The work of hemoglobin in our body looks quite simple: it transports oxygen molecules through our bloodstream. But this works only because the hemoglobin molecule is extremely complex. The same applies to chlorophyll, which converts sunlight into energy for plants.
In order to understand the subtle tricks of such complex molecules, it is worth investigating similar but simpler structures in the laboratory. In collaboration between TU Vien (Vienna) and research groups from Trieste, phthalocyanins have now been studied, whose molecular ring structure closely resembles key parts of hemoglobin or chlorophyll. It turned out that the center of these annular structures can be switched to different states by means of a green light, which affects their chemical behavior.
This not only helps to understand biological processes, but also opens up new opportunities for the use of nature's tricks in the laboratory for other purposes – a strategy called "biomimetics" which is becoming increasingly important around the world.
Rings with metal atoms in the center
"The phthalocyanines we study are colorful with a characteristic ring structure," says Prof. Gunther Rupprechter from the Institute of Materials Chemistry at the Vienna University of Technology. "It is crucial that this ring structure is capable of holding an iron atom at the center – just like heme, red in the shape of a ring in the hemoglobin. On the other hand, chlorophyll has a similar ring that occupies the magnesium attributes."
Unlike more complex natural molecules, the phthalocyanine-like colors adapted to making are regularly sideways to the surface, such as tiles on the wall of the bathroom. "The rings are placed on a graphite layer in a regular form so that a two-dimensional crystal is created," says Matteo Roiaz, who led experiments with Christophe Rameshan. "This has the advantage that we can simultaneously examine many molecules, which gives us much stronger measurement signals," explains Christoph Rameshan.
Carbon monoxide molecules served as probes for exploring these rings: one molecule can be connected to an atom of iron held in the center of the ring. From the vibrations of carbon monoxide molecules, information about the state of the iron atoms can be obtained.
To study vibrations, the molecule was irradiated by laser light – using a combination of green and infrared light. This measurement gave a result that at first glance looked very counterintuitive: "We did not measure just one vibration frequency of carbon monoxide, but we found four different frequencies, no one expected it," says Ginter Rupprechter. "Iron atoms are all identical, so that CO molecules that are bound to them must show exactly the same behavior."
As it turns out, the green light of the laser is responsible for the remarkable effect: at the beginning all the iron atoms were truly identical, but the interaction with green light can shift them to different states. "This also changes the oscillation frequency of CO molecules at the iron atom, which shows us how sensitive these structures react to small changes," says Ginter Rupprechter. "This is also the reason why biomolecules in our bodies have such a complex structure: widely branched protein components have minimal impact on the state of the metal atom, but this minimal effect can have very important implications."
Measurement at room temperature and atmospheric pressure
Until now, similar effects could be studied only at extremely low temperatures and in ultrahigh vacuum. "In the laboratory, we now have two ways in which such biologically relevant phenomena can be measured at room temperature and atmospheric pressure, with and without green light," emphasizes Rupprechter. This opens up new opportunities for a better understanding of the chemical behavior of biological substances; it could also provide an opportunity to adapt new molecules to optimize them in natural chemical applications.
Materials provided by Vienna University of Technology. Note: The content can be edited for style and length.