Postsynthetic Modification of Metal-Organic Frameworks through Nitrile Oxide-Alkyne Cycloaddition

von Zons T, Brokmann L, Lippke J, et al. Postsynthetic Modification of Metal-Organic Frameworks through Nitrile Oxide-Alkyne Cycloaddition. INORGANIC CHEMISTRY. 2018;57(6):3348-3359.Postsynthetic modification of metal-organic frameworks is an important method to tailor their properties. We report on the nitrile oxide-alkyne cycloaddition (NOAC) as a modification tool, a reaction requiring neither strained alkynes nor a catalyst. This is demonstrated with the reaction of nitrile oxides with PEPEP-PIZOF-15 and-19 at room temperature. PIZOF-15 and-19 are porous Zr-based MOFs (BET surface areas 1740 and 960 m(2) g(-1), respectively) consisting of two mutually interpenetrating UiO-type frameworks with linkers of the type -O2C[PE-P(R-1,R-2)-EP]CO2- (P, phenylene; E, ethynylene; and R-2, side chains at the central benzene ring with R-1 = R-2 = OCH2C CH or R-1 = OCH2C CH and R-2 = O(CH2CH2O)(3)Me). Their syntheses, using benzoic acid as a modulator, and their characterization are reported herein. The propargyloxy (OCH2C CH) side chains contain the ethyne moieties needed for NOAC. Formation of nitrile oxides through oxidation of oximes in aqueous ethanolic solution in the presence of PEPEP-PIZOF-15 and -19 resulted in the reaction of 96-100% of the ethyne moieties to give isoxazoles. Thereby the framework was preserved. The type of nitrile oxide RCNO was greatly varied with R being isopentyl, tolyl, 2-pyridyl, and pentafluorophenyl. A detailed NMR spectroscopic investigation showed the formation of the 3,5-disubstituted isoxazole to be clearly favored (>96%) over that of the constitutional isomeric 3,4-disubstituted isoxazole, except for one example

A Chemiluminescent Metal–Organic Framework

The synthesis and characterization of a chemiluminescent metal–organic framework with high porosity is reported. It consists of Zr6O6(OH)4 nodes connected by 4,4′‐(anthracene‐9,10‐diyl)dibenzoate as the linker and luminophore. It shows the topology known for UiO‐66 and is therefore denoted PAP‐UiO. The MOF was not only obtained as bulk material but also as a thin film. Exposure of PAP‐UiO as bulk or film to a mixture of bis‐(2,4,6‐trichlorophenyl) oxalate, hydrogen peroxide, and sodium salicylate in a mixture of dimethyl and dibutyl phthalate evoked strong and long lasting chemiluminescence of the PAP‐UiO crystals. Time dependent fluorescence spectroscopy on bulk PAP‐UiO and, for comparison, on dimethyl 4,4′‐(anthracene‐9,10‐diyl)dibenzoate provided evidence that the chemiluminescence originates from luminophores being part of the PAP‐UiO, including the luminophores inside the crystals

On-Surface Synthesis of Highly Oriented Thin Metal-Organic Framework Films through Vapor-Assisted Conversion

Virmani E, Rotter JM, Maehringer A, et al. On-Surface Synthesis of Highly Oriented Thin Metal-Organic Framework Films through Vapor-Assisted Conversion. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. 2018;140(14):4812-4819.Controlled on-surface film growth of porous and crystalline frameworks is a central prerequisite for incorporating these materials into functional platforms and operational devices. Here, we present the synthesis of thin zirconium-based metal organic framework (MOF) films by vapor-assisted conversion (VAC). We established protocols adequate for the growth of UiO-66, UiO-66(NH2), UiO-67, and UiO-68(NH2) as well as the porous interpenetrated Zr-organic framework, PPPP-PIZOF-1, as highly oriented thin films. Through the VAC approach, precursors in a cast solution layer on a bare gold surface are reacting to form a porous continuous MOF film, oriented along the [111] crystal axis, by exposure to a solvent vapor at elevated temperature of 100 degrees C and 3 h reaction time. It was found that the concentration of dicarboxylic acid, the modulator, the droplet volume, and the reaction time are vital parameters to be controlled for obtaining oriented MOF films. Using VAC for the MOF film growth on gold surfaces modified with thiol SAMs and on a bare silicon surface yielded oriented MOF films, rendering the VAC process robust toward chemical surface variations. Ethanol sorption experiments show that a substantial part of the material pores is accessible. Thereby, the practical VAC method is an important addition to the toolbox of synthesis methods for thin MOF films. We expect that the VAC approach will open new horizons in the formation of highly defined functional thin MOF films for numerous applications

Postsynthetic Modification of Metal–Organic Frameworks through Nitrile Oxide–Alkyne Cycloaddition

