Watching chemistry in motion: Chemical environments mapped using molecular vibrations

August 5, 2014
University of Chicago Postdoctoral fellows Carlos Baiz and Denise Schach worked with chemistry Professor Andrei Tokmakoff (not pictured), to develop ultrafast two-dimensional infrared microscopy. Credit: Robert Kozloff/University of Chicago

Scientists have long known that a molecule's behavior depends on its environment. Taking advantage of this phenomenon, a group of researchers at the University of Chicago developed a new technique to map microscopic environments using the vibrations of molecules.

"It's a special new advance that will be broadly useful in studies of molecular and materials phenomena," said Andrei Tokmakoff, the Henry G. Gale Distinguished Service Professor in Chemistry at UChicago. He and two of his associates report their new technique in a paper published online in the journal Optics Express.

The new technique builds on ultrafast two-dimensional , which emerged approximately 15 years ago as a method to probe molecular vibrations. When a laser pulse strikes a molecule, parts of its energy is transferred into the vibrations of the molecule. The ability of each single molecule to get rid of this excess energy, or relax, depends on the neighbors' ability to accept such energy. Thus in different environments will relax at different rates, which are then used to determine the environment of individual molecules. Combining two-dimensional spectroscopy with a microscope enabled the researchers to directly visualize the microscopic variations in chemical environments.

"It's a new, hybrid technique that combines the spatial resolution of microscopy with the molecular information of infrared spectroscopy," said Carlos R. Baiz, a and the article's lead author. The technique offers data on vibrational dynamics that traditional microscopy lacks, while adding spatial information that infrared spectroscopy alone can't provide.

"The new technique lends itself to multiple applications," said Denise Schach, a postdoctoral fellow in chemistry and co-author of the Optics Express article. "We aim to observe the protein folding process, which is the basis of biological function, inside a single cell." In the future, the new technique might especially benefit research in cellular biology and biomedicine.

Mapping vibrational frequencies

Two-dimensional IR spectroscopy can measure molecular dynamics at the femtosecond (quadrillionth of a second) timescale, which is the vibrational frequency of a chemical bond. The method is used to correlate different of a molecule, in order to learn about its structure as well as its chemical environment. Combined with microscopy, the method offers a spatial resolution of 20 microns, about the size of a human skin cell.

"Consider a system of coupled springs: you can pluck one spring and see the energy transfer from this one oscillator to all the other springs in the system," Baiz explained. "It's the same effect with molecules. The laser excites one vibration which then relaxes into other nearby vibrations on the same molecule or its neighbors, and where the vibrational energy ends up tells us about the structure and environment of the molecule."

Multiple factors contributed to the success of Tokmakoff's team, which conducted preliminary experiments for two years at MIT, that enabled the group to plot the best way to develop the new method. Once Tokmakoff joined the UChicago faculty in 2013, his startup funds financed the purchase of the sophisticated and expensive equipment that his team needed to implement the plan.

"The facilities are excellent here" said Baiz, referring to Tokmakoff's laboratory space in the Gordon Center for Integrative Science, which is equipped with stringent temperature and humidity controls, the most technologically advanced optical components, and a brand new microscope.

Also important was the purchase of a new pulse shaper that enabled the researchers to modulate individual laser pulses in a way that traditional optics cannot do, and developing a new way of collecting data that involved a different geometric alignment of the laser beams.

Explore further: Researchers use Raman spectroscopy and STM to allow chemical mapping of molecules to 1nm resolution

More information: "Ultrafast 2D IR Microscopy," by Carlos R. Baiz, Denise Schach, and Andrei Tokmakoff, Optics Express, Vol. 22, Issue 15, pp. 18724-18735, 2014.

Related Stories

Directly visualizing hydrogen bonds

July 15, 2014

Using a newly developed, ultrafast femtosecond infrared light source, chemists at the University of Chicago have been able to directly visualize the coordinated vibrations between hydrogen-bonded molecules—the first time ...

A molecule's transformation filmed at high resolution

July 21, 2014

François Légaré's team at the INRS Énergie Matériaux Télécommunications Research Centre successfully imaged a chemical reaction with a spatial and temporal resolution greatly exceeding that obtained to date using microscopes. ...

Recommended for you

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

Exploring the physics of a chocolate fountain

November 24, 2015

A mathematics student has worked out the secrets of how chocolate behaves in a chocolate fountain, answering the age-old question of why the falling 'curtain' of chocolate surprisingly pulls inwards rather than going straight ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Da Schneib
1 / 5 (1) Aug 05, 2014
Their application, observing protein folding during synthesis in living cells, is as interesting as their methodology. Investigation of nanomaterials is a very "hot" field right now, and this is an enabling technology for that, as well.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.