The Conversation – Page 7

Turning salt into exotic chemicals under high pressure

December 26, 2013January 25, 2014 Akshat RathiLeave a comment

Everything around you is made of elements that scientists have studied in quite some detail over the last 200 years. But all that understanding breaks down when these elements are subjected to high pressure and temperature. Now, using an advanced theoretical understanding and extreme conditions, researchers have converted table salt into exotic chemicals.

Salt is made from one part sodium (Na) and one part chlorine (Cl). If somehow salt were transported to the centre of the Earth, where the pressure is three million times that on the surface, its crystalline structure would change but the ratio of those two elements would remain the same.

Vitali Prakapenka at the University of Chicago and his colleagues wanted to find out what happens if there were an excess of either sodium or chlorine at such high pressures. Would the ratio between the elements change? “It might,” said Prakapenka, “because chemistry completely changes in such conditions.” If it did, the result would not just be formation of a new compound, but a serious revision of what we think about chemistry.

Elemental behaviour changes at such high pressures. For example, molecules of oxygen, which normally contain two atoms, break down at increased pressures, and the element forms an eight-atom box. Raise the pressure some more to about 300,000 atmospheres, and it starts to superconduct. Chemists are trying to develop chemicals that exhibit similar properties but are stable under normal conditions – learning about these exotic compounds can help them achieve that goal.

Sodium chloride (NaCl ie table salt) is a different beast. It is bound in a one-to-one ratio by very strong ionic bonds. However, calculations done by Prakapenka’s colleague and lead researcher Artem Oganov at the State University of New York in Stony Brook indicated that even sodium chloride could be twisted to produce exotic chemicals. Those calculations, just published in the journal Science, gave them precise pressures at which, in presence of excess sodium or chlorine, salt could be transformed.

The calculations indicated that NaCl₃, Na₃Cl, Na₂Cl, Na₃Cl₂, and NaCl₇ could all be stable at pressures ranging from 20GPa to 142GPa, where 1GPa is about 10,000 atmospheres of pressure. High pressure physicists have many models to predict behaviour of elements under extreme conditions, but rarely do those models agree with experiment.

Remarkably their calculations stood the test of experiment in at least two cases: Na₃Cl and NaCl₃. To run such an experiment, you need a fancy device called the diamond anvil cell. Chemicals are added between two diamonds, which can be compressed to produce pressures up to 300GPa. This is what Prakapenka’s colleague used to make Na₃Cl and NaCl₃, structures that were verified by Prakapenka using X-ray analysis.

“Nobody thought this could happen, given how strong the bond is between sodium and chlorine,” said Prakapenka. “What we have shown is that theory can be translated into experiment, which doesn’t happen often in high pressure physics.”

Malcolm McMahon, professor of high pressure physics at the University of Edinburgh, said, “These are surprising results, and they are guided by remarkable theoretical predictions. Without tools like the ones they have built, we would not have been able to think that sodium chloride could be transformed this way.”

There may not be any immediate application for these results. Instead, the researchers have opened the doors for scientists to start probing other chemicals in the hope of making exotic combinations that can remain stable at room temperature. Diamonds are a good example of that. In nature, they are formed deep inside the Earth when carbon is subjected to extreme pressure. Once formed, they remain stable even at ambient conditions. So there may be other diamond-like materials that we can make, ones that our current understanding of chemistry hasn’t even predicted could exist.

Other implications are non-terrestrial. Each planet in our Solar System and beyond has a lot of material held at extreme pressures. For example, Jupiter is predicted to have metallic hydrogen, where hydrogen’s electrons are free to move as they please. This material is expected to be a superconductor at room temperature. Understanding how chemicals we know about behave in those conditions would be vital to predicting the conditions in the host of exoplanets we are discovering.

If nothing else, Oganov and Prakapenka’s work shows that even something as simple as table salt can be successfully transformed – meaning we still have much to discover about the elements that we all know (and some of us love).

First published at The Conversation.

Image credit: richard_jones

Earliest evidence of cat domestication found in China

December 16, 2013January 25, 2014 Akshat RathiLeave a comment

There has been much debate about how cats went from hunting in the wild to a much-loved pet. That is because we know little about their domestication. Now researchers have found the earliest case of cat domestication, which happens to be in China, along with the first direct evidence of how it may have happened.

The oldest record of a cat’s association with humans comes from Cyprus where, about 9,500 years ago, a young wildcat was buried with a human. Egyptian art and cat mummies reveal that, by 4,000 years ago, cats had become loved pets. So it is clear that domestication happened in between these two dates. But many questions remains: how, where and when did it happen?

In a new study, just published in the Proceedings of the National Academy of Sciences, Yaowu Hu of the Chinese Academy of Sciences, Fiona Marshall of Washington University in St Louis, and their colleagues try to answer those questions. “We have never before been able to show the nature of the relationship that resulted in domestication, especially for an animal that is solitary like cats and so rare in archaeological sites. So it was surprising to be able to document this at all,” Marshall said.

