Kinetic control of interpenetration in Fe-biphenyl-4,4′-dicarboxylate metal-organic frameworks by coordination and oxidation modulation

Phase control in the self-assembly of metal-organic frameworks (MOFs) is often a case of trial and error; judicious control over a number of synthetic variables is required to select the desired topology and control features such as interpenetration and defectivity. Herein, we present a comprehensive investigation of self-assembly in the Fe-biphenyl-4,4′-dicarboxylate system, demonstrating that coordination modulation can reliably tune between the kinetic product, non-interpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). Density functional theory simulations reveal that correlated disorder of the terminal anions on the metal clusters results in hydrogen-bonding between adjacent nets in the interpenetrated phase and is the thermodynamic driving force for its formation. Coordination modulation slows self-assembly and therefore selects the thermodynamic product MIL-126(Fe), while offering fine control over defectivity, inducing mesoporosity, but electron microscopy shows MIL-88D(Fe) persists in many samples despite not being evident by diffraction. Interpenetration control is also demonstrated using the 2,2′-bipyridine-5,5′-dicarboxylate linker; it is energetically prohibitive for it to adopt the twisted conformation required to form the interpenetrated phase, although multiple alternative phases are identified due to additional coordination of Fe cations to its N-donors. Finally, we introduce oxidation modulation – the use of metal precursors in different oxidation states to that found in the final MOF – to kinetically control self-assembly. Combining coordination and oxidation modulation allows the synthesis of pristine MIL-126(Fe) with BET surface areas close to the predicted maximum for the first time, suggesting that combining the two may be a powerful methodology for the controlled self-assembly of high-valent MOFs

Modulated self-assembly of three flexible Cr(III) PCPs for SO2 adsorption and detection

Modulated self-assembly protocols are used to develop facile, HF-free syntheses of the archetypal flexible PCP, MIL-53(Cr), and novel isoreticular analogues MIL-53(Cr)-Br and MIL-53(Cr)-NO2. All three PCPs show good SO2 uptake (298 K, 1 bar) and high chemical stabilities against dry and wet SO2. Solid-state photoluminescence spectroscopy indicates all three PCPs exhibit turn-off sensing of SO2, in particular MIL-53(Cr)-Br, which shows a 2.7-fold decrease in emission on exposure to SO2 at room temperature, indicating potential sensing applications

City of Hitchcock Comprehensive Plan 2020-2040

Hitchcock is a small town located in Galveston County (Figure 1.1), nestled up on the Texas Gulf Coast. It lies about 40 miles south-east of Houston. The boundaries of the city encloses an area of land of 60.46 sq. miles, an area of water of 31.64 sq. miles at an elevation just 16 feet above sea level. Hitchcock has more undeveloped land (~90% of total area) than the county combined. Its strategic location gives it a driving force of opportunities in the Houston-Galveston Region.The guiding principles for this planning process were Hitchcock’s vision statement and its corresponding goals, which were crafted by the task force. The goals focus on factors of growth and development including public participation, development considerations, transportation, community facilities, economic development, parks, and housing and social vulnerabilityTexas Target Communitie

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance.

Investment in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing in Africa over the past year has led to a major increase in the number of sequences that have been generated and used to track the pandemic on the continent, a number that now exceeds 100,000 genomes. Our results show an increase in the number of African countries that are able to sequence domestically and highlight that local sequencing enables faster turnaround times and more-regular routine surveillance. Despite limitations of low testing proportions, findings from this genomic surveillance study underscore the heterogeneous nature of the pandemic and illuminate the distinct dispersal dynamics of variants of concern-particularly Alpha, Beta, Delta, and Omicron-on the continent. Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve while the continent faces many emerging and reemerging infectious disease threats. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Kinetic phase-tuning in the synthesis of iron and chromium metal-organic frameworks

