Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Resolving controversy at the water’s edge

30.01.2012
High-level spectroscopy and computer simulations of specially diluted liquids reveal the long-debated structure of air–water interfaces

Water (H2O) has a simple composition, but its dizzyingly interconnected hydrogen-bonded networks make structural characterizations challenging. In particular, the organization of water surfaces—a region critical to processes in cell biology and atmospheric chemistry—has caused profound disagreements among scientists.


Figure 1: A ‘snapshot’ from a molecular dynamic simulation reveals that water molecules align at air–water interfaces as coordinated pairs linked by hydrogen bonds. Copyright : 2012 RIKEN

Now, Tahei Tahara and colleagues from the RIKEN Advanced Science Institute in Wako, in collaboration with researchers in Japan and Europe, have uncovered the presence of strongly bonded water pairs at the air–water interface1, rather than previously hypothesized ‘ice-like’ surface structures.

Observing surface water molecules, just a few monolayers thick, requires special experimental techniques that prevent interference by more plentiful bulk particles. One such approach is called vibrational sum frequency generation (VSFG), a laser-based method that selectively vibrates interfacial molecules. Previous VSFG measurements of surface water showed two vibrations that resemble signals recorded from bulk ice and liquid water states. Some scientists have proposed that these vibrations correspond to a partially disordered mix of liquid and four-coordinated ice-like surface structures—a theory at odds with thermodynamic evidence.

Other VSFG experiments, however, have suggested that the two vibrations arise from one structure undergoing coupling interactions. To resolve this dispute, Tahara and colleagues turned to heterodyne-detected VSFG (HD-VSFG), a high-level spectroscopic method that detects how the phase of the vibrational signals shifts with respect to the incident laser beam—information that can pinpoint molecular orientation at interfaces.

The researchers then employed a trick using isotopes to account for coupling effects of water molecules: they added the deuterium (D)-bearing compounds HOD and D2O to pure water. By gradually diluting the number of oxygen–hydrogen (OH) bonds in the liquid, these isotopes suppress the interactions between the vibrational modes that normally occur. The remaining ‘stretching’ vibrations that extend and contract OH bonds then provide clear information about the interfacial water structure.
The team’s experiments revealed that as the isotopic dilution progressed, the two OH bands merged into a single peak, which is clear evidence of vibrational coupling within a single structure. After performing molecular dynamic simulations and comparing the results to the HD-VSFG data, a new picture emerged of the air–water interface (Fig. 1): the low-frequency OH vibrations were due to tightly joined pairs of liquid water molecules.

“We were wondering what kind of structure can have strong hydrogen-bonds other than ice at water surfaces,” says Tahara. “When our experiments and [co-author] Morita’s simulation answered the question, rather than surprise I felt that ‘This is it!’ because its structure is quite reasonable.”

The corresponding author for this highlight is based at the Molecular Spectroscopy Laboratory, RIKEN Advanced Science Institute

gro-pr | Research asia research news
Further information:
http://www.riken.jp
http://www.researchsea.com

More articles from Life Sciences:

nachricht At last, butterflies get a bigger, better evolutionary tree
16.02.2018 | Florida Museum of Natural History

nachricht New treatment strategies for chronic kidney disease from the animal kingdom
16.02.2018 | Veterinärmedizinische Universität Wien

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

Im Focus: Autonomous 3D scanner supports individual manufacturing processes

Let’s say the armrest is broken in your vintage car. As things stand, you would need a lot of luck and persistence to find the right spare part. But in the world of Industrie 4.0 and production with batch sizes of one, you can simply scan the armrest and print it out. This is made possible by the first ever 3D scanner capable of working autonomously and in real time. The autonomous scanning system will be on display at the Hannover Messe Preview on February 6 and at the Hannover Messe proper from April 23 to 27, 2018 (Hall 6, Booth A30).

Part of the charm of vintage cars is that they stopped making them long ago, so it is special when you do see one out on the roads. If something breaks or...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Fingerprints of quantum entanglement

16.02.2018 | Information Technology

'Living bandages': NUST MISIS scientists develop biocompatible anti-burn nanofibers

16.02.2018 | Health and Medicine

Hubble sees Neptune's mysterious shrinking storm

16.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>