Substituent Effects in the Photophysical and Electrochemical Properties of Meso-Tetraphenylporphyrin Derivatives.

Porphyrins were identified some years ago as a promising, easily accessible, and tunable class of organic photoredox catalysts, but a systematic study on the effect of the electronic nature and of the position of the substituents on both the ground-state and the excited-state redox potentials of these compounds is still lacking. We prepared a set of known functionalized porphyrin derivatives containing different substituents either in one of the meso positions or at a ß-pyrrole carbon, and we determined their ground- and (singlet) excited-state redox potentials. We found that while the estimated singlet excited-state energies are essentially unaffected by the introduction of substituents, the redox potentials (both in the ground- and in the singlet excited-state) depend on the electron-withdrawing or electron-donating nature of the substituents. Thus, the presence of groups with electron-withdrawing resonance effects results in an enhancement of the reduction facility of the photocatalyst, both in the ground and in the excited state. We next prepared a second set of four previously unknown meso-substituted porphyrins, having a benzoyl group at different positions. The reduction facility of the porphyrin increases with the proximity of the substituent to the porphine core, reaching a maximum when the benzoyl substituent is introduced at a meso position.

Oncogenic and telomeric G-quadruplexes: Targets for porphyrin-triphenylphosphonium conjugates.

DNA chains with sequential guanine (G) repeats can lead to the formation of G-quadruplexes (G4), which are found in functional DNA and RNA regions like telomeres and oncogene promoters. The development of molecules with adequate structural features to selectively stabilize G4 structures can counteract cell immortality, highly described for cancer cells, and also downregulate transcription events underlying cell apoptosis and/or senescence processes. We describe here, the efficiency of four highly charged porphyrins-phosphonium conjugates to act as G4 stabilizing agents. The spectrophotometric results allowed to select the conjugates P2-PPh3 and P3-PPh3 as the most promising ones to stabilize selectively G4 structures. Molecular dynamics simulation experiments were performed and support the preferential binding of P2-PPh3 namely to MYC and of P3-PPh3 to KRAS. The ability of both ligands to block the activity of Taq polymerase was confirmed and also their higher cytotoxicity against the two melanoma cell lines A375 and SK-MEL-28 than to immortalized skin keratinocytes. Both ligands present efficient cellular uptake, nuclear co-localization and high ability to generate 1O2 namely when interacting with G4 structure. The obtained data points the synthesized porphyrins as promising ligands to be used in a dual approach that can combine G4 stabilization and Photodynamic therapy (PDT).

Light exposure of tetra-cationic porphyrins containing peripheral Pd(II)-bipyridyl complexes and the induced effects on purified DNA molecule, fibroblast and melanoma cell lines.

Photodynamic therapy (PDT) combines a light source, oxygen, and a photosensitizer (PS) to generate reactive oxygen species (ROS) for treating diseases. In this study, we evaluated two meso-tetra-pyridyl porphyrins with [Pd(bpy)Cl]+, namely 3-PdTPyP and 4-PdTPyP, as PS for PDT application. DNA interaction was assessed by spectroscopic measurements (UV-Vis and fluorescence emission), viscosity analysis, and molecular docking simulations. The results indicate that Pd(II)-porphyrins do not intercalate into DNA, suggesting that the minor groove is the primary interaction site, mainly through van der Waals forces. These metalloporphyrins effectively induced nitrogenous bases oxidation, particularly in purines, after white light irradiation. The induced DNA lesions were able to inactivate plasmid DNA metabolism (DNA replication and transcription) in a bacterial model. 3-PdTPyP and 4-PdTPyP significantly decreased the viability of treated melanoma cell lines (A375 and B16-F10), demonstrating that melanoma cell lines were more sensitive to these Pd(II)-porphyrins than the fibroblast cell line (L929). Moreover, 3-PdTPyP was more photototoxic to A375 cells (IC50 = 0.43 µM), whereas 4-PdTPyP was more photototoxic to B16-F10 cells (IC50 = 0.51 µM). These findings suggest that these porphyrins are promising PS for future PDT research focused on skin cancer.

Porphyrin Production by Corynebacterium diphtheriae Strains from Clinical Isolates.

