An international team of scientists, led by IBM Research in Zurich, Switzerland, and the CiQUS from the University of Santiago de Compostela (USC), succeeded in controlling the formation of bonds between the atoms of a molecule by means of electrical impulses, favoring selective modifications of its molecular structure.
The breakthrough, which appears on the cover of “Science” magazine, represents unprecedented control at the molecular scale and opens a new avenue for the development of sophisticated molecular machines with a wide range of possible applications.
The study is on the cover of ‘Science’ magazine
In molecules, the atoms are linked by bonds forming a three-dimensional structure of nanometer size. Some may have the same number and type of atoms, but exhibit their bonds in different ways. These compounds are called structural isomers and they bring extraordinary variability to the molecular world.
Now the authors have found a method that allows one structural isomer to be transformed into another, reconnecting their bonds at will based on an external stimulus: different voltage pulses applied with the tip of a scanning probe microscope (STM ).
In concrete terms, they acted on a molecule made up of four carbon rings deposited on a saline surface, inducing very precise modifications to its structure associated with oxidation or reduction reactions.
“These redox processes, in turn, cause one or another of the carbon-carbon bonds to form in the molecule we are studying,” co-author Diego Peña, lead researcher, tells SINC at CiQUS, “but I have to say there was a bit of serendipity [casualidad] in the aftermath, since we wanted to provoke a kind of molecular regrouping and we found others even more interesting, and above all controlled. This would certainly be valid for other types of reactions, and even for discovering new chemical transformations.”
In addition to applying the voltage pulses, researchers use the STM microscope to study the electronics of molecules, although to visualize their bonds (the skeleton) they use high-resolution atomic force microscopy (AFM).
Different molecular transformations are selectively triggered by voltage pulses (colored from blue to red) from the tip of a scanning probe microscope. / Florian Albrecht/IBM
“Since the 19th century, chemists have tried to modify the connectivity between atoms in molecules to obtain new functionalities.” Peña points out, “but the novelty is that now we can do it extremely precisely and on individual molecules, as if we had nanometric tweezers the size of the molecules.”
“Not only do we control which bonds form, but we also do so reversibly, we can switch between the different structures repeatedly,” said Leo Gross, researcher at IBM and co-author of the study, who adds: “The selective formation and reversible binding can promote the creation of new molecular machines with more complex functions and tasks”.
Molecular machines are molecules that can perform a certain task in response to an external stimulus. Without going any further, our own body is home to a large number of molecular machines with functions as vital as DNA replication. However, designing artificial machines and synthesizing them in the laboratory is a very complex task, worthy of the 2016 Nobel Prize to Jean Pierre Sauvage, J. Fraser Stoddart and Ben L. Feringa.
The ability to make and break bonds within an individual molecule involves deliberate control of its structure, which, in turn, forms the basis of these machines. “Until now, artificial molecular machines have relied primarily on inducing changes in the spatial distribution of atoms by means of external stimuli. By adding control over the connectivity between atoms, we can tackle the fabrication of designs more complex,” says Peña.
In any case, he recognizes that it is a little early for the candidacies. “It’s really ground-breaking work, where we demonstrate the control of individual molecules by external stimuli, how to assemble atoms on demand, something that hasn’t been done until now. Although if I had to to choose a potential application, I would say the development of molecular machines that catalyze chemical transformations, mimicking the function of enzymes in organisms”.
New stimuli with light or electrons
His team works within the framework of a European project centered on the manipulation of individual molecules (MOLDAM – CKD SyG). The researchers plan to continue making progress on this knowledge, and among their next steps they are considering the possibility of the reactions being triggered by light or by transferring electrons between different parts of the same molecule, instead of through the tip of an STM microscope. .
“The goal is to control the molecular world with different stimuli, and even to combine them in the future to achieve more complex functionalities,” he concludes.
Florian Albrecht, Shadi Fatayer, Iago Pozo, Ivano Tavernelli, Jascha Repp, Diego Peña, Leo Gross. “Selectivity in single-molecule reactions by spike-induced redox chemistry”. “Science”, 2022.