A study offering new clues to the origin of life on Earth began at a family dinner. 鈥淲e try to avoid talking about science during Friday night meals, but it rarely works,鈥� recalls Prof. of the Weizmann Institute of Science. Two of her three siblings are scientists, including her brother, Prof. , a physicist at the Hebrew University of Jerusalem.
That evening, Paltiel described his research on separating molecules according to their spatial arrangement. The conversation sparked a collaboration between the two siblings 鈥� one that led them into a field new to both: the search for life鈥檚 origins. Their study, in Chem, offers a possible missing link in a theory proposing that life first emerged on magnetic surfaces, such as the beds of shallow lakes rich in magnetic minerals.
Left, right 鈥� and a magnetic twist
The molecular structure of living things has been one of nature鈥檚 enduring puzzles. Many biological molecules exist in two mirror-image forms, like left and right hands. Chemists call this property chirality. In principle, these forms should occur with the same frequency, yet living organisms show a striking bias. Amino acids, the building blocks of proteins, are almost exclusively left-handed, while DNA and RNA twist in the opposite direction, toward the right.
This asymmetry is not a trivial detail. Biological reactions depend on precise molecular structure; if the chirality is wrong, the reaction may fail entirely. Chirality is therefore considered a key chemical fingerprint of life.
At that Friday dinner, Paltiel described his work with Weizmann Institute鈥檚 Prof. Ron Naaman on separating molecules by chirality. Although chiral molecules are not magnetic, magnetized surfaces can selectively attract one 鈥渉andedness鈥� over the other. This effect has been used to separate mirror-image molecules and crystals. In fact, separating molecules by chirality is crucial in the manufacture of drugs, pesticides and many other bioactive chemicals that must be produced with the correct handedness to be effective.
“”I always thought Yossi and I worked in completely different areas. Now we鈥檝e discovered common ground 鈥� in trying to understand how life began”
When Paltiel described these studies, Sharon realized her own expertise might help. She specializes in mass spectrometry, a technique that identifies molecules by measuring their mass. She proposed using it to analyze the separation process and verify which molecules had been obtained.
In their joint study, Ofek Vardi, a PhD student in Paltiel鈥檚 lab, led an experiment designed by the two teams. She and colleagues used right- and left-handed versions of methionine 鈥� an amino acid that typically initiates protein synthesis 鈥� and passed a solution containing this amino acid through a paper filter embedded with micron-sized magnetic particles.
To track the molecules, the researchers incorporated two carbon isotopes 鈥� atoms of the same element with different weights 鈥� into the amino acid. In some experiments, right-handed molecules contained the more common, lighter carbon-12 isotope and left-handed ones the heavier carbon-13; in others, the assignment was reversed. The direction of magnetization was also switched: In different iterations of the experiment, the magnets first pointed toward the solution with one of their poles, north or south, then with the other. After filtering the solution, the scientists used mass spectrometry to measure the ratio of isotopes and the balance between the two chiral forms.
The result was unexpected. The magnetic filter appeared to separate methionine not only by chirality but also by isotope composition. Molecules containing the heavier carbon isotope 鈥� regardless of their handedness 鈥� showed a stronger attraction to particles magnetized in one direction over the other.
The researchers then pushed the idea further.
鈥淲e used left-handed methionine molecules that differ only in their isotopic composition,鈥� Vardi explains. 鈥淩emarkably, the magnetic filter consistently favored one composition over the other in the course of the separation.鈥�
In other words, magnetism could distinguish not only between mirror-image molecules but also between isotopes.
鈥淭his was the most important and the most surprising finding of the study,鈥� says Paltiel.
He explains that the magnetic separation of chiral molecules arises from a quantum property of electrons known as spin, a tiny magnetic moment that differs between mirror-image forms. Isotopes can also differ in spin 鈥� in their case, in the atomic nuclei 鈥� though the effect is usually much weaker. The researchers propose that the three-dimensional structure of chiral molecules may amplify interactions between these two types of spin, linking magnetic attraction and isotope composition in ways not previously recognized.
Two signatures of life 鈥� connected
Chirality is not the only chemical signature of life. Living organisms also display subtle but consistent differences in isotope ratios compared to the non-living matter around them. These small shifts serve as a second fingerprint of life and are widely used to detect traces of ancient biological activity.
Life tends to prefer lighter isotopes. Plants as well as animals, for example, contain slightly less carbon-13 than the surrounding environment. Such isotopic patterns can endure in rocks for billions of years, offering clues to the earliest life on Earth.
The new findings for the first time suggest a link between these two fingerprints 鈥� chirality and isotope ratios. If early biochemical reactions occurred on magnetic surfaces, that magnetism may have had a lasting influence on both properties.
This idea fits in with the hypothesis, first proposed by the group of Prof. Dimitar Sasselov from Harvard University, that life on Earth emerged on natural magnetic surfaces, such as the beds of ancient, mineral-rich lakes. Over time, reactions involving iron minerals could have produced magnetized sediments in the warm, shallow waters 鈥� environments potentially conducive to life鈥檚 beginnings. If so, these magnetic lakebeds might have favored molecules of one chirality, while also affecting their isotope composition.
鈥淚f life really began on magnetic surfaces, our results provide experimental evidence that magnetism could have been responsible both for the asymmetry of biological molecules and for the isotope ratios in living matter,鈥� Paltiel says.
Common ground for a scientific family
Beyond its implications for the origin of life, the study may have practical applications. It could lead to new technologies that combine magnetic effects with mass spectrometry to separate both chiral molecules and isotopes.
For Sharon and Paltiel, the project also has a personal dimension. Their father, Dr. Zvi Paltiel, a retired physicist from the Weizmann Institute, devoted much of his career to science education.
鈥淗e encouraged us to explore science from a very young age and shared his sense of wonder about nature 鈥� why sunsets are red, how rain forms and why it often falls at an angle,鈥� Sharon recalls.
The siblings had already collaborated previously, thanks to a student of Paltiel鈥檚, who once suggested they work with Sharon. That student had heard of Sharon鈥檚 reputation as a leading expert in mass spectrometry and asked Paltiel if he would have any objections to the collaboration. 鈥淣ot at all,鈥� Paltiel replied. 鈥淪he is my sister.鈥�
Still, until the present project, Sharon believed their research fields were far apart.
鈥淚 always thought Yossi and I worked in completely different areas,鈥� she says. 鈥淣ow we鈥檝e discovered common ground 鈥� in trying to understand how life began.鈥�
Science Numbers
The differences between isotopes are tiny, but they can have measurable effects. Carbon isotopes differ from one another by just 1 neutron; the isotope ratios between living and non-living matter often differ by less than 0.1 percent. Still, scientists can use these subtle differences to detect life.
Also participating in the study were Nir Yuran and Dr. Shira Yochelis from Paltiel鈥檚 lab; Dr. Gili Ben-Nissan from Sharon鈥檚 lab in Weizmann鈥檚 Biomolecular Sciences Department; and Dr. Ella M. Jakob of the Hebrew University鈥檚 Institute of Chemistry.
Prof. Michal Sharon鈥檚 research is supported by Magnus Konow in honor of his mother Olga Konow Rappaport. Prof. Sharon is the incumbent of the Aharon and Ephraim Katzir Memorial Professorial Chair in Translational Research.