Gallium(III) and Indium(III) Complexes with meso-Monophosphorylated Porphyrins: Synthesis and Structure. A First Example of Dimers Formed by the Self-Assembly of meso-Porphyrinylphosphonic Acid Monoester

Homochiral layered indium phosphonates: solvent modulation of morphology and chiral discrimination adsorption

Assembling chiral coordination polymers into nano/microflower structures may improve their performance in applications such as chiral recognition and separation. In this study, we chose a chiral metal phosphonate system, i.e., In(NO3)3/R-, S-pempH2 [pempH2 = (1-phenylethylamino)methylphosphonic acid], and carried out systematic work on the self-assembly of this system in different alcohol/H2O mixed solvents under solvothermal conditions. Enantiomeric compounds R-, S-[In2(pempH)2(μ2-OH)2(H2O)2](NO3)2 (R-, S-1) were obtained showing dense layered structures, but their morphologies varied with alcohol solvent. We obtained crystals of R-, S-1C in triethylene glycol (TEG)/H2O mixed solvent and spiral microflowers of R-, S-1MF in isopropanol (IPA)/H2O mixed solvent. Adsorption isotherms using enantiopure R-2-butanol and S-2-butanol as probe molecules revealed that compounds R-1MF and S-1MF had higher adsorption capacity compared to the crystalline sample and displayed enantioselective adsorption behaviour.

Indium Imidazo[4,5,-b]porphyrins as Photocatalysts for Oxidation of Sulfides

Over the past two decades, the application of photocatalytic reactions in organic synthesis has increased remarkably. Porphyrins, renowned for their exceptional photophysical properties, photostability, and prevalence in natural catalytic processes, are attracting significant attention as promising photocatalysts for reactions proceeding through energy transfer and one-electron transfer. In this work, we synthesized the indium(III) complex of 2-[4-(diethoxyphosphoryl)phenyl]-1H-imidazo[4,5-b]-5,10,15,20-tetramesitylporphyrin (InTMPIP) and explored its application as a photocatalyst for the oxidation of sulfides by dioxygen or air. Complex InTMPIP was found to generate singlet oxygen with quantum yield of 0.92 (toluene) and enables efficient photooxidation of sulfides to sulfoxides by dioxygen in "green" acetonitrile/water (4:1 v/v) or methanol/chloroform (2:1 v/v) solvent mixtures with almost quantitative yield. Furthermore, InTMPIP was grafted onto hydrated mesoporous titania and materials InTMPIP/TiO2-1 and InTMPIP/TiO2-2 with different In/Ti ratios were obtained and investigated. The composition and structure of the materials were studied using a combination of elemental analysis, various spectroscopic methods, gas adsorption measurements, and SEM imaging. Finally, the photocatalytic efficiency of InTMPIP/TiO2-2 was explored in aerobic photooxidation of sulfides. The heterogenized complex enables selective synthesis of sulfoxides under "green" conditions; however, it is prone to leaching into the solution when irradiated with both blue and red LEDs.

Water-soluble platinum and palladium porphyrins with peripheral ethyl phosphonic acid substituents: synthesis, aggregation in solution, and photocatalytic properties

