Self-Assembly of Porphyrin-Based Metallacages into Octahedra

Research Progress on the Application of Metal Porphyrin Electrochemical Sensors in the Detection of Phenolic Antioxidants in Food

This paper reviews the application of metal porphyrin electrochemical sensors in the detection of phenolic antioxidants in food, focusing on the latest progress and innovative applications in this field. Phenolic antioxidants are widely used in food and can effectively prolong the shelf life of food, but their excessive use may cause potential harm to human health, so the detection of their content is very important. In recent years, electrochemical analysis technology has gradually become an emerging method for quantitative detection of phenolic antioxidants due to its advantages of sensitivity, simplicity and high selectivity. As a new type of sensor, metal porphyrin electrochemical sensors have been widely used in the detection of phenolic antioxidants in food due to their excellent electrochemical performance and high selectivity. By modifying metal nanomaterials, the detection performance of these sensors has been significantly improved. This paper first introduces the basic concepts and physicochemical properties of phenolic antioxidants, analyzes their potential hazards and discusses relevant regulations and limit requirements. Then, the existing analysis methods of phenolic antioxidants are compared, and the development trend of traditional detection methods and new detection technologies is reviewed. Subsequently, the application progress of electrochemical sensors in the detection of phenolic antioxidants is discussed in depth, its working principle is expounded and the research results are summarized. Finally, the innovative applications of metalloporphyrins and their nanocomposites in electrochemical sensors are introduced in detail. The unique advantages of metalloporphyrins in the detection of phenolic antioxidants in food are highlighted, and the future development direction is laid out.

Supramolecular Coordination Complexes for Synergistic Cancer Therapy

Supramolecular coordination complexes (SCCs) are predictable and size-tunable supramolecular self-assemblies constructed through directional coordination bonds between readily available organic ligands and metallic receptors. Based on planar and 3D structures, SCCs can be mainly divided into two categories: metallacycles (e.g., rhomboidal, triangular, rectangular, and hexagonal) and metallacages (e.g., tetrahedral, hexahedral, and dodecahedral). The directional coordination bonds enable the efficient formation of metallacycles and metallacages with well-defined architectures and geometries. SCCs exhibit several advantages, including good directionality, strong interaction force, tunable modularity, and good solution processability, making them highly attractive for biomedical applications, especially in cellular imaging and cancer therapy. Compared with their molecular precursors, SCCs demonstrate enhanced cellular uptake and a strengthened tumor accumulation effect, owing to their inherently charged structures. These properties and the chemotherapeutic potential inherent to organic platinum complexes have promoted their widespread application in antitumor therapy. Furthermore, the defined structures of SCCs, achieved via the design modification of assembly elements and introduction of different functional groups, enable them to combat malignant tumors through multipronged treatment modalities. Because the development of cancer-treatment methodologies integrated in clinics has evolved from single-modality chemotherapy to synergistic multimodal therapy, the development of functional SCCs for synergistic cancer therapy is crucial. While some pioneering reviews have explored the bioapplications of SCCs, often categorized by a specific function or focusing on the specific metal or ligand types, a comprehensive exploration of their synergistic multifunctionality is a critical gap in the current literature.In this Account, we focus on platinum-based SCCs and their applications in cancer therapy. While other metals, such as Pd-, Rh-, Ru-, and Ir-based SCCs, have been explored for cancer therapy by Therrien and Casini et al., platinum-based SCCs have garnered significant interest, owing to their unique advantages in antitumor therapy. These platinum-based SCCs, which enhance antitumor efficacy, are considered prominent candidates for cancer therapies owing to their desirable properties, such as potent antitumor activity, exceptionally low systemic toxicity, active tumor-targeting ability, and enhanced cellular uptake. Furthermore, diverse diagnostic and therapeutic modalities (e.g., chemotherapy, photothermal therapy, and photodynamic therapy) can be integrated into a single platform based on platinum-based SCCs for cancer therapy. Consequently, herein, we summarize our recent research on platinum-based SCCs for synergistic cancer therapy with particular emphasis on the cooperative interplay between different therapeutic methods. In the Conclusions section, we present the key advancements achieved on the basis of our research findings and propose future directions that may significantly impact the field.

