Light but stable: novel cellulose-silica gel composite aerogels

Gels are familiar to us in forms like Jell-O or hair gel. A gel is a loose molecular network that holds liquids within its cavities. Unlike a sponge, it is not possible to squeeze the liquid out of a gel. An aerogel is a gel that holds air instead of a liquid. For example, aerogels made from silicon dioxide may consist of 99.98 % air-filled pores. This type of material is nearly as light as air and is translucent like solidified smoke. In addition, it is not flammable and is a very good insulator—even at high temperatures. One prominent application for aerogels was the insulation used on space shuttles. Because of their extremely high inner surface area, aerogels are also potential supports for catalysts or pharmaceuticals. Silica-based aerogels are also nontoxic and environmentally friendly.

One drawback, however, has limited the broader application of these airy materials: silica-based aerogels are very fragile, and thus require some reinforcement. In addition to reinforcement with synthetic polymers, biocompatible materials like cellulose are also under consideration.

The researchers at Wuhan University (China) and the University of Tokyo (Japan) have now developed a special composite aerogel from cellulose and silicon dioxide. They begin by producing a cellulose gel from an alkaline urea solution. This causes the cellulose to dissolve, and to regenerate to form a nanofibrillar gel. The cellulose gel then acts as a scaffold for the silica gel prepared by a standard sol–gel process, in which a dissolved organosilicate precursor is cross-linked, gelled, and deposited onto the cellulose nanofibers. The resulting liquid-containing composite gel is then dried with supercritical carbon dioxide to make an aerogel.

The novel composite aerogel demonstrates an interesting combination of advantageous properties: mechanical stability, flexibility, very low thermal conductivity, semitransparency, and biocompatibility. If required, the cellulose part can be removed through combustion, leaving behind a silicon dioxide aerogel. The researchers are optimistic: "Our new method could be a starting point for the synthesis of many new porous materials with superior properties, because it is simple and the properties of the resulting aerogels can be varied widely."

More information: Jie Cai, Cellulose–Silica Nanocomposite Aerogels by In Situ Formation of Silica in Cellulose Gel, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201105730

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Just the two of us: Stable dinucleotide-RNA duplexes show promise in biotechnology

A Swedish team headed by R. Strömberg recently reported in the European Journal of Organic Chemistry that modification of oligonucleotides with a 2'-O-carbamoyl moiety greatly increases the stability of these compounds, which may render their use in constructs for biotechnological and therapeutic applications viable.

Efficiency in the regulation of gene expression is readily achieved if turnover of the target RNA is obtained, but this can only occur if native enzymes recognize the relevant oligonucleotide complex. The ability to catalytically cleave a specific sequence of RNA at a specific site is of high potential value in biotechnology and oligonucleotide therapy. Thus, the development of oligonucleotide-based artificial nucleases (OBANs) as artificial enzymes capable of cleaving mRNA sequences arising from genetic or viral diseases is highly sought.

In this context, the scientists set out to modify oligonucleotides with the judicious choice of a 2'-carbamoylmethyl (CM) moiety. Substitution at the 2-position was an important prerequisite, as this has been shown to lead to the formation of stable duplexes with the target RNA, and it was also believed that the CM moiety could further increase the stability of the duplex through hydrogen bonding.

The team was able to show that the 2'-O-carbamoyl modification substantially protected the dinucleotide against enzyme-catalyzed degradation by phosphodiesterase I and made it virtually resistant to degradation by phosphodiesterase II. This, together with the reported increased thermal stability of the duplexes, makes the often-neglected 2'-O-carbamoyl moiety an interesting modification in the pursuit of future compounds that may one day help in the treatment of genetic diseases.

More information: Roger Strömberg, Stability of a 2'-O-(Carbamoylmethyl)adenosine-Containing Dinucleotide, European Journal of Organic Chemistry, http://dx.doi.org/ … oc.201101264

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Point defects in super-chilled diamonds may offer stable candidates for quantum computing bits

Diamond, nature's hardest known substance, is essential for our modern mechanical world -- drills, cutters, and grinding wheels exploit the durability of diamonds to power a variety of industries. But diamonds have properties that may also make them excellent materials to enable the next generation of solid-state quantum computers and electrical and magnetic sensors.

To further explore diamonds' quantum computing potential, researchers from the University of Science and Technology of China tested the properties of a common defect found in diamond: the nitrogen-vacancy (NV) center.

Consisting of a nitrogen atom impurity paired with a 'hole' where a carbon atom is absent from the matrix structure, the NV center has the potential to store information because of the predictable way in which electrons confined in the center interact with electromagnetic waves. The research team probed the energy level properties of the trapped electrons by cooling the diamonds to an extremely chilly 5.6 degrees Kelvin and then measuring the magnetic resonance and fluorescent emission spectra. The team also measured the same spectra at gradually warmer increments, up to 295 degrees Kelvin.

The results, as reported in the AIP's journal Applied Physics Letters, show that at temperatures below 100 Kelvin the electrons' transition energies, or the energies required to get from one energy level to the next, were stable. Shifting transition energies could make quantum mechanical manipulations tricky, so cooler temperatures may aid the study and development of diamonds for quantum computation and ultra-sensitive detectors, the authors write.

The above story is reprinted (with editorial adaptations ) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

X.-D. Chen, C.-H. Dong, F.-W. Sun, C.-L. Zou, J.-M. Cui, Z.-F. Han, and G.-C Guo. Temperature dependent energy level shifts of nitrogen-vacancy centers in diamond. Applied Physics Letters, 2011