Porphyrins are intermediate metabolites in the biosynthesis of vital molecules, including heme, cobalamin, and chlorophyll. Bacterial porphyrins are known to be proinflammatory and have been associated with biofilm production. This study investigated porphyrin production by strains of Corynebacterium diphtheriae using emission spectroscopy, high-performance liquid chromatography with fluorescence detection, a diode array detector, and mass spectrometry. Emission spectroscopy revealed characteristic porphyrin emission spectra in all strains, with coproporphyrin III predominating. Qualitative analysis via different chromatography methods revealed identified coproporphyrin III, uroporphyrin I, and protoporphyrin IX in all the strains. Quantitative analysis revealed strain-dependent coproporphyrin III production. More studies are needed to investigate the relationship between porphyrin production and the virulence potential of Corynebacterium diphtheriae.

Tailored Metal-Porphyrin Based Molecular Electrocatalysts for Enhanced Artificial Nitrogen Fixation to Green Ammonia.

Electrochemical nitrogen reduction (E-NRR) is one of the most promising approaches to generate green NH3. However, scarce ammonia yields and Faradaic efficiencies (FE) still limit their use on a large scale. Thus, efforts are focusing on different E-NRR catalyst structures and formulations. Among present strategies, molecular electrocatalysts such as metal-porphyrins emerge as an encouraging option due to their planar structures which favor the interaction involving the metal center, responsible for adsorption and activation of nitrogen. Nevertheless, the high hydrophobicity of porphyrins limits the aqueous electrolyte-catalyst interaction lowering yields. This work introduces a new class of metal-porphyrin based catalysts, bearing hydrophilic tris(ethyleneglycol) monomethyl ether chains (metal = Cu(II) and CoII)). Experimental results show that the presence of hydrophilic chains significantly increases ammonia yields and FE, supporting the relevance of fruitful catalyst-electrolyte interactions. This study also investigates the use of hydrophobic branched alkyl chains for comparison, resulting in similar performances with respect to the unsubstituted metal-porphyrin, taken as a reference, further confirming that the appropriate design of electrocatalysts carrying peripheral hydrophilic substituents is able to improve device performances in the generation of green ammonia.

Optically Mediated Nonvolatile Resistive Memory Device Based on Metal-Organic Frameworks.

Metal-organic frameworks (MOFs), characterized by tunable porosity, high surface area, and diverse chemical compositions, offer unique prospects for applications in optoelectronic devices. However, the prevailing research on thin-film devices utilizing MOFs has predominantly focused on aspects such as information storage and photosensitivity, often neglecting the integration of the advantages inherent in both photonics and electronics to enhance optical memory. This work demonstrates a light-mediated resistive memory device based on a highly oriented porphyrin-based MOFs film, in which the resistance state of the memristor is modulated by light, realizing the integration of the perception and storage of optical information. The memristor shows excellent performance with a wide light range of 405-785 nm and a persistent photoconductivity phenomenon up to 8.3 × 103 s. Further mechanistic studies have revealed that the resistive switching effect in the memristor is primarily associated with the reversible formation and annihilation of Ag conductive filaments.

How the Interplay between SnO2 and Zn(II) Porphyrins Impacts on the Electronic Features of Gaseous Acetone Chemiresistors.

