DNA Can Discern Between Two Quantum States, Research Shows
ScienceDaily (Mar. 31, 2011) — Do the principles of quantum mechanics apply to biological systems? Until now, says Prof. Ron Naaman of the Institute's Chemical Physics Department (Faculty of Chemistry), both biologists and physicists have considered quantum systems and biological molecules to be like apples and oranges. But research he conducted together with scientists in Germany, which appeared recently in Science, shows that a biological molecule -- DNA -- can discern between quantum states known as spin.
New research shows that a biological molecule -- DNA -- can discern between quantum states known as spin. (Credit: © Rodolfo Clix / Fotolia)
Quantum phenomena, it is generally agreed, take place in extremely tiny systems -- single atoms, for instance, or very small molecules. To investigate them, scientists must usually cool their material down to temperatures approaching absolute zero. Once such a system exceeds a certain size or temperature, its quantum properties collapse, and "every day" classical physics takes over. Naaman: "Biological molecules are quite large, and they work at temperatures that are much warmer than the temperatures at which most quantum physics experiments are conducted. One would expect that the quantum phenomenon of spin, which exists in two opposing states, would be scrambled in these molecules -- and thus irrelevant to their function."
But biological molecules have another property: they are chiral. In other words, they exist in either "left-" or "right-handed" forms that can't be superimposed on one another. Double-stranded DNA molecules are doubly chiral -- both in the arrangement of the individual strands and in the direction of the helices' twist. Naaman knew from previous studies that some chiral molecules can interact in different ways with the two different spins. Together with Prof. Zeev Vager of the Particle Physics and Astrophysics Department, research student Tal Markus, and Prof. Helmut Zacharias and his research team at the University of Münster, Germany, he set out to discover whether DNA might show some spin-selective properties.
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Science 18 February 2011:
Vol. 331 no. 6019 pp. 894-897
DOI: 10.1126/science.1199339
REPORT
Spin Selectivity in Electron Transmission Through Self-Assembled Monolayers of Double-Stranded DNA
B. Göhler1, V. Hamelbeck1, T. Z. Markus2, M. Kettner1, G. F. Hanne1, Z. Vager3, R. Naaman2,*, and H. Zacharias1
Author Affiliations
1Physikalisches Institut, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany.
2Department of Chemical Physics, Weizmann Institute, Rehovot 76100, Israel.
3Department of Particle Physics and Astrophysics, Weizmann Institute, Rehovot 76100, Israel.
*To whom correspondence should be addressed. E-mail: ron.naaman@weizmann.ac.il
ABSTRACT
In electron-transfer processes, spin effects normally are seen either in magnetic materials or in systems containing heavy atoms that facilitate spin-orbit coupling. We report spin-selective transmission of electrons through self-assembled monolayers of double-stranded DNA on gold. By directly measuring the spin of the transmitted electrons with a Mott polarimeter, we found spin polarizations exceeding 60% at room temperature. The spin-polarized photoelectrons were observed even when the photoelectrons were generated with unpolarized light. The observed spin selectivity at room temperature was extremely high as compared with other known spin filters. The spin filtration efficiency depended on the length of the DNA in the monolayer and its organization.
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