Scientists confirm original tetrahedral model of the molecular structure of water

Feb 12, 2013

Researchers at Johannes Gutenberg University Mainz (JGU) have confirmed the original model of the molecular structure of water and have thus made it possible to resolve a long-standing scientific controversy about the structure of liquid water. The tetrahedral model was first postulated nearly 100 years ago and it assumes that every water molecule forms a so-called hydrogen bond with four adjacent molecules. This concept was almost toppled in 2004 when an international research group announced that it had experimentally established that water molecules form bonds only with two other molecules. "The quality of the results was excellent but they merely represent a snapshot of the situation," explained Professor Dr. Thomas Kühne. He has demonstrated the fallacy of the 'double bonding' theory using computer simulations based on new types of combinations of two computational methods recently developed by his group.

Some very special and unique features of water, such as its liquid aggregate state and high boiling point, are attributable to the effect of the hydrogen bonds between the . The H bonds are formed due to the different charges carried by the oxygen and that make up water molecules and the resultant dipolar structure. The traditional, generally accepted view was that water had a tetrahedral structure at room temperature, so that on average each water molecule would be linked with four adjacent molecules via two donor and two acceptor bonds. "In our , the median result we observed over time was always for quadruple bonding," said Kühne. Thanks to the new simulations, he and his colleague Dr. Rhustam Khaliullin have now been able to confirm the old model and also supply an explanation for why double bonding was observed in 2004. According to Kühne, the result was not indicative of double bonding "but of instantaneous asymmetrical fluctuation" only.

There is thus significant asymmetry in the four H bonds of the tetrahedral model because of the different energy of the contacts. This asymmetry is the result of temporary disruptions to the hydrogen bond network, which take the form of extremely short term fluctuations occurring on a timescale of 100 to 200 femtoseconds. These fluctuations mean that one of the two donor or acceptor bonds is temporarily much stronger than the other. But these fluctuations precisely cancel each other out so that, on average over time, the tetrahedral structure is retained.

The results reported in 2004 using x-ray absorption spectroscopy were obtained using water molecules with high levels of momentary asymmetry, which is why essentially only two strong were observed in an otherwise tetrahedral structure. "Our findings have important implications as they help reconcile the symmetric and asymmetric views on the structure of water," write the scientists in an article published in Nature Communications. The results may also be relevant to research into molecular and biological systems in aqueous solutions and provide insight into protein folding, for example.

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More information: Nature Communications, February 2013 doi:10.1038/ncomms2459

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User comments : 7

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HannesAlfven
1 / 5 (2) Feb 12, 2013
Re: "The results may also be relevant to research into molecular and biological systems in aqueous solutions and provide insight into protein folding, for example."

Yes, but you won't get there without a single mention of hydrophilic surfaces, since water appears to exhibit a highly structured state for literally millions of molecules around them. This has been the big discovery which is almost certainly going to do away with these mechanical pump and channel notions associated with cell membranes. It's not that there are pumps and channels actively shifting ions across the membrane in order to maintain ionic gradients; proteins structure the water of the cell's cytoplasm into a gel state, and gels come, naturally prepackaged, with these ionic gradients.

People might actually be seeing things which look like pumps and channels, but they are not maintaining the ionic gradients. Why would nature pay for something it can get for free?
baudrunner
1 / 5 (1) Feb 12, 2013
They tried to fix something that worked. Typical. Now, back to hydrogen permeates everything and is always driving around looking for a parking spot.
StarGazer2011
2.3 / 5 (3) Feb 12, 2013
A computer model cant prove or falsify anything, it can only provide hypotheses for testing. The empirical result of only 2 bonds needs to be challenged with an empirical observation of 4 bonds. This work was an complete waste of time; get back to the lab and fire up the x-ray machine!
Caliban
1 / 5 (1) Feb 13, 2013
A computer model cant prove or falsify anything, it can only provide hypotheses for testing. The empirical result of only 2 bonds needs to be challenged with an empirical observation of 4 bonds. This work was an complete waste of time; get back to the lab and fire up the x-ray machine!


I'm not sure of the absorption regime in the XRay method, but isn't it possible that the use of xrays is responsble for the observed results in the experiment? That the energy added to the water molecules caused the temporary cancellation of the tetrahedral-bonding?

scatter
3.7 / 5 (3) Feb 13, 2013
This work is very far from a waste of time. All spectroscopic experiments need to be interpreted by modeling the electronic structure of the probed system and the interaction between probe and target. This modeling is in essence done by solving the many particle Schrödinger equation numerically. This nonsense attack on simulations must be stemming from ignorance on the physics involved here. The suggested two bond model was also concieved this way.

TheKnowItAll
5 / 5 (3) Feb 13, 2013
There is certainly nothing wrong with computer simulations as it is our way to verify acquired knowledge. When the simulation doesn't behave the way nature does than we know we're missing something. Besides, it does not take that long to translate a few formulas and algorithms into a computer program. On the other hand it is impossible for any of us to give credit of any related findings without taking a close look at the implemented code.
StarGazer2011
1 / 5 (1) Feb 14, 2013
This work is very far from a waste of time. All spectroscopic experiments need to be interpreted by modeling the electronic structure of the probed system and the interaction between probe and target. This modeling is in essence done by solving the many particle Schrödinger equation numerically. This nonsense attack on simulations must be stemming from ignorance on the physics involved here. The suggested two bond model was also concieved this way.



Sigh ... there is a difference between using a computer to interpret results and using a model to create results.
The two bond observation wasnt suggested by a model you fool; it directly contradicts the models! Thats the whole point!
To claim that an experimental result being interpreted by computer is somehow equivalent to claiming the output of a simulation can invalidate an experimental result is a shamefull anti-scientific 'bait and switch' and all intelligent people can see through it.

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