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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2014)

This dissertation focuses on the co-assembly of nanoparticles (NPs) and block copolymer (BCP)-based supramolecules in thin films for the generation of functional nanocomposites that may find applications in next-generation nanodevices. Nanocomposites, composed of organic and inorganic building blocks, can combine the properties from the parent constituents and generate new properties to meet current and future demands in functional materials. Recent developments in NP synthesis provide a plethora of inorganic building blocks, laying the foundation for constructing hybrid nanocomposites with unlimited possibilities. The properties of nanocomposite materials depend not only on those of individual NPs, but also on their spatial organization at different length scales. Block copolymer-based supramolecules, which microphase separate into various hierarchical nanostructures, have shown their potential for organizing inorganic NPs in bulk. For practical applications and device fabrication, it is requisite to translate the NP assemblies in bulk to thin films, which has yet to be realized due to the complicated energy landscape and assembly kinetics in thin film configurations.

Here, the thermodynamics and kinetics of the NP assemblies in supramolecular thin films were systematically investigated to achieve desirable and, potentially, functional NP assemblies over multiple length scales. In particular, the complicated interplay between the entropic and

enthalpic contribution in the co-assembly was explored by tuning the chain architecture of the supramolecules and the NP loading. The delicate balance among the thermodynamic driving forces was further manipulated by changing NP size, leading to a rich library of multidimensional assemblies of not only a single kind, but also mixtures of NPs in thin films. In addition, the assembly kinetics of the NPs was studied during solvent annealing. By varying the solvent volume fraction and small molecule loading in the film, the mobility, the activation energy barrier for inter-domain diffusion, and the thermodynamic driving force for defect elimination can be precisely tailored to manipulate the kinetic pathway. The results not only enable precise control over the macroscopic morphology of the supramolecular nanocomposite, but also optimize the processing conditions for the fabrication of functional nanocomposites.

Preliminary optical property results demonstrate strong wavelength dependence optical anisotropy in the supramolecular nanocomposites, showing the promise of this new family of materials for light manipulation and information transmission. To manipulate the coupling in the NP arrays over multiple length scales, faceted and lithographically patterned surfaces were employed to direct the macroscopic 2-D alignment as well as the 3-D structure in supramolecular nanocomposites. This work demonstrates that the hierarchically structured supramolecular nanocomposite thin films are fundamentally intriguing as well as technologically relevant. The fundamental knowledge gained lays a solid foundation for future studies on the investigation of structure-property correlations, which may enable the realization of novel functional nanocomposites for a wide range of applications including, but not limited to, nanoscopic energy waveguides, optical coatings, and nanoelectronics.

    Cover page: Hierarchical Nanoparticle Assemblies in Thin Films of Supramolecular Nanocomposites
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    Many macroscopic properties such as collective chiral responses enhanced by coupled plasmonic nanoparticles require complex nanostructures. However, a key challenge is to directly assemble nanosized building blocks into functional entities with designed morphologies. For example, the DNA templated nanoparticle assembly has low scalability and requires aqueous conditions, while other approaches such as controlled drying and polymer templating access only simple 1-D, 2-D, and 3-D structures with limited assembly patterns. Here, we demonstrate a new self-assembly strategy that expands the diversity of 3-D nanoparticle assemblies. By subjecting supramolecular nanocomposites to cylindrical confinement, a range of new nanoparticle assemblies such as stacked rings and single and double helices can be readily obtained with a precisely defined morphology. Circular dichroism dark field scattering measurements on the single nanowire with Au helical ribbon-like assembly show chiral plasmonic response several orders of magnitude higher than that of natural chiral materials. The phase behavior of supramolecular nanocomposite under geometric constraints is quite different from that of block copolymer. It depends on the complex interplay among nanoparticle packing and phase behavior of parent block copolymers under confinement and can be governed by nanoparticle diffusion.
      Cover page: Diversifying Nanoparticle Assemblies in Supramolecule Nanocomposites Via Cylindrical Confinement
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2016)
      The covalent attachment of a 14-carbon aliphatic tail on a glycine residue of nascent translated peptide chains is catalyzed in human cells by two N-myristoyltransferase (NMT) enzymes using the rare myristoyl-CoA (C(14)-CoA) molecule as fatty acid donor. Although, NMT enzymes can only transfer a myristate group, they lack specificity for C(14)-CoA and can also bind the far more abundant palmitoyl-CoA (C(16)-CoA) molecule. We determined that the acyl-CoA binding protein, acyl-CoA binding domain (ACBD)6, stimulated the NMT reaction of NMT2. This stimulatory effect required interaction between ACBD6 and NMT2, and was enhanced by binding of ACBD6 to its ligand, C(18:2)-CoA. ACBD6 also interacted with the second human NMT enzyme, NMT1. The presence of ACBD6 prevented competition of the NMT reaction by C(16)-CoA. Mutants of ACBD6 that were either deficient in ligand binding to the N-terminal ACBD or unable to interact with NMT2 did not stimulate activity of NMT2, nor could they protect the enzyme from utilizing the competitor C(16)-CoA. These results indicate that ACBD6 can locally sequester C(16)-CoA and prevent its access to the enzyme binding site via interaction with NMT2. Thus, the ligand binding properties of the NMT/ACBD6 complex can explain how the NMT reaction can proceed in the presence of the very abundant competitive substrate, C(16)-CoA.
        Cover page: Association of NMT2 with the acyl-CoA carrier ACBD6 protects the N-myristoyltransferase reaction from palmitoyl-CoA[S]
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2019)
        Neonatal hypoxia-ischemia (HI) in the preterm human results in damage to subcortical developing white matter and cognitive impairments. Subplate neurons (SPNs) are among the first-born cortical neurons and are necessary for normal cerebral development. While moderate or severe HI at P1 in rats leads to SPN loss, it is unclear if HI, esp. forms not associated with overt cell loss lead to altered SPN circuits. Thus, we used two HI models with different severities in P1 rats. Cauterization of the common carotid artery (CCA) causes a largely transient and thus milder ischemia (HI-Caut) while CCA ligation causes more severe ischemia (HI-Lig). While HI-Lig caused subplate damage, HI-Caut did not cause overt histological damage on the light microscopic level. We used laser-scanning photostimulation (LSPS) in acute thalamocortical slices of auditory cortex during P5-10 to study the functional connectivity of SPNs. Both HI categories resulted in hyperconnectivity of excitatory and inhibitory circuits to SPNs. Thus, alterations on the circuit level are present in the absence of cell loss. Our results show that SPN circuits are uniquely susceptible to HI. Given the key developmental role of SPNs, our results suggest that altered SPN circuits might underlie the abnormal development of cortical function after HI.
          Cover page: Neonatal Hypoxia–Ischemia Causes Functional Circuit Changes in Subplate Neurons
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