Supramolecular coordination platinum metallacycle-based multilevel wound dressing for bacteria sensing and wound healing

The exploitation of novel wound healing methods with real-time infection sensing and high spatiotemporal precision is highly important for human health. Pt-based metal-organic cycles/cages (MOCs) have been employed as multifunctional antibacterial agents due to their superior Pt-related therapeutic efficiency, various functional subunits and specific geometries. However, how to rationally apply these nanoscale MOCs on the macroscale with controllable therapeutic output is still challenging. Here, a centimeter-scale Pt MOC film was constructed via multistage assembly and subsequently coated on a N,N'-dimethylated dipyridinium thiazolo[5,4-d]thiazole (MPT)-stained silk fabric to form a smart wound dressing for bacterial sensing and wound healing. The MPT on silk fabric could be used to monitor wound infection in real-time through the bacteria-mediated reduction of MPT to its radical form via a color change. The MPT radical also exhibited an excellent photothermal effect under 660 nm light irradiation, which could not only be applied for photothermal therapy but also induce the disassembly of the Pt MOC film suprastructure. The highly ordered Pt MOC film suprastructure exhibited high biosafety, while it also showed improved antibacterial efficiency after thermally induced disassembly. In vitro and in vivo studies revealed that the combination of the Pt MOC film and MPT-stained silk can provide real-time information on wound infection for timely treatment through noninvasive techniques. This study paves the way for bacterial sensing and wound healing with centimeter-scale metal-organic materials.

Chirality-Regulated Clusteroluminescence in Polypeptides

The low emission efficiency of clusteroluminogens restricts their practical applications in the fields of sensors and biological imaging. In this work, the clusteroluminescence of ordered/disordered polypeptides was observed, and the photoluminescence (PL) intensity of polypeptides can be modulated by the chirality of amino acid residues. Polyglutamates with different chiral compositions were synthesized, and the racemic polypeptides exhibited a significantly higher PL intensity than the enantiopure ones. This emission originates from the n-π* transition between C═O groups of polypeptides and is enhanced by clusterization of polypeptides. CD and Fourier transform infrared spectra demonstrated that the enantiopure and racemic polypeptides form α-helix and random coil structures, respectively. The disordered polypeptides can form more chain entanglements and interchain interactions because of their high flexibility, leading to more clusterizations and stronger PL intensity. The rigidity of ordered helical structures restrains the chain entanglements, and the formation of intrachain hydrogen bonds between amide groups of the backbone impairs the interchain interaction between polypeptides, resulting in lower PL intensity. The PL intensity of the polypeptides can also be manipulated by the addition of urea or trifluoroacetic acid. Our study not only elucidates the chirality/order-based structure-property relationship of clusteroluminescence in peptide-based polymers but also offers implications for the rational design of fluorescent peptides/proteins.

Molecular Co-Catalyst Confined within a Metallacage for Enhanced Photocatalytic CO2 Reduction

The construction of structurally well-defined supramolecular hosts to accommodate catalytically active species within a cavity is a promising way to address catalyst deactivation. The resulting supramolecular catalysts can significantly improve the utilization of catalytic sites, thereby achieving a highly efficient chemical conversion. In this study, the Co-metalated phthalocyanine (Pc-Co) was successfully confined within a tetragonal prismatic metallacage, leading to the formation of a distinctive type of supramolecular photocatalyst (Pc-Co@Cage). The host-guest architecture of Pc-Co@Cage was unambiguously elucidated by single-crystal X-ray diffraction (SCXRD), NMR, and ESI-TOF-MS, revealing that the single cobalt active site can be thoroughly isolated within the space-restricted microenvironment. In addition, we found that Pc-Co@Cage can serve as a homogeneous supramolecular photocatalyst that displays high CO2 to CO conversion in aqueous media under visible light irradiation. This supramolecular photocatalyst exhibits an obvious improvement in activity (TONCO = 4175) and selectivity (SelCO = 92%) relative to the nonconfined Pc-Co catalyst (TONCO = 500, SelCO = 54%). The present strategy provided a rare example for the construction of a highly active, selective, and stable photocatalyst for CO2 reduction through a cavity-confined molecular catalyst within a discrete metallacage.

