2 research outputs found
Domain-Specific Phase Transitions in a Supramolecular Nanostructure
Understanding thermal phase behavior within nanomaterials
can inform
their rational design for medical technologies like drug delivery
systems and vaccines, as well as for energy technologies and catalysis.
This study resolves thermal phases of discrete domains within a supramolecular
aramid amphiphile (AA) nanoribbon. Dynamics are characterized by X-band
EPR spectroscopy of spin labels positioned at specific sites through
the nanoribbon cross-section. The fitting of the electron paramagnetic
resonance (EPR) line shapes reveals distinct conformational dynamics,
with fastest dynamics at the surface water layer, intermediate dynamics
within the flexible cationic head group domain, and slowest dynamics
in the interior aramid domain. Measurement of conformational mobility
as a function of temperature reveals first- and second-order phase
transitions, with melting transitions observed in the surface and
head group domains and a temperature-insensitive crystalline phase
in the aramid domain. Arrhenius analysis yields activation energies
of diffusion at each site. This work demonstrates that distinct thermal
phase behaviors between adjacent nanodomains within a supramolecular
nanostructure may be resolved and illustrates the utility of EPR spectroscopy
for thermal phase characterization of nanostructures
Geometric Transformations Afforded by Rotational Freedom in Aramid Amphiphile Nanostructures
Molecular self-assembly in water
leads to nanostructure
geometries
that can be tuned owing to the highly dynamic nature of amphiphiles.
There is growing interest in strongly interacting amphiphiles with
suppressed dynamics, as they exhibit ultrastability in extreme environments.
However, such amphiphiles tend to assume a limited range of geometries
upon self-assembly due to the specific spatial packing induced by
their strong intermolecular interactions. To overcome this limitation
while maintaining structural robustness, we incorporate rotational
freedom into the aramid amphiphile molecular design by introducing
a diacetylene moiety between two aramid units, resulting in diacetylene
aramid amphiphiles (D-AAs). This design strategy enables rotations
along the carbon–carbon sp hybridized bonds
of an otherwise fixed aramid domain. We show that varying concentrations
and equilibration temperatures of D-AA in water lead to self-assembly
into four different nanoribbon geometries: short, extended, helical,
and twisted nanoribbons, all while maintaining robust structure with
thermodynamic stability. We use advanced microscopy, X-ray scattering,
spectroscopic techniques, and two-dimensional (2D) NMR to understand
the relationship between conformational freedom within strongly interacting
amphiphiles and their self-assembly pathways