Porphyrin Monomers Research Articles

Facile strategy to prepare a metalloporphyrin-based hydrophilic porous organic polymer with enhanced peroxidase-like activity and high stability for colorimetric detection of H2O2 and glucose.

Nanozymes, nanomaterial-based artificial enzymes, have attracted researchers' enormous interest due to their unique properties compared with natural enzymes. To mimic the catalytic function of natural enzymes, designing high-efficient, novel nanozymes is crucial yet challenging task. In this article, we described the synthesis and functions of a metalloporphyrin-based porous organic polymer, namely FePPOPs-SO3H. FePPOPs-SO3H was synthesized effortlessly via an extensive aromatic electrophilic substitution and the following sulfonation reactions. This strategy was cost-efficient without the participation of precious metal catalysts. The resultant FePPOPs-SO3H is intriguing since the framework itself is constructed by covalently linked porphyrin units, which could serve as a built-in catalyst and strengthen the stability of polymer. With sulfonic acid side groups, FePPOPs-SO3H is well water-dispersive. Owing to these unique characteristics, FePPOPs-SO3H exhibited excellent peroxidase-like activity toward a classical peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue product only within 20 s. The peroxidase-mimicking performance of FePPOPs-SO3H outperforms the ferric porphyrin monomer and normal Fe3O4 nanoparticles. Based on the excellent catalytic activity of FePPOPs-SO3H, two visual colorimetric sensors for ultrafast detecting H2O2 and glucose, respectively, were constructed with a wide linear range of 50-1800 μM (for H2O2) and 200-1500 μM (for glucose), as well as a relative lower limit of detection (LOD) [26.70 μM (for H2O2) and 16.38 μM (for glucose)]. Our strategy highlights opportunities for the design of new metalloporphyrin-based porous organic polymers with built-in catalytic skeletons and inherently excellent peroxidase-mimicking performance.

Mechanism for Copper(II)-Mediated Disaggregation of a Porphyrin J-Aggregate.

J-aggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3–3.1) in the presence of NiSO4 or ZnSO4 (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to ΔH≠ = (+163 ± 15) kJ·mol–1 and ΔS≠ = (+136 ± 11) J·K–1. A mechanism is proposed in which copper(II) cation is in pre-equilibrium with a reactive site at the rim of the J-aggregate. An intermediate copper species is thus formed that eventually leads to the final metallated porphyrin either through an assisted attack of a second metal ion or through a direct insertion of the metal cation into the macrocycle core.

ABC–ABC‐Type Directly meso–meso Linked Porphyrin Dimers

AbstractInvited for the cover of this issue is the group of Hiroshi Imahori at Kyoto University. The image depicts an artistic representation of the evolution from porphyrin monomers to a porphyrin dimer. Read the full text of the article at 10.1002/chem.201805405.

Interaction between the end groups and the main chain of conjugated polymers by time-resolved EPR and fluorescence spectroscopy

ABSTRACTInteraction between a zinc porphyrin (ZnPor) as the end-group and poly(9,9-di-n-octylfluorene-2,7-vinylene) (PFV) as the main chain in a porphyrin end-modified fluorescent conjugated polymer, ZnPFV, was studied by time-resolved electron paramagnetic resonance (EPR) and fluorescence spectroscopy. While fluorescence from the PFV part of ZnPFV showed a spectral profile almost identical to that of a PFV oligomer without end-modification, the emission spectrum of the ZnPor part exhibited a much broader profile compared to that of the reference zinc porphyrin monomer. Based on the analysis of lifetimes and quantum yields, it was found that radiative rate constant of the ZnPor part was enhanced by nearly three times. The observed unusual enhancement in the radiative rate constant was rationalised in terms of a partial π-conjugation between the end group and the main chain, as a result of co-planarisation in fluid solution. On the other hand, the time-resolved EPR spectrum of ZnPFV at 100 K basically showed a similar spectral pattern to that of the reference zinc porphyrin, but with significant differences in zero-field spitting parameters and initial population ratios. The π-system of the excited triplet state is deduced to deviate from D4h symmetry in the end zinc porphyrin groups. The obtained results show that interaction of the porphyrin end group with the main chain of the polymer significantly influences the excited singlet state properties of the porphyrin, while its triplet state properties were affected to a lesser extent.

Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study

ABSTRACTLinear porphyrin oligomers have found various applications as synthetic molecular wires in the context of light harvesting, solar energy conversion and molecular electronics. In many of these applications a partial ordering of the molecules helps to improve the reaction efficiency or device performance. In this work we study the orientational properties of the building blocks of such porphyrin-based molecular wires, namely a porphyrin monomer and the corresponding butadiyne-bridged dimer. The porphyrins have been embedded in the nematic liquid crystal solvent 4-cyano-4'-pentylbiphenyl (5CB) and the anisotropic properties of their photogenerated triplet states were characterised by transient electron paramagnetic resonance (EPR) spectroscopy. When aligned in strong magnetic fields, the liquid crystal molecules impose their orientational anisotropy onto the solute guest molecules whose orientation-dependent magnetic properties can then be explored. The line shape analysis of the porphyrin triplet state EPR spectra – highly sensitive to small conformational changes – confirms the orientation of the zero-field-splitting (ZFS) tensors previously determined for these molecules by magnetophotoselection experiments. A biaxial distribution function is shown to be necessary to simulate the experimental EPR data. The biaxial behaviour, in conjunction with symmetry considerations, allows an unambiguous assignment of the three ZFS tensor axes to the molecular axes. From the determined orientational distributions of the porphyrins in 5CB, the biaxial order parameters for both molecules were calculated.

Enhancement of the Electrocatalytic Activity of Thienyl‐Substituted Iron Porphyrin Electropolymers by a Hangman Effect

AbstractThe thiophene‐modified iron porphyrin FeT3ThP and the respective iron Hangman porphyrin FeH3ThP, incorporating a carboxylic acid hanging group in the second coordination sphere of the iron center, were electropolymerized on glassy carbon electrodes using 3,4‐ethylenedioxythiophene (EDOT) as co‐monomer. Scanning electron microscopy images and Resonance Raman spectra demonstrated incorporation of the porphyrin monomers into a fibrous polymer network. Porphyrin/polyEDOT films catalyzed the reduction of molecular oxygen in a four‐electron reaction to water with onset potentials as high as +0.14 V vs. Ag/AgCl in an aqueous solution of pH 7. Further, FeT3ThP/polyEDOT films showed electrocatalytic activity towards reduction of hydrogen peroxide at highly positive potentials, which was significantly enhanced by introduction of the carboxylic acid hanging group in FeH3ThP. The second coordination sphere residue promotes formation of a highly oxidizing reaction intermediate, presumably via advantageous proton supply, as observed for peroxidases and catalases making FeH3ThP/polyEDOT films efficient mimics of heme enzymes.

Self-Assembly of Monomeric Hydrophobic Photosensitizers with Short Peptides Forming Photodynamic Nanoparticles with Real-Time Tracking Property and without the Need of Release in Vivo.

Employing nanoscaled materials as photosensitizer (PS) carriers is an effective strategy to solve the problem of poor solubility and low tumor selectivity of hydrophobic PS in photodynamic therapy (PDT), which compulsorily requires the PS release in PDT implementation. However, the complicated environment in vivo makes it difficult to precisely design and control the release process and the delivery process requires real-time tracking. Developing a delivery strategy of hydrophobic PS in the monomeric form with fluorescent emission and without consideration of the PS release in the PDT process, is in urgent demand. Herein, we report a versatile and potent strategy for fabrication of photodynamic nanoparticles (nanoPSs) with featuring the monomeric PS based on aromatic peptide-modulated self-assembly of porphyrin derivatives. Aromatic peptides within nanoPSs can isolate hydrophobic porphyrins from each other, resulting in monomeric porphyrin delivery with real-time fluorescence tracking property and avoiding self-aggregation and hence porphyrin release. Moreover, partially charged porphyrins tend to expose on the surface of nanoPSs, facilitating production and diffusion of 1O2. The highest 1O2 yield can be achieved with porphyrin loading as low as 6 wt %, reducing side effects of excessive porphyrin injection. The nanoPSs show enhanced PDT efficacy in vitro and in vivo leading to complete tumor eradication. This study highlights opportunities for development of active photodynamic nanoparticles and provides an alternative strategy for delivery of hydrophobic photosensitive drugs with enhanced therapeutic effects.

