Scientists at the Weizmann Institute of Science and the Hebrew University have found that chiral molecules that appear to be mirror images do not behave identically when electrons move through them. The finding may explain why life on Earth chose a single orientation of RNA and proteins.
Imagine looking at your reflection in a mirror and discovering that different laws govern it – identical movements of yours lead to different results in the reflection, and what appears to be a perfect copy behaves completely differently. It sounds far-fetched, but scientists at the Weizmann Institute of Science and the Hebrew University have discovered that this is exactly how “chiral” molecules behave – molecules that can exist in two forms that are mirror images of each other, similar to a left and right hand. In a new study thatHis findings were published in the scientific journal Science Advances It was revealed that an electron crossing each of the mirror images experiences a magnetic field of different strength along its path. This asymmetric behavior not only contradicts conventional wisdom, but also provides support for a theory about the origin of life on Earth.
Chiral molecules can exist in two forms, but more than 150 years ago it was discovered that in living organisms one form was "selected" – a "left-handed" form in the case of proteins and a "right-handed" form in the case of sugars, DNA and RNA. It is difficult to understand how this happened, since according to the accepted rules of chemistry and physics, mirror images have exactly the same energy. This mystery has occupied many scientists and its interpretation could shed light on how biological molecules were first formed, that is, on the origin of life.
A journey of almost 30 years
The first step towards a solution was taken inYear 1999, so they streamed Prof. Ron Naaman from the Weizmann Institute of Science and his colleagues passed an electric current – a flow of electrons – through chiral molecules and discovered that each mirror image behaves differently. Electrons function like tiny magnets, with a north pole and a south pole, and they have a property called “spin,” which describes which direction each magnetic pole is pointing. When the tiny magnets flow through a chiral molecule, they are required to move in a spiral path, and this causes them to “feel” that a magnetic field is acting on them, which can accelerate or block their movement. What was discovered at the time is that the magnetic field in each mirror image has the opposite effect – one shape quickly moves electrons whose north pole is facing the direction of their movement, and vice versa.
"This still did not reveal why nature 'preferred' a specific shape," explains Prof. Naaman. "The next clue was evidence that began to accumulate that mirror images not only favor electrons with opposite spin, but also transmit them with different levels of efficiency. Almost everyone assumed that this was due to contamination in the samples, but the gaps were so large and the degree of purity of the samples so good that the explanation did not satisfy us."
In the new study, led by Prof. Naaman of the Institute and Prof. Yossi Paltiel of the Hebrew University, the scientists used chiral gold and silver and a chiral biological molecule and passed an electric current through each of their mirror images. The experiment revealed large gaps in the strength of the magnetic field felt by electrons moving through each of the two forms of chiral material – differences that reached about 30% in chiral gold. Using mathematical proofs and computer simulations, the scientists were able to explain how the difference in strength is possible: when a magnetic field is not aligned with the direction of movement of the electron, it “feels” only part of its strength, and it turns out that in each mirror image the magnetic field is in a different direction and the electron feels a different part of its strength.
The difference comes when the formations start moving.
"Our breakthrough was the understanding that the difference between the two forms that seemed to be twins comes to life only in motion," emphasizes Prof. Paltiel. "In a state of rest there is no difference, but when electrons begin to move in a certain direction and are exposed to a magnetic force of different intensity in their movement - a huge gap is created between the forms that changes their chemical and physical behavior."
The implications of the discovery go far beyond the boundaries of chemistry and physics, as they provide a clue to understanding the origins of life on Earth. About three years ago, the research group of Professor Dimitar Seslov of Harvard University published a theory according to which life began on natural magnetic surfaces at the bottom of ancient lakes. These soils were rich in "magnetite" - the most magnetic mineral in nature.
When a chiral molecule approaches a magnetic surface, its electrons begin to move, and at the edge electrons are collected that all point the same pole toward the surface. When this pole is opposite to that presented by the surface itself, the chiral molecule is attracted to it, and when it is the same – it is repelled. Therefore, if the surface presents a permanent magnetic pole, and each of the mirror images presents a different pole, only one of them will be attracted to it. This attraction causes only that mirror image to accumulate and become a stable crystal. According to the theory developed at Harvard, this is exactly what happened to an ancient chiral molecule called RAO, from which RNA evolved.
"This theory explains well how one of the mirror images can take over, if the magnetic surface always presents a certain pole that attracts it," explains Prof. Naaman. "The problem was that the magnetite surfaces are not uniform, as there are areas in them that face a north pole outward and others that face a south pole, and so it seems that each of the mirror images can accumulate."
Differences in Magnot
This is where the new discovery comes in. Because a single mirror image transfers electrons with one pole more efficiently to the tip, it will magnetize better to a surface that has both possibilities. The scientists even observed in experiments that when a biological chiral molecule comes into contact with a metal surface, the differences in magnetic field between its mirror images increase—and may be strong enough to ensure that only one form accumulates.
In the case of the ancient molecule RAO, the right-handed form was found to be preferable. This physical advantage made this form the default for all RNA molecules in nature. Proteins are translated from RNA, and the translation process is such that if all RNA molecules are right-handed, then all proteins will be left-handed. Thus, the new findings solve a 150-year-old mystery and also support the possibility that life on Earth did indeed originate on magnetic rocks at the bottom of ancient lakes.
The same natural selection process from the days of Genesis can now be imitated in the laboratory for the benefit of humanity. "In biological reactions, the mirror image involved is of great importance, and industrial use in the wrong way can be useless at best, and destructive to human health and nature at worst," says Prof. Naaman. "Based on our discovery, it is possible to ensure with greater precision than ever before, using magnetic surfaces, that only crystals of a chiral substance of the desired shape will accumulate in manufacturing processes. This will allow for the production of much more effective and safer medicines, fertilizers, and pesticides in the future."
Also participating in the study were Daniel Goldberg, Nir Yoran, and Dr. Shira Yochlis from the Hebrew University of Jerusalem; Jia Hao Su, Christopher Seibel, and Prof. Anna A. Krylov from the University of Southern California; Prof. Jürgen Gauss from Johannes Gutenberg University Mainz, Germany; Prof. Shmuel Silberg from Ariel University; Prof. S. Furkan Ozturk from the California Institute of Technology; and Prof. Jonas Fransson from Uppsala University, Sweden.
Short FAQ:
What is chirality?
Chirality is a property of molecules that can appear in two forms that are mirror images of each other, similar to right-handed and left-handed.
What did the new study reveal?
The study found that two mirror images of chiral molecules do not behave identically when electrons move through them. The electrons “feel” a magnetic field of different strength in each form.
How does this relate to the origin of life?
The finding may explain why nature has established a single orientation of biological molecules: RNA and sugars are right-handed, while proteins are built from left-handed amino acids.
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