2 research outputs found
From Chain Collapse to New Structures: Spectroscopic Properties of Poly(3-thiophene acetic acid) upon Binding by Alkyl Trimethylammonium Bromide Surfactants
The binding of cationic surfactants with varying alkyl
chain length to a regiorandom conjugated polyanion,
polyÂ(3-thiophene acetic acid) (PTAA), is studied in an aqueous buffer
by using absorption and emission spectroscopies, photon correlation
spectroscopy, isothermal titration calorimetry, and cryogenic transmission
electron microscopy. We study the mixed solutions as a function of
composition ratio <i>R</i> of surfactant molecules to monomer
units molar concentrations, at low polymer concentration and in a
very wide composition range (10<sup>–6</sup> < <i>R</i> < 10<sup>2</sup>) below the critical micellar concentration.
Upon surfactant binding, the molecularly dispersed chains first collapse
progressively and then form new structures as the mixed aggregates
get enriched in surfactant. The collapse leads to a strong decrease
of the conjugation length and to a blue shift of the absorption spectra
by 30 to 50 nm. The new structures are responsible for a new intense
emission band at about 600 nm, red-shifted by nearly 130 nm from the
initial emission maximum of the polymer (∼472 nm). As the surfactant
tail becomes shorter, the blue shift of the absorption spectra and
the intensity raise of the new emission are delayed to larger composition
ratios while their variations become smoother functions of the surfactant
concentration. These particular spectroscopic properties of PTAA seem
related to its unique combination of a strongly hydrophobic backbone,
a large ratio of contour length to persistence length, and an overall
good aqueous solubility. Our results show that such features are well
suited to design a colorimetric biosensor at small composition ratio,
and a fluorescent biomarker at large composition ratio
Phase Separation and Nanodomain Formation in Hybrid Polymer/Lipid Vesicles
Hybrid
polymer/lipid large unilamellar vesicles (LUVs) were studied
by small angle neutron scattering (SANS), time-resolved Förster
resonance energy transfer (TR-FRET), and cryo-transmission electron
microscopy (cryo-TEM). For the first time in hybrid vesicles, evidence
for phase separation at the nanoscale was obtained, leading to the
formation of stable nanodomains enriched either in lipid or polymer.
This stability was allowed by using vesicle-forming copolymer with
a membrane thickness close to the lipid bilayer thickness, thereby
minimizing the hydrophobic mismatch at the domain periphery. Hybrid
giant unilamellar vesicles (GUVs) with the same composition have been
previously shown to be unstable and susceptible to fission, suggesting
a role of curvature in the stabilization of nanodomains in these structures