Paddlewheel Framework Research Articles

Fine tuning of porphyrin based-paddlewheel framework by imidazole derivative to boost electrochemiluminescence performance

Precise tuning the structure of catalytic center is of great importance for the construction of enhanced electrochemiluminescence (ECL) emitters and the development of ECL amplification strategies, which is a key factor in improving the sensitivity of biosensors. In this work, we report the enhanced ECL emitters based on the porphyrin-based paddlewheel framework (PPF) with axial coordinated imidazole-like ligands (PPF/X, X = 2-methylimidazole (MeIm), imidazole (Im), benzimidazole (BIM)). In this system, the electron-donating ability of the axial ligands is positively correlated to its coordination ability to the paddlewheel units and the catalytic ability of the axially coordinated paddlewheel units. In addition, the electrochemical and ECL behavior of PPF/X (X = MeIm, Im, BIM) with different axial coordinated ligands are explored.

Development of High Throughput Photopolymerizations Using Micron-Sized Ultrathin Metal-Organic Framework Nanosheets.

Polymer syntheses in a high throughput format are still challenging due to the tedious procedures for prior deoxygenation and catalyst removal. 2D metal-organic framework (MOF) nanosheets are advantageous for elevating the catalytic efficiency and catalyst recyclability. Polymerization of a wide variety of monomers, including hydrophilic acrylamides and hydrophobic acrylates, is attempted directly in a multi-well plate by employing Zn-ZnPPF-2D nanosheets (PPF=porphyrin paddlewheel framework) as a heterogeneous photocatalyst. Various parameters such as monomer concentration, catalyst concentration, and light wavelength are investigated with respect to their effects on polymerization rate and the degree of control over the molecular weight and molecular weight distribution. Due to the larger surface area and more accessible catalytic sites, the top-performing Zn-ZnPPF-2D exhibits fast polymerization kinetics over the Zn-ZnPPF-3D bulk crystals. In addition, the synthesis of triblock copolymers with a single loading of catalysts confirms the outstanding catalytic performance of these 2D MOF catalysts. Finally, photopolymerization is demonstrated to be achievable entirely in a microliter-scale human cell culture medium. As such, this strategy provides high levels of control and precision over macromolecular synthesis outcomes that best align with the requirements of high throughput approaches toward biological applications.

Porphyrin Based 2D-MOF Structures as Dual-Kinetic Sorafenib Nanocarriers for Hepatoma Treatment.

The existing clinical protocols of hepatoma treatment require improvement of drug efficacy that can be achieved by harnessing nanomedicine. Porphyrin-based, paddle-wheel framework (PPF) structures were obtained and tested as dual-kinetic Sorafenib (SOR) nanocarriers against hepatoma. We experimentally proved that sloughing of PPF structures combined with gradual dissolving are effective mechanisms for releasing the drug from the nanocarrier. By controlling the PPF degradation and size of adsorbed SOR deposits, we were able to augment SOR anticancer effects, both in vitro and in vivo, due to the dual kinetic behavior of SOR@PPF. Obtained drug delivery systems with slow and fast release of SOR influenced effectively, although in a different way, the cancer cells proliferation (reflected with EC50 and ERK 1/2 phosphorylation level). The in vivo studies proved that fast-released SOR@PPF reduces the tumor size considerably, while the slow-released SOR@PPF much better prevents from lymph nodes involvement and distant metastases.

An electrochemiluminescence biosensor for p53 antibody based on Zn-MOF/GO nanocomposite and Ag+-DNA amplification.

An ultrasensitive electrochemiluminescence biosensor was established based on the Zn-MOF/GO nanocomposite. Ag(I)-embedded DNA complexes were used as a signal amplification reagent. In this work, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and Zn2+ were integrated into a porphyrin paddlewheel framework (Zn-MOF) by a hydrothermal method. The synthesized Zn-MOF material has electrochemiluminescence property, and the luminescence intensity isimproved after being composited with graphene oxide (GO). Based on the composite material, we constructed an ultrasensitive ECL biosensor for the p53 antibody detection. The composite material acted as an admirable substrate and then loaded plenty of p53 antigens to recognize the target (p53 antibody) accurately. Because of the bridging effect of streptavidin and biotin-conjugated goat anti-rabbit IgG (bio-ab2), the rich-C DNA with positive correlation with the target was modified on the electrode and then captured the co-reactant accelerator Ag+ to amplify the signal. Therefore, the ECL biosensor response increases with increasing p53 antibody concentration. In the range 0.1fg/mL-0.01ng/mL, the response signal of the biosensor has a good linear relationship with the p53 antibody concentration. The detection limit is 0.03fg/mL (S/N= 3). Impressively, the biosensor not only featured high sensitivity, good stability, and excellent specificity for the detection of p53 antibody, but also provides a new way for early detection of cancer. Graphical abstract Schematic representation of the electrochemiluminescence sensor based on a Zn-MOF/GO nanocomposite, which can be applied to the determination of p53 antibody.

