University of Bielefeld, Germany

A chemist finds beauty in molecules that resemble an early model of the Solar System.

Since Plato's time, people have been fascinated by the beauty of highly symmetrical objects. The symmetry of the C60 buckyball surely contributed to scientists' tremendous interest in this spherical molecule. Indeed, I was convinced that the discovery of C60 would induce a rush among chemists to search for other symmetrical structures.

That rush may not have happened, but scientists have still turned up some surprising highly symmetrical structures. A recent report from researchers at Xiamen University in China (X.-J. Kong et al. J. Am. Chem. Soc. 129, 7016–7017; 2007) describes a cluster in which beauty cages beauty; it consists of an icosidodecahedron of nickel ions, having 20 triangular faces and 12 pentagonal faces, inside of which sits a dodecahedron of lanthanum ions.

The team describes the magnificent structure as 'Keplerate', a term that I and my colleagues first used around ten years ago to describe structures that contain Platonic and Archimedean solids (regular polyhedra, and polyhedra with two types of face, respectively) one inside another, like Russian dolls. It honours Johannes Kepler, who in the sixteenth century developed a model of the cosmos in which "the radii of the successive planetary orbits are proportional to the radii of spheres that are successively circumscribed around and inscribed within the five Platonic solids".

Another recent report found these same shapes — the icosidodecahedron and dodecahedron — in Keplerate-type arrangements in quasicrystals (H. Takakura et al. Nature Mater. 6, 58–63; 2007). Such crystals are still poorly understood. I hope that future work will correlate these materials' properties with their beauty.

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Swiss Federal Institute of Technology, Zürich, Switzerland

A climate scientist worries that attempts to curb atmospheric carbon dioxide levels are challenged on two fronts.

What is your carbon footprint? I must admit that, as someone who frequently travels across continents, mine is well above the Swiss average. Even worse, my footprint has grown over the past few years despite the fact that I am well aware of the consequences of my actions.

Now, imagine that everyone else on this planet has increased their carbon footprint as well. This is not hypothetical. A recent paper tells us that global carbon emissions have grown at the unexpectedly high rate of more than 3% per year since 2000 (M. Raupach et al. Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0700609104; 2007).

In particular, the rapidly increasing appetite for energy of the emerging markets in Asia has led to a dramatic increase in fossil-fuel burning. As a result, global CO2 emissions now exceed the worst-case scenarios of just a few years ago. This is far from the direction that we ought to be taking to achieve a stabilization of greenhouse gases that "prevents dangerous interference with the climate system", as the Climate Convention in Rio set out to achieve in 1992.

Unfortunately, the situation may become even more difficult. Earth's biosphere has so far helped to mitigate the carbon problem by removing a substantial fraction of the emitted CO2, but this 'sink' function may diminish.

There is some evidence that sinks are already weakening (C. Le Quéré et al. Science doi:10.1126/science.1136188; 2007), and coupled climate–carbon-cycle models tend to support the view that the trend will persist. If so, we are challenged at both ends — by unexpectedly rapidly increasing emissions and by diminishing sink strengths — making climate stabilization a truly grand challenge.

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Massachusetts Institute of Technology, USA

A bioengineer sees a future for safe gene-silencing therapies.

The possibility of treating genetic disorders by modifying gene expression has been an attractive yet elusive goal for decades. Problems with the safety and efficacy of various types of gene therapy have held back progress. In particular, there have been some high-profile failures, including a number of deaths during clinical trials.

But seminal studies reported by Andrew Fire and Craig Mello in 1998 led to a potentially new class of therapeutic agent. These researchers, who went on to share a Nobel prize for their work, found that small pieces of RNA, dubbed siRNAs, can silence genes.

Although switching off genes may have fewer complications than adding new ones, the safe and effective delivery of genetic agents remains a critical challenge. I was therefore pleased to see a recent paper reporting tests of an siRNA-delivery system in monkeys (J. Heidel et al. Proc. Natl Acad. Sci. USA 104, 5715–5721; 2007), suggesting that safe, repeated systemic administration of siRNAs is possible.

Mark Davis of the California Institute of Technology in Pasadena and his colleagues created nanoparticles composed of siRNAs and a novel polymer based on the sugar cyclodextrin. These particles were injected into the monkeys and their health was monitored. The monkeys tolerated multiple doses of siRNA of increasing amounts.

This paper was of interest to me not only because my group works on lipid formations that might serve as delivery systems for siRNA or other genetic agents, but also because I was pleased to see a former student doing well. Jeremy, the first author, once worked in my lab as an undergraduate.

Studies such as this one are bringing back to the field the excitement that surrounded gene therapies in the 1980s.

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University of Hyderabad, India

A chemist applauds an algorithm able to predict crystal structures from chemical composition alone.

I work in crystal engineering, a field that involves designing and constructing crystals with desired physical, chemical or pharmaceutical properties from small organic molecules. It is an experimental science based on pattern recognition and retrosynthetic strategies, in which the structure is considered as the sum of smaller, simpler parts.

Improvements to computational crystal-structure prediction could make design protocols more reliable. But this is such a difficult problem that only a handful of groups in the field work on it. In this context, I found a recent paper presenting a seemingly reliable method to be thought-provoking (A. R. Oganov and C. W. Glass J. Chem. Phys. 124, 244704; 2006).

Typically, crystal-structure prediction involves computer generation of putative crystal structures using a force field, which represents the interactions between atoms in neighbouring molecules. The correct structure is presumed to be that which minimizes the crystal's energy.

The procedure is problematic because the force fields may not be well tailored to the molecules being studied, and because the experimental structure may not be the lowest-energy arrangement. It is also impossible to explore all conceivable structures, which are mind-boggling in number.

Oganov and Glass use an evolutionary algorithm to localize the search to the most promising structures. Their approach is attractive in that it requires no system-specific knowledge — the input is just the molecule's chemical composition, not even its structure — and their ability to predict the unusual tetragonal structure of urea is impressive.

Is this the long-awaited breakthrough in crystal engineering? Perhaps not, but surely it's an important step forward.

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