Water-soluble porphyrins have garnered significant attention due to their broad range of applications in biomedicine, catalysis, and material chemistry. In this work, water-soluble platinum(II) and palladium(II) complexes with porphyrins bearing ethyl phosphonate substituents, namely, Pt/Pd 10-(ethoxyhydroxyphosphoryl)-5,15-di(p-carboxyphenyl)porphyrins (M3m, M = Pt(II), Pd(II)) and Pt/Pd 5,10-bis(ethoxyhydroxyphosphoryl)-10,20-diarylporphyrins (M1d-M3d; aryl = p-tolyl (1), mesityl (2), p-carboxyphenyl (3)), were synthesized by alkaline hydrolysis of the corresponding diethyl phosphonates M6m and M4d-M6d. NMR, UV-vis, and fluorescence spectroscopy revealed that the mono-phosphonates M3m tend to form aggregates in aqueous media, while the bis-phosphonates M3d exist predominantly as monomeric species across a wide range of concentrations (10-6-10-3 M), ionic strengths (0-0.81 M), and pH values (4-12). Single-crystal X-ray diffraction studies of the diethyl phosphonates Pt6d and Pd6d revealed that π-π stacking of the aromatic macrocycles is sterically hindered in the crystals, providing a rationale for the low degree of solution aggregation observed for ethyl phosphonate M3d. Photophysical studies of M3m and M1d-M3d demonstrated that these compounds are phosphorescent and generate singlet oxygen in aqueous solutions. Pd(II) complex Pd3d is an excellent photocatalyst for the oxidation of sulfides using di-oxygen in a solvent mixture (MeCN/H2O, 4 : 1 v/v). Under these conditions, various alkyl and aryl sulfides were quantitatively converted into the desired sulfoxides. For the oxygenation of mixed alkyl-aryl sulfides, Pd3d outperforms Pd(II) meso-tetrakis(p-carboxyphenyl)porphyrin (PdTCPP). This photocatalyst can be recycled and reused to afford sulfoxides with no loss of product yield.

Ruthenium(II) complexes with phosphonate-substituted phenanthroline ligands as reusable photoredox catalysts

Ru(II) complexes with polypyridyl ligands (2,2'-bipyridine = bpy, 1,10-phenanthroline = phen) play a central role in the development of photocatalytic organic reactions. In this work, we synthesized four mixed-ligand [Ru(phen)(bpy)2]2+-type complexes (Ru-Pcat-A) bearing two phosphonate substituents P(O)(OH)(OR) (R = H, Et) attached to the phen core at positions 3,8 (Ru-3,8PH and Ru-3,8PHEt) and 4,7 (Ru-4,7PH and Ru-4,7PHEt) of the heterocycle in high yields (87-99%) and characterized them using spectral methods. Single crystal X-ray diffraction was employed to determine the coordination mode of the ditopic phen ligand in Ru-4,7PH. This complex exists as the neutral species and forms a 1D hydrogen-bonded framework in the crystals. The light absorption characteristics were found to be similar for all complexes prepared in this work. However, the emission maxima in aqueous solutions were significantly affected by the substitution of the heterocycle, ranging from 629 nm for Ru-4,7PH to 661 nm for Ru-3,8PHEt. The emission quantum yields in Ar-saturated deionized water showed a strong dependence on the substitution pattern of the phen ligand, with maximal values reaching approximately 0.11 for Ru-4,7PHEt and Ru-4,7PH, which is twice as high as that of the classical [Ru(bpy)3]2+ complex (Ru-bpy). The photocatalytic performance of Ru-Pcat-A was investigated using visible light photoredox catalytic transformations of tertiary amines. With Ru-Pcat-A, we achieved the phosphonylation of N-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) and cyanation of THIQs and N,N-dimethylaniline in methanol, while a mixture of nitromethane/methanol (1 : 1 v/v) proved to be the optimal solvent for conducting the nitromethylation of THIQs. In the majority of the studied reactions, Ru-4,7PHEt exhibited greater efficiency compared to Ru-bpy, and it could be easily separated from the products using water extraction and reused in the next catalytic cycle. We successfully performed seven consecutive nitromethylation and phosphonylation of N-phenyl-1,2,3,4-tetrahydroisoquinoline using the recycled homogeneous photoredox catalyst.

Modern Developments in Bifunctional Chelator Design for Gallium Radiopharmaceuticals

The positron-emitting radionuclide gallium-68 has become increasingly utilised in both preclinical and clinical settings with positron emission tomography (PET). The synthesis of radiochemically pure gallium-68 radiopharmaceuticals relies on careful consideration of the coordination chemistry. The short half-life of 68 min necessitates rapid quantitative radiolabelling (≤10 min). Desirable radiolabelling conditions include near-neutral pH, ambient temperatures, and low chelator concentrations to achieve the desired apparent molar activity. This review presents a broad overview of the requirements of an efficient bifunctional chelator in relation to the aqueous coordination chemistry of gallium. Developments in bifunctional chelator design and application are then presented and grouped according to eight categories of bifunctional chelator: the macrocyclic chelators DOTA and TACN; the acyclic HBED, pyridinecarboxylates, siderophores, tris(hydroxypyridinones), and DTPA; and the mesocyclic diazepines.

