Inorganic chemistry: Triple connection

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0707035104 (2007)

The synthesis of molecules with triple bonds between uranium and carbon atoms is possible, according to the findings of researchers based in America and China.

Lester Andrews of the University of Virginia in Charlottesville, Jun Li at Tsinghua University in Beijing and their colleagues reacted uranium atoms with halomethanes. They then used infrared spectroscopy to show that the complexes formed contained relatively strong uranium–carbon triple bonds. Changing the atoms close to those in the bond could 'tune' its strength, says Andrews.

But creating these quirky molecules under normal laboratory conditions is a long way off. This team needed lasers to generate the uranium atoms, plus a caesium iodide block held at a frosty 8 kelvin in an argon-rich atmosphere to produce the complexes.

Acoustics: Nostril navigation

Credit: R. MÜLLER

Phys. Rev. E 76, 051902 (2007)

The sonar squeak of a bat is governed by the shape of its nose, according to physicists at Shandong University in Jinan, China.

Using X-ray tomography of the face of Rhinolophus rouxi (pictured), a type of horseshoe bat, the researchers created a three-dimensional model of the structures around its nostrils, known the noseleaf. Qiao Zhuang and Rolf Müller programmed sonar waves to propagate through their model, noting where the waves resonated inside the nose and what shape the waves formed when they left it.

Low-frequency waves bounced off structures that shaped them into a wide beam. Meanwhile, high-frequency waves resonated in a separate part of the noseleaf that focused the sonar signal. This could explain why switching frequency seems to help horseshoe bats shift from general navigation to homing in on prey.

Epigenetics: The single life

Science 318, 1136–1140 10.1126/science.1148910 (2007)

Although endowed with two versions of most genes, humans seem to rely on just one surprisingly often. Geneticists had thought that, with rare exceptions, when a gene is turned on both its maternal and paternal versions are expressed. But Andrew Chess and his colleagues at Harvard Medical School in Boston, Massachusetts, have screened almost 4,000 genes in B lymphocytes, a type of immune cell, and found that 371 of them sometimes break this rule.

The authors found that the choice of which version these cells use is random, but that every daughter cell follows its progenitor's decision. Further study will firm up how this effect might influence human traits.

Molecular biology: Starting block

Cancer Cell 12, 432–444 (2007)

An arrangement that inactivates genes on one of the two X chromosomes in female mammalian cells is also involved in certain cancers.

In some inactivated X-chromosome genes the sites at which transcription would begin are wrapped in structures known as nucleosomes, making them inaccessible. According to Peter Jones and his colleagues at the University of Southern California in Los Angeles, nucleosomes also become bound in — and inactivate — promoter regions of several genes with a tumour-suppressor role.

Working with several cancer cell lines, Jones and his team removed methyl groups, which draw in nucleosomes, from DNA in the promoter region of a gene that is frequently turned off in colon cancer. Doing so freed three start sites and switched the gene into a non-cancerous 'on' mode.

Organic chemistry: Sifting for bonds

J. Am. Chem. Soc. advance online publication doi:10.1021/ja074155j (2007)

Reactions that form bonds between two chemical groups are the basic tools of molecule-building. These have mostly been discovered by trial and error, but David Liu and his co-workers at Harvard University in Cambridge, Massachusetts, have devised a method for screening large numbers of reactant pairs in organic solvents to find out which join up under different conditions.

It involves tethering two different chemical groups to a single strand of DNA that is unique to each combination. If two groups react, the product remains stuck to the pair-specific DNA, even though the DNA's link to one of the groups is cut.

A chemical hook attached to one reactant group sticks to the surface of magnetic beads, which can then be separated. But the hooks only retain the DNA of pairs that have reacted — otherwise the earlier cleavage process cuts it free. DNA hybridization then reveals the identities of the product-forming pairs.

Plant evolution: Taking after mother

Science 318, 1134–1136 (2007)

Mother plants can transmit information about their environment to their offspring, thereby increasing their progeny's fitness.

Laura Galloway at the University of Virginia in Charlottesville and Julie Etterson at the University of Minnesota-Duluth studied Campanulastrum americanum, a small forest plant that grows both in sunny spots and in the shade of the forest canopy. Its seeds tend to sprout near the mother plant, within the same patch of sun or shade.

When the researchers grew plants in the opposite light environment from that of their mothers, the population grew at a slower rate. This suggests that maternal plants cue their offspring about the light environment they are likely to experience. Because this signal can change each generation, it is a flexible way of enhancing the success of offspring.

Cell biology: Size control

J. Cell Biol. doi: 10.1083/jcb.200708054 (2007)

Fission yeast regulates the size of its nucleus to stay in sync with the volume of its cytoplasm, researchers have found.

How cells control organelle size is a century-old question. Frank Neumann and Paul Nurse at the Rockefeller University in New York measured nuclear and cellular volumes in the fission yeast Schizosaccharomyces pombe. Using various mutants, they found similar nucleus-to-cell volume ratios over a 35-fold variation in cell size and a 16-fold difference in DNA content.

And from studies of cells with four nuclei, they suggest that the cytoplasmic environment that the nucleus resides in is an important regulator of its size. The molecular basis of this control remains unknown.

Materials science: Out of reach

Credit: STUDIOATA

Nanotoday 2, 44–47 (2007)

Space elevators (depicted) are a mainstay of science fiction. But advances in nanotechnology have spurred Nicola Pugno at Torino Polytechnic in Italy to consider whether shooting a payload into space up a 100,000-kilometre-long cable may one day be possible.

Previously, he worked out that the tensile strength of a huge carbon nanotube bundle would drop from 100 gigapascals to 80 gigapascals, were each nanotube to have one atom out of place. Now his calculations show that each rod would inevitably contain at least one defect four atoms long, making it less than 45 gigapascals strong and weaker than the 63 gigapascals required for a line of uniform thickness. Manufacturing constraints would force engineers to make a cable up to 600 times fatter at the height of its geosynchronous orbit.

Quantum physics: Early jiggles

Phys. Rev. Let. 99, 201301 (2007)

A line of ions could provide clues about the early Universe. Ralf Schützhold at the Technical University of Dresden in Germany and his colleagues have calculated that quantum fluctuations in the vibrations of a column of trapped magnesium ions are mathematically similar to the period of rapid expansion that followed the Big Bang.

Stretching and squeezing the column should cause the quantum fluctuations to become real vibrations, in much the same way that the stretching of space-time created matter and energy in the young cosmos. The group is now trying an experiment to see how well the analogy holds up.

Evolution: Sweet insight

Credit: S. JOHNSON

Biol. Lett. doi:10.1098/rsbl.2007.0496 (2007)

Researchers in South Africa have overturned a long-held belief that hummingbirds and perching birds consume different nectars. Steven Johnson of the University of KwaZulu-Natal and Susan Nicolson of the University of Pretoria suggest that a more accurate distinction falls between specialist nectar-feeders and omnivorous species.

Flowers make either small amounts of concentrated sucrose-rich nectar or larger volumes of dilute liquid containing simpler sugars. Conventional wisdom held that flowers pollinated by sunbirds — perching birds that specialize in drinking nectar — make dilute nectar similar to that of blooms providing for generalist perching birds (such as the Cape weaver, pictured), and unlike the concentrated nectar of hummingbird-adapted flowers. These authors report that this is not the case, a finding that alters ecologists' ideas about the evolutionary links between flowers and their avian pollinators.

Differences in the digestive enzymes of bird guts may explain why the types of sugars found in the two recipes are distinct, the researchers add.