Metal-Organic Frameworks (MOFs) are solid-state materials which display exceptional permanent porosity and unprecedented structural diversity. These unique properties have garnered significant attention for potential applications, including gas storage, catalysis, and drug delivery. This thesis focuses on kinetic phase-tuning in the synthesis of Fe and Cr-MOFs and aims to explore novel strategies for phase-control, as well as assessing their biocompatibility for therapeutic applications such as drug delivery. The introduction chapter discusses reticular chemistry and other key concepts relating to the synthesis of MOFs, as well as exploring some of the synthetic methods employed for high valent MOFs and their subsequent development for biomedical applications. In Chapter 2, a comprehensive investigation of self-assembly in the Fe–biphenyl-4,4′-dicarboxylate system is conducted by exploring the use of coordination modulation - the addition of monotopic ligands which can compete with the bridging linkers during the self-assembly process - as a tool for phase control. It was found that coordination modulation can reliably tune between the kinetic product, non-interpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). Coordination modulation slows self-assembly and therefore selects the thermodynamic product MIL-126(Fe), while also offering fine control over defectivity and inducing mesoporosity. Interpenetration control is also demonstrated using the 2,2′-bipyridine-5,5′-dicarboxylate linker; it is energetically prohibitive for it to adopt the twisted conformation required to form the interpenetrated phase, although multiple alternative phases are identified due to additional coordination of Fe cations to its N donors. In addition, oxidation modulation - the deliberate use of metal precursors in different oxidation states to that found in the resulting MOF - is employed as a novel method to kinetically control self-assembly. Combining coordination and oxidation modulation enables the synthesis of pristine MIL-126(Fe) with surface areas close to the predicted maximum for the first time, suggesting that combining the two may be a powerful methodology for the controlled self-assembly of high-valent MOFs. Chapter 3 details work conducted on the synthesis of Fe-terephthalate MOFs, utilising the two methodologies that were developed in the previous chapter - coordination and oxidation modulation - to control the phase that crystallises. An extensive crystallisation study was performed by variation of key parameters such as synthesis time, temperature, quantity of modulator, and Fe precursor. The results have established synthetic routes to various MOFs containing the common metal hydroxide chain and oxo-centred trigonal secondary building units (SBUs), as well as gaining insight into the kinetic and thermodynamic relationships between the different phases. The thermodynamic relationship between two topologically identical frameworks - MOF-235(Fe) and MIL-88B(Fe) – could subsequently be ascertained, with MOF-235(Fe) being the thermodynamically preferred product when using chloride salts as the metal precursor. MOF-235(Fe) differs from MIL-88B(Fe) in that it contains non-coordinating [FeCl4]- counterions, and as such a novel analogue of MOF-235(Fe) could be obtained when using Fe(BF4)2 which provides suitable [BF4]- anions. The role of the counterion was found to be crucial for directing the structure and has broad implications for other MOF syntheses. In addition, these synthetic efforts yielded suitably large crystals of a prototypical flexible MOF - MIL-53(Fe) - which enabled study of its flexibility by single-crystal X-ray diffraction. In Chapter 4 the synthesis of Cr-MOFs is explored using coordination modulation as a strategy for phase control. The ligand exchange rate of Cr3+ is much slower than for Fe3+, making it more challenging to obtain crystalline materials as there is less ‘error-checking’, hence, modulation was considered a viable strategy for enhancing crystallisation. Two synthetic routes were established in this study and were found to reliably control the crystallinity and SBU in the resulting MOF: synthesis in water and pyridine with acetic acid as modulator yields frameworks with the trigonal [Cr3O(RCO2)6(H2O)2X] (X = monoanion) SBU, while synthesis in water with HCl yields those with chain [Cr(OH)(RCO2)2] SBU. The ability to control the SBU in this manner is extremely useful and has enabled the synthesis of many novel Cr-MOFs in this study. A series of flexible dicarboxylate MOFs with MIL-88 topology were synthesised successfully using the acetic acid route, and their flexible behaviour was investigated by powder X-ray diffraction. Interestingly, synthesis with the longest linker - 4,4′-stilbenedicarboxylic - yields a two-fold interpenetrated framework (Cr-SDC) which, despite interpenetration, exhibits comparable flexibility to the MIL-88 frameworks. The use of higher connectivity linkers has also been explored, generating novel frameworks with greater rigidity and permanent porosities surpassing the dicarboxylates. The most notable of these frameworks is MIL-100(Cr)_BTB, containing benzene-1,3,5-tribenzoate (BTB) as linker, which demonstrates exceptional sorption capacity (4000 m2g-1). The HCl route enabled the synthesis of novel isoreticular analogues of MIL-53(Cr), two of which could be grown as large single crystals, which has never previously been reported for directly synthesised Cr-MOFs. The remarkable stability of Cr-MOFs suggests that many of these frameworks could find use in demanding applications where their high porosities and flexible properties can be utilised. MOFs have been widely studied for their potential use in biomedical applications, particularly as drug delivery systems, however these have typically been limited to frameworks consisting of either Zr4+ or Fe3+, with those consisting of Cr3+ largely neglected due to the associated stigma relating to the toxicity of Cr6+. In Chapter 5 the biocompatibility of several of the Cr-MOFs developed in Chapter 4 were tested using cell culture experiments. The results showed that all the MOFs were biocompatible within the doses expected to be used in drug delivery applications. In summary, novel synthetic strategies for phase-tuning in Fe3+ and Cr3+ carboxylate systems have been developed, providing better control over the obtained phase, and enhancing crystallinity. These enhanced synthetic protocols have enabled discovery of novel MOFs, investigation of the flexibility, gas sorption, and biocompatibility of these and existing benchmark materials, and has revealed that Cr-MOFs are promising candidates for biomedical applications

Exploring and Expanding the Fe-Terephthalate Metal-Organic Framework Phase Space by Coordination and Oxidation Modulation