Spectral Filtering as a Tool for Two-Dimensional Spectroscopy: A Theoretical Model.

Two-dimensional optical spectroscopy is a powerful technique for the probing of coherent quantum superpositions. Recently, the finite width of the laser spectrum has been employed to selectively tune experiments for the study of particular coherences. This involves the exclusion of certain transition frequencies, which results in the elimination of specific Liouville pathways. The rigorous analysis of such experiments requires the use of ever more sophisticated theoretical models for the optical spectroscopy of electronic and vibronic systems. Here we develop a nonimpulsive and non-Markovian model, which combines an explicit definition of the laser spectrum, via the equation of motion-phase matching approach (EOM-PMA), with the hierarchical equations of motion (HEOM). This theoretical framework is capable of simulating the 2D spectroscopy of vibronic systems with low frequency modes, coupled to environments of intermediate and slower time scales. In order to demonstrate the spectral filtering of vibronic coherences, we examine the elimination of lower energy peaks from the 2D spectra of a zinc porphyrin monomer upon blue-shifting the laser spectrum. The filtering of Liouville pathways is revealed through the disappearance of peaks from the amplitude spectra for a coupled vibrational mode.

Combined Photodynamic and Photothermal Therapy Using Cross-Linked Polyphosphazene Nanospheres Decorated with Gold Nanoparticles

A rational combination of photodynamic therapy (PDT) and photothermal therapy (PTT) could achieve a synergistic therapeutic effect to enhance therapeutic efficacy in the cancer treatment. Herein, polyphosphazene nanospheres as a novel kind of photosensitizer carriers were synthesized by anchoring and isolating photosensitizing porphyrin monomers covalently in the cross-linked structure. Gold nanoparticles were then immobilized on the surface of the nanospheres to introduce the photothermal performance. The hybrid system was eventually conjugated by polyethylene glycol to decrease its cytotoxicity. The morphology analysis showed that the nanospheres were covered by homogeneously dispersed gold nanoparticles. In this way, the resulted system could afford efficient photodynamic and photothermal effect simultaneously, as confirmed by the cancer cell killing studies. The cell experiments demonstrated that the as-prepared polyphosphazene nanospheres with inherent fluorescence could be internalized by HeLa cells...

Development of New CO2 Reduction Catalysts and Construction of Efficient Electro-Reduction Systems

Reduction of CO2 in exhaust gases and its conversion to useful carbon resources are an urgent and important issue to prevent . Carbon positive processes, which consume CO2, are the more effective way to reduce CO2 and to be able to recycle it. We have found that the porphyrin dimers bearing two iron metal centers separated by an appropriate separation as homogeneous catalysts realize CO2 reduction at remarkable high catalytic turnover frequencies (log TOFmax = 5.8), low overpotentials (η > 0.4 V), and high CO selectivity under neutral wet conditions, i.e. without any addition of acidic reagents.[1, 2] According to this highly efficient CO2 reduction, the performance of these dinuclear iron catalysts becomes a bench mark of CO2 reduction catalysts. Such high catalytic activity comes from the CO2 binding to the Fe(II) dimer, though an Fe(II) porphyrin monomer is intact in CO2 atmosphere. The formation of these pre-associated complexes could efficiently promote the succeeding reduction of the bound CO2-to-CO. In order to apply this kind of catalysts to aqueous heterogeneous electro-reduction system, a FTO electrode is modified with Fe porphyrin dimers bearing a phosphonic acid anchor group (Fe2DPPO3H2 ) on its surface.[3] Electrochemical CO2 reduction with the resultant catalyst-modified electrode in a neutral aqueous solution shows CO and H2 formation without any selectivity. Proton reduction could occur on the bare SnO2 surface. The SAM modification of the unmodified FTO surface can successfully block H2 formation by the prevention of the contact of the electrode surface from the solution. However, the low amount of the surface modified catalyst (Γ ≈ 5 x 10-12 mol/cm2) only gave 30-40 μA/cm2 in the electrolysis at -0.95 V vs. NHE (η = 0.42 V) in CO2-saturated 0.1 M KPi solution (pH = 7). In order to increase the surface area of the electrode, meso porous SnO2 layer modification with nano SnO2 particles was applied to a FTO. The resultant 2-μm SnO2 layered electrode co-modified with Fe2DPPO3H2 and SAM was applied to CO2 reduction in 0.1 M KPi and gave 10 times higher current density (i = 1.5 mA/cm2) than that of an ordinary catalyst-modified FTO. The continuous electrolysis for 6 h showed stable current and this proved the electrode is sufficiently stable under these conditions. Since the thickness of the meso porous SnO2 layer on a FTO can be increased up to ≈10 μm, further increase of the current density is possible. In this talk, the latest results of the cell-electrode system involving a non-precious metal anode will be discussed.

