6 research outputs found
Minimizing Defects in Polymer-Based LangmuirâBlodgett Monolayers and Bilayers via Gluing
Polymeric surfactants were prepared by quaternization
of polyÂ(4-chloromethylstyrene)
with <i>N</i>,<i>N</i>-dimethyl-<i>N</i>-<i>n</i>-dodecylamine and <i>N</i>,<i>N</i>-dimethyl-<i>N</i>-<i>n</i>-octylamine to give <b>1</b> and <b>2</b>, respectively. Each of these polymers
formed stable monolayers at the air/water interface. Injection of
polyÂ(acrylic acid) (PAA) beneath the surface of these films led to
a substantial increase in their cohesiveness (i.e., âgluingâ),
as evidenced by a dramatic increase in their surface viscosity. Examination
of monolayers of <b>1</b> by atomic force microscopy, after
being transferred to silicon wafers that were surface-modified with <i>n</i>-octadecyltrichlorosilane, showed that the presence of
PAA leads to intact film. In contrast, transfer of unglued monolayers
resulted in poor coverage. Comparison of the barrier properties of
single glued and unglued LB bilayers formed in the presence and in
the absence of PAA have shown that PAA minimizes defect formation
within these ultrathin assemblies
A 7 nm Thick Polymeric Membrane With a H<sub>2</sub>/CO<sub>2</sub> Selectivity of 200 That Reaches the Upper Bound
A 7 nm
Thick Polymeric Membrane With a H<sub>2</sub>/CO<sub>2</sub> Selectivity
of 200 That Reaches the Upper Boun
A Molecular Umbrella Approach to the Intracellular Delivery of Small Interfering RNA
A series of diwalled and tetrawalled molecular umbrellas
have been
synthesized using cholic acid, spermidine, and lysine as starting
materials. Coupling of these molecular umbrellas to an octaarginine
peptide afforded agents that were capable of promoting the transport
of small interfering RNA to HeLa cells, as judged by the knockdown
of enhanced green fluorescent protein expression. The efficiency of
this knockdown was found to increase with an increasing number of
facially amphiphilic walls present, and also when a cleavable disulfide
linker was replaced with a noncleavable, maleimido moiety; i.e., a
group that is not susceptible to thiolate-disulfide interchange. The
knockdown efficiency that was observed for one tetrawalled molecular
umbrellaâoctaargine conjugate was comparable to that observed
with a commercially available transfection agent, Lipofectamine 2000,
but the conjugate showed less cytotoxicity
Stimulated Release of Cholesterol from Liposomal Membranes by a PEGylated Phospholipid
PEGylated phospholipids are commonly used to increase
the blood-circulation
time of liposomes by providing a steric barrier around them. This
paper documents a fundamentally new property of these lipidsî¸an
ability to stimulate the release of cholesterol from phospholipid
membranes. Evidence for such stimulation has been obtained by measuring
the transport of dehydroergosterol (DHE), a fluorescent simulant of
cholesterol, from donor liposomes made from 1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphocholine (POPC), 1,2-distearoyl-<i>sn</i>-glycero-3-phosphoethanolamine-<i>N</i>-[methoxyÂ(polyethylene
glycol)-2000 (DSPE-PEG<sub>2000</sub>), and DHE to acceptor liposomes
made from POPC, 1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphoglycerol
(POPG), and cholesterol. The potential of PEGylated lipids to serve
as novel cholesterol-lowering agents is briefly discussed
Taming Amphotericin B
A strategy
is introduced for enhancing the cellular selectivity
of Amphotericin B (AmB) and other classes of membrane-disrupting agents.
This strategy involves attaching the agent to a molecular umbrella
to minimize the disruptive power of aggregated forms. Based on this
approach, AmB has been coupled to a molecular umbrella derived from
one spermidine and two cholic acid molecules and found to have antifungal
activities approaching that of the native drug. However, in sharp
contrast to AmB, the hemolytic activity and the cytotoxcity of this
conjugate toward HEK293 T cells have been dramatically reduced
Molecular Umbrella Conjugate for the Ocular Delivery of siRNA
The synthesis, computer modeling,
and biological activity of an
octawalled molecular umbrella short interfacing RNA (siRNA) conjugate
is described. This molecular umbrellaâsiRNA conjugate exhibited
mRNA knockdown activity <i>in vitro</i> in the absence of
a transfection reagent. Evaluation of this molecular umbrella conjugate <i>in vivo</i>, using the rat eye via intravitreal injection, resulted
in sequence specific <i>m</i>RNA knockdown in the retina
with no obvious signs of toxicity, as judged by ophthalmic examination