The researchers use stiff stilbene, a small, inert structure, as a molecular force probe to generate well-defined forces on various molecules, atom by atom.
“By pulling on different pairs of atoms, we can explore what happens when we stretch a molecule in different ways,” said chemistry professor Roman Boulatov. “That information tells us a lot about the properties of fleeting structures called transition states that govern how, and how fast, chemical transformations occur.”
Boulatov, research associate Qing-Zheng Yang, postdoctoral researcher Daria Khvostichenko, and graduate students Zhen Huang and Timothy Kucharski describe the molecular force probe and present early results in a paper accepted for publication in Nature Nanotechnology. The paper is to be posted on the journal’s Web site on Sunday (March 29).
Similar to the force that develops when a rubber band is stretched, restoring forces occur in parts of molecules when they are stretched. Those restoring forces contain information about how much the molecule was distorted, and in what direction.
The molecular force probe allows reaction rates to be measured as a function of the restoring force in a molecule that has been stretched or compressed.
This information is essential for developing a chemomechanical kinetic theory that explains how force affects rates of chemical transformations.
Such a theory will help researchers better understand a host of complex phenomena, from the operation of motor proteins that underlie the action of muscles, to the propagation of cracks in polymers and the mechanisms by which living cells sense forces in their surroundings.
“Localized reactions offer the best opportunity to gain fundamental insights into the interplay of reaction rates and molecular restoring forces,” Boulatov said, “but these reactions are extremely difficult to study with a microscopic force probe.”
Microscopic force probes, which are utilized by atomic force microscopes, are much too large to grab onto a single pair of atoms. Measuring microns in size, the probe tips contact many atoms at once, smearing experimental results.
“By replacing microscopic force probes with small molecules like stiff stilbene, we can study the relationship between restoring force and reaction rate for localized reactions,” Boulatov said. “The more accurately we know where our probe acts, the better control we have over the distortion, and the easier it is to interpret the results.”
Using conventional methods, Boulatov and his students first attach stiff stilbene to a molecule they wish to study. Then they irradiate the resulting molecular assembly with visible light. The light causes the stilbene to change from a fully relaxed shape to one that exerts a desired force on the molecule. The chemists then measure the reaction rate of the molecule as a function of temperature, which reveals details of what caused the reaction to accelerate.
One type of chemical transformation the researchers studied is the breaking of one strong (covalent) chemical bond at a time. The experimental results were sometimes counterintuitive.
“Unlike a rubber band, which will always break faster when stretched, pulling on some chemical bonds doesn’t make them break any faster; and sometimes it’s a bond that you don’t pull on that will break instead of the one you do pull,” Boulatov said. “That’s because experiences in the macroscopic world do not map particularly well to the molecular world.”
Molecules do not live in a three-dimensional world, Boulatov said. Molecules populate a multi-dimensional world, where forces applied to a pair of atoms can act in more than three dimensions.
“Even small molecules will stretch and deform in many different ways,” Boulatov said, “making the study of molecular forces even more intriguing.”
Funding was provided by the National Science Foundation, the U.S. Air Force Office of Scientific Research, the American Chemical Society Petroleum Research Fund and the U. of I. The National Center for Supercomputing Applications and the U.S. Department of Defense High-Performance Computing Modernization Program provided computational resources.
James E. Kloeppel | University of Illinois
Further reports about: > Atom > Microscopic force probes > Molecular Target > Molecules > Stretches > Stretches Molecules > chemical transformations > chemomechanical kinetic theory > covalent chemical bond > expensive atomic force microscope > macroscopic world > molecular technique > molecular world > small molecules
Bare bones: Making bones transparent
27.04.2017 | California Institute of Technology
Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
27.04.2017 | Life Sciences
27.04.2017 | Physics and Astronomy
27.04.2017 | Earth Sciences