Porphyrin-stabilized CNT in nanofiber via non-covalent interaction for enhanced electrochemical performance

Herein, a new fabrication method for CNT nanofiber composite (pPC-FP) through non-covalent interaction between porphyrin monomers with CNTs is reported. This led to the alleviated agglomeration of pristine CNT without acid pre-treatment, producing a highly porous material with high surface area of 444 m2/g and narrow pore size distribution for all pPC-FP nanofiber composites. Enhanced performances of pPC-FP3 and pPC-FP5 (CNT nanofiber with porphyrin monomers) were brought about by the enhanced CNT dispersion, hence, better porosity as compared to pPC. Moreover, through the incorporation of porphyrin monomer, M-NC bond was simultaneously formed and served as a contributor to the excellent capacitive performance of the material, resulting in the highest capacitance of 150 A/cm2 at 0.25 mAh/cm2 with 77 A/cm2 at 2.5 mAh/cm2. The composites also exhibited stable performance even after cycling at different current densities (0.25–2.5 mAh/cm2) for 3000 cycles with almost 100% columbic efficiency. Through π-π stacking interaction, the agglomeration was prevented and CNT was aligned along the axis of the polymer which rendered the nanofibers highly porous resulting to a conductive composite material with excellent electrochemical performance.

Chirality and spatially pre-organized multi-porphyrinoids

We report herein that chiral and enantiopure compounds such nucleosides and peptides can pre-organize multi-porphyrinic systems and influence their properties. The first example given concerns star-shaped mutli-porphyrins with chiral and enantiopure nucleosidic linkers. If the configuration is indeed a star-shaped nanomolecule, it appears that the induced conformation is nothing as expected. The four peripheral Zn(II) porphyrins collapse over the free-base central one, inducing totally different photo-physical properties. Despite a minor expected light energy harvesting behavior, the principal capability of this system is to quench the collected light energy and convert it from radiative to non-radiative de-activation. The second example concerns polypeptides with pendant porphyrins. The peptidic backbone confers to the systems, after a certain degree of oligomerization, a 3[Formula: see text] right handed helical conformation which induces cavities within the multi-porphyrinc architecture, ready to welcome guests and render, for example, the complexation of C[Formula: see text] much easier. We thus have constructed novel organic photovoltaic systems using supramolecular complexes of porphyrin–peptide oligomers with fullerene clusters. The composite cluster OTE/SnO[Formula: see text] electrode prepared with (P(ZnP)[Formula: see text] C[Formula: see text], exhibits an impressive incident photon-to-photocurrent efficiency (IPCE) with values reaching as high as 56%. The power conversion efficiency of the (P(H[Formula: see text]P)[Formula: see text] C[Formula: see text] modified electrode reaches 1.6%, which is 40 times higher than the value (0.043%) of the porphyrin monomer (P(H[Formula: see text]P)[Formula: see text] [Formula: see text] C[Formula: see text] modified electrode. Thus, the organization approach between porphyrins and fullerenes with polypeptide structures is promising, and may make it possible to further improve the light energy conversion properties by using a larger number of porphyrins in a polypeptide unit.

