DNA can detect quantum spin

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, definitively shows that a biological molecule – DNA – can discern between quantum states known as spin.

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.

The researchers fabricated self-assembling, single layers of DNA attached to a gold substrate. They then exposed the DNA to mixed groups of electrons with both directions of spin. Indeed, the team’s results surpassed expectations: The biological molecules reacted strongly with the electrons carrying one of those spins, and hardly at all with the others. The longer the molecule, the more efficient it was at choosing electrons with the desired spin, while single strands and damaged bits of DNA did not exhibit this property. These findings imply that the ability to pick and choose electrons with a particular spin stems from the chiral nature of the DNA molecule, which somehow “sets the preference” for the spin of electrons moving through it.

In fact, says Naaman, DNA turns out to be a superb “spin filter,” and the team’s findings could have relevance for both biomedical research and the field of spintronics. If further studies, for instance, bear out the finding that DNA only sustains damage from spins pointing in one direction, then exposure might be reduced and medical devices designed accordingly. On the other hand, DNA and other biological molecules could become a central feature of new types of spintronic devices, which will work on particle spin rather than electric charge, as they do today.

Prof. Ron Naaman is head of the Nancy and Stephen Grand Research Center for Sensors and Security, and his research is supported by Rachel Schwartz, Canada. Prof. Naaman is the incumbent of the Aryeh and Mintzi Katzman Professorial Chair.

2 COMMENTS

  1. Quantum Physics? A priority? Until America resolves its energy dilemma, all else is for naught! America sinks like a stone, the dollar worth less now than ever before in its history, and Americans worry about NASA, pretty photos from outer-space? What lies beyond the realm of the electron? We bombed the living spirit out a a whole nation! We destroyed a whole culture, decimated its people, ruined its infrastructure, even erased part of its history, for cheaper gasoline? Is the gasoline at the pumps in your part of America cheaper? Did you make sacrifices? Do you owe astounding taxes due to this war for energy? Did you know, that communist China has the same energy problems, but sane, effective realistic solutions? Google, Tsinghua University, China, pebble bed, gas reactors! Fail-safe? Not like the cronyism protected, corporate flogged, GE – American designed reactors in Japan?
    Be advised: As we speak, China has devoted Billions of solid, stable, undepreciated, highly valued, Yuan to the development of safe, sane, cheaply decommissionable, cheaper to build, Thorium fueled nuclear reactors. reactors proven effective by American scientists as long ago as the 1970’s but as a threat to the existing corporate interests, were discarded, buried, moth-balled, coerced out of the American energy picture?
    Is America suffering from displaced priorities? Sadly reaching out into the nether worlds of science, spending fortunes it does not have there, in place of real development of Solar, Wind, Wave, Hydro, Tidal, Geothermal, thorium nuclear, bio-mass electric sources?
    Will the stars, DNA, Quantum Physics, Gross Military build-up, Asinine over-kill Military achievements, astounding military aircraft, matter much in an America with a crashed dollar? In an America with $12.00 a gallon gasoline, and no Wind Turbine supplied, rechargeable cars? In an America facing oil boycotts, as once before we did, from Middle Eastern interests? In an America with no cheaper, safer, thorium fueled reactors? In an America still stubbornly clinging to foreign oil energy, putting all its energy eggs in the one basket?
    It is time now, for all other scientific endeavors in America to turn their energies, their intelligence, their efforts towards securing safe, cheap, domestically controlled, renewable if possible, energy sources. This is an emergency situation, made even more dangerous with the rising cloud of Muslim theocratic notions, and the gasoline thirsty burgeoning Asian empire in the world today, bidding the price of gasoline ever upward.

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