Like most evolutionary adaptations, domestication of animals can happen in multiple ways. A mutually-beneficial relationship can drive small changes that lead to a permanent change in behaviour, with or without direct human meddling. Or it could be that a prey’s numbers dwindled because of excessive hunting, which forced humans to come up with smarter animal management ideas, such as herding, that led to domestication.

The latter happened to sheep, goats and cattle. The former it was thought must have happened to cats, dogs and pigs. And thanks to Hu and Marshall, we now have evidence in case of cats. It comes from Quanhucun, a site in central China, that was a human settlement about 6,000 years ago. Archaeologists have discovered houses, storage pits, pottery, and some floral and faunal remains there, but few human burials. Piecing all the evidence together makes a compelling case for how domestication of cats may have happened.

The floral remains show that the settlement cultivated millet on a large scale. And the faunal remains of cats, dogs, deer and other animals tell us what these animals present at the site ate.

The isotopes in bones can tell us how old they are, but the ratio of carbon and nitrogen isotopes can also reveal an animal’s diet. These bones were about 5,300 years old. The dietary analysis showed that dogs, pigs and rodents mostly ate millet, and, not surprisingly, cats mostly hunted animals that ate millet (probably rodents). The archaeological dig revealed a rodent burrow near a storage pit, which meant farmers had a rodent problem, something that cats could help with.

“Cats were probably brought into the human environment by farming and the rodents and other food available to them in farming villages,” Marshall said. “This might have made it possible to domesticate an animal that was nocturnal and not social.”

There are other clues that show that humans had a closer relationship with the felids. The remains of one cat indicate that it got more nutrition from millet than did by hunting, which may mean that humans fed the cat. Hu and Marshall also found a cat bone that showed it had survived well into its old age, again indicating that humans may have cared for the animal, allowing it to live longer.

There is one problem that has left Marshall perplexed. Most cats today are the descendants of Felis silvestris lybica, or the Near Eastern Wildcat. But Marshall cannot be certain that Quanhucun cats belong to that lineage, because they could not find enough DNA data to probe lineages. “That is main limitation of the paper – the uncertainty of the cat species,” Hu said.

Comparison of Hu and Marshall’s data with that of domesticated cats shows that Quanhucun cats were domesticated or very close to being domesticated. However, without evidence of the lineage, we cannot be certain that what happened in Quanhucun ended up producing all modern domesticated cats.

First published at The Conversation.

Image: mobilestreetlife

‘Clone by phone’ means faster vaccine preparation

May 24, 2013January 25, 2014 Akshat RathiLeave a comment

The 2009 influenza pandemic prompted the fastest effort in history to develop a vaccine. Within six months of the pandemic declaration, vaccine-makers had developed, produced and distributed hundreds of millions of doses. Unfortunately for some of the flu’s victims, even that response was not fast enough.

Now researchers in the US have created a vital part of a flu jab using a process that takes less than five days. As reported in Science Translational Medicine, the team led by Philip Dormitzer of drug company Novartis has shown that their method is superior to traditional vaccine efforts in both speed and quality. Their hope is that it will make regulators rethink current practice, which does not allow the use of their technology.

Approved methods for making vaccines involve collecting flu virus from patients and, if it’s different enough from previous strains, sending it to vaccine-makers. Once researchers complete the necessary genetic manipulation, a version of the virus is injected into chicken egg cells and allowed to replicate. After safety tests, this version of the virus becomes the vaccine that gets distributed.

These methods are regulated by the World Health Organisation, and have been used for many decades without much change, Sarah Gilbert, professor of vaccinology at University of Oxford said.

Instead, Dormitzer and his colleagues wanted to use a technique that has become much faster: gathering genetic data on site, for example, where the flu breakout occurred in China, and manufacturing a synthetic version of the virus in a lab, for example in the US. They also wanted to replicate the modified version of the virus in cells derived from a dog’s kidney, because they allow for faster production of virus “seed stock”, which can be used to manufacture vaccines.

To test whether these ideas stood the test, Dormitzer was provided genetic data of an unknown flu virus by the US Biomedical Advanced Research and Development Authority on a Monday morning. Dormitzer’s team used the data to make DNA that would create a version of the unknown virus mixed with a laboratory strain, which is required to make the vaccine safe. Crucially, the hybrid they made contained information to instruct cells to make proteins (hemagglutinin and neuraminidase), from the unkown virus, that give new strains of flu the ability to evade the human immune system.

This was done by noon on Thursday, in just four days and four hours. The “seed” version was then successfully tested in ferrets, an animal model for flu vaccines. But Wendy Barclay, an influenza virologist at Imperial College London who did not work on the study, has warned, “This time does not account for the vast majority of time delay in rolling the vaccine out from seed virus.”

Nevertheless, the research shows that it is now possible to cut down the time needed to produce a seed virus significantly. Any time saved in responding to a flu pandemic is welcome. “Regulators need to capitalise on such developments,” Gilbert said.

First published on The Conversation.

Image credit: ekigyuu