Low temperature synthesis study of metal-organic framework CPO-27 : investigating metal, solvent and base effects down to -78 °C

We thank the EPSRC (EP/K005499/1) (EP/K503162/1) for their financial support of this project and the EPSRC Capital for Great Technologies (EP/L017008/1).CPO-27-M (M = Co, Mg, Ni, Zn) metal-organic frameworks have been successfully synthesized at temperatures down to -78 °C in a range of solvent systems and their crystallinity and morphology analyzed by powder X-ray diffraction and scanning electron microscopy. CPO-27-Mg and -Zn could be synthesized at lower temperatures using MeOH-NaOH as the solvent with CPO-27-Zn showing the most crystalline material at -78 °C. CPO-27-Zn afforded the most crystalline samples of all studies in MeOH-TEA. However, in MeOH a non-porous monomeric [Zn(H2dhtp)(H2O)2] complex was formed when no base was present. In THF with base (NaOH, TEA) the reaction produced crystalline MOFs in a controlled and stable manner at low temperatures, whilst the reagents were insoluble in THF at low temperature when no base was present. SEM was used to analyze the morphologies of the products.PostprintPeer reviewe

A single crystal study of CPO-27 and UTSA-74 for nitric oxide storage and release

Funding: UK EPSRC EP/K005499/1, EP/K503162, and EP/L017008/1).Single crystal CPO-27-Mg, -Zn and its structural isomer UTSA-74 have been prepared through use of acid modulators; salicylic acid and benzoic acid, respectively. Salicylic acid directed the synthesis of CPO-27-Mg/Zn whereas benzoic acid the synthesis of UTSA-74. Through “in-house” SCXRD, DMF was seen to bind to the Zn2+ and water to the Mg2+ metal sites in CPO-27-M. Although the synthesis conditions were analogous for UTSA-74, DMF is too large to bind due to the proximity of the binding sites. A dissolution–recrystallisation transformation was examined from UTSA-74 to CPO-27-Zn. The release of nitric oxide was measured for each material.PostprintPeer reviewe

Mixed metal-organic framework mixed-matrix membranes : insights into simultaneous moisture-triggered and catalytic delivery of nitric oxide using cryo-scanning electron microscopy

Funding: This work was supported by the European Research Council grant ADOR (Advanced Grant 787073). The authors acknowledge the EPSRC Light Element Analysis Facility Grant (EP/T019298/1) and the EPSRC Strategic Equipment Resource Grant (EP/R023751/1).The fundamental chemical and structural diversity of metal–organic frameworks (MOFs) is vast, but there is a lack of industrial adoption of these extremely versatile compounds. To bridge the gap between basic research and industry, MOF powders must be formulated into more application-relevant shapes and/or composites. Successful incorporation of varying ratios of two different MOFs, CPO-27-Ni and CuBTTri, in a thin polymer film represents an important step toward the development of mixed MOF mixed-matrix membranes. To gain insight into the distribution of the two different MOFs in the polymer, we report their investigation by Cryo-scanning electron microscopy (Cryo-SEM) tomography, which minimizes surface charging and electron beam-induced damage. Because the MOFs are based on two different metal ions, Ni and Cu, the elemental maps of the MOF composite cross sections clearly identify the size and location of each MOF in the reconstructed 3D model. The tomography run was about six times faster than conventional focused ion beam (FIB)-SEM and the first insights to image segmentation combined with machine learning could be achieved. To verify that the MOF composites combined the benefits of rapid moisture-triggered release of nitric oxide (NO) from CPO-27-Ni with the continuous catalytic generation of NO from CuBTTri, we characterized their ability to deliver NO individually and simultaneously. These MOF composites show great promise to achieve optimal dual NO delivery in real-world medical applications.Publisher PDFPeer reviewe

Hierarchical MTW zeolites in tetrahydropyranylation of alcohols : comparison of bottom-up and top-down methods

