7 research outputs found
Order–disorder transition induced by surfactant micelles in single-walled carbon nanotubes dispersions
Rheological investigation of single-walled carbon nanotubes – induced structural ordering in CTAB solutions
Cardinal Role of Intraliposome Doxorubicin-Sulfate Nanorod Crystal in Doxil Properties and Performance
The
uniqueness of Doxil can be attributed, to a large extent, to
its intraliposomal doxorubicin-sulfate nanorod crystal. We re-examine
these nanocrystal features and their mechanism of the formation by
studying pegylated liposomal doxorubicins (PLDs) of the same lipid
composition, size distribution, and extraliposome medium that were
prepared at different ammonium sulfate (AS) concentrations. This study
includes a comparison of the thermotropic behavior, morphology, and
in vitro ammonia-induced doxorubicin release (relevant to Doxil’s
in vivo performance) of these PLDs. In this study, we confirm that
a transmembrane ammonium gradient is critical for doxorubicin remote
loading, and we demonstrate that the intraliposomal concentration
of sulfate counteranions and ammonium ions determine to a large extent
the physical state and stability of the PLDs’ remote loaded
doxorubicin. “Fully-developed” intraliposome doxorubicin-sulfate
nanorod crystals (as defined by cryogenic transmission electron microscopy
imaging) develop only when the ammonium sulfate (AS) concentration
used for PLD preparation is ≥150 mM. Less than 10% of PLDs
prepared with 100 mM AS show fully developed nanorod crystals. Intraliposomal
AS concentration ≥200 mM is required to support the stable
nanocrystallization in PLDs. The presence of nanocrystals and their
melting enthalpy and phase transition co-operativity strongly affect
the ammonia-induced doxorubicin release of PLDs. A quick, biphasic
release occurs for PLDs that lack the nanorod crystals or have crystals
of poor crystallinity, whereas PLDs prepared with ≥200 mM AS
show a monophasic, zero-order slow release. This study also demonstrates
that after remote loading, residual intraliposomal ammonium concentration
and the transmembrane pH gradient related to it also play an important
role in doxorubicin-sulfate intraliposomal crystallization and ammonia-induced
doxorubicin release
Nematic Ordering of SWNT in Meso-Structured Thin Liquid Films of Polystyrenesulfonate
The
formation of nematic-like islands of single-walled carbon nanotubes
(SWNT) in polystyrenesulfonate (PSS) dispersions confined into nanometrically
thin films is reported. The SWNT are observed to assemble into orientationally
ordered phases, where the intertube distance, as measured via transmission
electron microscopy at cryogenic temperatures, matches the polyelectrolyte’s
bulk correlation length deduced from X-ray scattering. The micrometers-long
islands of orientationally ordered carbon nanotubes are observed in
both SWNT and double-walled carbon nanotubes (DWNT) but not in specimens
prepared from similar dispersions of multiwalled carbon nanotubes
(MWNT). These observations, together with relaxation and rheological
experiments, suggest that the orientational ordering may result from
coupling between confinement of the polymer-wrapped SWNT and DWNT
and the microstructure of the solvated polyelectrolyte