Reaction of dirhodium(II) tetraacetate with S-methyl-L-cysteine

The reaction of antitumor active dirhodium(II) tetraacetate, [Rh2(AcO)4], with S-methyl-L-cysteine (HSMC) was studied at the pH of mixing (=4.8) in aqueous media at various temperatures under aerobic conditions. The results from UV–vis spectroscopy and electrospray ionization mass spectrometry (ESI–MS) showed that HSMC initially coordinates via its sulfur atom to the axial positions of the paddlewheel framework of the dirhodium(II) complex, and was confirmed by the crystal structure of [Rh2(AcO)4(HSMC)2]. After some time (48 h at 25 °C), or at elevated temperature (40 °C), Rh-SMC chelate formation causes breakdown of the paddlewheel structure, generating the mononuclear Rh(III) complexes [Rh(SMC)2]+, [Rh(AcO)(SMC)2] and [Rh(SMC)3], as indicated by ESI–MS. These aerobic reaction products of [Rh2(AcO)4] with HSMC have been compared with those of the two proteinogenic sulfur-containing amino acids methionine and cysteine. Comparison shows that the (S,N)-chelate ring size influences the stability of the [Rh2(AcO)4] paddlewheel cage structure and its RhII–RhII bond, when an amino acid with a thioether group coordinates to dirhodium(II) tetraacetate.

Coordinative Reduction of Metal Nodes Enhances the Hydrolytic Stability of a Paddlewheel Metal-Organic Framework.

Enhancement of hydrolytic stability of metal-organic frameworks (MOFs) is a challenging issue in MOF chemistry because most MOFs have shown limitations in their applications under a humid environment. Meanwhile, inner sphere electron transfer has constituted one of the most intensively studied subjects in contemporary chemistry. In this report, we show, for the first time, a new conceptual coordinative reduction of Cu2+ ion, which is realized in a paddlewheel MOF, HKUST-1, with a postsynthetic manner via inner sphere "single" electron transfer from hydroquinone (H2Q) to Cu2+ through its coordination bond. H2Q treatment of HKUST-1 under anhydrous conditions leads to the single charge (1+) reduction of approximately 30% of Cu2+ ions. Thus, this coordinative reduction is an excellent reduction process to be self-controlled in both oxidation state and quantity. As described below, once Cu2+ ions are reduced to Cu+, the reduction reaction does not proceed further, in terms of their oxidation state as well as their amount. Also, we demonstrate that a half of the Cu+ ions (about 15%) remains in paddlewheel framework with pseudo square planar geometry and the other half of the Cu+ ions (about 15%) forms [Cu(MeCN)4]+ complex in a small cage in the fashion of a ship-in-a-bottle after dissociation from the framework. Furthermore, we show that the coordinative reduction results in substantial enhancement of the hydrolytic stability of HKUST-1 to the extent that its structure remains intact even after exposure to humid air for two years.

Semiconducting Langmuir-Blodgett Films of Porphyrin Paddle-Wheel Frameworks for Photoelectric Conversion.

Understanding the photocurrent transportation within porphyrin-containing metal-organic frameworks (PMOFs) will be a critical step in applying these materials in light-harvesting molecular devices in the future. Two copper porphyrin paddle-wheel frameworks (Cu-PPFs) were employed to study the influence of metal ions coordinated into the porphyrin ligands on conductivity and photoelectron transfer capability. To compare the electronic and optical properties of both materials, we prepared an ultrathin film of each PPF via a Langmuir-Blodgett method. The resulting films exhibited uniform morphology and single-crystalline domains, in addition to photoelectric conversion capabilities. We confirmed that both Cu-PPFs have semiconducting properties with an optical band gap of around 2.7 eV. The current density generated by both Cu-PPFs was studied through a mercury drop junction approach. We observed a slightly higher conductivity from the Cu-PPF film consisting of metalloporphyrins than the one without copper doping in the porphyrin centers. In addition, the copper-ion-coordinated porphyrins were found to be more favorable for facilitating photoinduced electron transfer from the Cu-PPF film to a conductive glass substrate. This work presents a new approach of combining thin film fabrication and electro-heterojunction measurement to study electron transfer within an ultrathin film.

