Interfaces: Different for every molecule

Contrary to expectations, structurally different molecules can display different solvent properties at an interface between air and water, researchers in Japan have discovered1.

Tahei Tahara and colleagues from the RIKEN Advanced Science Institute in Wako showed that polarity at this interface cannot be defined simply, because it depends on the nature of the solute molecule at the interface.

The finding could have significant consequences for chemistry at interfaces, since the polarity of a molecule’s environment affects how it reacts with other molecules. Fields such as atmospheric science, where air/water interfaces abound, will be particularly affected.

The researchers made their discovery using an interface-selective spectroscopic technique that they developed earlier2. The spectra that the technique produces are of comparable quality to those of bulk solutions, enabling previously impossible comparisons between systems.

The researchers looked at the electronic spectra of five coumarin dyes at the interface between air and water; electronic spectra are essentially a graphical representation of a molecule’s color. Coumarin dyes all share the same basic chemical structure and are used to probe the polarity of solvents because their spectra differ depending on the molecules’ environment.

Tahara and colleagues found that the spectra of all five coumarin dyes at the air/water interface resembled a cross between the bulk spectra of coumarin in polar water and non-polar hexane. This is because the dye molecules were positioned partly in the polar water and partly in the non-polar air at the interface. However, the closeness of the spectra to either the spectrum in water or in hexane changed depending on the precise structure of each coumarin dye.

Previously it was thought that, in ordinary cases, molecules experience the same polarity—the average of that of polar water and non-polar air. The spectra Tahara and colleagues measured, however, showed that even molecules having similar structures experience substantially different polarity at the air/water interface.

The researchers found that the different molecules were positioned at slightly different angles at the interface of air and water so have different sections of their structures submerged and are, consequently, in quantitatively different surroundings.

“This work showed that, even at the same air/water interface, the interaction between the solute and solvent is significantly varied,” says Tahara. This means the molecules experience different environments at the interface, similar to being in different solvents from a view point of the stabilization energy. “This fundamental understanding of molecular behavior will be very important when people consider chemical reactivity at liquid interfaces.”

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

1. Sen, S., Yamaguchi, S. & Tahara, T. Different molecules experience different polarities at the air/water interface. Angewandte Chemie International Edition 48, 6439–6442 (2009).

2. Yamaguchi, S. & Tahara, T. Precise electronic ÷(2) spectra of molecules adsorbed at an interface measured by multiplex sum frequency generation. Journal of Physical Chemistry B 108, 19079–19082 (2004).

Media Contact

Saeko Okada Research asia research news

All latest news from the category: Life Sciences and Chemistry

Articles and reports from the Life Sciences and chemistry area deal with applied and basic research into modern biology, chemistry and human medicine.

Valuable information can be found on a range of life sciences fields including bacteriology, biochemistry, bionics, bioinformatics, biophysics, biotechnology, genetics, geobotany, human biology, marine biology, microbiology, molecular biology, cellular biology, zoology, bioinorganic chemistry, microchemistry and environmental chemistry.

Back to home

Comments (0)

Write a comment

Newest articles

Lighting up the future

New multidisciplinary research from the University of St Andrews could lead to more efficient televisions, computer screens and lighting. Researchers at the Organic Semiconductor Centre in the School of Physics and…

Researchers crack sugarcane’s complex genetic code

Sweet success: Scientists created a highly accurate reference genome for one of the most important modern crops and found a rare example of how genes confer disease resistance in plants….

Evolution of the most powerful ocean current on Earth

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets….

Partners & Sponsors