The synthesis of phase pure metal-organic frameworks (MOFs) – network solids of metal clusters connected by organic linkers – is often complicated by the possibility of forming multiple diverse phases from one metal-ligand combination. For example, there are at least six Fe-terephthalate MOFs reported to date, with many examples of erroneous assignment of phase based on diffraction data alone. Herein, we show that modulated self-assembly can be used to influence the kinetics of self-assembly of Fe-terephthalate MOFs. We comprehensively assess the effect of addition of both coordinating modulators and pH modulators to the outcome of syntheses, as well as probing the influence of the oxidation state of the Fe precursor (oxidation modulation) and the role of the counteranion on the phase(s) formed. In doing so, we shed light on the thermodynamic landscape of this phase system, uncover mechanistics of modulation, provide robust routes to phase pure materials, often as single crystals, and introduce two new Fe-terephthalate MOFs to an already complex system. The results highlight the potential of modulated self-assembly to bring precision control and new structural diversity to systems that have already received significant study

Exploring and Expanding the Fe-Terephthalate Metal-Organic Framework Phase Space by Coordination and Oxidation Modulation

The synthesis of phase pure metal–organic frameworks (MOFs) – network solids of metal clusters connected by organic linkers – is often complicated by the possibility of forming multiple diverse phases from one metal–ligand combination. For example, there are at least six Fe-terephthalate MOFs reported to date, with many examples in the literature of erroneous assignment of phase based on diffraction data alone. Herein, we show that modulated self-assembly can be used to influence the kinetics of self-assembly of Fe-terephthalate MOFs. We comprehensively assess the effect of addition of both coordinating modulators and pH modulators on the outcome of syntheses, as well as probing the influence of the oxidation state of the Fe precursor (oxidation modulation) and the role of the counteranion on the phase(s) formed. In doing so, we shed light on the thermodynamic landscape of this phase system, uncover mechanistics of modulation, provide robust routes to phase pure materials, often as single crystals, and introduce two new Fe-terephthalate MOFs to an already complex system. The results highlight the potential of modulated self-assembly to bring precision control and new structural diversity to systems that have already received significant study

Kinetic Control of Interpenetration in Fe-Biphenyl-4,4′-dicarboxylate MOFs by Coordination and Oxidation Modulation

Phase control in the self-assembly of metal-organic frameworks (MOFs) – materials wherein organic ligands connect metal ions or clusters into network solids with potential porosity – is often a case of trial and error. Judicious control over a number of synthetic variables is required to select for the desired topology and control features such as interpenetration and defectivity, which have significant impact on physical properties and application. Herein, we present a comprehensive investigation of self-assembly in the Fe-biphenyl-4,4\u27-dicarboxylate system, demonstrating that coordination modulation, the addition of competing ligands into solvothermal syntheses, can reliably tune between the kinetic product, non-interpenetrated MIL-88D(Fe), and the thermodynamic product, two-fold interpenetrated MIL-126(Fe). DFT simulations reveal that correlated disorder of the terminal anions on the metal clusters in the interpentrated phase results in H-bonding between adjacent nets and is the thermodynamic driving force for its formation. Coordination modulation slows self-assembly and therefore selects the thermodynamic product MIL-126(Fe), while offering fine control over defectivity, inducing mesoporosity, but electron microscopy shows the MIL-88D(Fe) phase persists in many samples despite not being evident in diffraction experiments, suggesting its presence accounts for the lower than predicted surface areas reported for samples to date. Interpenetration control is also demonstrated by utilizing the 2,2\u27-bipyridine-5,5\u27-dicarboxylate linker; DFT simulations show that it is energetically prohibitive for it to adopt the twisted conformation required to form the interpenetrated phase, and are confirmed by experimental data, although multiple alternative phases are identified due to additional coordination of the Fe cations to the N-donors of the ligand. Finally, we introduce oxidation modulation – the concept of using metal precursors in a different oxidation state to that found in the final MOF – as a further protocol to kinetically control self-assembly. Combining coordination and oxidation modulation allows the synthesis of pristine MIL-126(Fe) with BET surface areas close to the predicted maximum capacity for the first time, suggesting that combining the two may be a powerful methodology for the controlled self-assembly of high-valent MOFs.<br /

Modulated Self-Assembly of an Interpenetrated MIL-53 Sc Metal-Organic Framework with Excellent Volumetric H2 Storage and Working Capacity

To achieve optimal performance in gas storage and delivery applications, metal-organic frameworks (MOFs) must combine high gravimetric and volumetric capacities. One potential route to balancing high pore volume with suitable crystal density is interpenetration, where identical nets sit within the void space of one another. Herein, we report an interpenetrated MIL-53 topology MOF, named GUF-1, where one-dimensional Sc(µ2-OH) chains are connected by 4,4’-(ethyne-1,2-diyl)dibenzoate linkers into a material that is an unusual example of an interpenetrated MOF with a rod-like secondary building unit. A combination of modulated self-assembly and grand canonical Monte Carlo simulations are used to optimise the porosity of GUF-1; H2 adsorption isotherms reveal a very high Qst for H2 of 7.6 kJ mol-1 and a working capacity of 41 g L-1 in a temperature-pressure swing system, which is comparable to benchmark MOFs. These results show that interpenetration is a viable route to high performance gas storage materials comprised of relatively simple building blocks