Nitrogen-fixing aliens

Scientists hope that Titan, a moon of Saturn, with its nitrogen-rich atmosphere, could act as a model system for terrestrial chemistry before life began on our planet. Now, another step towards that goal has emerged as researchers at the University of Arizona have incorporated atmospheric nitrogen into organic macromolecules under conditions resembling those on Titan.

“Titan is so interesting because its nitrogen-dominated atmosphere and organic chemistry might give us a clue to the origin of life on our Earth,” explains Hiroshi Imanaka, who is an assistant research scientist in the UA’s Lunar and Planetary Laboratory. “Nitrogen is an essential element of life.” Titan looks orange through a telescope because its atmosphere is a rich smog of organic molecules. Particles in the smog could settle on the surface and be exposed to conditions that might eventually create life, said Imanaka.

Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)
Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)

Of course, nitrogen alone is not enough, nitrogen molecules must be converted to a chemically active form that can drive the necessary biochemical reactions that underpin biological systems.

Imanaka and Mark Smith converted a nitrogen-methane gas mixture similar to Titan’s atmosphere into a collection of nitrogen-containing organic molecules by irradiating the gas with high-energy ultraviolet light. The laboratory set-up was designed to mimic how solar radiation affects Titan’s atmosphere.

Most of the nitrogen simply formed solid compounds directly, rather than gaseous ones, explains Smith, whereas previous theories suggested that nitrogen would move from gaseous compounds to solid ones in stepwise process. But, those settling particles may not contain nitrogen at all. If some of the particles are the same nitrogen-containing organic molecules created by the UA team in the laboratory then it would suggest that conditions conducive to life might just exist on Titan, Smith says.

These and other laboratory observations help scientists planning future space missions to decide on what to look for on other worlds that might hint at life and what instruments should be developed to help in the search.

Links

Proc Natl Acad Sci, 2010, online
Mark A. Smith homepage
UA lunar and planetary laboratory

Low-temperature fraud detection

A low-temperature plasma probe can identify art fraud without damaging the artwork, which is important should the work turn out to be genuine.

Many priceless works of art are very delicate, so restoration, conservation, dating and authentication require sophisticated technical methods that avoid interfering with the substance of the work. Now, Sichun Zhang and colleagues at Tsinghua University in Beijing, China, have developed a new mass spectrometric imaging technique that can characterise paintings and calligraphy by barely scratching the surface.

In conventional mass spectrometry a substance is vaporised and then ionised to produce electrically charged particles of different sizes depending on the chemical structure of the compound. The ions are accelerated by an electric field and spread out by a magnetic field to produce a spectrum as the magnetic field makes particles of different mass to charge ratio deviate more or less than each other. Imaging mass spectrometry involves scanning a surface and releasing ions directly from the surface using special ionization methods. Unfortunately, these techniques require vacuum conditions, which limits sample size so that previously a tiny cutting would need to be removed from an artwork for analysis.

Probing reveals hidden information about art work without causing damage

The Chinese team has developed a low-temperature plasma probe, which consists of a fused capillary and two electrodes made of aluminium foil. High voltage alternating current applied to this probe induces a discharge in the capillary forming a low-temperature plasma; the probe reaches a mere 30 Celsius. However, in this state the helium plasma has energetic and excited enough to eject a few molecules from the surface of a sample and ionize them without measureable damage to a work of art.

The researchers used their approach to test seals, stamped signatures on Chinese paintings and calligraphy. They could reveal variations in ink composition easily, making it possible to differentiate between authentic and forged seals.

Links

Angew Chem Int Edn, 2010, online
Professor Dr. Xinrong ZHANG

Metallic liquid crystals

A new class of materials formed by combining liquid crystals and metal clusters glow intensely red in the infra-red region of the electromagnetic spectrum when irradiated over a broad range of wavelengths. The materials, dubbed clustomesogens, could be used in analytical instrumentation and potentially in display technologies.

Liquid crystals are well known in display technologies from digital watches to flat panel televisions. As their name suggests, they are at once liquid and can flow, but their molecules can also be oriented into something akin to a crystal state, usually under the influence of an electric field.

A second class of materials of interest to the optoelectronics field is metal clusters. Clusters are aggregates of just a few atoms, and so their properties are not those of individual atoms nor of the bulk metal, but somewhere in between. Indeed, metal clusters show some rather unusual electronic, magnetic, and optical properties because of the presence of the particular types of bonds that form between metals when just a few are present.

Now, Yann Molard, of the University of Rennes, in France, and colleagues there and at the University of Bucharest have united the two classes in clustomesogens to create metal clusters that exist in a liquid-crystalline phase.

Liquid crystals containing bonds between metal atoms are rare and usually limited to compounds in which just two metal atoms are connected in each unit. Molard and colleagues have produced liquid crystals that contains octahedral clusters made of six molybdenum atoms. Eight bromide ions sit on the eight surfaces of the octahedron, six fluorides and an aromatic organic group, or ligand, is at each vertex of the octahedron. These aromatic ligands each have three long hydrocarbon chains also ending in a pair of aromatic rings.

Yann Molard
Yann Molard

Simple warming these materials initiates a process of self-organization in which the clusters stretch out to form long, narrow units arranged in what is known as a lamellar, plate-like, structure. The flat rings at the ends of the ligands of neighbouring layers are interleaved and the structure has liquid-crystalline properties.

“The association of mesomorphism with the peculiar properties of metallic clusters should lead to clustomesogens that offer great potential in the design of new electricity-to-light energy conversion systems, optically based sensors, and displays,” the team says.

Links

Angew Chem Int Edn, 2010, 49, 3351-3355
Yann Molard homepage