When Itai Carmeli first came to his Ph.D. adviser with his results, he was gently told to get back to work. “I told him there was no such physics,” recalls a smiling Prof. Ron Naaman of the Institute’s Chemical Physics Department. “A year later he was back - with similar findings.”

Carmeli had been tinkering around with organic molecules, which he used to create extremely thin, single-layered films on a gold substrate. The surprise was that the films were behaving like a powerful magnet.

There are different types of magnets, Naaman explains, from the common fridge magnets we all played with as kids, which always display magnetic behavior; to temporary magnets such as paperclips and nails, which only work when exposed to a strong magnetic field; to magnets powered by an electric current. Nearly all of these contain one or more components with magnetic properties. The twist in our case was that the films lacked any magnetic materials.

In their study, recently published in Physical Review Letters and the Journal of Chemical Physics, the Institute team experimented with films made of three types of organic molecules. The molecules each had a positive and negative pole, and they were tightly packed, such that their negative poles faced the gold substrate, while their positive poles faced away. And this, says Naaman, might have been the trick: while opposite charges are known to attract, like charges repel, particularly when in close proximity on the surface of the film. The team - which included physicist Prof. Zeev Vager and materials scientists Prof. Shimon Reich and Dr. Gregory Leitus - believes that this repulsion force causes electrons to flow from the gold substrate to neutralize charged sites on the molecules in an attempt to stabilize the system. This extremely thin layer of flowing electrons in turn induces an electric current - forming a leading type of magnet dubbed an electromagnet (see box).

“We believe that the electrons are behaving as if in a co-op,” says Vager. “Electrons usually orbit in small circles, around individual molecules; but in this case they may be orbiting domains in the film containing hundreds of thousand of molecules, thus creating an electric current that transforms the system into a powerful magnet. Films of this sort might feature in electromagnets used in futuristic high-density discs and other electronics.”

Magnetic moments

Birds do it, bees do it, so do whales, salmon and, according to a new study, even Caribbean spiny lobsters - all use the Earth’s magnetic field as a navigating compass.

Magnetism was first discovered by the ancient Greeks and Chinese. Experimenting with the materials of their natural environment, they found that certain rare stones, called lodestones, attract small pieces of iron. Adding to their “magic,” these stones were found to always point in a north-south direction when suspended on a string. They quickly became invaluable to navigators, fortune-tellers and builders.

During the 13th century, French-man Pierre de Maricourt discovered that magnets had two magnetic poles - north and south - and in the 1600s, England’s Sir William Gilbert concluded that Earth itself was a giant magnet with north and south poles - which explains the wonder of animal migration treks.

The 1800s saw the first connection made between electricity and magnetism, when Danish physicist Hans Christian discovered that running an electric current through a wire creates a magnetic field - a phenomenon that quickly became known as electromagnetism. And today, this form of magnetism is everywhere - in the electric motors in refrigerators, washing machines and racecars; the read/write heads of discs and videotape players, and far more.

Prof. Naaman’s research is supported by the Fritz Haber Center for Physical Chemistry; the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research; the Wolfson Advanced Research Center; the Philip M. Klutznick Fund for Research, Chicago, IL; and Dr. Pamela Scholl, Northbrook, IL. He is the incumbent of the Aryeh and Mintze Katzman Professorial Chair.

Lucio Frydman devotes much of his time to one of the oldest traditions of humankind - making tools and using them to explore the world that surrounds us. But things have changed quite a bit since early blade-shaping, fire-making and glass-blowing attempts. “The goal is to craft ever-sensitive recording methods for peering into the heart of matter,” says Frydman, a professor in the Institute’s Chemical Physics Department.

The tool he is working to perfect is called nuclear magnetic resonance (NMR), which, since its development in the 1940s, has proven invaluable to studying the structure of molecules, designing new drugs and even exploring the human brain (see box).

The key to NMR is magnetism. All matter is made up of atoms, and each atom contains a nucleus. When exposed to electromagnetic radiation, nuclei “get excited” - they start spinning, creating their own electromagnetic sounds. The nucleus of each type of atom emits a sound that is entirely unique. The challenge facing NMR scientists is to study the dispersion patterns of the sound waves produced by the excited molecules - in other words, to work backward from the resulting “nuclear symphony” to reconstruct a precise three-dimensional picture of the molecule.

It’s not an easy task. To date, scientists wishing to obtain a full NMR picture of complex molecules needed to perform numerous measurements: hundreds or thousands of one-dimensional scans, which could only be performed one after the other. These scans were then combined to create a unified three-dimensional picture. While a single scan took a fraction of a second, the multidimensional procedures leading to the overall picture of the molecule could last several hours or even days.

Now Frydman and his team have developed an approach called ultrafast multidimensional NMR that significantly expedites the analysis of the electromagnetic sounds produced, making it possible to acquire complete multidimensional NMR spectra within a fraction of a second.