Molecular Engineering of Metalloporphyrins for High-Performance Energy Storage: Central Metal Matters

Porphyrin derivatives represent an emerging class of redox-active materials for sustainable electrochemical energy storage. However, their structure-performance relationship is poorly understood, which confines their rational design and thus limits access to their full potential. To gain such understanding, we here focus on the role of the metal ion within porphyrin molecules. The A₂ B₂ -type porphyrin 5,15-bis(ethynyl)-10,20-diphenylporphyrin and its first-row transition metal complexes from Co to Zn are used as models to investigate the relationships between structure and electrochemical performance. It turned out that the choice of central metal atom has a profound influence on the practical voltage window and discharge capacity. The results of DFT calculations suggest that the choice of central metal atom triggers the degree of planarity of the porphyrin. Single crystal diffraction studies illustrate the consequences on the intramolecular rearrangement and packing of metalloporphyrins. Besides the direct effect of the metal choice on the undesired solubility, efficient packing and crystallinity are found to dictate the rate capability and the ion diffusion along with the porosity. Such findings open up a vast space of compositions and morphologies to accelerate the practical application of resource-friendly cathode materials to satisfy the rapidly increasing need for efficient electrical energy storage.

Ultrasensitive Electrochemical Detection of Butylated Hydroxy Anisole via Metalloporphyrin Covalent Organic Frameworks Possessing Variable Catalytic Active Sites

Three novel two-dimensional metalloporphyrin COFs (MPor-COF-366, M = Fe, Mn, Cu) were fabricated by changing the metal atoms in the center of the porphyrin framework. The physicochemical characteristics of MPor-COF-366 (M = Fe, Mn, Cu) composites were fully analyzed by diverse electron microscopy and spectroscopy. Under optimal conditions, experiments on determining butylated hydroxy anisole (BHA) at FePor-COF-366/GCE were conducted using differential pulse voltammetry (DPV). It is noted that the FePor-COF-366/GCE sensor showed excellent electrocatalytic performance in the electrochemical detection of BHA, compared with MnPor-COF-366/GCE and CuPor-COF-366/GCE. A linear relationship was obtained for 0.04-1000 μM concentration of BHA, with a low detection limit of 0.015 μM. Additionally, the designed sensor was successfully employed to detect BHA in practical samples, expanding the development of COF-based composites in electrochemical applications.

Shifting the Triangle-Square Equilibrium of Self-Assembled Metallocycles by Guest Binding with Enhanced Photosensitization

Shifting a triangle-square equilibrium in one direction is an important problem in supramolecular self-assembly. Reaction of a benzothiadiazole-based diimidazole donor with a cis-Pt(II) acceptor yielded an equilibrium mixture of a triangle ([C₁₈H₂₄N₁₀O₆S₁Pt₁]₃≡ PtMC^T) and a square ([C₁₈H₂₄N₁₀O₆S₁Pt₁]₄≡ PtMC^S). We report here the shifting of such equilibrium toward a triangle using a guest (pyrene aldehyde, G1). While both benzothiadiazole and pyrene aldehyde can form reactive oxygen species (ROS) in organic solvents, their therapeutic use in water is restricted due to aqueous insolubility. The enhanced water solubility of the benzothiadiazole unit and G1 by macrocycle formation and host-guest complexation, respectively, enabled enhanced ROS generation by the host-guest complex (G1' ⊂ PtMC^T) in water (G1' = hydrated form of G1). The guest-encapsulated metallacycle (G1' ⊂ PtMC^T) has shown synergistic antibacterial activity compared to the mixture of macrocycles upon white-light irradiation due to enhanced ROS generation. The mechanism for such enhanced activity was established by measuring the oxidative stress and relative internalization of PtMCs and G1' ⊂ PtMC^T.

