBr, which would be caused by dual interactions of TEOA with the Re and Zn ions in the dyad. As the highest catalytic activity was observed in ZnP-5Bpy[double bond, length as m-dash]ReBr among the three dyads, which had no room-temperature phosphorescence (RTP), the catalytic activities and RTP properties are considered independent, but they are greatly influenced by the connecting positions on the bpy ligand in ZnP-nBpy[double bond, length as m-dash]ReBr.

Recent advances in the rational designing of metalloporphyrinoid-based CO2 reduction catalysts: From molecular structural tuning to the application in catalysis

Electro and photochemical [Formula: see text] reduction ([Formula: see text]R) has emerged as a contemporary research field for tackling the fossil fuel problems and construction of a modern chemical industry. For efficient [Formula: see text]R, a catalyst is needed, and Earth-abundant Fe, Co, and Ni-based metalloporphyrinoids have appeared as promising molecular catalysts for [Formula: see text]R. Several metal complexes of porphyrins, phthalocyanines, corroles, and chlorins-type porphyrinoids have been designed and tested for this purpose. The unique advantages in the judicious tuning of the porphyrinoid structures and their susceptibility towards different functionalization reactions allow an impressive scope to explore and establish a direct structure-activity relationship of metalloporphyrinoids towards [Formula: see text]R. There have been rapid advances in this field in the last few years. For the homogeneous [Formula: see text]R, the electronic and steric aspects of the porphyrinoids are fine-controlled by installing favorable functional groups at the periphery of the porphyrinoids. On the other hand, in heterogenous [Formula: see text]R, the design principle is guided by integrating metalloporphyrinoids in composite material after mixing with carbon supports, semiconductors, or adopting reticular chemistry. All the advancements further result in the testing of excellent metalloporphyrinoids in industrially feasible [Formula: see text] electrolyzers or photoelectrochemical devices. This review focuses on the recent advances in designing principles of metalloporphyrnoids catalysts in homogeneous, heterogeneous, and [Formula: see text]R reactors.

Synthetic strategies towards functionalizedN-bridged μ-nitrido diiron porphyrin complexes

[Formula: see text]-bridged diiron porphyrinoid complexes are powerful oxidation biomimetic catalysts. Their use as oxidation catalysts is quite recent, as it started approximately one decade ago. Many mechanistic works and elucidation of properties are conducted on simple derivatives which are not functionalized, preventing their covalent incorporation into advanced materials, even though it would expand their scope of applications. With the ultimate purpose to produce [Formula: see text]-bridged diiron porphyrinoid complexes that can be incorporated into advanced functionalized materials and thereby increase the range of their utilization, we have explored synthetic strategies to prepare di- and octafunctionalised [Formula: see text]-bridged diiron porphyrin complexes, either with hydroxyl or propargyl functions, which have been selected for their versatility. The considerations taken into account for the synthetic strategies are detailed and the complexes are fully characterized.

Iron porphyrin-catalysed C(sp3)–H amination with alkyl azides for the synthesis of complex nitrogen-containing compounds

With the readily prepared iron porphyrin complex as a catalyst and starting with alkyl azides, a panel of nitrogen-containing skeletons representing the families of natural alkaloids and bioactive compounds could be prepared in good yields.

Structure of the green heme isolated from allylbenzene-modified chloroperoxidase: A novel heme architecture implicating the mechanisms of CPO inactivation and epoxidation

The chemical identification of the modified heme (the green heme) during chloroperoxidase catalyzed epoxidation of allylbenzene remains unestablished due to its high instability within the protein matrix, the absence of paramagnetically shifted signals, and the difficulty in obtaining crystals of the modified enzyme. We have established the unambiguous structure of the modified prosthetic heme group, which was extracted from the protein matrix using 2D NMR spectroscopy and LC-MS spectrometry. The modified heme was isolated as a µ-oxo dimer that can be quantitatively converted to the corresponding monomer. The depolymerized green heme displayed characteristic NMR signatures of iron porphyrin complexes, but no Nuclear Overhauser Effect was observable to assist in signal assignment. An alternative strategy was applied by removing the iron center of the green heme, resulting in a stable demetallated green porphyrin species. Complete assignment of all the NMR resonances in the demetallated green heme allowed us to establish the molecular architecture of the modified species as a novel N-alkylated heme. Decisive space correlations between the propyl protons of allylbenzene and the γ meso proton coupled with clear dipolar connectivities between the propyl-2H of the substrate and the β proton in the side chain of the propionic acid at carbon-6 of the porphyrin ring, clearly indicate that allylbenzene was covalently attached to the nitrogen atom of the pyrrole ring III of the prosthetic heme. In this study, the mechanism of green CPO formation and its relation to CPO catalyzed chiral transformations are also discussed. It is concluded that the double-phenyl clamp formed by two phenylalanine residues at the distal heme pocket plays a critical role in fine-tuning substrate orientation that determines the outcome of CPO catalyzed epoxidation of substituted styrenes.

