By tracking water molecules, physicists hope to unlock secrets of life

Feb 08, 2010

(PhysOrg.com) -- Compared to any other liquid on Earth, water behaves in strange and unexpected ways, yet its unusual properties enable and protect life as we know it. By tracking individual water molecules in a "supercooled" state, scientists find what explains one of water's most notable and life-saving features: its astounding capacity to resist gaining or losing heat.

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 , 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.

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 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 drugs whose side effects arise from their solubility or insolubility in water.

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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 imperfections give rise to some of water’s most unusual and life-sustaining features.

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 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.”

Explore further: World's most complex crystal simulated

More information: Proceedings of the National Academy of Sciences online: December 14, 2009. A tetrahedral entropy for water. Pradeep Kumar, Sergey V. Buldyrev and H. Eugene Stanley

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seneca
not rated yet Feb 08, 2010
The understanding of water is not so difficult. Water molecules are highly polar and asymmetric at the same time - they're sticking each other by strong forces. We can compare it to situation in polygamic society, where every man handles at least two women and he is even attracted the women of his neighbours. Such society is therefore much more compact, then the one, composed of individualistic pairs.

As the result, inside of every droplet of water the pressure of water molecules is much higher, then at the case of other fluids. We can compare it to situation inside of highly compressed gases: the density fluctuations are forming tiny dynamics domains here, which are clearly visible inside of supercritical fluids. They could be approximated by tetrahedral sponge or foam, described in the article.

http://www.chem.l...co24.jpg

These domains are behaving like rather solid, still flexible clusters of water molecules, which are colliding like single body.
seneca
not rated yet Feb 08, 2010
We can compare the water clusters inside of droplet to rather rigid pebbles inside of tight elastic sack. When we shake such sack, these pebbles will collide, thus eroding watter molecules from their surface by much higher forces, then inside of homogeneous mixture.

In 2007 radio-engineer John Kanzius developed an apparatus for cancer treatment by polarized radiowaves in 13 MHz frequency range. During tests of his device with tube filled by marine watter he observed an evolution of hydrogen, which can be ignited by lighter (http://www.youtub...m5a1Lc). Experiments were confirmed and replicated by scientists at Pennsylvania State University.

What is significant on this experiment, the rather slow radiowaves (13 MHz, i.e. 5.10E-8 eV) can split water molecules, which requires at least 1,2 eV per molecule. It's evident, such result could be explained only by collisions of quite large clusters of water, which are able to resonate with radiowaves of low frequency.
seneca
not rated yet Feb 08, 2010
..understanding hydrophobicity, and how different conditions change it..
I presume, hydrophobicity of small droplets could even explain problem of chirality of life. Due the asymmetry of water molecules and high surface curvature of tiny droplets the hydrophofilic molecules (like sugars with many -OH groups) are attracted to surface of droplets, while rather hydrophobic molecules like proteins are attracted to interior of droplets. The point is, the chirality of molecules adsorbed to curved surface differs too, which explains, why sugar molecules inside of cells are of mirror chirality, then the proteins molecules, which are forming their walls. Just the immense surface tension forces of water are making this effect well pronounced. This explanation supports the old hypothesis, in which life was formed inside of coacervates, i.e. small droplets. It means too, the mirror like-life could never form inside of small droplets, even if the solution would be full of racemic molecules

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