Physicists Hope to Unlock Secrets of Life

Physicists Hope to Unlock Secrets of Life

  11:09:00 PM    Science Lover

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The key to life as we know it is water, a tiny molecule with some highly unusual properties, such as the ability to retain large amounts of heat and to lose, instead of gain, density as it solidifies. It behaves so differently from other liquids, in fact, that by some measures it shouldn't even exist. Now scientists have made a batch of new discoveries about the ubiquitous liquid, suggesting that an individual water molecule's interactions with its neighbors could someday be manipulated to solve some of the world's thorniest problems -- from agriculture to cancer.

Supercool. As individual water molecules fluctuate, breaking and forming bonds with their nearest neighbors, the result is slightly imperfect tetrahedral structures that are constantly in flux. Research suggests that these fluctuations give rise to some of water's most unusual and life-sustaining features. (Credit: Image courtesy of Rockefeller University)

The work, led by Pradeep Kumar, a fellow at Rockefeller University's Center for Studies in Physics and Biology who looks at the role of water in biology, makes it possible to measure how interaction between water molecules affect any number of properties in a system. It also paves the way for understanding how water can be manipulated to facilitate or prevent substances from dissolving in it, an advance that could impact every corner of society, from reforming agricultural practices to improving chemotherapy drugs whose side effects arise from their solubility or insolubility in water.

Kumar and his colleagues first tracked individual water molecules in a "supercooled" state (water that remains in liquid form even at below freezing temperatures), during which water's many anomalies are enhanced. "When you put water in a freezer, it doesn't freeze instantaneously," says Kumar. "It takes some time. If you have extremely pure water, then you can go down to about 230 Kelvin and still have enough time to measure different physical properties of water including the specific heat in its liquid state." Kumar and his colleagues then used theoretical and computational approaches to simulate the activity of these water molecules and measure their interactions with neighbors.

In the liquid state, every water molecule fleetingly interacts with its four nearest neighbors, forming a tetrahedron, explains Kumar. These tetrahedrons, however, are slightly imperfect and the degree to which they are changes as temperature and pressure change, ultimately affecting which individual water molecules partner up with each other. Kumar found that it is the fluctuations in the degree of tetrahedrality that contribute most to one of water's most notable and valuable features -- its capacity to resist heating or cooling and thereby regulating and maintaining the temperature of biological systems.

The ability to measure water's shifting degrees of tetrahedrality also gives scientists a means of measuring how much order or disorder each water molecule imparts. The better the tetrahedron, the more order it imparts in the system. "What we have done essentially is define the structural entropy of every molecule in our system," says Kumar. "And since water molecules are constantly moving in space and time, this gives you a way to study the transport of entropy associated with local tetrahedrality -- something that has never been done before."

Understanding how individual water molecules maneuver in a system to form fleeting tetrahedral structures and how changing physical conditions such as temperatures and pressures affect the amount of disorder each imparts on that system may help scientists understand why certain substances, like drugs used in chemotherapy, are soluble in water and why some are not.

It could also help understand how this changing network of bonds and ordering of local tetrahedrality between water molecules changes the nature of protein folding and degradation. "Understanding hydrophobicity, and how different conditions change it, is probably one of the most fundamental components in understanding how proteins fold in water and how different biomolecules remain stable in it," says Kumar. "And if we understand this, we will not only have a new way of thinking about physics and biology but also a new way to approach health and disease."

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Satellites Unlock Secret To Northern India's Vanishing Water

Satellites Unlock Secret To Northern India's Vanishing Water

  9:50:00 PM    Science Lover

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Using satellite data, UC Irvine and NASA hydrologists have found that groundwater beneath northern India has been receding by as much as 1 foot per year over the past decade – and they believe human consumption is almost entirely to blame.

The map shows groundwater changes in India during 2002-08, with losses in red and gains in blue, based on GRACE satellite observations. The estimated rate of depletion of groundwater in northwestern India is 4.0 centimeters of water per year, equivalent to a water table decline of 33 centimeters per year. Increases in groundwater in southern India are due to recent above-average rainfall, whereas rain in northwestern India was close to normal during the study period. (Credit: I. Velicogna/UC Irvine)

More than 109 cubic kilometers (26 cubic miles) of groundwater disappeared from the region's aquifers between 2002 and 2008 – double the capacity of India's largest surface-water reservoir, the Upper Wainganga, and triple that of Lake Mead, the largest manmade reservoir in the U.S.

People are pumping northern India's underground water, mostly to irrigate cropland, faster than natural processes can replenish it, said Jay Famiglietti and Isabella Velicogna, UCI Earth system scientists, and Matt Rodell of NASA's Goddard Space Flight Center.

"If measures are not soon taken to ensure sustainable groundwater usage, consequences for the 114 million residents of the region may include a collapse of agricultural output, severe shortages of potable water, conflict and suffering," said Rodell, lead author of the study and former doctoral student of Famiglietti's at the University of Texas at Austin.

Study results will be published online Aug. 12 in the journal Nature.

Groundwater comes from the percolation of precipitation and other surface waters down through Earth's soil and rock, accumulating in aquifers – cavities and layers of porous rock, gravel, sand or clay. In some subterranean reservoirs, the water may be thousands to millions of years old; in others, water levels decline and rise again naturally each year.

Groundwater levels do not respond to changes in weather as rapidly as lakes, streams and rivers do. So when groundwater is pumped for irrigation or other uses, restoration of original levels can take months or years.

"Groundwater mining – that is when withdrawals exceed replenishment rates – is a rapidly growing problem in many of the world's large aquifers," Famiglietti said. "Since groundwater provides nearly 80 percent of the water required for irrigated agriculture, diminishing groundwater reserves pose a serious threat to global food security."

Data provided by India's Ministry of Water Resources had suggested that groundwater use across the nation was exceeding natural replenishment, but the regional rate of depletion had been unknown.

In the new study, the hydrologists analyzed six years of monthly data for northern India from twin satellites called GRACE – NASA's Gravity Recovery and Climate Experiment – to produce a chronology of underground water storage changes.

GRACE detects differences in gravity brought about by fluctuations in water mass, including water below the Earth's surface. As the satellites orbit 300 miles above Earth, their positions change – relative to each other – in response to variations in the pull of gravity. They fly about 137 miles apart, and microwave ranging systems measure every microscopic variance in the distance between the two.

"With GRACE, we can monitor water storage changes everywhere in the world from our desk," said Velicogna, also with NASA's Jet Propulsion Laboratory. "The satellites allow us to observe how water storage evolves from one month to the next in critical areas of the world."

Groundwater loss in northern India is particularly alarming because there were no unusual trends in rainfall – in fact, it was slightly above normal during the study period. The researchers also examined data on soil moisture, lake and surface reservoir storage, vegetation and glaciers in the nearby Himalayas to confirm that the apparent groundwater trend was real. The only influence they couldn't rule out was human.

"For the first time, we can observe water use on land with no additional ground-based data collection," Famiglietti said. "This is critical because in many developing countries, where hydrological data are both sparse and hard to access, space-based methods provide perhaps the only opportunity to assess changes in freshwater availability across large regions."

About GRACE: The Gravity Recovery and Climate Experiment is a partnership between NASA and the German Aerospace Center. The University of Texas Center for Space Research, Austin, has overall mission responsibility. NASA's Jet Propulsion Laboratory developed the twin satellites. The German Aerospace Center provided the launch, and GeoForschungsZentrum Potsdam, Germany, operates GRACE.

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