Balancing the phosphorescence and fluorescence of a double-ring porphyrin using different lanthanides for ratiometric oxygen sensing

A new mixed-lanthanide porphyrin complex with balanced phosphorescence and fluorescence was engineered for O2 detection. Characterization revealed the photophysical mechanism of the unique dual luminescence properties.

C-N linked donor type porphyrin derivatives: unrevealed hole-transporting materials for efficient hybrid perovskite solar cells.

A new series of Zn(II) and Cu(II)-based porphyrin complexes 5a and 5b doubly functionalised with carbazole units were developed to be used as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). These complexes were obtained via a nucleophilic substitution reaction mediated by PhI(OAc)2/NaAuCl4·2H2O, or using C-N transition metal-assisted coupling. The hole extraction capability of 5a and 5b was assessed using cyclic voltammetry; this study confirmed the better alignment of the Zn(II) complex 5a with the perovskite valence band level, compared to the Cu(II) complex 5b. The optimised geometry and molecular orbitals of both complexes also corroborate the higher potential of 5a as a HTM. Photoluminescence characterisation showed that the presence of 5a and 5b as HTMs on the perovskite surface resulted in the quenching of the emission, matching the hole transfer phenomenon. The photovoltaic performance was evaluated and compared with those of reference cells made with the standard HTM spiro-OMeTAD. The optimised 5-based devices showed improvements in all photovoltaic characteristics; their open circuit voltage (Voc) reached close to 1 V and short-circuit current density (Jsc) values were 13.79 and 9.14 mA cm-2 for 5a and 5b, respectively, disclosing the effect of the metallic centre. A maximum power conversion efficiency (PCE) of 10.01% was attained for 5a, which is 65% of the PCE generated by using the spiro-OMeTAD reference. This study demonstrates that C-N linked donor-type porphyrin derivatives are promising novel HTMs for developing efficient and reproducible PSCs.

Introducing proton/electron mediators enhances the catalytic ability of an iron porphyrin complex for photochemical CO2 reduction.

A novel iron porphyrin complex with hydroquinone moieties as proton/electron mediators at meso positions was designed and synthesised. The complex serves as an efficient catalyst for photochemical CO2 reduction, and its turnover frequency (TOF = 1.3 × 104 h-1) was the highest among those of comparable systems with sufficient durability.

Spontaneous reduction of iron(III)porphyrin to iron(II)porphyrin-CO complex in mouse circulation.

Iron(II/III)porphyrin/cyclodextrin inclusion complexes serve as hemoprotein models in vivo. Here we showed the iron(III)porphyrin complex to be spontaneously reduced to its iron(II) state in mouse circulation. The reduced complex bound endogenous CO from carboxyhemoglobin, which was followed by urinary excretion. The natural reduction system was found to be effective for synthetic heme-model compounds.

Does one hydrogen atom matter? Crystal structures and spectroscopic studies of five-coordinate manganese porphyrin complexes

Metalloporphyrins and imidazole(ate) have long been employed to mimic metalloenzymes such as five-coordinate heme complexes. In this work, several five-coordinate manganese(II) porphyrin complexes utilizing sterically hindered 2-methylimidazole (2-MeHIm) or 2-methylimidazolate (2-MeIm‾) as axial ligand are isolated and characterized by single-crystal X-ray, UV–vis, DFT and electronic paramagnetic resonance (EPR) spectroscopies to explore their geometric and electronic structures. Both UV–vis and crystal structural investigations revealed noteworthy differences between the two species (e.g. the unusual Soret band split of 2-MeIm‾ derivatives) which are consistent with the stronger ligand nature of 2-methylimidazolate. Low temperature (4 K) EPR measurements have been carried out for all the products in both solid and solution states which gave characteristic signals of a high-spin (S = 5/2) d5 system with g⊥ ≈ 5.9 and g// ≈ 2.0. Notably, the positive correlation between λ (E/D) and the numbers of hyperfine splittings are confirmed by double measurements e.g. [Mn(TPP)(2-MeHIm)] exhibits two more hyperfine splittings than [Mn(TMP)(2-MeIm‾)]‾ with a larger λ (0.018 vs. 0.002).

