Minimizing Defects in Polymer-Based Langmuir–Blodgett Monolayers and Bilayers via Gluing

Polymeric surfactants were prepared by quaternization of poly­(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 poly­(acrylic acid) (PAA) beneath the surface of these films led to a substantial increase in their cohesiveness (i.e., “gluing”), 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 H₂/CO₂ Selectivity of 200 That Reaches the Upper Bound

A 7 nm Thick Polymeric Membrane With a H₂/CO₂ 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 umbrella–octaargine 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 lipids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>-[methoxy­(polyethylene glycol)-2000 (DSPE-PEG₂₀₀₀), 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 umbrella–siRNA 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