Systematic Tuning of Zn(II) Frameworks with Furan, Thiophene, and Selenophene Dipyridyl and Dicarboxylate Ligands

Twelve Zn(II) frameworks with furan, thiophene, and selenophene dicarboxylate and dipyridyl ligands have been synthesized by solvothermal methods in both the presence and the absence of water to investigate the subtle differences in structure and properties of the framework with changes in the linearity of the ligands. The large change in the ligand bend angle (10°) of the furan ring when compared to either thiophene or selenophene results in the formation of a number of frameworks with unexpected topologies. By using only ligands containing thiophene and selenophene, which differ in their ligand bend angle by only 2°, a series of four isostructural Zn(II) paddlewheel frameworks were obtained and their subtle differences investigated using UV/vis/NIR spectroscopy and gas adsorption experiments with N2, H2, and CO2.

A study of the CO2/CO/CH4 adsorption ability of porphyrin paddle–wheel frameworks (PPFs)

Over 25 porphyrin-based paddle–wheel frameworks (PPFs), which are composed of porphyrin and metal paddle–wheels, have been reported. However, only one study describing the gas adsorption of PPFs has been reported. In this study, gas adsorption of PPFs for several gases is reported. Additionally, the selectivity of PPF-1 toward carbon dioxide was observed.

Controlled Nucleation and Growth of Pillared Paddlewheel Framework Nanostacks onto Chemically Modified Surfaces

The nucleation and growth of metal-organic frameworks onto functional surfaces stands to facilitate the utility of these supramolecular crystalline materials across a wide range of applications. Here, we demonstrate the solvothermal nucleation and growth of a pillared paddlewheel porphyrin framework 5 (PPF-5) onto semiconductor surfaces modified with carboxylic acids. Using versatile diazonium and catechol chemistries to modify silicon and titania surface chemistries, we show that solvothermally grown PPF-5 selectively nucleates and grows as stacked crystalline sheets with preferential (001), (111), and (110) crystallographic orientations. Furthermore, variations in the synthesis temperature produce modified stack morphologies that correlate with changes in the surface-nucleated PPF-5 photoluminescence.

Mechanism of Preferential Adsorption of SO2 into Two Microporous Paddle Wheel Frameworks M(bdc)(ted)0.5

The selective adsorption of a corrosive gas, SO$_2$, into two microporous pillared paddle-wheel frameworks M(bdc)(ted)0.5 [M = Ni, Zn; bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine] is studied by volumetric adsorption measurements and a combination of in-situ infrared spectroscopy and ab initio density functional theory (DFT) calculations. The uptake of SO$_2$ in M(bdc)(ted)0.5 at room temperature is quite significant, 9.97 mol/kg at 1.13 bar. The major adsorbed SO$_2$ molecules contributing to the isotherm measurements are characterized by stretching bands at 1326 and 1144 cm$^{-1}$. Theoretical calculations including van der Waals interactions (based on vdW-DF) suggest that two adsorption configurations are possible for these SO$_2$ molecules. One geometry involves an SO$_2$ molecule bonded through its sulfur atom to the oxygen atom of the paddle-wheel building unit and its two oxygen atoms to the C-H groups of the organic linkers by formation of hydrogen bonds. Such a configuration results in a distortion of the benzene rings, which is consistent with the experimentally observed shift of the ring deformation mode. In the other geometry, SO$_2$ establishes hydrogen bonding with -CH$_2$ group of the ted linker through its two oxygen atoms simultaneously. The vdW-DF-simulated frequency shifts of the SO$_2$ stretching bands in these two configurations are similar and in good agreement with spectroscopically measured values of physisorbed SO$_2$.In addition, the IR spectra reveal the presence of another minor species, characterized by stretching modes at 1242 and 1105 cm$^{-1}$ and causing significant perturbations of MOFs vibrational modes (CH$_x$ and carboxylate groups). This species is more strongly bound, requiring a higher temperature ($\sim$150 $^\circ$C) to remove it than for the main physisorbed species.

