Boosting Antibacterial Photodynamic Therapy in a Nanosized Zr MOF by the Combination of Ag NP Encapsulation and Porphyrin Doping.

Antibacterial photodynamic therapy (aPDT) is regarded as one of the most promising antibacterial therapies due to its nonresistance, noninvasion, and rapid sterilization. However, the development of antibacterial materials with high aPDT efficacy is still a long-standing challenge. Herein, we develop an effective antibacterial photodynamic composite UiO-66-(SH)2@TCPP@AgNPs by Ag encapsulation and 4,4',4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (TCPP) dopant. Through a mix-and-match strategy in the self-assembly process, 2,5-dimercaptoterephthalic acid containing -SH groups and TCPP were uniformly decorated into the UiO-66-type framework to form UiO-66-(SH)2@TCPP. After Ag(I) impregnation and in situ UV light reduction, Ag NPs were formed and encapsulated into UiO-66-(SH)2@TCPP to get UiO-66-(SH)2@TCPP@AgNPs. In the resulting composite, both Ag NPs and TCPP can effectively enhance the visible light absorption, largely boosting the generation efficiency of reactive oxygen species. Notably, the nanoscale size enables it to effectively contact and be endocytosed into bacteria. Consequently, UiO-66-(SH)2@TCPP@AgNPs show a very high aPDT efficacy against Gram-negative and Gram-positive bacteria as well as drug-resistant bacteria (MRSA). Furthermore, the Ag NPs were firmly anchored at the framework by the high density of -SH moieties, avoiding the cytotoxicity caused by the leakage of Ag NPs. By in vitro experiments, UiO-66-(SH)2@TCPP@AgNPs show a very high antibacterial activity and good biocompatibility as well as the potentiality to promote cell proliferation.

Zr-Based Metal-Organic Frameworks with Intrinsic Peroxidase-Like Activity for Ultradeep Oxidative Desulfurization: Mechanism of H2O2 Decomposition.

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H2O2 as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol-1) and an extraordinarily high TOF value (42.7 h-1) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH(H2O) catalytic sites decorated in MOF-808. The superoxide radicals (•O2-) and hydroxyl radicals (•OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Brönsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH(H2O) groups promoting the H2O2 decomposion in to both •O2- and •OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.

Intrinsic catalytic activity of rhodium nanoparticles with respect to reactive oxygen species scavenging: implication for diminishing cytotoxicity.

Noble metal nanoparticles (NPs) and their hybrids have demonstrated a strong potential to mimic the catalytic activity of natural enzymes and diminish oxidative stress. There is a large space to explore the intrinsic catalytic activity of Rh NPs with respect to reactive oxygen species (ROS) scavenging. We found that Rh NPs can quench H2O2, •OH, O2•-, 1O2 and inhibit lipid peroxidation under physiological conditions. In vitro cell experiments proved that Rh NPs have great biocompatibility and protect cells from oxidative damage caused by H2O2. This study can provide important insights that could inform future biological applications.

MOF-808: A Metal-Organic Framework with Intrinsic Peroxidase-Like Catalytic Activity at Neutral pH for Colorimetric Biosensing.

Natural enzyme mimetics with high catalytic activity at nearly neutral pH values are highly desired for their applications in biological systems. Herein for the first time a stable MOF, namely MOF-808, has been shown to possess high intrinsic peroxidase-like catalytic activity under acidic, neutral, and alkaline conditions. As a novel peroxidase mimetic, MOF-808 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine when H2O2 serves as oxidant, accompanied by a significant color variation in the solution. The catalytic activity and the color variation were greatly dependent on H2O2 concentration, and thus MOF-808 can be applied to the colorimetric sensing of H2O2. The H2O2 detection limit is 4.5 µM, and the linear range is 10 µM to 15 mM. In view of the significant inhibition effect produced by ascorbic acid, a facile and sensitive approach for colorimetric sensing of ascorbic acid was successfully established. The AA detection limit is 15 µM, and the linear range is 30-1030 µM. Further investigation found that the catalytic activity of MOF-808 could be mainly ascribed to the Zr-OH(OH2) groups. Such active Zr-OH(OH2) groups can be effectively shielded by gluconic acid, and subsequently the catalytic activity of MOF-808 was significantly suppressed. With these findings, a facile and selective colorimetric assay for glucose sensing has been successfully explored via combination of the glucose oxidation with the TMB oxidation. The glucose detection limit is 5.7 µM, and the linear range is 5.7-1700 µM. MOF-808 is one of the best colorimetric biosensors among the peroxidase mimics reported for H2O2, AA, and glucose detection.

Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material.

Selective separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties. We report a microporous material [Zn(dps)2(SiF6)] (UTSA-300, dps = 4,4'-dipyridylsulfide) with two-dimensional channels of about 3.3 Å, well-matched for the molecular sizes of C2H2. After activation, the network was transformed to its closed-pore phase, UTSA-300a, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF62- pillars. Strong C-H···F and π-π stacking interactions are found in closed-pore UTSA-300a, resulting in shrinkage of the structure. Interestingly, UTSA-300a takes up quite a large amounts of acetylene (76.4 cm3 g-1), while showing complete C2H4 and CO2 exclusion from C2H2 under ambient conditions. Neutron powder diffraction and molecular modeling studies clearly reveal that a C2H2 molecule primarily binds to two hexafluorosilicate F atoms in a head-on orientation, breaking the original intranetwork hydrogen bond and subsequently expanding to open-pore structure. Crystal structures, gas sorption isotherms, molecular modeling, experimental breakthrough experiment, and selectivity calculation comprehensively demonstrated this unique metal-organic framework material for highly selective C2H2/CO2 and C2H2/C2H4 separation.

A metal-organic framework constructed using a flexible tripodal ligand and tetranuclear copper cluster for sensing small molecules.

A new porous metal-organic framework (MOF) {[Cu4(OH)2(tci)2(bpy)2]·11H2O} (1) based on a tetranuclear copper cluster with intracluster antiferromagnetic interactions was synthesized. Quartz crystal microbalance (QCM) sensor studies reveal sensitive and selective sensing for small molecules.

Structure and magnetic properties of a mixed-ligand copper(II) complex.

The hydrothermal synthesis of the novel complex poly[[µ2-N(1),N(4)-bis(pyridin-3-yl)naphthalene-1,4-dicarboxamide-κ(2)N(3):N(3')](µ4-phthalato-κ(4)O(1):O(1):O(1'):O(2'))copper(II)], [Cu(C8H4O4)(C22H16N4O2)]n, is described. With the phthalate ligand connecting neighbouring Cu(II) cations, an infinite one-dimensional chain is formed. Adjacent one-dimensional chains are connected by the dicarboxamide ligand, forming an intriguing two-dimensional framework. The magnetic properties and thermal stability of this complex are also described.

Photochromic hybrid containing in situ-generated benzyl viologen and novel trinuclear [Bi3Cl14]5-: improved photoresponsive behavior by the π···π interactions and size effect of inorganic oligomer.

Two new member of (V)((2n+2)/2)[Bi(2n)Cl(8n+2)] series hybrids, (BzV)2[Bi2Cl10] (1) and (BzV)5[Bi3Cl14]2·(C6H5CH2)2O (2) (where BzV(2+) = N,N'-dibenzyl-4,4'-bipyridinium and (C6H5CH2)2O = dibenzyl ether) have been obtained, and compound 2 contains an unprecedented discrete trimer [Bi3Cl14](5-) counterion. The novel in situ-synthesized symmetric viologen cation with aromatic groups on both sides of 4,4'-bipy would provide more opportunities to create π···π interactions to optimize the photochromic property of the hybrid, and different bismuthated-halide oligomers enable us to discuss the size effect in this series of compounds. Both 1 and 2 are photochromic, and their photoresponsive rate is faster than that of reported viologen-metal halide hybrids. Experimental and theoretical data illustrated that the size of the inorganic oligomer can significantly influence the photoresponsive rate of the viologen dication, and the π···π interaction behaves as not only a powerful factor to stabilize the viologen monocation radical but also the second electron-transfer pathway, from a π-conjugated substituent to a viologen cation, for the photochromic process.