Authors thank the Czech Science Foundation for financial support (17-06524Y). H.P. and J.Y. thank to the 111 project of the Ministry of Education of China (B17020). M.M. and S.M.V. acknowledge the support of EPSRC grant EP/K025112/1 and Capital for Great Technologies Grant EP/L017008/1.Despite a widespread application of zeolites in catalysis, these microporous materials still suffer from a low accessibility of active sites located deep in crystals due to limited size of channels (< 1 nm). Here, we prepared a series of micro-mesoporous zeolites with MTW topology and similar Si/Al molar ratio (50). Two topical approaches were applied here: i. bottom-up synthesis with a surfactant-SDA leading to so-called nanosponge material; ii. top-down desilication of bulk crystals by NaOH solution in the presence of tetraalkylammonium cations (TAA+). Prepared materials were characterized by powder X-ray diffraction, sorption of nitrogen, adsorption of pyridine and di-tert-butyl-pyridine followed by FTIR, solid state 27Al NMR, ICP-OES, SEM, TEM, and STEM-EDS. It was found that the desilication of MTW in the presence of TAA+ proceeds in different pathway compared to well-studied MFI. This variance was attributed to the different dimensionality of their channel systems (1D vs. 3D). Materials were tested in tetrahydropyranylation of alcohols differing in a chain length and degree of branching. The nanosponge MTW shows generally very good performance. Nevertheless, in cases of the branched alcohols MTW materials desilicated in the presence of TAA+ exhibited comparable or even higher activity than nanosponge based on TOF values. Therefore, desilicated MTW presents cheaper and equally or more effective catalyst compared to nanosponge material with the same topology.PostprintPeer reviewe

In situ single-crystal X-ray diffraction studies of physisorption and chemisorption of SO2 within a metal-organic framework and its competitive adsorption with water

Funding: The authors are also grateful for financial assistancefrom the ERC under advanced grant 787073, the EPSRC for a studentship (EP/N509759/1) and support via the Collaborative Computational Projecton NMR Crystallography CCP-NC (EP/T02662/1), and the CRITICAT Centre for Doctoral Training (EP/L016419/1).Living on an increasingly polluted planet, the removal of toxic pollutants such as sulfur dioxide (SO2) from the troposphere and power station flue gas is becoming more and more important. The CPO-27/MOF-74 family of metal–organic frameworks (MOFs) with their high densities of open metal sites is well suited for the selective adsorption of gases that, like SO2, bind well to metals and have been extensively researched both practically and through computer simulations. However, until now, focus has centered upon the binding of SO2 to the open metal sites in this MOF (called chemisorption, where the adsorbent–adsorbate interaction is through a chemical bond). The possibility of physisorption (where the adsorbent–adsorbate interaction is only through weak intermolecular forces) has not been identified experimentally. This work presents an in situ single-crystal X-ray diffraction (scXRD) study that identifies discrete adsorption sites within Ni-MOF-74/Ni-CPO-27, where SO2 is both chemisorbed and physisorbed while also probing competitive adsorption of SO2 of these sites when water is present. Further features of this site have been confirmed by variable SO2 pressure scXRD studies, DFT calculations, and IR studies.Publisher PDFPeer reviewe

