3 research outputs found
Influence of Phosphonium Alkyl Substituents on the Rheological and Thermal Properties of Phosphonium-PAA-Based Supramolecular Polymeric Assemblies
A noncovalent synthetic strategy
to supramolecular polymeric assemblies,
including network structures, is described by the complexation of
various phosphonium monocations and dications with the multianion,
polyĀ(acrylic acid). The alkyl chains surrounding the phosphonium cation
were systematically varied from butyl, hexyl, to octyl in order to
probe the effect of sterics and ion pairing on the resulting macroscopic
properties of the assemblies. The supramolecular assemblies were characterized
by TGA, DSC, oscillatory rheometry, steady-state flow rheometry, and
SAXS. The rheological and thermal properties, as well as the flow
activation energies, are highly dependent on the alkyl chain length.
All of the supramolecular assemblies have glass transition temperatures
lower than room temperature and range from 8 Ā°C to below ā40
Ā°C. Di-ButC10PAA has the shortest alkyl chain length and affords
the highest glass transition temperature. Correspondingly, it shows
the largest viscosity and storage and loss moduli. For example, its
viscosity is 3 orders of magnitude greater than di-OctC10PAA. In creep-recovery
experiments, di-ButC10PAA shows the highest percent of strain recovery
after the stress is removed, followed by di-HexC10PAA and di-OctC10PAA.
The rheological and thermal properties of monoIL-PAA assemblies show
similar alkyl chain length dependence, but the magnitude is significantly
less because of the lack of cross-linking. A reversibility test of
the supramolecular networks demonstrates that the ionic network material
can fully reassemble within a short time period after disruption of
the network due to heat or shear without sacrificing the mechanical
properties
Amino AcidāNucleotideāLipids: Effect of Amino Acid on the Self-Assembly Properties
Hybrid amphiphiles
composed of a lipid covalently linked to biomolecules
are attracting considerable attention, owing to their unique physicochemical
and biological properties. Herein, we have synthesized novel amino
acidānucleotideālipids (ANLs), presenting phenylalanine
and thymidine residues and saturated or unsaturated diacyl glycerol
lipid moieties to investigate the effect of the specific aminoacid
moieties on both aggregation properties and interactions of ANLs with
single strand polyA RNA. Physicochemical studies (DLS, cryo-TEM, and
small angle X-ray scattering) indicate that phenylanaline amino acids
inserted at the 5ā² position of the nucleotide-lipids stabilize
multilamellar systems, whereas unilamellar vesicles are formed preferentially
in the case of nucleotideālipids (NLs). Both NLs and ANLs exhibit
weak interactions with complementary polyA RNA as revealed by isothermal
titration calorimetry investigations. The multilamellar vesicles obtained
with ANLs could be used as a versatile carrier, suitable for both
hydrophobic and hydrophilic therapeutic molecules
Unexpected Bilayer Formation in Langmuir Films of Nucleolipids
Langmuir monolayers have been extensively investigated
by various
experimental techniques. These studies allowed an in-depth understanding
of the molecular conformation in the layer, phase transitions, and
the structure of the multilayer. As the monolayer is compressed and
the surface pressure is increased beyond a critical value, usually
occurring in the minimal closely packed molecular area, the monolayer
fractures and/or folds, forming multilayers in a process referred
to as collapse. Various mechanisms for monolayer collapse and the
resulting reorganization of the film have been proposed, and only
a few studies have demonstrated the formation of a bilayer after collapse
and with the use of a Ca<sup>2+</sup> solution. In this work, Langmuir
isotherms coupled with imaging ellipsometry and polarization modulation
infrared reflection absorption spectroscopy were recorded to investigate
the airāwater interface properties of Langmuir films of anionic
nucleolipids. We report for these new molecules the formation of a
quasi-hexagonal packing of bilayer domains at a low compression rate,
a singular behavior for lipids at the airāwater interface that
has not yet been documented