Porphyrin-Based Multicomponent Metallacage: Host-Guest Complexation toward Photooxidation-Triggered Reversible Encapsulation and Release

The development of supramolecular hosts with effective host-guest properties is crucial for their applications. Herein, we report the preparation of a porphyrin-based metallacage, which serves as a host for a series of polycyclic aromatic hydrocarbons (PAHs). The association constant between the metallacage and coronene reaches 2.37 × 107 M-1 in acetonitrile/chloroform (ν/ν = 9/1), which is among the highest values in metallacage-based host-guest complexes. Moreover, the metallacage exhibits good singlet oxygen generation capacity, which can be further used to oxidize encapsulated anthracene derivatives into anthracene endoperoxides, leading to the release of guests. By employing 10-phenyl-9-(2-phenylethynyl)anthracene whose endoperoxide can be converted back by heating as the guest, a reversible controlled release system is constructed. This study not only gives a type of porphyrin-based metallacage that shows desired host-guest interactions with PAHs but also offers a photooxidation-responsive host-guest recognition motif, which will guide future design and applications of metallacages for stimuli-responsive materials.

A porphyrin-based metallacage for enhanced photodynamic therapy

In this study, we designed an effective nanoplatform to improve the photodynamic therapy (PDT) of porphyrins. Combining a porphyrin-based metallacage (PM), hyaluronidase (HAase) and DSPE-mPEG2000 together, the nanoparticle (PM@HAase-mPEG) showed enhanced PDT efficacy. The PM improved the stability of the porphyrin, avoided its aggregation and provided cavities to concentrate oxygen molecules, which was beneficial for enhancing PDT. HAase degraded HA to increase the intracellular accumulation of nanoparticles, normalized blood vessels and relieved hypoxia in tumors. PM@HAase-mPEG inhibited the growth of tumors in a 4T1 mouse model by the generated singlet oxygen with excellent PDT efficacy. This study resolved the problems of the instability of PSs, less cellular accumulation of drugs, and tumor hypoxia that limited the anti-tumor application of PDT.

Pt(ii)-coordinated tricomponent self-assemblies of tetrapyridyl porphyrin and dicarboxylate ligands: are they 3D prisms or 2D bow-ties?

Thermodynamically favored simultaneous coordination of Pt(ii) corners with aza- and carboxylate ligands yields tricomponent coordination complexes with sophisticated structures and functions, which require careful structural characterization to paint accurate depiction of their structure-function relationships. Previous reports claimed that heteroleptic coordination of cis-(Et3P)2PtII with tetrapyridyl porphyrins (M'TPP, M' = Zn or H2) and dicarboxylate ligands (XDC) yielded 3D tetragonal prisms containing two horizontal M'TPP faces and four vertical XDC pillars connected by eight Pt(ii) corners, even though such structures were not supported by their 1H NMR data. Through extensive X-ray crystallographic and NMR studies, herein, we demonstrate that self-assembly of cis-(Et3P)2PtII, M'TPP, and four different XDC linkers having varied lengths and rigidities actually yields bow-tie (⋈)-shaped 2D [{cis-(Et3P)2Pt}4(M'TPP) (XDC)2]4+ complexes featuring a M'TPP core and two parallel XDC linkers connected by four heteroleptic PtII corners instead of 3D prisms. This happened because (i) irrespective of their length (∼7-11 Å) and rigidity, the XDC linkers intramolecularly bridged two adjacent pyridyl-N atoms of a M'TPP core via PtII corners instead of connecting two cofacial M'TPP ligands and (ii) bow-tie complexes are entropically favored over prisms. The electron-rich ZnTPP core of a representative bow-tie complex selectively formed a charge-transfer complex with highly π-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-heaxacarbonitrile but not with a π-donor such as pyrene. Thus, this work not only produced novel M'TPP-based bow-tie complexes and demonstrated their selective π-acid recognition capability, but also underscored the importance of proper structural characterization of supramolecular assemblies to ensure accurate depiction of their structure-property relationships.