Kinetic and mechanistic studies on reactions of diruthenium(ii,iii) with biologically relevant reducing agents

Diruthenium(ii,iii)-tetracarboxylates have shown promising anticancer properties as metallotherapeutics. On the basis of the role that bio-reducing agents may play on the mode of action of ruthenium-based anticancer drugs, we performed detailed kinetic studies on the reaction of ascorbic acid and glutathione with the [Ru2(RCOO)4](+) paddlewheel framework by using the non-drug, diaqua complex ion [Ru2(CH3COO)4(H2O)2](+). In the presence of the reducing agents, the diaqua-Ru2 species first undergo a ligand substitution reaction by which the axially-coordinated water is displaced by the reducing agent. In both cases, this reaction is followed by an intra-molecular electron transfer process during which the metal-metal center is reduced from Ru2(5+) to Ru2(4+) and the reducing agent is oxidized. Product analyses were performed with the application of ESI-MS and (1)H-NMR techniques. Rate and activation parameters are reported for the different reaction steps.

Stability and Hydrolyzation of Metal Organic Frameworks with Paddle-Wheel SBUs upon Hydration

Instability of most prototypical metal organic frameworks (MOFs) in the presence of moisture is always a limita- tion for industrial scale development. In this work, we examine the dissociation mechanism of microporous paddle wheel frameworks M(bdc)(ted)0.5 [M=Cu, Zn, Ni, Co; bdc= 1,4-benzenedicarboxylate; ted= triethylenediamine] in controlled humidity environments. Combined in-situ IR spectroscopy, Raman, and Powder x-ray diffraction measurements show that the stability and modification of isostructual M(bdc)(ted)0.5 compounds upon exposure to water vapor critically depend on the central metal ion. A hydrolysis reaction of water molecules with Cu-O-C is observed in the case of Cu(bdc)(ted)0.5. Displacement reactions of ted linkers by water molecules are identified with Zn(bdc)(ted)0.5 and Co(bdc)(ted)0.5. In contrast,. Ni(bdc)(ted)0.5 is less suscept- ible to reaction with water vapors than the other three compounds. In addition, the condensation of water vapors into the framework is necessary to initiate the dissociation reaction. These findings, supported by supported by first principles theoretical van der Waals density functional (vdW-DF) calculations of overall reaction enthalpies, provide the necessary information for de- termining operation conditions of this class of MOFs with paddle wheel secondary building units and guidance for developing more robust units.

Thermodynamics of Axial Substitution and Kinetics of Reactions with Amino Acids for the Paddlewheel Complex Tetrakis(acetato)chloridodiruthenium(II,III)

The known paddlewheel, tetrakis(acetato)chloridodiruthenium(II,III), offers a versatile synthetic route to a novel class of antitumor diruthenium(II,III) metallo drugs, where the equatorial ligands are nonsteroidal anti-inflammatory carboxylates. This complex was studied here as a soluble starting prototype model for antitumor analogues to elucidate the reactivity of the [Ru(2)(CH(3)COO)(4)](+) framework. Thermodynamic studies on equilibration reactions for axial substitution of water by chloride and kinetic studies on reactions of the diaqua complexes with the amino acids glycine, cysteine, histidine, and tryptophan were performed. The standard thermodynamic reaction parameters ΔH°, ΔS°, and ΔV° were determined and showed that both of the sequential axial substitution reactions are enthalpy driven. Kinetic rate laws and rate constants were determined for the axial substitution reactions of coordinated water by the amino acids that gave the corresponding aqua(amino acid)-Ru(2) substituted species. The results revealed that the [Ru(2)(CH(3)COO)(4)](+) paddlewheel framework remained stable during the axial ligand substitution reactions and was also mostly preserved in the presence of the amino acids.

First-Principles Study of Electronic Structure and Hydrogen Adsorption of 3d Transition Metal Exposed Paddle Wheel Frameworks

Open-site paddle wheels, comprised of two transition metals bridged with four carboxylate ions, have been widely used for constructing metal–organic frameworks with large surface area and high binding energy sites. Using first-principles density functional theory calculations, we have investigated atomic and electronic structures of various 3d transition metal paddle wheels before and after metal exposure and their hydrogen adsorption properties at open metal sites. Notably, the hydrogen adsorption is impeded by covalent metal–metal bonds in early transition metal paddle wheels from Sc to Cr and by the strong ferromagnetic coupling of diatomic Mn and Fe in the paddle wheel configurations. A significantly enhanced H2 adsorption is predicted in the nonmagnetic Co2 and Zn2 paddle wheel with the binding energy of ∼0.2 eV per H2. We also propose the use of two-dimensional Co2 and Zn2 paddle wheel frameworks that could have strongly adsorbed dihydrogen up to 1.35 wt % for noncryogenic hydrogen storage applications.