Spectroscopic Investigations of Porphyrin-TiO2 Nanoparticles Complexes

This study presents the spectral characterization of TiO2 nanoparticles (NPs) functionalized with three porphyrin derivatives: 5,10,15,20-(Tetra-4-aminophenyl) porphyrin (TAPP), 5,10,15,20-(Tetra-4-methoxyphenyl) porphyrin (TMPP), and 5,10,15,20-(Tetra-4-carboxyphenyl) porphyrin (TCPP). UV-Vis absorption and Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) spectroscopic studies of these porphyrins and their complexes with TiO2 NPs were performed. In addition, the efficiency of singlet oxygen generation, the key species in photodynamic therapy, was investigated. UV-Vis absorption spectra of the NPs complexes showed the characteristic bands of porphyrins. These allowed us to determine the loaded porphyrins on TiO2 NPs functionalized with porphyrins. FTIR-ATR revealed the formation of porphyrin-TiO2 complexes, suggesting that porphyrin adsorption on TiO2 may involve the pyrroles in the porphyrin ring, or the radicals of the porphyrin derivative. The quantum yield for singlet oxygen generation by the studied porphyrin complexes with TiO2 was higher compared to bare porphyrins for TAPP and TMPP, while for the TCPP-TiO2 NPs complex, a decrease was observed, but still maintained a good efficiency. The TiO2 NPs conjugates can be promising candidates to be tested in photodynamic therapy in vitro assays.

Development of heavy metal passivators in residue fluid catalytic cracking process

The advancement of residual fluid catalytic cracking (RFCC) is significantly influenced by the development of heavy metals passivation technology. Resids often include larger concentrations of heavy metals (Ni, V, and Fe) than gas oils, primarily in the form of porphyrin complexes and salts of organic acids. Under cracking conditions, metals, especially Ni and V in residues and gas oil deposit on the cracking catalyst and induce adverse dehydrogenation reactions. The catalyst's zeolite component is destroyed by these metals. While reducing the yield of gasoline, active metals increase the yields of coke and hydrogen. Because most cracking FCC units can only tolerate limited amounts of coke and hydrogen, the level of heavy metals on the catalyst needs to be kept under control in order to achieve maximum productivity and profit. Metal passivation enhances catalytic activity and/or selectivity to more desired products by minimizing the detrimental effects of contaminating metals. In this study, we will review heavy metals deactivation mechanism in RFCC process and the potential technological solutions to the catalyst deactivation concern.

Structures and dissociation of iron porphyrin complexes by ion mobility and collision-induced dissociation mass spectrometry

A combination of ion mobility mass spectrometry (IMS-MS), collision-induced dissociation (CID), Rice–Ramsperger–Kassel–Marcus modeling, and computational chemistry was used to determine the structure and unimolecular chemistry of dimeric and trimeric sulfonated meso-tetraphenylporphyrins with negative charges from −2 to −5. By comparing experimental collision cross sections obtained from calibrated IMS drift times with calculated cross sections for the lowest energy calculated structures, it was confirmed that dimer species have a bridged structure where the two monomers are connected through iron–sulfonic interactions. Dimer species with the charge states −4 and −5 dissociate into two monomer units where the charge is distributed between the monomers. Dimers with lower charge states also lose neutral SO2 and SO3 groups. For trimeric species with charge states of −3 and −4, IMS identifies three and two isomers, respectively. It was confirmed that the −4 charged trimer isomers consist of one with three stacked monomers and one in which the third monomer unit is connected to a stacked dimer via two iron–sulfonic bonds (bridged/stacked). Both yielded the same CID breakdown diagram confirming that the two isomers likely interconvert prior to dissociation. The significantly larger density of states of the bridged–stacked structure compared with the stacked structure means the former is likely the reactive configuration.