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100-Year-Old Tetrahedral Model Reconfirmed

February 13, 2013
Image Caption: Model of a symmetrical four bond water molecule (oxygen red and hydrogen white). Credit: Thomas D. Kühne / Johannes Gutenberg University Mainz

Lee Rannals for redOrbit.com – Your Universe Online

For all those who worried back in 2004 that the sky was falling because the original model of the molecular structure of water toppled out, have no fear, because things can go back to the way they used to be.

Johannes Gutenberg University Mainz (JGU) researchers confirmed the original tetrahedral model, after an international research group challenged the model nine-years ago, claiming that water molecules form bonds only with two other molecules.

However, Professor Dr. Thomas Kühne and his team have resurrected the 100-year-old model, which assumes water molecules form a hydrogen bond with four adjacent molecules.

He and his colleagues have demonstrated the mistakes of the 2004 “double bonding” theory by using computer simulations based on new types of combinations of two computational methods recently developed by his group.

The effect of the hydrogen bonds between the water molecules is associated with several features of water, such as its liquid state and high boiling point. The hydrogen bonds are formed due to the different charges carried by the oxygen and hydrogen atoms that make up water molecules.

The traditional 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 through two donor and two acceptor bonds. Kühne said that in his team’s approach, the average result they observed over time was always for quadruple bonding.

Researchers used new simulations to help confirm the old model, and put to rest those mistaken beliefs back in 2004. Their simulations helped explain why double bonding was observed in 2004. Kühne says that the result was not indicative of double bonding, but of instantaneous asymmetrical fluctuation.

Asymmetry in the four hydrogen bonds is the result of temporary disruptions to the hydrogen bond network, which takes 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 stronger than the other.

In the 2004, the team used water molecules with high levels of momentary asymmetry to obtain the results, showing only two strong hydrogen bonds.

“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.

This research could open up future studies into molecular and biological systems in aqueous solutions, helping to provide insights into protein folding.


Source: Lee Rannals for redOrbit.com - Your Universe Online



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