New type of water found: It's in the mix

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  • Published: Dec 15, 2012
  • Channels: Chemometrics & Informatics
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Water form

Raman scattering and multivariate curve resolution allows an unprecedented signal-to-noise ratio of 10,000-to-1 in a study that reveals a previously unknown structure lying between liquid water and its vapour when oil is present.

Raman scattering and multivariate curve resolution allows an unprecedented signal-to-noise ratio of 10,000-to-1 in a study that reveals a previously unknown structure lying between liquid water and its vapour when oil is present.

Water is not only essential for life as we know it, it presents myriad physical and chemical properties that seem anomalous when compared to other substances but continues to intrigue with an entirely new form discovered that lies in the limbo between liquid and vapour phase. Given water's critical place in life, understanding its intriguing behaviour is important to understanding life itself and the stuff from which it is made, the proteins and other biomolecules. 

Philiphobic

Researchers at Purdue University have demonstrated that in the presence of alcohol molecules with long, hydrophobic chains, water adopts a structure that lies between the liquid and the vapour state. In contrast, if the alcohols contain short hydrophobic chains, the structure adopted is more akin to ice than liquid or gaseous water. The team led by Dor Ben-Amotz, found that as they examined alcohols with increasingly long carbon chains, the transformation to this peculiar form of water occurred at lower and lower temperatures. For example, when in contact with a chain seven carbon atoms long, the water molecules behaved as if they were in the vapour phase at 60 Celsius.

"For oils with chains longer than four carbons, or about one nanometre in length, we saw the water transform into a completely new structure as the temperature rose," Ben-Amotz explains. "If the trend we saw holds true, then this transformation could be happening at body temperature around important physiological molecules like proteins and phospholipids." This could be important for understanding the form and function of biomolecules given that proteins contain both hydrophobic and hydrophilic regions. It seems from the Purdue work that water might change the way it interacts with different regions depending on the temperature.

Ben-Amotz and colleagues Joel Davis, Kamil Gierszal and Ping Wang give details of their findings in the journal Nature this month. Their observations add a new twist to a scientific debate that has raged for more than 70 years about whether water forms sub-microscopic ice-like crystals around hydrophobic compounds, like oil, or whether the interaction involves a more disordered vapour-like state. 

Grabbing the question

"This question was really up for grabs until we introduced an experimental method that could see these subtle changes in water structure," Ben-Amotz explains. "Surprisingly, we found that both sides are right, and it depends on the size of the oil. The signal-to-noise boost in Raman scattering the team achieved allowed them to see what had not been revealed before in the interaction of water with hydrophobic molecules.

"Most people never take a spectrum with a signal-to-noise ratio greater than 100-to-1, but if we performed this experiment that way we wouldn't see anything," Ben-Amotz said. "We needed to have a higher signal-to-noise ratio because we were looking for a needle in a mountain-sized haystack." He adds that in their Raman scattering experiments the bulk water produces mountainous peaks in the spectrum under which any other spectral lines that might be present are simply buried. "Multivariate curve resolution lets us see small changes in water structure under that mountain. As is often the case in science, the key was combining two already established techniques in a new way." 

Related Links

Nature, 2012, 491, 582-585: "Water structural transformation at molecular hydrophobic interfaces"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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