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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2015)

A grand challenge in materials science is to create materials with complex, rationally designed structures and functionalities. Self-assembly is a promising route to fabricate these materials with nano-scale precision, and efficiency in terms of cost and time. Nanocomposites comprised of block copolymer (BCP)-based supramolecules and nanoparticles (NPs) represent a promising platform to access nanostructures of various structures, chemistries, and functionalities. The thermodynamic landscape, and thus self-assembly behavior, of these supramolecular nanocomposites is dominated by entropic factors. While entropy is often considered a detrimental factor that prevents the formation of ordered phases and the co-assembly of BCPs and NPs, it can also be harnessed to stabilize nanostructures that are not accessible to traditional BCPs. This dissertation will focus on controlling the self-assembly of supramolecular nanocomposites by manipulating the entropy in these systems.

In bulk and thin films of supramolecular nanocomposites, self-assembly is governed by a balance between NP translational entropy and supramolecule chain conformational entropy. By systematically varying the NP size within these systems, this entropic balance can be perturbed, leading to a change in NP spatial distribution within the nanocomposite and the stabilization of cubic and anisotropic microphases that are unique from traditional BCP morphologies, as confirmed by TEM, TEM tomography, and small angle X-ray scattering techniques.

Geometrically confining supramolecular nanocomposites into cylindrical pores introduces boundary conditions that impose additional entropic frustration to the composite system, leading to exotic nanostructures such as NP stacked rings and single and double helices. The single helical structures are also demonstrated, via dark field scattering and finite integration technique simulations, to possess strong chiral plasmonic properties due to the chiral arrangement of NPs and strong plasmonic interparticle coupling.

Finally, replacing alkyl side groups of the supramolecules with liquid crystalline side groups further increases chain rigidity and presents another avenue towards entropic modulation. These modified supramolecules and their associated nanocomposites are thoroughly investigated for their self-assembly behavior. It is observed that the liquid crystalline small molecule side chains introduce hierarchical smectic ordering and thermally triggered, non-reversible order-order transitions to the supramolecular nanocomposite.

These studies demonstrate entropic modulation in supramolecular nanocomposites to be an important tool in creating uniquely structured and functional materials with potential applications in memory storage, energy transport, and metamaterials.

    Cover page: Manipulating Supramolecular Nanocomposite Self-Assembly via Entropy Modulation
    • 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 Diego Previously Published Works (2022)
      ADP-ribosylation, a modification of proteins, nucleic acids, and metabolites, confers broad functions, including roles in stress responses elicited, for example, by DNA damage and viral infection and is involved in intra- and extracellular signaling, chromatin and transcriptional regulation, protein biosynthesis, and cell death. ADP-ribosylation is catalyzed by ADP-ribosyltransferases (ARTs), which transfer ADP-ribose from NAD+ onto substrates. The modification, which occurs as mono- or poly-ADP-ribosylation, is reversible due to the action of different ADP-ribosylhydrolases. Importantly, inhibitors of ARTs are approved or are being developed for clinical use. Moreover, ADP-ribosylhydrolases are being assessed as therapeutic targets, foremost as antiviral drugs and for oncological indications. Due to the development of novel reagents and major technological advances that allow the study of ADP-ribosylation in unprecedented detail, an increasing number of cellular processes and pathways are being identified that are regulated by ADP-ribosylation. In addition, characterization of biochemical and structural aspects of the ARTs and their catalytic activities have expanded our understanding of this protein family. This increased knowledge requires that a common nomenclature be used to describe the relevant enzymes. Therefore, in this viewpoint, we propose an updated and broadly supported nomenclature for mammalian ARTs that will facilitate future discussions when addressing the biochemistry and biology of ADP-ribosylation. This is combined with a brief description of the main functions of mammalian ARTs to illustrate the increasing diversity of mono- and poly-ADP-ribose mediated cellular processes.
        Cover page: ADP‐ribosyltransferases, an update on function and nomenclature
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