01/08/19 - 9:45 AM to 11:00 AM
Department Seminar: Lily Robertson, Ph.D.
From Ionic Liquid Crystal Design and Polymerization to Bioapplicable Mucoadhesive Polymers
Liquid crystals (LCs), the so-called “fourth state of matter,” possess nanoscale order while maintaining fluidity. By tailoring LC molecular structure, desirable materials properties can be elucidated. In particular, amphiphilic designs such as ionic liquid crystals (ILCs), with structurally-segregated ionic and non-polar components, add favorable ionic liquid characteristics such as high conductivity and molecular separations utility. The bicontinuous cubic LC phases are particularly desirable due to their distinctive 3D ordered nanostructure that predisposes their use in transport and uptake/release applications. A novel amphiphilic ILC platform using a hexyl-bridged bis(imidazolium) headgroup connected to a single alkyl tail exhibited both thermotropic (thermal-induced) and lyotropic (solvent-induced) bicontinuous cubic LC phases. By varying amphiphile tail length (12–20 carbons, evens) and anion (Br–, BF4–, or Tf2N–), variegated LC behavior was observed, with many compounds showing both thermotropic and lyotropic LC behavior in general. Seeking new cross-linkable designs, which are highly useful to “lock” these nanostructures in place, we probed the structural perturbations of polymerizable groups. As non-polymerizable mono-imidazolium salts with long alkyl tails (12+ carbons) are well established for their thermotropic smectic LC phase behavior, this system was chosen as a model platform. Thus, a series of radically-polymerizable non-symmetric mono-imidazolium salts containing polymerizable groups on opposing molecular ends (to enable cross-linking) were prepared. The optimal thermotropic LC phase conditions were screened based on polymerizable group type (e.g., n-alkyl-2,4-hexadiene, olefin ester, and vinyl) and alkyl spacer length. Long alkyl tail spacers and less polar polymerizable groups favored thermotropic LC behavior while more polar olefin ester groups greatly diminished or eliminated the smectic LC order. A novel n-alkyl-2,4-hexadiene polymerizable group had the best thermotropic LC phase behavior, and in situ photo-cross-linking was successfully demonstrated. Initial engineering properties (ionic conductivity) of the cross-linked nanostructures were also examined.
On a much larger length scale than liquid crystals, biological mucins are fascinating in their structural complexity and polydispersity. These biomacromolecules range from 500 kDa to 20 MDa molecular weight and are theorized to possess a “dumbbell-like” structure, with two large globular protein regions connected by a highly glycosylated protein core. Mucoadhesives, materials which “stick” to mucin, are important for applications such as soft tissue drug delivery and biomimetic bioadhesive materials. Mucoadhesive polymers are actively studied for these applications; however, there is limited polymer development, with natural chitosan-based polymers and synthetic poly(acrylic acid) derivatives the most frequently studied. To expand the scope of mucoadhesive polymers, we pursued ring-opening metathesis polymerization (ROMP) of 7-oxanorbornene (ONB) monomers. We hypothesized that the carbohydrate-like oxygen-containing backbone of poly(ONB) coupled with attached carboxylic acid groups would enable strong mucoadhesion via complexation with the glycan brushes of the mucin core. Physical mucoadhesion to porcine gastric mucin (PGM) by initial aqueous rheological shear rate studies showed increased bioadhesion with increasing poly(ONB) molecular weight. Additional adhesive interaction was demonstrated by pulsed-gradient spin-echo NMR (PGSE-NMR) and dynamic light scattering experiments. These preliminary results also suggest that poly(ONB) performs better than poly(acrylic acid). Current work is focused on post-functionalization of the polymer backbone (hydrogenation) to probe the effect of flexibility on mucoadhesion.
Lily Robertson, Ph.D., is a post-doctoral research associate, working with Professor Jeff Moore. She earned her doctorate in chemistry in 2016 from the University of Colorado, Boulder, working with Professor Douglas L. Gin. She obtained her bachelor's degree in chemistry and mathematics from the University of Oregon, Eugene, where her adviser was Professor Mark Lonergan.
Robertson's primary research develops hydrophilic polymers using ring-opening metathesis polymerization for mucoadhesive applications and characterization of mucoadhesion. She is interested in how structural changes in polymer design and changes in polymer size correlate with mucoadhesion. Her research also involves interdisciplinary collaboration through the Joint Center for Energy Storage Research. These include measurement of dynamics of nonaqueous redox flow battery (NRFB) solutions via neutron scattering techniques, a collaboration with Professor Yang Zhang's group at the University of Illinois at Urbana-Champaign, and exploration of redox-active molecules that are both soluble and stable for NRFBs in collaboration with Argonne National Laboratory
Event DetailsLocation: 331 Smith HallHost: Professor Theresa ReinekeSpeakers:
- Lily Robertson, Ph.D.
- Department of Chemistry
- University of Illinois at Urbana-Champaign