BODIPY based Metal-Organic Macrocycles and Frameworks: Recent Therapeutic Developments

Boron dipyrromethene, commonly known as BODIPY, based metal-organic macrocycles (MOCs) and metal-organic frameworks (MOFs) represent an interesting part of materials due to their versatile tunability of structure and functionality as well as significant physicochemical properties, thus broadening their applications in various scientific domains, especially in biomedical sciences. With increasing concern over the efficacy of cancer drugs versus quality of patient's life dilemma, scientists have been trying to fabricate novel comprehensive therapeutic strategies along with the discovery of novel safer drugs where research with BODIPY metal complexes has shown vital advancements. In this review, we have exclusively examined the articles involving studies related to light harvesting and photophysical properties of BODIPY based MOCs and MOFs, synthesized through self-assembly process, with a special focus on biomolecular interaction and its importance in anti-cancer drug research. In the end, we also emphasized the possible practical challenges involved during the synthetic process, based on our experience on dealing with BODIPY molecules and steps to overcome them along with their future potentials. This review will significantly help our fellow research groups, especially the budding researchers, to quickly and comprehensively get the near to wholesome picture of BODIPY based MOCs and MOFs and their present status in anti-cancer drug discovery.

Design of a Metallacycle-Based Supramolecular Photosensitizer for In Vivo Image-Guided Photodynamic Inactivation of Bacteria

Bacterial infection is one of the greatest threats to public health. In vivo real-time monitoring and effective treatment of infected sites through non-invasive techniques, remain a challenge. Herein, we designed a PtII metallacycle-based supramolecular photosensitizer through the host-guest interaction between a pillar[5]arene-modified metallacycle and 1-butyl-4-[4-(diphenylamino)styryl]pyridinium. Leveraging the aggregation-induced emission supramolecular photosensitizer, we improved fluorescence performance and antimicrobial photodynamic inactivation. In vivo studies revealed that it displayed precise fluorescence tracking of S. aureus-infected sites, and in situ performed image-guided efficient PDI of S. aureus without noticeable side effects. These results demonstrated that metallacycle combined with host-guest chemistry could provide a paradigm for the development of powerful photosensitizers for biomedicine.

Recent Advances in Nanomaterials Development for Nanomedicine and Cancer

Cancer is considered one of the leading causes of death, with a growing number of cases worldwide. However, the early diagnosis and efficient therapy of cancer have remained a critical challenge. The emergence of nanomedicine has opened up a promising window to address the drawbacks of cancer detection and treatment. A wide range of engineered nanomaterials and nanoplatforms with different shapes, sizes, and composition has been developed for various biomedical applications. Nanomaterials have been increasingly used in various applications in bioimaging, diagnosis, and therapy of cancers. Recently, numerous multifunctional and smart nanoparticles with the ability of simultaneous diagnosis and targeted cancer therapy have been reported. The multidisciplinary attempts led to the development of several exciting clinically approved nanotherapeutics. The nanobased materials and devices have also been used extensively to develop point-of-care and highly sensitive methods of cancer detection. In this review article, the most significant achievements and latest advances in the nanomaterials development for cancer nanomedicine are critically discussed. In addition, the future perspectives of this field are evaluated.

Spectrophotometric Study of Bridging N-Donor Ligand-Induced Supramolecular Assembly of Conjugated Zn-Trisporphyrin with a Triphenylamine Core

This article studies the supramolecular assembly behavior of a Zn-trisporphyrin conjugate containing a triphenylamine core (1) with bridging N-donor ligands using the UV-vis spectrophotometric titration method at micromolar concentrations. Our results show that pyridine, a non-bridging ligand, formed a 3:1 open complex with 1. The corresponding binding constant was estimated to be (2.7 ± 0.15) × 1014 M-3. In contrast, bridging ligands, 4,4-bipyridine (BIPY) and 1,3-di(4-pyridyl)propane (DPYP), formed stable 3:2 double-decker complexes with 1 in solution, which collapsed to yield a 3:1 open complex when excess BIPY or DPYP was added. The binding constants for forming BIPY and DPYP double-decker complexes were estimated to be (9.26 ± 0.07) × 1027 M-4 and (3.62 ± 0.16) × 1027 M-4, respectively. The UV-vis titration profiles supported the conclusion that the degradation of the 3:2 double-decker 1∙BIPY complex is less favorable compared to that of 1∙DPYP. Consequently, the formation of the 3:1 1∙DPYP open complex proceeded more readily than that of 1∙BIPY.