Design and syntheses of electron-transfer photochromic metal-organic complexes using nonphotochromic ligands: a model compound and the roles of its ligands.

The model compound [Zn(HCOO)2(4,4'-bipy)] (1; 4,4'-bipy = 4,4'-bipyridine) is selected in this work to demonstrate the effectiveness of our previously proposed design strategy for electron-transfer photochromic metal-organic complexes. The electron-transfer photochromic behavior of 1 has been discovered for the first time. Experimental and theoretical data illustrate that the photochromism of 1 can be attributed to the electron transfer from formato to 4,4'-bipy and the formation of a radical photoproduct. The electron transfer prefers to occur between formato and 4,4'-bipy, which are combined directly by the Zn(II) atoms. A high-contrast (up to 8.3 times) photoluminescence switch occurs during the photochromic process. The similarity of photochromic behaviors among 1 and its analogues as well as viologen compounds has also been found. Photochromic studies of this model compound indicate that new electron-transfer photochromic metal-organic complexes can be largely designed and synthesized by the rational assembly of nonphotochromic electron-donating and electron-accepting ligands.

Improved photochromic properties on viologen-based inorganic-organic hybrids by using π-conjugated substituents as electron donors and stabilizers.

A series of inorganic-organic hybrid compounds L(2)(Bi(2)Cl(10)) (L = HMV(2+) = N-proton-N'-methyl-4,4'-bipyridinium for 1, L = HBzV(2+) = N-proton-N'-benzyl-4,4'-bipyridinium for 2, and L = HPeV(2+) = N-proton-N'-phenethyl-4,4'-bipyridinium for 3) have been successfully synthesized by an in situ solvothermal reaction. Compounds 1-3, with the same metal halide as anions but different asymmetric viologen molecules as cations, are ideal model compounds for investigating the detailed effect of different photochromically active molecules on the photochromic properties of the hybrids. Compound 1 shows no photochromic behavior, but compounds 2 and 3 possess photochromism and show a faster photoresponse rate than other reported viologen metal halide hybrids. Studies on the relationship between the structure and photochromic behavior clearly reveal that π-conjugated substituents could be used to improve the photoresponsibility and enrich the developed color efficiently and that the π···π interaction among organic components may not only be a powerful factor to stabilize the viologen monocation radical but also act as the second path of electron transfer from the π-conjugated substituent to the viologen cation for the photochromic process, which significantly influences the photochromic properties.

A room-temperature X-ray-induced photochromic material for X-ray detection.

A color change: X-ray-induced photochromic species are rare and can be used for detection of X-rays. A highly robust X-ray-sensitive material with the discrete structure of a metal-organic complex has been found to show both soft and hard X-ray-induced photochromism at room temperature. A new ligand-to-ligand electron-transfer mechanism was proposed to elucidate this photochromic phenomenon.

Photochromic metal complexes of N-methyl-4,4'-bipyridinium: mechanism and influence of halogen atoms.

Photochromism of N-methyl-4,4'-bipyridinium (MQ(+)) salts and their metal complexes has never been reported. A series of MQ(+) coordinated halozinc complexes [(MQ)ZnX(3)] (X = Cl (1), Br (2), I (3)) and [(MQ)ZnCl(1.53)I(1.47)](2)(MQ)ZnCl(1.68)I(1.32) (4), with better physicochemical stability than halide salts of the MQ(+) cation, have been found to exhibit different photochromic behaviors. Compounds 1-3 are isostructural, but only 1 and 2 show photochromism. Introduction of partial Cl atoms to nonphotochromic compound 3 yields compound 4, which also displays photochromism. The photochromic response of 1, 2, and 4 indicates the presence of their long-lived charge separation states, which originate from X → MQ(+) electron transfer according to ESR and XPS measurements. Studies on the influence of different coordinated halogen atoms demonstrate that the Cl atom may be a more suitable electron donor than Br and I atoms to design redox photochromic metal complexes.