Herein, the integration of SnO2 nanoparticles with two Zn(II) porphyrins─Zn(II) 5,10,15,20-tetraphenylporphyrin (ZnTPP) and its perfluorinated counterpart, Zn(II) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (ZnTPPF20)─was investigated for the sensing of gaseous acetone at 120 °C, adopting three Zn-porphyrin/SnO2 weight ratios (1:4, 1:32, and 1:64). For the first time, we were able to provide evidence of the correlation between the materials' conductivity and these nanocomposites' sensing performances, obtaining optimal results with a 1:32 ratio for ZnTPPF20/SnO2 and showcasing a remarkable detection limit of 200 ppb together with a boosted sensing signal with respect to bare SnO2. To delve deeper, the combination of experimental data with density functional theory calculations unveiled an electron-donating behavior of both porphyrins when interacting with tin dioxide semiconductor, especially for the nonfluorinated one. The study suggested that the interplay between electrons injected, from the porphyrins' highest occupied molecular orbital to SnO2 conduction band, and the latter's available electronic states has a dramatic impact to boost the chemiresistive sensing. Indeed, we highlighted that the key lies in preventing the full saturation of SnO2 electronic states concomitantly increasing the materials' conductivity: in this respect, the best compromise turned out to be the perfluorinated porphyrin. A further corroboration of our findings was obtained by illuminating the sensors during measurements with light-emitting diode (LED) light. Actually, we demonstrated that it does not have any impact on improving the sensing behavior, most probably due to the electronic oversaturation and scattering caused by LED excitation in porphyrins. Lastly, the most effective hybrids (1:32 ratio) were physicochemically characterized, confirming the physisorption of the macrocycles onto the SnO2 surface. In conclusion, herein, we underscore the feasibility of customizing the porphyrin chemistry and porphyrin-to-SnO2 ratio to enhance the gaseous sensing of bare metal oxides, providing valuable insights for the engineering of highly performing light-free chemiresistors.

Advancements of Porphyrin-Derived Nanomaterials for Antibacterial Photodynamic Therapy and Biofilm Eradication.

The threat posed by antibiotic-resistant bacteria and the challenge of biofilm formation has highlighted the inadequacies of conventional antibacterial therapies, leading to increased interest in antibacterial photodynamic therapy (aPDT) in recent years. This approach offers advantages such as minimal invasiveness, low systemic toxicity, and notable effectiveness against drug-resistant bacterial strains. Porphyrins and their derivatives, known for their high molar extinction coefficients and singlet oxygen quantum yields, have emerged as crucial photosensitizers in aPDT. However, their practical application is hindered by challenges such as poor water solubility and aggregation-induced quenching. To address these limitations, extensive research has focused on the development of porphyrin-based nanomaterials for aPDT, enhancing the efficacy of photodynamic sterilization and broadening the range of antimicrobial activity. This review provides an overview of various porphyrin-based nanomaterials utilized in aPDT and biofilm eradication in recent years, including porphyrin-loaded inorganic nanoparticles, porphyrin-based polymer assemblies, supramolecular assemblies, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Additionally, insights into the prospects of aPDT is offered, highlighting its potential for practical implementation.

Supramolecular Self-Assembled Nanostructures Derived from Amplified Structural Isomerism of Zn(II)-Sn(IV)-Zn(II) Porphyrin Triads and Their Visible Light Photocatalytic Degradation of Pollutants.

Two structural isomeric porphyrin-based triads (Zn(II)porphyrin-Sn(IV)porphyrin-Zn(II)porphyrin) denoted as T1 and T2 were prepared from the reaction of meso-[5-(4-hydroxyphenyl)-10,15,20-tris(3,5-di-tert-butylphenyl)porphyrinato]zinc(II) (ZnL) with trans-dihydroxo-[5,10-bis(3-pyridyl)-15,20-bis(phenyl)porphyrinato]tin(IV) (SnP1) and trans-dihydroxo-[5,15-bis(3-pyridyl)-10,20-bis(phenyl)porphyrinato]tin(IV) (SnP2), respectively. All the compounds were characterized using UV-vis spectroscopy, emission spectroscopy, ESI-MS, 1H NMR spectroscopy, and FE-SEM. Most importantly, the two structurally isomeric porphyrin-based triads supramolecularly self-assembled into completely different nanostructures. T1 exhibits a nanosphere morphology, whereas T2 exhibits a nanofiber morphology. The amplified geometric feature in the structural isomeric porphyrin-based triads dictates the physical and chemical properties of the two triads. Both compounds showed the morphology-dependent visible light catalytic photodegradation of rhodamine B dye (74-97% within 90 min) and tetracycline antibiotic (44-71% within 45 min) in water. In both cases, the photodegradation efficiency of T2 was higher than that of T1. The present investigation can significantly contribute to the remediation of wastewater by tuning the conformational changes in porphyrin-based photocatalysts.

Ultra-Performance Liquid Chromatography (UPLC) Analysis of Heme Biosynthesis Intermediates.