Developing a Novel Indium(III) Agent Based on Liposomes to Overcome Cisplatin-Induced Resistance in Breast Cancer by Multitargeting the Tumor Microenvironment Components

To overcome the resistance of cancer cells to platinum-based drugs and effectively suppress tumor growth, we developed a novel indium (In) agent based on liposomes (Lips). Thus, we not only obtained an In(III) thiosemicarbazone agent (5b) with remarkable cytotoxicity by optimizing a series of In(III) thiosemicarbazone agents (1b-5b) but also successfully constructed a novel 5b-loaded Lip (5b-Lip) delivery system. Importantly, in vitro and in vivo results revealed that 5b/5b-Lip overcame the tumor cell resistance and effectively inhibited MCF-7/DDP tumor growth. In addition, Lips improved the intracellular accumulation of 5b. We also confirmed the mechanism by which 5b/5b-Lip overcomes breast cancer cell resistance. 5b/5b-Lip cannot act against DNA in cancer cells but attacks the two cell components in the tumor microenvironment, namely, by inducing apoptosis and lethal autophagy of cancer cells and resetting tumor-promoting M2 macrophages to the tumor-killing M1 phenotype.

Structural Investigations, Cellular Imaging, and Radiolabeling of Neutral, Polycationic, and Polyanionic Functional Metalloporphyrin Conjugates

Over the past decade, porphyrin derivatives have emerged as invaluable synthetic building blocks and theranostic kits for the delivery of cellular fluorescence imaging and photodynamic therapy. Tetraphenylporphyrin (TPP), its metal complexes, and related derivatives have been investigated for their use as dyes in histology and as components of multimodal imaging probes. The photophysical properties of porphyrin–metal complexes featuring radiometals have been a focus of our attention for the realization of fluorescence imaging probes coupled with radioimaging capabilities and therapeutic potential having “true” theranostic promise. We report hereby on the synthesis, radiochemistry, structural investigations, and preliminary in vitro and in vivo uptake studies on a range of functionalized porphyrin-based derivatives. In pursuit of developing new porphyrin-based probes for multimodality imaging applications, we report new functionalized neutral, polycationic, and polyanionic porphyrins incorporating nitroimidazole and sulfonamide moieties, which were used as targeting groups to improve the notoriously poor pharmacokinetics of porphyrin tags. The resulting functional metalloporphyrin species were stable under serum challenges and the nitroimidazole and sulfonamide derivatives remained fluorescent, allowing in vitro confocal studies and visualization of the lysosomal uptake in a gallium(III) sulfonamide derivative. The molecular structures of selected porphyrin derivatives were determined by single crystal X-ray diffraction using synchrotron radiation. We also investigated the nature of the emission/excitation behavior of model functional porphyrins using in silico approaches such as TD DFT in simple solvation models. The conjugation of porphyrins with the [7-13] and [7-14] fragments of bombesin was also achieved, to provide targeting of the gastrin releasing peptide receptor (GRPR). Depending on the metal, probe conjugates of relevance for single photon emission computed tomography (SPECT) or positron emission tomography (PET) probes have been designed and tested hereby, using TPP and related functional free base porphyrins as the bifunctional chelator synthetic scaffold and ¹¹¹In[In] or ⁶⁸Ga[Ga], respectively, as the central metal ions. Interestingly, for simple porphyrin conjugates good radiochemical incorporation was obtained for both radiometals, but the presence of peptides significantly diminished the radio-incorporation yields. Although the gallium-68 radiochemistry of the bombesin conjugates did not show radiochemical incorporation suitable for in vivo studies, likely because the presence of the peptide changed the behavior of the TPP-NH₂ synthon taken alone, the optical imaging assays indicated that the conjugated peptide tags do mediate uptake of the porphyrin units into cells.

