Most natural systems, including the brain, display oscillatory phenomena that occur at different speeds and frequencies yet involve coupled time scales, such as brain waves. The oscillatory patterns in these biological rhythms change spontaneously at a very slow pace.
In 2010, a group of researchers at the University of São Paulo’s São Carlos Chemistry Institute (IQSC-USP) in Brazil described a slow evolutionary process that distorts rapid oscillations in a system and culminates in their “death.” Now, the same researchers have identified the effect of temperature on the coupling of disparate time scales.
The study resulted from a Thematic Project conducted under the aegis of FAPESP’s Bioenergy Research Program (BIOEN), and from Ph.D. research supported by a scholarship from FAPESP. A paper describing its findings has been published by Scientific Reports, an online journal that belongs to Nature Publishing Group.
“Our discoveries contribute to a deeper understanding of several processes that occur in coupled time scales,” said Hamilton Varela, a professor at IQSC-USP and a co-author of the paper, in an interview with Agência FAPESP.
The researchers used the electro-oxidation of formic acid on platinum as a model to study the effect of temperature on coupled slow and fast dynamics.
The system, consisting of a glass flask equipped with a platinum electrode with an area of 0.2 cm2 in a solution of sulfuric acid in water with a small amount of formic acid, functions as an electrochemical cell in which electricity controls chemical reactions.
Application of electricity to the electrode triggers an electrochemical reaction in which formic acid, whose molecules contain a single carbon atom plus two oxygen atoms and two hydrogen atoms (HCOOH), bonds temporarily with platinum and, after a number of intermediate steps, releases carbon gas (CO2), which coats the platinum electrode.
This electrochemical reaction is considered the best model system for investigating fundamental aspects of the electrocatalysis of small organic molecules, which are of interest due to their relevance to the development of energy conversion systems, such as low-temperature fuel cells. These convert chemical energy into electric energy and are used to power vehicles, for example.
It is also considered a good model for studying coupled slow and fast dynamics because it oscillates autonomously over time like a living system, explained Alana Zülke, another co-author of the paper. Zülke’s Ph.D. research was supported by a scholarship from FAPESP and supervised by Varela.
“The interesting point is that we succeeded in observing a commonplace aspect of thermoregulation of live organisms in the lab, in a non-biological environment,” Zülke said. “By using simple electrochemical systems, we obtained useful clues to the functioning of complex systems and the mechanisms involved in temperature compensation.”
Effect of temperature
In 2009, this same group of researchers at IQSC-USP discovered that the electrochemical reaction in question displayed external temperature compensation behavior also observed in biological systems.
The intermediate stages of the reaction of formic acid with platinum are coupled in such a way that the oscillation frequency remains constant even as the temperature rises, Varela explained.
“This is similar to the behavior of living systems, such as warm-blooded animals like mammals and birds, where the heart rate and brain rhythm remain more or less constant when the ambient temperature varies within a given range because the biochemical networks associated with these processes operate to compensate for this temperature variation,” he said. “This was highly important to evolution.”
Until now, no one knew the reason for this temperature compensation in the electro-oxidation of formic acid on platinum.
The researchers measured the oscillation frequency in the electrochemical cell at five temperatures between 5°C and 45°C. They observed an increase in frequency as the temperature rose from 5°C to 25°C and a decrease as the temperature rose from 25°C to 45°C. “Completely by chance, we observed a break in the oscillation frequency curve at 25°C,” Varela said.
The researchers used this break in the oscillation frequency, which they called a turning point, to analyze stages of the reaction linked to fast and slow evolution, identifying one that might be linked to temperature compensation.
“We succeeded in interpreting the dynamics of the slow process in comparison with the fast process and isolated a stage that could be involved in temperature compensation, which is very hard to do in a network of reactions,” Varela said.
“We suggest for the first time a method of performing research on coupling between different time scales, which can be applied to other systems to discover temperature dependency in complex chemical networks.”
“The effect of temperature on the coupled slow and fast dynamics of an electrochemical oscillator” (doi: 10.1038/srep24553) by Zülke and Varela can be read in Scientific Reports at www.nature.com/articles/srep24553.