Decahexanuclear Zinc(II) Coordination Container Featuring a Flexible Tetracarboxylate Ligand: A Self-Assembly Supermolecule for Highly Efficient Drug Delivery of Anti-Inflammatory Agents

The application of a coordination container in biomedicine is hindered by single binding domains and unsatisfactory biostability and biocompatibility. Herein, we designed a sulfonylcalix[4]arene-based decahexanuclear zinc(II) coordination container employing a flexible tetracarboxylate ligand as a linker and utilized it as a novel drug delivery system. The coordination container consisting of one endo and four exo cavities provides multiple binding domains for efficient encapsulation of drug molecules as clearly revealed by systematic host-guest studies using NMR techniques of ¹H NMR titration experiments and 2D NOESY and diffusion-ordered NMR spectroscopy studies. Incorporation of a flexible p-phenylene-bis(methanamino) spacer into the container via the carboxylate linker allowed a stepwise drug loading process through sequential binding at endo and exo cavities, as well as enabling pH-responsive stepwise drug release. The drug-loaded coordination container not only exhibits excellent biostability and biocompatibility but also provides encouraging therapeutic efficiency toward inflammatory macrophages as revealed by in vitro studies. The novel strategy for engineering the endo cavity of a coordination container provides a new approach to achieving controlled drug delivery and opens up new opportunities for designing novel functional supramolecular materials.

A Flexible Synthetic Strategy for the Preparation of Heteroleptic Metallacycles of Porphyrins

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl₂(CO)₂}₂(4'cisDPyP)(3'cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4'cisDPyP [i.e., 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin] and 3'cisDPyP [i.e., 5,10-bis(3'-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90°-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl₂(CO)₂(dmso-O)}₂(4'cisDPyP)] (3) with 1 equiv of 3'cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl₂(CO)₂(dmso-O)}₂(3'cisDPyP)] (4) with 1 equiv of 4'cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments.

Anthracene-induced formation of highly twisted metallacycle and its crystal structure and tunable assembly behaviors

Polycyclic aromatic hydrocarbons (PAHs) continue to attract increasing interest with respect to their applications as luminescent materials. The ordered structure of the metal-organic complex facilitates the selective integration of PAHs that can be tuned to function cooperatively. Here, a unique highly twisted anthracene-based organoplatinum metallacycle was prepared via coordination-driven self-assembly. Single-crystal X-ray diffraction analysis revealed that the metallacycle was twisted through the cooperation of strong π···π stacking interactions and steric hindrance between two anthracene-based ligands. Notably, the intramolecular twist and aggregation behavior introduced restrictions to the conformational change of anthracenes, which resulted in increased emission intensity of the metallacycle in solution. The emission behaviors and suprastructures based on the highly twisted metallacycle can be modulated by the introduction of different solvents. This study demonstrates that this metallacycle with highly twisted structure is a promising candidate for sensing and bioimaging applications.

Platinum(II) Metallatriangle: Construction, Coassembly with Polypeptide, and Application in Combined Cancer Photodynamic and Chemotherapy

The development of the supramolecular coordination complex with different shapes and dimensionalities lays the basis for its application in different areas. In this study, a porphyrin-based 3D organo-Pt(II) metallatriangle (MTA) was fabricated through the reported method termed as "coordination driven self-assembly". ³¹P NMR, ¹H NMR, HR-MS, and theoretical calculation were employed to characterize the resultant MTA fully. Furthermore, the fabricated nanocomposite through coassembly of MTA and an amphiphilic polypeptide (PEG-PPT) could generate singlet oxygen (¹O₂) under the NIR irradiation and release a Pt drug under a low-pH microenvironment. ¹O₂ and the Pt drug can both damage the cancer cells, which improves the efficiency of cancer therapies. The fabrication of a Pt-porphyrin metallatriangle expands the topological structures, and the Pt-porphyrin metallatriangle can be applied to the combined cancer therapies. Moreover, various stimuli-responsive groups can be modified to the triangle, so a new method is created to develop high-performance biosupramolecular materials.