Recent advances in synthesis of organometallic complexes of indium

The indium complexes are being used in many applications like catalysis, optoelectronics, sensors, solar cells, biochemistry, medicine, infrared (IR) mirrors and thin-film transistors (TFTs). In organometallic complexes of indium, it forms different types of complexes with single, double, triple and tetra linkages by coordinating with numerous elements like C, N, O and S and also with some other elements like Se and Ru. So, the present study comprises all the possible ways to synthesize the indium complexes by reacting with different organic ligands; most of them are N-heterocyclic carbenes, amines, amides and phenols. The commonly used solvents for these syntheses are tetrahydrofuran, dichloromethane, toluene, benzene, dimethyl sulfoxide (DMSO) and water. According to the nature of the ligands, indium complexes were reported at different temperatures and stirring time. Because of their unique characteristics, the organometallic chemistry of group 13 metal indium complexes remains a subject of continuing interest in synthetic chemistry as well as material science.

Assembling Homometallic Sb6 and Heterometallic Ti4Sb2 Oxo Clusters

Isolation and structural characterization of novel organoantimony(V)-based oxo clusters are reported. (RSb)₄(OH)₄(t-BuPO₃)₆ and (RSb)₂(O)(t-BuPO₃H)₆ independently in the presence of pyridine under solvothermal conditions afford the hexanuclear organoantimonate clusters [(RSb)₆(μ₃-O)₂(μ₂-O)₆(t-BuPO₃)₄], where R = p-i-PrC₆H₄ (1), p-ClC₆H₄ (2). Further, reaction of organostibonate phosphonate with Ti(OⁱPr)₄ in the presence of pyridine under solvothermal conditions afforded the mixed-metal titanium stibonate hexanuclear clusters [(RSb)₂Ti₄(μ₃-O)₂(μ₂-O)₂(t-BuPO₃)₄(μ-OCH₃)₄(OCH₃)₄], where R = p-i-PrC₆H₄ (3), p-ClC₆H₄ (4). Band gap measurements were performed on 1-4. They reveal a remarkable reduction in the band gap on moving from the heavier main-group-based oxo cages (1 and 2) to the titanium-incorporated oxo cages (3 and 4).

Porphyrin Derivative Nanoformulations for Therapy and Antiparasitic Agents

Porphyrins and analogous macrocycles exhibit interesting photochemical, catalytic, and luminescence properties demonstrating high potential in the treatment of several diseases. Among them can be highlighted the possibility of application in photodynamic therapy and antimicrobial/antiparasitic PDT, for example, of malaria parasite. However, the low efficiency generally associated with their low solubility in water and bioavailability have precluded biomedical applications. Nanotechnology can provide efficient strategies to enhance bioavailability and incorporate targeted delivery properties to conventional pharmaceuticals, enhancing the effectiveness and reducing the toxicity, thus improving the adhesion to the treatment. In this way, those limitations can be overcome by using two main strategies: (1) Incorporation of hydrophilic substituents into the macrocycle ring while controlling the interaction with biological systems and (2) by including them in nanocarriers and delivery nanosystems. This review will focus on antiparasitic drugs based on porphyrin derivatives developed according to these two strategies, considering their vast and increasing applications befitting the multiple roles of these compounds in nature.

Metal phosphonates incorporating metalloligands: assembly, structures and properties

This feature article summarizes the current status of metal–metalloligand phosphonates including the synthetic strategies, crystal structures and properties. Future challenges in this field are discussed.

