Incorporating Microporous Zn3 and Zn2Cd MOFs into Pebax/PVDF Mixed Matrix Membranes for Improved Carbon Dioxide Separation Performance

A pair of related metal–organic frameworks (Zn3 and Zn2Cd) developed in our group were incorporated into Pebax 30R51 and PVDF Kynar 761 polymers to fabricate mixed matrix membranes (MMMs). These MOFs were chosen due to the carbon dioxide molecular sieving ability of Zn3, and the slightly larger pore aperture of Zn2Cd that allows carbon dioxide and larger gases to enter the pores. For Pebax-based MMMs, this work demonstrated an over two-fold and four-and-a-half-fold increase in carbon dioxide permeability for Zn3- (15 wt %) and Zn2Cd-containing (10 wt %) MMMs over the pristine polymer. Separation selectivity (CO2:N2) of 4.21 and 7.33 were observed for Zn3 and Zn2Cd (10 wt %). For PVDF-based MMMs, the incorporation of Zn3 and Zn2Cd (10 wt %) increased the carbon dioxide permeability approximately two- and three-fold. The CO2/N2 selectivity of the PVDF membranes increased 73% (1.01 to 1.86) and 68% (1.01 to 1.68) when 15 wt % Zn3 and Zn2Cd were incorporated into PVDF. The improved performance of Pebax over PVDF based MMMs is attributed to matching the permeability of the polymer bulk phase (Pebax over PVDF) and the dispersed phase (Zn3 and Zn2Cd). The lower permeability allows the MOF, which has slow kinetics associated with molecular sieving, to participate in the permeation process better. With regards to Zn3 vs Zn2Cd, while Zn3 acts as a molecular sieve and Zn2Cd does not, we hypothesize that the faster diffusion of carbon dioxide gas in Zn2Cd can outcompete the lower nitrogen gas permeability and molecular sieving properties of Zn3. However, we expect that further increasing the pore aperture would increase the permeabilities of nitrogen gas such that differences in diffusion kinetics due to molecular size would be unimportant

Age, Disease Severity and Ethnicity Influence Humoral Responses in a Multi-Ethnic COVID-19 Cohort

The COVID-19 pandemic has affected all individuals across the globe in some way. Despite large numbers of reported seroprevalence studies, there remains a limited understanding of how the magnitude and epitope utilization of the humoral immune response to SARS-CoV-2 viral anti-gens varies within populations following natural infection. Here, we designed a quantitative, multi-epitope protein microarray comprising various nucleocapsid protein structural motifs, including two structural domains and three intrinsically disordered regions. Quantitative data from the microarray provided complete differentiation between cases and pre-pandemic controls (100% sensitivity and specificity) in a case-control cohort (n = 100). We then assessed the influence of disease severity, age, and ethnicity on the strength and breadth of the humoral response in a multi-ethnic cohort (n = 138). As expected, patients with severe disease showed significantly higher antibody titers and interestingly also had significantly broader epitope coverage. A significant increase in antibody titer and epitope coverage was observed with increasing age, in both mild and severe disease, which is promising for vaccine efficacy in older individuals. Additionally, we observed significant differences in the breadth and strength of the humoral immune response in relation to ethnicity, which may reflect differences in genetic and lifestyle factors. Furthermore, our data enabled localization of the immuno-dominant epitope to the C-terminal structural domain of the viral nucleocapsid protein in two independent cohorts. Overall, we have designed, validated, and tested an advanced serological assay that enables accurate quantitation of the humoral response post natural infection and that has revealed unexpected differences in the magnitude and epitope utilization within a population

Age, Disease Severity and Ethnicity Influence Humoral Responses in a Multi-Ethnic COVID-19 Cohort