Surface functionalized metal-organic frameworks for binding coronavirus proteins

This work was supported by University of St Andrews Restarting Research Funding Scheme (SARRF), funded through the SFC grant reference SFC/AN/08/020 (XRR064) and European Research Council grant ADOR (Advanced Grant 787073). The authors acknowledge the EPSRC Light Element Analysis Facility Grant (EP/T019298/1) and the EPSRC Strategic Equipment Resource Grant (EP/R023751/1).Since the outbreak of SARS-CoV-2, a multitude of strategies have been explored for the means of protection and shielding against virus particles: filtration equipment (PPE) has been widely used in daily life. In this work, we explore another approach in the form of deactivating coronavirus particles through selective binding onto the surface of metal–organic frameworks (MOFs) to further the fight against the transmission of respiratory viruses. MOFs are attractive materials in this regard, as their rich pore and surface chemistry can easily be modified on demand. The surfaces of three MOFs, UiO-66(Zr), UiO-66-NH2(Zr), and UiO-66-NO2(Zr), have been functionalized with repurposed antiviral agents, namely, folic acid, nystatin, and tenofovir, to enable specific interactions with the external spike protein of the SARS virus. Protein binding studies revealed that this surface modification significantly improved the binding affinity toward glycosylated and non-glycosylated proteins for all three MOFs. Additionally, the pores for the surface-functionalized MOFs can adsorb water, making them suitable for locally dehydrating microbial aerosols. Our findings highlight the immense potential of MOFs in deactivating respiratory coronaviruses to be better equipped to fight future pandemics.Publisher PDFPeer reviewe

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Novel metal-organic frameworks and polymer formulations for biomedical applications

The research presented in this thesis aimed to develop new metal-organic framework (MOF) materials and MOF composites for biomedical applications. New synthesis methods of CPO-27-M (M = Co, Mg, Ni, Zn) were explored with particular focus on the formation of single crystals. Low temperature syntheses showed formation of crystalline CPO-27-Zn down to 195 K. Single crystals of CPO-27-Mg and -Zn were afforded from a modulated solvothermal synthesis using salicylic acid, and an isomorph called UTSA-74 was obtained when benzoic acid was used. All three materials proved suitable for structural analysis through in-house single crystal X-ray diffraction (SXRD). The concept of modulation chemistry was employed to control the crystallite size and a novel mixed-linker synthesis approach yielded large single crystals of CPO-27-Ni. All materials displayed phase pure through PXRD, compositional analysis, TGA, and electron microscopy methods. Large single crystals of CPO-27-Ni were used in synchrotron based in situ gas cell experiments to probe the adsorption of nitric oxide (NO). An efficient activation protocol was developed leading to a dehydrated structure after just 4 h. For the first time, single crystal structure models of CPO-27-Ni were presented of the as-synthesised, dehydrated, and subsequently NO loaded conformation. A multifaceted study of the interactions between CPO-27-Ni and polyurethane (PU) was conducted to rationalise the NO release performance of composite films used as proxy for antibacterial coatings. From a range of MOF loadings (5, 10, 20, and 40 wt%) an optimal MOF loading of 10 wt% was identified, where highest amounts of NO with a potent bactericidal efficacy are released. Molecular dynamics simulations and FIB-SEM techniques revealed an excellent compatibility and connectivity between the MOF/PU interface. Reconstruction of the microstructure of a high MOF loading composite (40 wt%) showed that the MOF exhibits a highly connected network, which was proposed to contribute to a more tortuous gas transport. This also may be the reason for reduced NO efficiencies and tensile strengths seen in high MOF loading composites (20−40 wt%). The Kolbe-Schmitt reaction was utilised for the synthesis of new functional linkers. Two methylated 4,6-dihydroxyisophthalic acids were obtained and used to generate new MOF materials for storage and release of NO. The 2,3-dihydroxyterephthalic acid linker was used to synthesise a new MOF system that has properties of isoreticular chemistry and is systematically named SIMOF-0, 1, 2, and 3 (St Andrews Isoreticular MOF). All four phases were characterised through SXRD. SIMOF-3 displayed an interesting, pillared crystal structure with indication of flexibility. A drug loading study using flutamide showed a prolonged release of the drug over the course of 72 h and solid-state NMR indicated that the drug may be adsorbed in the pore system of the MOF. SIMOF-1 was used as a precursor for other materials. In a ‘regeneration’ synthesis approach, a sample of SIMOF-1 was transformed to phase pure SIMOF-3."[T]his work was supported by the EPSRC (grant number EP/K005499/1) and the ERC (grant number 787073)." -- Acknowledgement