Surfactant-Assisted Synthesis of Tetragonal Porphyrin Microparticles

ABSTRACTIn an effort to utilize their unique photoactive properties, porphyrin monomers were assembled into tetragonal microparticles by a surfactant-assisted neutralization method through the cooperative interactions between the porphyrin building blocks including π-π stacking, J-aggregation and metal-ligand coordination. Electron microscopy characterization in combination with x-ray diffraction confirmed the three-dimensional ordered tetragonal microstructures with stable crystalline frameworks and well defined external surface morphology. Optical absorption and fluorescence spectroscopy revealed enhanced absorbance properties as compared with the raw porphyrin material, favourable for chromophore excitation and energy transport. With active and responsive optical properties, these new porphyrin microparticles look to serve as promising components for a wide range of applications including sensing, diagnostics, solar cells, and optoelectronic devices.

Freestanding photocatalytic materials based on 3D graphene and polyporphyrins

A new concept in the formulation of hybrid nanostructured materials combining high quality graphene 3D supported by Nickel foam and polyporphyrins for visible light photocatalytic application is here reported. Our innovative approach involves the development of a freestanding device able to: i) offer a high surface area to bind the photosensitizers by π-π interactions, and ii) enhance stability and photocatalytic efficiency by using cyclic porphyrin polymers. For these purposes, homo- and co-polymerization reactions by using different porphyrin (free or zinc complexed) monomers were performed. The microscopic structures and morphology of graphene polymer nanocomposites were investigated by using Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM). Finally, photocatalytic activity under visible light irradiation of the obtained nanocomposites was tested, by using methylene blue (MB) as organic pollutant. The obtained data suggested that hindered cyclic polymeric structures stacked on graphene surface by non-covalent interactions, restrict the formation of non photoactive aggregates and, as a consequence, induce an enhancement of photocatalytic activity. Remarkably, our systems show a degradation efficiency in the visible-light range much higher than other similar devices containing nanoporphyrin units reported in literature.

The sequential structure of tripyridiniumylporphyrin pendants in water-soluble copolymers and their association behaviour with tetrasulfonatophenylporphyrin guests: UV-vis absorption and fluorescence emission spectra study.

A novel cationic tripyridiniumylporphyrin monomer, 5-[4-[2-(acryloyloxy)ethoxy]phenyl]-l0,l5,20-tris(N-methyl-4-pyridiniumyl)porphyrinate zinc(ii) (ZnTrMPyP), was synthesized, and its self-aggregation in water was studied by UV-vis absorption. The monomer was copolymerized with acrylamide in water and DMSO, respectively, to prepare the water-soluble polymers P-W and P-D. The aggregation behaviour of the copolymers in aqueous solution was investigated by UV-vis absorption and fluorescence emission spectra. The polymer P-D displayed very similar absorption and emission spectra to those of ZnTrMPyP in water, indicating that the polymer chains in P-D have no significant effect on the aggregate structure of ZnTrMPyP in aqueous media. In comparison, two new absorption bands appeared in the Q band range of polymer P-W and its fluorescence spectra red shifted and the fluorescence quantum yield decreased obviously. These characteristics remained unchanged even in a good solvent for the monomer, suggesting that a new aggregation structure for the porphyrin pendants fixed by the covalent bond was formed. According to the different dispersed states of the porphyrin monomer in water and DMSO, the porphyrin pendants should distribute randomly in the P-D polymer chains while having micro-blocky sequences in polymer P-W. The association behaviour between the copolymers and tetra(p-sulfonatophenyl)porphyrin, TSPP, bearing opposite charged substituents were studied by absorption and emission Spectra and further analyzed by the Benesi–Hildebrand and the Stern–Volmer methods. The results showed that relatively discrete porphyrin pendants in P-D formed a 1 : 1 stoichiometric complex with TSPP and both static and dynamic mechanisms were active in this quenching process, while the tightly associated porphyrin pendants in P-W interacted with TSPP as an entirety and static quenching was dominant in this process. This observation was in accordance with their sequential structure. The polymer P-W has a wider absorption range and higher absorption intensity in the long wavelength region than the porphyrin monomer, which can more efficiently absorb light to accomplish light harvesting in water.