Postsynthetic modification of metal–organic frameworks is an important method to tailor their properties. We report on the nitrile oxide–alkyne cycloaddition (NOAC) as a modification tool, a reaction requiring neither strained alkynes nor a catalyst. This is demonstrated with the reaction of nitrile oxides with PEPEP-PIZOF-15 and -19 at room temperature. PIZOF-15 and -19 are porous Zr-based MOFs (BET surface areas 1740 and 960 m² g^–1, respectively) consisting of two mutually interpenetrating UiO-type frameworks with linkers of the type ^–O₂C­[PE-P­(R¹,R²)-EP]­CO₂^– (P, phenylene; E, ethynylene; R¹ and R², side chains at the central benzene ring with R¹ = R² = OCH₂CCH or R¹ = OCH₂CCH and R² = O­(CH₂CH₂O)₃Me). Their syntheses, using benzoic acid as a modulator, and their characterization are reported herein. The propargyloxy (OCH₂CCH) side chains contain the ethyne moieties needed for NOAC. Formation of nitrile oxides through oxidation of oximes in aqueous ethanolic solution in the presence of PEPEP-PIZOF-15 and -19 resulted in the reaction of 96–100% of the ethyne moieties to give isoxazoles. Thereby the framework was preserved. The type of nitrile oxide RCNO was greatly varied with R being isopentyl, tolyl, 2-pyridyl, and pentafluorophenyl. A detailed NMR spectroscopic investigation showed the formation of the 3,5-disubstituted isoxazole to be clearly favored (≥96%) over that of the constitutional isomeric 3,4-disubstituted isoxazole, except for one example

Evaluation of a Flow Cytometry-Based Assay for Natural Killer Cell Activity in Clinical Settings

Natural killer (NK) cells are not only important in first line defence against viral and bacterial infections, but also in immune surveillance of malignant cells and thus NK cell cytotoxicity is primary indicator of immune function. Although chromium release assay is recognized as 'gold standard' for measuring NK cell activity, it has disadvantages like use of radioactive compounds, poor loading and high spontaneous release. It is difficult to perform this assay in clinical laboratory because of difficulties with disposal of radioactive waste and standardization problems. We describe a flow cytometry-based assay for the measurement of NK cell activity by incorporating fluorescent dye, DiO, into membranes of target cells. NK cell activity was measured at baseline, 1 and 4 weeks follow-up in 20 normal healthy individuals on a dietary supplement immunomodulator to enhance NK cell function. Mean baseline NK cell activity percentage (21.5; SD = 9.3) increased significantly to a maximum level at 1 week (31.3%; SD = 7.9; P = 0.007) and then returned to baseline level at 4 weeks (21.5; SD = 8.3). An important feature of flow cytometry-based assays is its ability to discriminate effector cells from target cells, and potential for explaining molecular interactions underlying target cell lysis. Under clinical settings, this assay will be of interest for frequently monitoring immunological status of patients on treatment for various diseases that affect their immune status. The assay is easy to perform without using radioactive material and thus could become a tool for monitoring pathogenesis and immune reconstitution

Expanding the Group of Porous Interpenetrated Zr-Organic Frameworks (PIZOFs) with Linkers of Different Lengths

A Zr-based MOF of the PIZOF type, which consists of two independent and mutually interpenetrating UiO-type frameworks with [Zr₆O₄(OH)₄(O₂C)₁₂] nodes, does not only form with a PEPEP dicarboxylic acid (P = phenylene, E = ethynylene). Also dicarboxylic acids with the shorter PPPP and PEPP spacers were found to give PIZOFs, denoted PPPP-PIZOF and PEPP-PIZOF, respectively. Reducing the spacer length even further to a PEEP segment caused a switchover to the formation of a UiO framework. The hysteresis in the Ar sorption curve of PEPP-PIZOF-1 and the slightly too large amount of combustion residue from PPPP-PIZOF-1 suggest structural defects. These hint at a mismatch between the requirement of the optimal linker length for PIZOF formation and the lengths of the PEPP and PPPP dicarboxylates. Nevertheless, these dicarboxylates prefer the formation of a PIZOF over the formation of a UiO structure. PEPEP-PIZOF-2, PPPP-PIZOF-1, and PEPP-PIZOF-1 are stable in air up to 325, 350, and 300 °C, respectively, and have BET surface areas of 2350, 2020, and 1650 m² g^–1, respectively. PEPEP-PIZOFs, even those with very hydrophilic oligo­(ethylene glycol) side chains on the linkers, are very stable in water and also during drying from a water-wetted state. On the contrary, PEPP-PIZOF-1 and PPPP-PIZOF-1 that had been exposed to water required exchange of water for ethanol before drying to mostly preserve the framework. The results emphasize the importance of differentiating between framework damage caused through hydrolysis in water and through drying from a water-wetted state. The sensitivity of PEPP-PIZOF-1 and PPPP-PIZOF-1 against drying from a water-wetted state may be the consequence of defects. The drying stability of water-wetted PEPEP-PIZOFs lets us suggest that reversible bending of the linkers contributes to the stability of the PEPEP-PIZOFs