The utilization of ultra-performance liquid chromatography (UPLC) to analyze the various intermediates in the heme biosynthetic pathway is presented. The first product, ALA, was derivatized to a highly fluorescent pyrrolizine; PBG, the second intermediate, was enzymatically converted to uroporphyrinogen, and all the porphyrinogen intermediates were oxidized in acid to form fluorescent porphyrins. Heme was measured as hemin. The stable porphyrin forms of the intermediates, are then resolved and quantified by UPLC. Further details about the various methods are discussed to promote successful UPLC analyses. Method variations that may be preferable in certain situations are also presented.

Electrocatalytic Dinitrogen Reduction to Ammonia Using Easily Reducible N-Fused Cobalt Porphyrins.

Single-site molecular electrocatalysts, especially those that perform catalytic conversion of N2 to NH3 under mild conditions, are highly desirable to derive fundamental structure-activity relations and as potential alternatives to the current energy-consuming Haber-Bosch ammonia production process. Combining theoretical calculations with experimental evidence, it has been shown that easily reducible cobalt porphyrins catalyze the six-electron, six-proton reduction of dinitrogen to NH3 at neutral pH and under ambient conditions. Two easily reducible N-fused cobalt porphyrins - CoNHF and CoNHF(Br)2 - reveal NRR activity with Faradic efficiencies between 6 - 7.5% with ammonia yield rates of 300 - 340 µmol g-1 h-1.  Contrary to this, much harder-to-reduce N-fused porphyrins - CoNHF(Ph)2 and CoNHF(PE)2 - reveal no NRR activity. The present study highlights the significance of tuning the redox and structural properties of single-site NRR electrocatalysts for improved NRR activity under mild conditions.

Aromaticity in the Spectroscopic Spotlight of Hexaphyrins.

Spectroscopic properties are commonly used in the experimental evaluation of ground- and excited-state aromaticity in expanded porphyrins. Herein, we investigate if the defining photophysical properties still hold for a diverse set of hexaphyrins with varying redox states, topologies, peripheral substitutions, and core-modifications. By combining TD-DFT calculations with several aromaticity descriptors and chemical compound space maps, the intricate interplay between structural planarity, aromaticity, and absorption spectra is elucidated. Our results emphasize that the general assumption that antiaromatic porphyrinoids exhibit significantly attenuated absorption bands as compared to aromatic counterparts does not hold even for the unsubstituted hexaphyrin macrocycles. To connect the spectroscopic properties to the hexaphyrins' aromaticity behaviour, we analyzed chemical compound space maps defined by the various aromaticity indices. The intensity of the Q-band is not well described by the macrocyclic aromaticity. Instead, the degeneracy of the frontier molecular orbitals, the HOMO-LUMO gap, and the |ΔHOMO-ΔLUMO|2 values appear to be better indicators to identify hexaphyrins with enhanced light-absorbing abilities in the near-infrared region. Regions with highly planar hexaphyrin structures, both aromatic and antiaromatic, are characterized by an intense B-band. Hence, we advise using a combination of global and local aromaticity descriptors rooted in different criteria to assess the aromaticity of expanded porphyrins instead of solely relying on the absorption spectra.

Dioxygen Activation by Gold(I)-Distorted Porphyrin Dinuclear Complexes.

Interactions between gold-based materials and dioxygen (O2) have motivated researchers to understand reaction mechanisms for O2 activation by homo- and heterogeneous gold catalysts. In this work, gold(I) porphyrin dinuclear complexes were synthesized with a saddle-distorted porphyrin ligand. The gold(I) porphyrin complexes showed unprecedented O2 activation in the presence of protic solvents to form gold(III) tetradentate porphyrin complexes. Mechanistic insights into the O2 activation by the gold(I) center were elucidated by spectroscopic measurements and theoretical calculations, revealing that dissociation of halides on the gold(I) center by alcohol solvents and hydrogen bonding of an N-H proton in the distorted porphyrin with dioxygen played important roles in establishing the unique reactivities of gold(I) complexes.

Co-Assembly of Polyoxometalates and Porphyrins as Anode for High-Performance Lithium-Ion Batteries.

