Catalytic Synthesis of Cyclic Polymers
Zhihui Miao, Weijia Niu, Tomohiro Kubo, Vineet Jhakar, Kyle Vents, Daniel A. Savin, Brent S. Sumerlin, Adam S. Veige
University of Florida
This presentation will include a discussion on aspects of catalysis design for the synthesis of novel cyclic polymers. Four distinct transition metal catalysts that polymerize monomers via ring expansion will be presented. Polymer characterization techniques include SEC, DLS, viscosity, NMR, and preliminary rheology. Conclusions to be drawn from this work are: 1) we are now able to synthesis pure cyclic polymers on a bulk scale efficiently from readily available monomers, and 2) stereoregular cyclic polymers can now be synthesized via ring expansion metathesis polymerization (REMP).
Engineering Polyelectrolyte Complex Micelles with Solid or Liquid Cores
University of Central Florida
Polyelectrolyte complexes form by mixing oppositely charged polymers in solution. The resultant complex phase separates from solution into either irregularly shaped solids (or rather glasses), called precipitates, or micron sized liquid droplets that can coalesce into a distinct phase, called a coacervate. Using oppositely charged polypeptides, one can tune between solid and liquid complexes by manipulating the chirality of the polyelectrolyte. Homochiral complexes form precipitates with hydrogen bonded b-strand structure. In contrast, if one or more polypeptide is composed of both L and D monomers, coacervates are formed with no secondary structure. This inability to form secondary structure is attributed to steric hindrance of the racemic polypeptide impeding hydrogen bond formation. Therefore, since both types of complexes are formed using weak polyelectrolytes, the ability of the homochiral molecules to hydrogen bond causes the difference in phase. Using oppositely charged block-copolyelectrolytes that contain neutral blocks covalently linked to charged blocks allows the phase separation to be stabilized on the nanoscale, creating self-assembled micellar structures in dilute solutions. These polyelectrolyte complexes micelles can be used as drug and gene delivery vehicles for charged therapeutics like nucleic acids and proteins. Using diblock copolypeptides of varying chirality the resulting micellar structure can have both solid and liquid polyelectrolyte cores. This presentation will focus on characterization of polypeptide based polyelectrolyte complex micelles using scattering techniques (light, x-rays, neutrons), circular dichroism, and electron microscopy to reveal structural differences of solid and liquid micellar cores. Insight will be provided as to how differences in solid and liquid cores influence the design of drug delivery vehicles. If time permits, investigations into related micelles with dynamic coronas will be discussed.
Moving Commodity Plastics Forward Utilizing Bio-Cycles
Gabriel N. Short, Haley Donow, Ha T. H. Nguyen, Patricia I. Scheurle, Stephen A. Miller
University of Florida
Society utilized polymers at an ever increasing rate. This increase leads to two problems, source of monomers and ultimate fate of the polymers. With most commodity plastics made from fossil fuels, there is a finite future for these polymers. These petroleum based polymers do not degrade which has led to a build-up in natural environments. Monomers synthesized from biorenewable starting materials are the future. Sources include ferulic acid, citric acid, succinic acid, amino acids, and a range of renewable diols. To increase usable of these biorenewable starting materials, cyclization to form bio-cycles are used in the synthesis to increase glass transition temperature and subsequent range of application. A succinic acid based poly(ethylene terephthalate) mimic has been successfully synthesized with thermal properties above that of some commodity plastics, showing this is a viable future route.
Control and Stabilization of Human Galectin-3 with Polymer Conjugation
Amanda Pritzlaff, Dominic Rucco, and Daniel Savin
University of Florida
The human signaling protein galectin-3 (gal3) is being investigated as a polymer conjugate partner in order to control and study gal3 function. Gal3 contains a large disordered N-terminal domain (NTD) which is thought to mediate aggregation and therefore regulate the biological function of the protein. This region also makes the protein difficult to isolate and study due to its propensity to precipitate, so modification with soluble polymers is anticipated to have a stabilizing effect. Variants of the protein were created including a gal3 S7C mutant with a cysteine replacing the seventh serine in the unstructured NTD. Mutants were then conjugated to poly ethylene oxide (PEO) acrylate or methacrylate (500 g/mol PEO methacrylate, 2000 and 5000 g/mol PEO acrylate) through a thiol-Michael addition at the mutated cysteine.
Kandinsky Circles: Nested Supramolecular Hexagons with High Antibacterial Activity
University of South Florida
Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. In art field, concentric rings are also known as Kandinsky circles named after Wassily Kandinsky, a pioneer in abstract art, because of his prominent and profound painting Color Study; Squares with Concentric Circles.2 In addition to art and mathematics study, chemists have been fascinated by nested architectures with discovery and/or creation of a significant number of 2D and 3D systems that display nested layer and shell arrangements of atoms, molecules and materials. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2−G4) of giant nested supramolecules, or Kandinsky circles have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts was applied to modularize the synthesis. These discrete nested supramolecules were prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules displayed high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands didn’t show potent antimicrobial activity. The membrane-activity of these supramolecules was confirmed via electrophysiology study of planar lipid bilayer, subcellular localization by 3D deconvolution fluorescence microscopy, and bacterial morphology by TEM. We believe that those 2D multi-layered supramolecules were able to assemble into channels with multi-layered structure and distinct pore size inside the bacterial membrane and thus, lead to enhanced leakage of cytoplasmic components and cell death. Our endeavors will shed light into both antibiotics and supramolecular chemistry field and pave a new avenue into the development and application of antimicrobial agents.