Recent advances in porphyrinic metal–organic frameworks: materials design, synthetic strategies, and emerging applications

This highlight presents a review of porphyrin paddlewheel frameworks (PPFs) created using porphyrin metalloligands and paddlewheel secondary building units. The combination of these two components, along with dipyridyl pillaring linkers, results in the assembly of 25 PPFs. We describe the topology control exhibited in this series by considering the preferred coordination geometry of the porphyrin building blocks, the length and steric effects of the pillars, and the use of sequential self-assembly. These PPFs and related porphyrinic metal–organic frameworks are emerging as important materials for applications such as heterogeneous catalysis, gas storage, and light harvesting.

3,5-Lutidine coordinated zinc(II) aryl carboxylate complexes: Precursors for zinc(II) oxide

The reaction of Zn( κ 2O,O′–OAc) 2·2H 2O with two equiv of 3,5-lutidine in methanol at room temperature for 12 h afforded [Zn(OAc) 2(3,5-lutidine) 2]· H 2O ( 1) in 91% yield. The acetate exchange reaction of 1 with two equiv of aryl carboxylic acids in methanol at room temperature for 12 h afforded [Zn( μ 2- κ 1O: κ 1O′–O 2CAr) 2(3,5-lutidine)] 2 [Ar = C 6H 5 ( 2) and C 6H 4Me-3 ( 3)], [Zn(OC(O)C 6H 4Me-2) 2(3,5-lutidine) 2] ( 4) and [Zn( κ 2O,O′−O 2CC 6H 4Me-4) 2(3,5-lutidine) 2] ( 5) in ⩾90% yield. Complexes 1– 5 were characterized by microanalytical, IR, solution ( 1H and 13C) and solid-state cross-polarization magic angle spinning 13C NMR and X-ray diffraction data. The zinc atom in 1 is surrounded by nitrogen atom of two 3,5-lutidine and oxygen atom of two monodentate acetate moiety and thus attains a tetrahedral geometry. One of the acetate moieties is hydrogen bonded with a water molecule in the crystal lattice. Complexes 2 and 3 possess a dinuclear paddlewheel framework with a square pyramidal geometry around the zinc atom whereas 4 and 5 are mononuclear species with the zinc atom in tetrahedral and an octahedral geometry, respectively. Thermogravimetric analyses of 2– 5 suggested ZnO as the decomposed product followed by the confirmation from the powder X-ray diffraction patterns. Enormous gas evolution resulting in porous ZnO during thermal decomposition was evidenced from scanning electron microscopic images.

Origin of Enhanced Dihydrogen-Metal Interaction in Carboxylate BridgedCu2–Paddle-Wheel Frameworks

The experimentally observed enhancement of hydrogen adsorption in Cu2-tetracarboxylate paddle-wheel frameworks is investigated by ab initio density-functional theory calculations. We reveal that the puzzling enhancement is due to the effective orbital coupling between the occupied H2 σ and the unoccupied Cu 4s-derived states. The nontrivial dihydrogen-metal σ-s interaction is enabled by a strong localization of the Cu 4s orbital after hybridizing with the neighboring oxygen 2p orbitals. Based on this understanding, we predict that the dihydrogen-metal interaction can be further increased by alloying Cu with s-orbital element Zn or Mg.

Metal−Organic Framework Assembled from T-Shaped and Octahedral Nodes: A Mixed-Linker Strategy To Create a Rare Anatase TiO2 Topology

A novel porphyrin paddlewheel framework (PPF-25), assembled from a zinc paddlewheel cluster and mixed linkers (4,4'-bipyridyl; zinc 5,15-di(4-carboxyphenyl)-10,20-diphenylporphyrin), has been synthesized and structurally characterized. T-shaped organometallic nodes are generated, and the resulting structure is closely related to anatase, a polymorph of TiO(2).

Structural Variation in Porphyrin Pillared Homologous Series: Influence of Distinct Coordination Centers for Pillars on Framework Topology

A new series of porphyrin paddlewheel frameworks (PPFs) has been assembled from 5,10,15,20-tetrakis(4-carboxyl)-21H,23H-porphine (TCPP), Zn(NO3)2·6H2O, and organic pillars such as N,N′-di-(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNI) and 3,6-di-4-pyridyl-1,2,4,5-tetrazine (DPT). Here we report the synthesis and structural characterization of five new PPFs based on 2D porphyrin paddlewheel grid. In this homologous series, the stacking patterns of such 2D porphyrin sheets are varied and exhibit two new structures, namely, bilayer and interpenetrated AA stacking pattern, in addition to the ABBA pattern previously observed.