Polyoxometalates (POMs) have been considered one of the most promising anode candidates for lithium-ion batteries (LIBs) in virtue of their high theoretical capacity and reversible multielectron redox properties. However, the poor intrinsic electronic conductivity, low specific surface area, and high solubility in organic electrolytes hinder their widespread applications in LIBs. Herein, a novel hybrid nanomaterial is synthesized by co-assembling POMs and porphyrins (PMo12/CoTPyP) through a facile solvothermal method. The POM clusters are stabilized by porphyrin units through electrostatic interactions, which simultaneously realize the uniform dispersion of POMs and porphyrin units. Benefiting from the generated sub-1 nm channels for fast ion transport and the synergistic effect between evenly distributed PMo12 clusters and high-conductive CoTPyP units, the LIB based on the optimized PMo12/CoTPyP anode exhibits significantly improved Li+ storage capability as well as superior rate and cycling performance. The results of density functional theory simulations further reveal that the co-assembly of PMo12 and CoTPyP can accelerate the mobility of Li+ and electrons, which in turn promotes the enhancement of LIBs performance. This work paves a strategy for synthesizing POMs-based anode materials with simultaneously high dispersibility, redox activity, and stability.

A life in light - in honor of David Mauzerall on his 95th birthday.

David Mauzerall was born on July 22, 1929 to a working-class family in the small, inland textile town of Sanford, Maine. Those humble origins instilled a lifelong frugality and an innovative spirit. After earning his PhD degree in 1954 in physical organic chemistry with Frank Westheimer at the University of Chicago, he joined The Rockefeller Institute for Medical Research (now University) as a postdoctoral fellow that summer, rose to the rank of professor, and remained there for the rest of his career. His work over more than 60 years encompassed porphyrin biosynthesis, photoinduced electron-transfer reactions in diverse architectures (solutions, bilayer lipid membranes, reaction centers, chromatophores, and intact leaves), the light-saturation curve of photosynthesis, statistical treatments of photoreactions, and "all-things porphyrins." His research culminated in studies he poetically referred to as "listening to leaves" through the use of pulsed photoacoustic spectroscopy to probe the course and thermodynamics of photosynthesis in its native state. His research group was always small; indeed, of 185 total publications, 39 were singly authored. In brief, David Mauzerall has blended a deep knowledge of distinct disciplines of physical organic chemistry, photochemistry, spectroscopy and biophysics with ingenious experimental methods, incisive mathematical analysis, pristine personal integrity, and unyielding love of science to deepen our understanding of photosynthesis in its broadest context. He thought creatively - and always independently. His work helped systematize the fields of photosynthesis and the origin of life and made them more quantitative. The present article highlights a number of salient scientific discoveries and includes comments from members of his family, friends, and collaborators (Gary Brudvig, Greg Edens, Paul Falkowski, Alzatta Fogg, G. Govindjee, Nancy Greenbaum, Marilyn Gunner, Harvey Hou, Denise and Michele Mauzerall, Thomas Moore, and William Parson) as part of a celebration of his 95th birthday.

Experimental and theoretical aspects of magnetic circular dichroism and magnetic circularly polarized luminescence in the UV, visible and IR ranges: A review.

A historical sketch of the MCD (magnetic circular dichroism) spectroscopy is reported in its experimental and theoretical aspects. MCPL (magnetic circularly polarized luminescence) is also considered. The main studies are presented encompassing porphyrinoid systems, aggregates and materials, as well as simple organic molecules useful for the advancement of the interpretation. The MCD of chiral systems is discussed with special attention to new studies of natural products with potential pharmaceutical valence, including Amaryllidaceae alkaloids and related isocarbostyrils. Finally, the vibrational form of MCD, called MVCD, which is recorded in the IR part of the spectrum is also discussed. A final brief note on perspectives is given.

In vitro antimicrobial, antibiofilm photodynamic activity, and molecular dynamic simulations of tetra-cationic porphyrinmembrane interactions against foodborne microorganisms.

