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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2018)

Metal-organic frameworks (MOFs) are porous, crystalline, extended structures made by linking inorganic and organic molecular building blocks together through strong coordination bonds. Due to their high surface areas, pore volumes, and the possibility of decorating them with a great variety of chemical functionalities through the judicious choice and design of their inorganic joints and organic struts, MOFs have been studied extensively and found useful in widespread industrial applications, such as gas storage, separation, and catalysis.

The design and synthesis of new MOFs with desirable properties and functions is a central theme in MOF chemistry. Generally, the structural design of MOFs is realized by a reticular synthesis approach, whereby the metal-based nodes and rigid organic linkers have predetermined geometries. However, when it comes to MOFs with flexible coordination geometries, it can become challenging to successfully guide the synthesis.

The work herein describes my Ph.D. research, dealing with the structural design of two important subclasses of MOFs, zeolitic imidazolate frameworks (ZIFs) and calcium-based environmentally friendly MOFs. Due to the structural unpredictability arising from the flexible coordinative behavior of the metal centers and organic linkers, the development of both classes of materials has so far relied heavily on synthetic “trial and error”, which has greatly limited their structural diversities. The work presented here shows that such challenges can be addressed by the synergistic assembly of linkers with different functionalities (mixed-linker approach). Following this strategy, fifteen new porous ZIF structures (amongst which structures presenting the largest cage and aperture reported for ZIFs), and two new porous calcium lactate frameworks were created. Furthermore, this work allowed the identification and establishment of three general principles for the guided structural design of ZIFs.

Chapter 1 introduces the concept, synthesis, characterization, and classification of MOFs. Then the importance and existing approaches for structural design are summarized. Finaly, the structure-function relationship is discussed to address the potentials of MOF materials in practical industrial applications.

Chapter 2 reports the synthesis and characterization of a series of ZIFs with ultra-large pores and aperture sizes via the mixed-linker approach. The synthesis of fifteen new ZIFs (ZIF-303, -360, -365, -376, -386, -408, -410, -486, -412, -413, -414, -516, -586, -615, and -725) is presented. Members of this list represent ZIFs with the largest pore sizes and aperture sizes (ZIF-412 and ZIF-516, -586, -615, -725) reported so far. Morevoer, a tertiary combination of linkers with different functionalities is reported for the first time in these new structures.

Chapter 3 builds upon the work of Chapter 3 and addresses the desire to uncover general synthetic principles to guide the synthesis of ZIFs. It begins with the analysis of relationship between the imidazolate starting material and framework structure based on the fifteen new ZIFs presented in Chapter 2. The ring in the ZIF structure is identified as the bridge, and the mixed imidazolate approach is the key to tune the ring size and composition. Based on these analyses, three general principles are identified which are applicable to the whole class of ZIF materials.

Chapter 4 switches focus from the previous chapters, and explores the use of a mixed-linker approach in another subfield of MOFs: calcium-based MOFs. The successful implementation of the mixed-linker approach in the ZIF synthesis encouraged us to explore similar synthetic challenges in other fields. In this chapter, the environmentally-friendly calcium-based MOFs are selected as topic of investigation. Using a combination of naturally existing lactate and acetate linkers, the first two examples of porous of calcium lactate frameworks are synthesized and presented. I demonstrate that both of these linkers are essential to the successful formation of the final structure.

Chapter 5 presents potential applications of the newly-made MOFs described in the previous chapters. A particular attention is paid to environmental applications benefiting from the structural and componential characters of the MOFs. The hydrophobic large-pore ZIF is demonstrated to be highly efficient for air purification through the removal of volatile organic compounds, and the calcium-based MOF, exhibiting an environmentally-friendly composition, is shown to be an effective pesticide carrier for agriculture purposes.

Chapter 6 is the final chapter of my thesis, in which I provide my humble thoughts and perspectives of the future development of the structural design of MOFs. MOFs are highly potential in real world applications, and the rational design of their structures and compositions, in order to meet the requirements for targeted applications, is the key to success.

