Facile synthesis of silver nanoparticles in CO2-expanded liquids from silver isostearate precursor.

This approach provides a new technique to synthesize silver nanoparticles (AgNPs) using CO(2)-expanded liquids (CXLs) as the processing medium. A soluble form of silver carboxylate, silver isostearate (AgISt), was synthesized and characterized. The XRD and DSC analyses indicated that the methylated branched alky chains in AgISt exhibited a steric hindrance to impede the growth of layered structure of AgISt molecules, which led to the high solubility of AgISt in nonpolar solvents. By using AgISt as silver precursor, AgNPs of 2.64 +/- 0.51 nm in diameter were synthesized in CO(2)-expanded heptane with H(2) as the reducing agent. The ATR-FTIR analysis showed that the produced AgNPs were capped with isostearic acid, which was derived from the reduction of AgISt. Hence, the isostearic acid capped AgNPs were well-dispersed in heptane to form a stable silver organosol.

Effect of molecular weight on the transfection efficiency of novel polyurethane as a biodegradable gene vector.

New polyurethane 2-diethylaminoethylamine-polyurethane (LGEA-PU) containing poly(ethylene glycol) segments and tertiary amines was synthesized. LGEA-PU self-assembled readily with the plasmid DNA (pCMV-betagal) in HEPES buffer and was characterized by dynamic light scattering, zeta potential, atomic force microscopy, and XTT cell viability assays. To examine the effect of molecular weight of LGEA-PU systems on transfection, LGEA-PU systems of four different molecular weights (LGEA-PU99, LGEA-PU59, LGEA-PU24, and LGEA-PU7) were prepared. This study found that LGEA-PU99, LGEA-PU59, and LGEA-PU24 were able to bind plasmid DNA and yielded positively charged complexes with a nano-sized transfection (<200 nm). The LGEA-PU59/DNA complexes were able to transfect COS-7 cells in vitro with higher transfection efficiency than the other LGEA-PU systems. These results demonstrated that molecular weights of LGEA-PU systems had a significant effect on transferring ability, except for LGEA-PU99, which showed the strongest DNA condensation. Examination of the cytotoxicity of PEI and LGEA-PU systems revealed that LGEA-PU systems had lower cytotoxicity. In this article, LGEA-PU59 seemed to be a novel cationic polyurethane for gene delivery and an interesting candidate for further study.

Photorefractive effect in nematic-clay nanocomposites.

The orientational photorefractive effect was observed in an organic-inorganic nanocomposite of nematic liquid crystal hybridized with montmorillonite clay. Both the self-diffraction and beam-coupling effects were evaluated in a two-wave-mixing experiment in conjunction with an externally applied dc field. The experimental results indicate that photoinduced generation was enhanced by the addition of smectite clay with adequate concentration. Physically, the drifting ion charges were trapped by clay layers and separated by interlayer cations, creating an internal, spatially modulated space-charge field, which led to nematic molecular orientation and, then, refractive-index modulation via the electro-optical response. The diffraction efficiency as well as the beam-coupling ratio of the phase gratings recorded in the cells of the nematic liquid crystal hybridized with montmorillonite clay was found to be two to three times higher than that in the pristine nematic cell.

Nanoparticles-doped guest-host liquid crystal displays.

The technique, nanoparticles-induced vertical alignment (NIVA), was applied to fabricate a guest-host liquid crystal display (GH-LCD) without conventional alignment layers. The GH-LCD produced by NIVA exhibited a high reflectance of approximately 59% in the voltage-off state and a low threshold voltage of approximately 2.1 V(rms). NIVA is very suitable to be applied for fabricating a plastic LCD requiring a low temperature process, and a flexible timepiece by using NIVA was demonstrated.

Synthesis of novel biodegradable cationic polymer: N,N-diethylethylenediamine polyurethane as a gene carrier.

A new cationic polymer, N,N-diethylethylenediamine-polyurethane (DEDA-PU), bearing tertiary amines in the backbone and side chains, was synthesized and used as a nonviral vector for gene delivery. The DEDA-PU readily self-assembled with the plasmid DNA (pCMV-betagal) in water and buffer at physiological pH, as determined by agarose gel retardation, dynamic light scattering, zeta potential, atomic force microscopy (AFM), and restriction endonuclease protection assays. The results revealed that DEDA-PU was able to bind with plasmid DNA, yielding positively charged complexes with a size around 100 nm at a DEDA-PU/DNA ratio of 50/1 (w/w). The DEDA-PU/DNA complexes were able to transfect HEK 293 cells in vitro with an efficiency comparable to a well-known gene carrier [poly(2-dimethylaminoethyl methacrylate), PDMAEMA]. The cytotoxicity of DEDA-PU was substantially lower than PDMAEMA. The degradation studies indicated that DEDA-PU degrades hydrolytically in 20 mM HEPES buffer at pH 7.4 with a half-life of approximately 60 h. This study shows that DEDA-PU holds promise as biodegradable polycations for gene delivery and is interesting candidate for further study.