Bioinspired Applications of Porphyrin Derivatives

Porphyrin derivatives are ubiquitous in nature and have important biological roles, such as in light harvesting, oxygen transport, and catalysis. Owing to their intrinsic π-conjugated structure, porphyrin derivatives exhibit characteristic photophysical and electrochemical properties. In biological systems, porphyrin derivatives are associated with various protein molecules through noncovalent interactions. For example, hemoglobin, which is responsible for oxygen transport in most vertebrates, consists of four subunits of a globular protein with an iron porphyrin derivative prosthetic group. Furthermore, noncovalently arranged porphyrin derivatives are the fundamental chromophores in light-harvesting systems for photosynthesis in plants and algae. These biologically important roles originate from the functional versatility of porphyrin derivatives. Specifically, porphyrins are excellent host compounds, forming coordination complexes with various metal ions that adds functionality to the porphyrin unit, such as redox activity and additional ligand binding at the central metal ion. In addition, porphyrins are useful building blocks for functional supramolecular assemblies because of their flat and symmetrical molecular architectures, and their excellent photophysical properties are typically utilized for the fabrication of bioactive functional materials. In this Account, we summarize our endeavors over the past decade to develop functional materials based on porphyrin derivatives using bioinspired approaches. In the first section, we discuss several synthetic receptors that act as artificial allosteric host systems and can be used for the selective detection of various chemicals, such as cyanide, chloride, and amino acids. In the second section, we introduce multiporphyrin arrays as mimics of natural light-harvesting complexes. The active control of energy transfer processes by additional guest binding and the fabrication of organic photovoltaic devices using porphyrin derivatives are also introduced. In the third section, we introduce several types of porphyrin-based supramolecular assemblies. Through noncovalent interactions such as metal-ligand interaction, hydrogen bonding, and π-π interaction, porphyrin derivatives were constructed as supramolecular polymers with formation of fiber or toroidal assembly. In the last section, the application of porphyrin derivatives for biomedical nanodevice fabrication is introduced. Even though porphyrins were good candidates as photosensitizers for photodynamic therapy, they have limitations for biomedical application owing to aggregation in aqueous media. We suggested ionic dendrimer porphyrins and they showed excellent photodynamic therapy (PDT) efficacy.

Recharged Catalyst with Memristive Nitrogen Reduction Activity through Learning Networks of Spiking Neurons

Electrocatalysis from N2 to NH3 has been increasingly studied because it provides an environmentally friendly avenue to take the place of the current Haber-Bosch method. Unfortunately, the conversion of N2 to NH3 is far below the necessary level for implementation at a large scale. Inspired by signal memory in a spiking neural network, we developed rechargeable catalyst technology to activate and remember the optimal catalytic activity using manageable electrical stimulation. Herein, we designed double-faced FeReS3 Janus layers that mimic a multiple-neuron network consisting of resistive switching synapses, enabling a series of intriguing multiphase transitions to activate undiscovered catalytic activity; the activation energy barrier is clearly reduced via an active site conversion between two nonequivalent surfaces. Electrical field-stimulated FeReS3 demonstrates a Faradaic efficiency of 43% and the highest rate of 203 μg h-1 mg-1 toward NH3 synthesis. Moreover, this rechargeable catalyst displays unprecedented catalytic performance that persists for up to 216 h and can be repeatedly activated through a simple charging operation.

Supramolecular Coordination Complexes as Optical Biosensors

In recent years, luminescent supramolecular coordination complexes (SCCs), including 2D-metallacycles and 3D-metallacages have been utilised for biomolecular analysis. Unlike small-molecular probes, the dimensions, size, shape, and flexibility of these complexes can easily be tuned by combining ligands designed with particular geometries, symmetries and denticity with metal ions with strong geometrical binding preferences. The well-defined cavities that result, in combination with the other non-covalent interactions that can be programmed into the ligand design, facilitate great selectivity towards guest binding. In this Review we will discuss the application of luminescent metallacycles and cages in the binding and detection of a wide range of biomolecules, such as carbohydrates, proteins, amino acids, and biogenic amines. We aim to explore the effect of the structural diversity of SCCs on the extent of biomolecular sensing, expressed in terms of sensitivity, selectivity and detection range.

Solvent-regulated biomorphs from the intense π,π-mediated assemblies of tetracenequinone fused porphyrin

Tetracenequninone fused porphyrin exhibits remarkable π,π-stacking, which can be regulated by solvents to afford various biomorphs or cubic-shaped architectures.