Coordination self-assembly through weak interactions in meso-dialkoxyphosphoryl-substituted zinc porphyrinates

The self-assembly of seven zinc 10-(dialkoxyphosphoryl)-5,15-diarylporphyrinates Zn5-Zn11 containing different substituents at the phosphonate and aryl groups was investigated. Single crystals of Zn5-Zn9 complexes were grown under the same conditions and analyzed by X-ray structural analysis. A supramolecular self-assembly is observed in all crystals through weak coordinative bonding of the phosphoryl group of one porphyrin molecule to the zinc(ii) ion of a second molecule. The geometry of the porphyrin macrocycle is similar in all of the studied crystals and the central zinc atom in each case adopts a distorted tetragonal pyramidal environment. However, the Zn5-Zn7 porphyrins display a 1D polymeric structure while the Zn8 and Zn9 complexes exist as discrete cyclotetramers in the crystals. This data demonstrates that the non-coordinating meso-aryl substituents of meso-(dialkoxyphosphoryl)porphyrins influence their crystalline organization. A self-assembly of the Zn5-Zn11 complexes is also observed in toluene and chloroform solutions over a large temperature range (223-323 K). According to NMR studies, the associates exhibit dynamic behavior. A well-defined supramolecular aggregate of complex Zn10 at 10-3 M in toluene and chloroform solutions was unambiguously characterized as a cyclotetramer [Zn10]4 by 1H NMR spectroscopy at 223 K. The structure of the Zn10 association in toluene and chloroform shows a concentration dependence. When a solution of Zn10 in toluene was diluted from 10-3 M to 10-5 M, the average number of molecules in the associated unit decreased to about two.

Electrochemical, Spectroelectrochemical, and Structural Studies of Mono- and Diphosphorylated Zinc Porphyrins and Their Self-Assemblies

Three series of porphyrins containing a Zn(II) central metal ion and zero, one, or two phosphoryl groups at the meso-positions of the macrocycle were characterized as to their electrochemical, spectroscopic, and structural properties in nonaqueous media. The investigated compounds are represented as 5,15-bis(4'-R-phenyl)porphyrinatozinc, 10-(diethoxyphosphoryl)-5,15-bis(4'-R-phenyl)porphyrinatozinc, and 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-R-phenyl)porphyrinatozinc, where R = OMe, Me, H, or CN. Linear-free energy relationships are observed between the measured redox potentials at room temperature and the electronic nature of the substituents at the 5 and 15 meso-phenyl groups of the macrocycle. The mono- and bis-phosphoryl derivatives with two p-cyanophenyl substituents provide electrochemical evidence for aggregation at low temperature, a greater degree of aggregation being observed in the case of 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-cyanophenyl)porphyrinatozinc(II). This compound was characterized in further detail by variable-temperature ¹H and ³¹P{¹H} NMR spectroscopy in solution combined with single crystal X-ray analysis in the solid state. The data obtained from these measurements indicate that this porphyrin has a dimeric structure in CDCl₃ at 223-323 K but forms a 2D polymeric network when it is crystallized from a CHCl₃/MeOH mixture.

Tin(IV)-Porphyrin Tetracarbonyl Cobaltate: An Efficient Catalyst for the Carbonylation of Epoxides

Cationic tin(IV) porphyrins with tetracarbonyl cobaltates were synthesized, exhibiting bifunctional catalytic reactivity. The Lewis acidic tin-porphyrin center activated epoxides; concurrently, cobalt carbonyl anions efficiently opened epoxides and delivered carbonyl moieties. Thus, a series of β-lactones with a high synthetic value were obtained. This catalytic system showed excellent efficiency exceeding a turnover number of one thousand with a broad substrate scope. In addition, the presented tin porphyrin-based catalyst exhibited exclusive chemoselectivity to terminal epoxides over internal ones. The selective carbonylation of di-epoxides demonstrated the usefulness of these catalysts in the synthesis of complex molecular structures.

Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate

First evidence of self-assembling of imidazoporphyrins is revealed with the example of zinc(ii) 5,10,15,20-tetramesityl-2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrin in the solid state and in solution.

Platinum(ii) and palladium(ii) complexes with electron-deficient meso-diethoxyphosphorylporphyrins: synthesis, structure and tuning of photophysical properties by varying peripheral substituents

The luminescence quenching by O₂ and photodegradation of Pt(ii) and Pd(ii) phosphorylporphyrins are reported.