Tailored homo- and hetero- lanthanide porphyrin dimers: a synthetic strategy for integrating multiple spintronic functionalities into a single molecule.

We present the design, synthesis and magnetic properties of molecular magnetic systems that contain all elements necessary for spin-valve control in molecular spintronic devices in a single molecule. We investigate the static and dynamic magnetic properties and quantum spin properties of butadiyne-linked homo- and hetero-nuclear lanthanide-porphyrin dimers. A heterometallated porphyrin dimer containing both TbIII and DyIII centres is created rationally by the stepwise oxidative homocoupling of distinct lanthanide-porphyrin monomers. TbIII and DyIII mononuclear porphyrin complexes, homodimers and heterodimers all exhibit slow magnetic relaxation below 10 kelvin under a static magnetic field. The coherence times for GdIII porphyrin monomers and dimers are found to be in excess of 3.0 μs at 2 K, allowing distinct magnetic manipulations in low temperature transport experiments.

Self-Assembled One-Dimensional Porphyrin Nanostructures with Enhanced Photocatalytic Hydrogen Generation.

There has been a widespread interest in the preparation of self-assembled porphyrin nanostructures and their ordered arrays, aiming to emulate natural light harvesting processes and energy storage and to develop new nanostructured materials for photocatalytic process. Here, we report controlled synthesis of one-dimensional porphyrin nanostructures such as nanorods and nanowires with well-defined self-assembled porphyrin networks that enable efficient energy transfer for enhanced photocatalytic activity in hydrogen generation. Preparation of these one-dimensional nanostructures is conducted through noncovalent self-assembly of porphyrins confined within surfactant micelles. X-ray diffraction and transmission electron microscopy results reveal that these one-dimensional nanostructures contain stable single crystalline structures with controlled interplanar separation distance. Optical absorption characterizations show that the self-assembly enables effective optical coupling of porphyrins, resulting in much more enhanced optical absorption in comparison with the original porphyrin monomers, and the absorption bands red shift to more extensive visible light spectrum. The self-assembled porphyrin network facilitates efficient energy transfer among porphyrin molecules and the delocalization of excited state electrons for enhanced photocatalytic hydrogen production under visible light.

Synthesis and Complex Formation of Porphyrin Polymers on the Basis of Methyl Methacrylate

Copolymers of methyl methacrylate with various porphyrin monomers were prepared by radical copolymerization in solution. The yields, molecular weight characteristics of the copolymers and the molar content of porphyrin in the copolymers were determined. Copper and zinc complexes of the synthesized porphyrin polymers were obtained.

Enhancing solution-phase supramolecular interactions between monomeric porphyrins and [60]fullerene by simple chemical modification

The supramolecular interactions of N-methylporphyrin and iridium porphyrin with C60 in toluene solution were investigated using NMR spectroscopy and absorption spectroscopy. Our results demonstrate that both the N-methylation and iridium metalation of porphyrin are effective means to enhance the binding affinity to C60, resulting in 1:1 complexation for N-methylporphyrin/C60 and 2:1 complexation for iridium porphyrin/C60.

Photophysical Properties of Porphyrin Dimer–Single-Walled Carbon Nanotube Linked Systems

Porphyrin dimers were covalently grafted onto electron-accepting single-walled carbon nanotube (SWNT) sidewalls by direct aryl radical addition reaction with an m- or p-phenylene linker with the help of π–π interaction between the porphyrins. A splitting of the porphyrin Soret band and DFT calculations supported the selective formation of the porphyrin dimers on the sidewall of SWNTs. Photoexcitation of the porphyrin dimers on the SWNT resulted in the formation of the exciplex state, which directly decayed to the ground state without yielding the complete charge-separated state. Lifetimes of the porphyrin dimer–SWNT exciplex were longer than that of a porphyrin monomer–SWNT exciplex due to the stabilization by π-electron interaction over two porphyrin rings. In addition, the weaker electronic coupling through the meta-linkage than the para-one may be responsible for the exciplex lifetime of the porphyrin dimer–SWNT with the m-phenylene linker (49 ps) longer than that with the p-phenylene one (24 ps). The ...