This manuscript presents a new report on the in vitro antimicrobial photo-inactivation of foodborne microorganisms (Salmonella spp. and Listeria monocytogenes) using tetra-cationic porphyrins. Isomeric tetra-cationic porphyrins (3MeTPyP, 4MeTPyP, 3PtTPyP, and 4PtTPyP) were tested, and antimicrobial activity assays were performed at specific photosensitizer concentrations under dark and white-light LED irradiation conditions. Among the tested bacterial strains, 4MeTPyP exhibited the highest efficiency, inhibiting bacterial growth within just 60 min at low concentrations (17.5 µM). The minimal inhibitory concentration of 4MeTPyP increased when reactive oxygen species scavengers were present, indicating the significant involvement of singlet oxygen species in the photooxidation mechanism. Furthermore, the checkerboard assay testing the association of 4MeTPyP showed an indifferent effect. Atomic force microscopy analyses and dynamic simulations were conducted to enhance our understanding of the interaction between this porphyrin and the strain's membrane.

Combining Nickel- and Zinc-Porphyrin Sites via Covalent Organic Frameworks for Electrochemical CO2 Reduction.

Covalent organic frameworks (COFs) are ideal platforms to spatially control the integration of multiple molecular motifs throughout a single nanoporous framework. Despite this design flexibility, COFs are typically synthesized using only two monomers. One bears the functional motif for the envisioned application, while the other is used as an inert connecting building block. Integrating more than one functional motif extends the functionality of COFs immensely, which is particularly useful for multistep reactions such as electrochemical reduction of CO2. In this systematic study, we synthesized five Ni(II)- and Zn(II)-porphyrin-based COFs, including two pure component COFs (Ni100 and Zn100) and three mixed Ni/Zn-COFs (Ni75/Zn25, Ni50/Zn50, and Ni25/Zn75). Among these, the Ni50/Zn50-COF exhibited the highest catalytic performance for the electroreduction of CO2 to CO and formate at -0.6 V vs RHE, as was observed in an H-cell. The catalytic performance of the COF catalysts was further extended to a zero-gap membrane electrode assembly (MEA) operation where, utilizing Ni50/Zn50, CH4 was detected along with CO and formate at a high current density of 150 mA cm-2. In contrast, under these conditions predominantly H2 and CO were detected at Ni100 and Zn100 respectively, indicating a clear synergistic effect between the Ni- and Zn-porphyrin units.

Practical recommendations for biochemical and genetic diagnosis of the porphyrias.

The porphyrias are a group of rare inborn errors of metabolism associated with various clinical presentations and long-term complications, making them relevant differential diagnoses to consider for many clinical specialities, especially hepatologists, gastroenterologists and dermatologists. To diagnose a patient with porphyria requires appropriate biochemical investigations, as clinical features alone are not specific enough. Furthermore, it is important to be aware that abnormalities of porphyrin accumulation and excretion occur in many other disorders that are collectively far more common than the porphyrias. In this review, we provide an overview of porphyria-related tests with their strengths and limitations, give recommendations on requesting and diagnostic approaches in non-expert and expert laboratories for different clinical scenarios and discuss the role of genetic testing in the porphyrias. To diagnose porphyria in a currently symptomatic patient requires analysis of biochemical markers to demonstrate typical patterns of haem precursors in urine, faeces and blood. The use of genomic sequencing in diagnostic pathways for porphyrias requires careful consideration, and the demonstration of increased porphyrin-related markers is necessary prior to genomic testing in symptomatic patients. In the acute porphyrias, genomic testing is presently a useful adjunct for genetic counselling of asymptomatic family members and the most common cutaneous porphyria, porphyria cutanea tarda, is usually a sporadic, non-hereditary disease. Getting a correct and timely porphyria diagnosis is essential for delivering appropriate care and ensuring best patient outcome.

Synthesis and Photovoltaic Performance of ß-Amino-Substituted Porphyrin Derivatives.

New ß-amino-substituted porphyrin derivatives bearing carboxy groups were synthesized and their performance as sensitizers in dye-sensitized solar cells (DSSC) was evaluated. The new compounds were obtained in good yields (63-74%) through nucleophilic aromatic substitution reactions with 3-sulfanyl- and 4-sulfanylbenzoic acids. Although the electrochemical studies indicated suitable HOMO and LUMO energy levels for use in DSSC, the devices fabricated with these compounds revealed a low power conversion efficiency (PCE) that is primarily due to the low open-circuit voltage (Voc) and short-circuit current density (Jsc) values.