The COVID-19 pandemic has affected all individuals across the globe in some way. Despite large numbers of reported seroprevalence studies, there remains a limited understanding of how the magnitude and epitope utilization of the humoral immune response to SARS-CoV-2 viral anti-gens varies within populations following natural infection. Here, we designed a quantitative, multi-epitope protein microarray comprising various nucleocapsid protein structural motifs, including two structural domains and three intrinsically disordered regions. Quantitative data from the microarray provided complete differentiation between cases and pre-pandemic controls (100% sensitivity and specificity) in a case-control cohort (n = 100). We then assessed the influence of disease severity, age, and ethnicity on the strength and breadth of the humoral response in a multi-ethnic cohort (n = 138). As expected, patients with severe disease showed significantly higher antibody titers and interestingly also had significantly broader epitope coverage. A significant increase in antibody titer and epitope coverage was observed with increasing age, in both mild and severe disease, which is promising for vaccine efficacy in older individuals. Additionally, we observed significant differences in the breadth and strength of the humoral immune response in relation to ethnicity, which may reflect differences in genetic and lifestyle factors. Furthermore, our data enabled localization of the immuno-dominant epitope to the C-terminal structural domain of the viral nucleocapsid protein in two independent cohorts. Overall, we have designed, validated, and tested an advanced serological assay that enables accurate quantitation of the humoral response post natural infection and that has revealed unexpected differences in the magnitude and epitope utilization within a population

Ultramicroporous metal-organic frameworks and porphyrin linker design toward gas-based applications

Metal-Organic Frameworks (MOFs) are a class of materials characterized by their highly porous nature. MOFs are ordered structures made up of well-defined metal ‘nodes’ that are bridged to each other through coordinating organic ‘linkers’. These frameworks have been an appealing area of research in recent years thanks to their numerous applications. Regarding gas separation in MOFs, a conventional approach is to develop a material that has a high affinity for one gas of interest, and lower affinities for other gases that may appear in a mixture. A typical example is the removal of carbon dioxide from flue gas exhaust. MOFs have been developed that can strongly and selectively bind carbon dioxide while in the presence of gases such as nitrogen, oxygen, and nitrogen oxides, and even water vapour. These separations can be challenging when the gases to be separated are low in abundance (e.g., atmospheric sequestration) or when they cannot be bound selectively over other gases. An alternative approach to separation is a method that relies on the differences in molecular size of the gases in a mixture, so-called molecular sieving. Chapter 2 describes two such MOFs (Zn2M; M = Zn or Cd), whose ultramicropores (pore width < 0.7 nm) make them capable of molecular sieving. The crystal structures of these MOFs were examined at different temperatures (100 and 273 K) and with different solvent molecules in the pores (DMSO and methanol) to help better understand the structural effects on their gas adsorption and separation properties. Critically, changing from Zn to Cd in the trimetallic node of the MOFs results in a sub-˚A change in the pore opening. At the molecular scale, this change resulted in a drastic difference in gas adsorption between the two MOFs. Zn3 only allows carbon dioxide to enter its framework, whereas Zn2Cd permits carbon dioxide, argon, nitrogen, and methane to enter the pores. The data suggest that Zn3 could be an excellent sieve for separating carbon dioxide from mixtures, even at environmental concentrations. Regarding the synthesis of MOFs, one of the ways to obtain MOFs with new topologies and unique properties is to design novel organic linkers. One class of organic molecules that lends itself well to creativity and modification is porphyrins. As the ‘pigments of life’, porphyrins are found everywhere in nature and have been used in applications ranging from catalysis to optics to therapeutics, and of course have been used as linkers in MOFs. Porphyrins in MOFs offer an additional dimension to the tuneability of the framework, as the porphyrin linker itself can coordinate a metal through the central nitrogens, changing the properties of the framework without affecting its structure. To date, porphyrin linkers have been predominantly made to coordinate to MOF nodes through substituents on their meso methine regions. Porphyrin MOF linkers where the linking moieties extend from the β-positions are as of yet unknown, leaving plenty of room for exploration. Chapter 3 discusses the synthetic methods that could give access to these linkers, as well as the progress made towards these linkers. Although ultimately the desired porphyrins could not be isolated and used in MOF synthesis due to the delays associated with the COVID-19 pandemic, Chapter 3 illustrates that the chemistry works and puzzles out the synthetic route necessary to obtain β-subsituted porphyrin linkers

