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Quantum effect could explain how chiral molecules interact

Electron spin polarization promotes recognition between molecules of similar chirality

by Jyllian Kemsley
March 9, 2017 | A version of this story appeared in Volume 95, Issue 11

Credit: Weizmann Institute of Science
A chiral helical peptide (green) interacts with a portion of a protein with the same chirality (blue helix). As the two helices approach each other, their electron clouds distort, generating charge polarization that induces spin polarization (red balls and arrows) and allows the helices to better interact.

Biomolecules from small amino acids to large DNA helices are chiral, and how they interact depends on their chirality. A newly identified quantum effect could help explain how biomolecules’ chirality persists.

When two molecules interact, their electron clouds reorganize. In chiral molecules, that reorganization is accompanied by electron spin polarization that enables molecules of the same chirality to interact more strongly than molecules of opposite chirality, reports a research team led by Ron Naaman and Jan M. L. Martin of the Weizmann Institute of Science and David H. Waldeck of the University of Pittsburgh (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1611467114).

“The mechanism that they have demonstrated is different from any that was previously reported,” comments David N. Beratan of Duke University. “If the idea holds up, it could entirely change the way we think about molecular recognition in biological and organic chemistry.”

In the new work, Naaman and colleagues combined experimental studies of helical oligopeptides with computational analysis. They found that the electron spin polarization induced by molecular interactions constrains the symmetry of the wave functions involved in the interactions. The symmetry constraints in turn lead to energy differences when molecules of the same chirality interact compared with molecules of opposite chirality, favoring homochiral interactions.

“It’s a real quantum mechanical property that can’t be represented in classical-physics-based models,” Naaman emphasizes.

The effect is short-range and arises only when electrostatic and other noncovalent interactions bring molecules together, making it more likely to influence enantiospecific recognition in a crowded cellular environment than in dilute solutions. It is also additive and becomes more significant when many chiral functional groups interact across the surfaces of large biomolecules.


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