    Cover page: Mixed-linker Approach toward the Structural Design of Metal-Organic Frameworks
    • Article
    Recent Work (2016)
    This paper develops robust testing procedures for nonparametric kernel methods in the presence of temporal dependence of unknown forms. Based on the fixed-bandwidth asymptotic variance and the pre-asymptotic variance, we propose a heteroskedasticity and autocorrelation robust (HAR) variance estimator that achieves double robustness --- it is asymptotically valid regardless of whether the temporal dependence is present or not, and whether the kernel smoothing bandwidth is held constant or allowed to decay with the sample size. Using the HAR variance estimator, we construct the studentized test statistic and examine its asymptotic properties under both the fixed-smoothing and increasing-smoothing asymptotics. The fixed-smoothing approximation and the associated convenient t-approximation achieve extra robustness --- it is asymptotically valid regardless of whether the truncation lag parameter governing the covariance weighting grows at the same rate as or a slower rate than the sample size. Finally, we suggest a simulation-based calibration approach to choose smoothing parameters that optimize testing oriented criteria. Simulation shows that the proposed procedures work very well in finite samples.
      Cover page: A Fixed-bandwidth View of the Pre-asymptotic Inference for Kernel Smoothing with Time Series Data
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2018)
      Energy-efficient production of water from desert air has not been developed. A proof-of-concept device for harvesting water at low relative humidity was reported; however, it used external cooling and was not desert-tested. We report a laboratory-to-desert experiment where a prototype using up to 1.2 kg of metal-organic framework (MOF)-801 was tested in the laboratory and later in the desert of Arizona, USA. It produced 100 g of water per kilogram of MOF-801 per day-and-night cycle, using only natural cooling and ambient sunlight as a source of energy. We also report an aluminum-based MOF-303, which delivers more than twice the amount of water. The desert experiment uncovered key parameters pertaining to the energy, material, and air requirements for efficient production of water from desert air, even at a subzero dew point.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2018)
        The synthesis of new isoreticular non-interpenetrated woven covalent organic frameworks (COFs) was achieved by linking aldehyde-functionalized copper(I) bisphenanthroline complexes with benzidine linkers in the presence of a bulky anion, diphenylphosphinate (PO2Ph2-) to give metalated COF-506-Cu and, upon removal of copper(I), the demetalated COF-506. The structures of these COFs were determined by a combination of powder X-ray diffraction and electron microscopy techniques. Guest-accessibility to the pores of the two frameworks was examined by vapor and dye inclusion studies and compared to the already reported doubly-interpenetrated COF-505-Cu.  Remarkably, COF-506 was found to take up guest molecules that exceed the size of the COF-506-Cu pores, thus giving credence to the notion of a novel mode of motional dynamics in solids we term 'adaptive inclusion'.
          Cover page: Molecular Weaving of Covalent Organic Frameworks for Adaptive Guest Inclusion
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2023)
          BACKGROUND: Hereditary angioedema (HAE) is a genetic condition characterized by dysregulation of the contact (kallikrein-bradykinin) pathway, leading to recurrent episodes of angioedema. OBJECTIVE: This project sought to determine whether a suspicion index screening tool using electronic health record (EHR) data can identify patients with an increased likelihood of a diagnosis of HAE. METHODS: A suspicion index screening tool for HAE was created and validated by using known patients with HAE from the medical literature as well as positive and negative controls from HAE-focused centers. Through the use of key features of medical and family history, a series of logistic regression models for 5 known genetic causes of HAE were created. Top variables populated the digital suspicion scoring system and were run against deidentified EHR data. Patients at 2 diverse sites were categorized as being at increased, possible, or no increased risk of HAE. RESULTS: Prediction scoring using the strongest 13 variables on the real-world EHR-positive control data identified all but 1 patient with C1 inhibitor deficiency and patient with non-C1 inhibitor deficiency without false-positive results. The 2 missed patients had no documented family history of HAE in their EHR. When the prediction scoring variables were expanded to 25, the screening algorithm approached 100% sensitivity and specificity. The 25-variable algorithm run on general population EHR data identified 26 patients at the medical centers as being at increased risk for HAE. CONCLUSIONS: These results suggest that development, validation, and implementation of suspicion index screening tools can be useful to aid providers in identifying patients with rare genetic conditions.
            Cover page: Validation of a suspicion index to identify patients at risk for hereditary angioedema.
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2022)
              Cover page: Multiprocess Laser Lifting‐Off for Nanostructured Semiconductive Hydrogels
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2019)
              The self-assembly of nanoparticles, a process whereby nanocrystal building blocks organize into even more ordered superstructures, is of great interest to nanoscience. Here we report the layer-by-layer assembly of 2D perovskite nanosheet building blocks. Structural analysis reveals that the assembled superlattice nanocrystals match with the layered Ruddlesden-Popper perovskite phase. This assembly proves reversible, as these superlattice nanocrystals can be reversibly exfoliated back into their building blocks via sonication. This study demonstrates the opportunity to further understand and exploit thermodynamics to increase order in a system of nanoparticles and to study emergent optical properties of a superlattice from 2D, weakly attracted, perovskite building blocks.
                Cover page: Self-Assembly of Two-Dimensional Perovskite Nanosheet Building Blocks into Ordered Ruddlesden–Popper Perovskite Phase
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2023)
                Heteroaromatic stacking interactions are important in drug binding, supramolecular chemistry, and materials science, making protein-ligand model systems of these interactions of considerable interest. Here we studied 30 congeneric ligands that each present a distinct heteroarene for stacking between tyrosine residues at the dimer interface of procaspase-6. Complex X-ray crystal structures of 10 analogs showed that stacking geometries were well conserved, while high-accuracy computations showed that heteroarene stacking energy was well correlated with predicted overall ligand binding energies. Empirically determined KD values in this system thus provide a useful measure of heteroarene stacking with tyrosine. Stacking energies are discussed in the context of torsional strain, the number and positioning of heteroatoms, tautomeric state, and coaxial orientation of heteroarene in the stack. Overall, this study provides an extensive data set of empirical and high-level computed binding energies in a versatile new protein-ligand system amenable to studies of other intermolecular interactions.
                  Cover page: Systematic Study of Heteroarene Stacking Using a Congeneric Set of Molecular Glues for Procaspase-6.
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