Incorporating Microporous Zn₃ and Zn₂Cd MOFs into Pebax/PVDF Mixed Matrix Membranes for Improved Carbon Dioxide Separation Performance

A pair of related metal–organic frameworks (Zn3 and Zn2Cd) developed in our group were incorporated into Pebax 30R51 and PVDF Kynar 761 polymers to fabricate mixed matrix membranes (MMMs). These MOFs were chosen due to the carbon dioxide molecular sieving ability of Zn3, and the slightly larger pore aperture of Zn2Cd that allows carbon dioxide and larger gases to enter the pores. For Pebax-based MMMs, this work demonstrated an over two-fold and four-and-a-half-fold increase in carbon dioxide permeability for Zn3- (15 wt %) and Zn2Cd-containing (10 wt %) MMMs over the pristine polymer. Separation selectivity (CO2:N2) of 4.21 and 7.33 were observed for Zn3 and Zn2Cd (10 wt %). For PVDF-based MMMs, the incorporation of Zn3 and Zn2Cd (10 wt %) increased the carbon dioxide permeability approximately two- and three-fold. The CO2/N2 selectivity of the PVDF membranes increased 73% (1.01 to 1.86) and 68% (1.01 to 1.68) when 15 wt % Zn3 and Zn2Cd were incorporated into PVDF. The improved performance of Pebax over PVDF based MMMs is attributed to matching the permeability of the polymer bulk phase (Pebax over PVDF) and the dispersed phase (Zn3 and Zn2Cd). The lower permeability allows the MOF, which has slow kinetics associated with molecular sieving, to participate in the permeation process better. With regards to Zn3 vs Zn2Cd, while Zn3 acts as a molecular sieve and Zn2Cd does not, we hypothesize that the faster diffusion of carbon dioxide gas in Zn2Cd can outcompete the lower nitrogen gas permeability and molecular sieving properties of Zn3. However, we expect that further increasing the pore aperture would increase the permeabilities of nitrogen gas such that differences in diffusion kinetics due to molecular size would be unimportant

Ultra-High Size Exclusion Selectivity for Carbon Dioxide from Nitro-gen/Methane in an Ultramicroporous Metal-Organic Framework

Separations based on molecular size (molecular sieving) are a solution for environmental remediation. We have synthesized and characterized two new metal-organic frameworks (Zn2M; M = Zn, Cd) with ultramicropores (<0.7 nm) suitable for molecular sieving. We explore the synthesis of these MOFs and the role that the DMSO/H2O/DMF solvent mix-ture has on the crystallization process. We further explore the crystallographic data for the DMSO and methanol solvated structures at 273 and 100K; this not only results in high quality structural data, but also allows us to better understand the structural features at temperatures around the gas adsorption experiments. Structurally, the main difference between the two MOFs is that the central metal in the trimetallic node can be changed from Zn to Cd and that results in a sub-Å change in the size of the pore aperture, but a stark change in the gas adsorption properties. The separation selectivity of the MOF when M = Zn is infinite given the pore aperture of the MOF can accommodate CO2 while N2 and/or CH4 is excluded from en-tering the pore. Furthermore, due to the size exclusion behaviour, the MOF has an adsorption selectivity of 4800:1 CO2:N2 and 5×1028:1 CO2:CH4. When M = Cd, the pore aperture of the MOF increases slightly, allowing N2 and CH4 to enter the pore, resulting in a 27.5:1 and a 10.5:1 adsorption selectivity, respectively; this is akin to UiO-66, a MOF that is not able to function as a molecular sieve for these gases. The data delineates how subtle sub-Å changes to the pore aperture of a framework can drastically affect both the adsorption selectivity and separation selectivity