Their approach, described in the Proceedings of the National Academy of Sciences (PNAS), USA, “slices up” the molecular sample into numerous thin layers and then simultaneously performs all the measurements required on every one of these slices. The protocol then integrates these measurements according to their precise location, generating an image that amounts to a full multidimensional spectrum from the entire sample.

Thanks to the speed with which the new method collects the data, scientists will now be able to observe rapid changes taking place in molecules, such as the folding of proteins. In a sense, the method amounts to a transition from taking NMR “stills” to making NMR “movies.”

Frydman’s team is applying the techniques they’ve developed to study a variety of molecular structures and their potential interactions with their surroundings. One of their projects examines how nucleic acids and other biological molecules bind to metal ions (metals play vital roles in a range of systems, including serving as catalysts, which speed up reactions or enable them to occur). Additional projects aim to facilitate the efficient use of NMR in pharmaceutical and biochemical studies.

The team’s approach should make it possible to examine molecular and biological systems with a much higher time resolution than was previously possible, yielding detailed insights into molecular-level interactions. These, in turn, might advance the design of new drugs as well as industrial catalysts and novel materials.

Contributing to this research were Dr. Adonis Lupulescu of the Chemical Physics Department and Dr. Tali Scherf of Chemical Services at the Weizmann Institute of Science.

Prof. Frydman’s research is supported by the Fritz Haber Center for Physical Chemistry; the Henri Gutwirth Fund for Research; the estate of Ilse Katz, Switzerland; the Philip M. Klutznick Fund for Research; the Minerva Stiftung Gesellschaft fuer die Forschung m.b.H.; and the Abraham and Sonia Rochlin Foundation.

First magnetic steps

Research using nuclear magnetic resonance dates back to the 1940s, when Felix Bloch of Stanford University and Harvard’s Edward Purcell first applied NMR to examine solids and liquids, earning themselves the 1952 Nobel Prize in Physics. Weizmann Institute scientists Shlomo Alexander and Shaul Meiboom built one of the world’s first high-resolution NMR spectrometers in the early 1950s. They and other Institute scientists later developed an NMR approach for measuring the behavior of molecules in crystals and solutions. Since then NMR and its daughter technique, MRI, have evolved into what is arguably the most commonly used analytical and diagnostic tool in scientific research, spanning the fields of medicine, structural biology, pharmaceutical chemistry, condensed matter physics and earth sciences.

Making of a toolmaker

Argentinean-born Prof. Frydman received a Ph.D. in chemistry from the University of Buenos Aires. Following a postdoctoral period at the University of California, Berkeley he joined the faculty of the University of Chicago, where after seven years he became a full professor. He and his family settled in Rehovot, Israel, in 2001, when he joined the Institute’s Chemical Physics Department.

And why choose NMR research? “This field is unique in the way it combines quantum mechanical principles with instrumental and computational challenges,” says Frydman. “Moreover, its importance as a diagnostic tool in a variety of scientific fields means that there’s always a new question just waiting to be explored.”

'The Lord above gave man an arm of iron, so he could do his job and never shirk,' sings Alfred Doolittle in the musical My Fair Lady. 'But with a little bit o' luck,... someone else will do the blinkin' work.' Doolittle was lazy; but the dislike for wasting energy, or more precisely the desire to reach a goal with a minimum investment of energy, is a universal phenomenon common to humans and molecular particles alike. In the case of simple molecules, it drives them to create dense structures (such as solids or liquids), characterized by a large number of bonds between molecules 'costing' a minimum of energy per bond.

But molecular particles (and perhaps people as well) have another, conflicting characteristic that is just as important: under certain conditions they prefer a state of maximum disorder (entropy). The key factor influencing these conflicting tendencies is temperature: at very high temperatures entropy wins and the particles assume a gaseous state, the freest and most disorderly state possible. For example, at high temperatures, water turns to steam. But when the particles are cooled, the energy-saving tendency begins to dominate, causing them to reorganize into more orderly structures. Thus water vapor, when cooled, condenses into a liquid or a solid.

These tendencies apply to simple liquids, called isotropic liquids, composed of particles in which the energy 'cost' of bonding between the particles is independent of their orientation. But what about anisotropic systems, which are made up of particles whose bonding energy is highly dependent on their mutual orientation? Can cooling cause these systems to condense?

This is a fundamental physics question, but one that may also have important applications, since anisotropic liquids play an important role in modern technology. Dr. Tsvi Tlusty and Prof. Sam Safran, his doctoral adviser and Dean of the Weizmann Institute's Feinberg Graduate School decided to tackle this challenge.

In the past, most scientists believed that the answer to this question depended on the nature of the mutual attraction between the particles constituting a liquid. That is, if the mutual attraction is strong enough, it can 'compensate' for the loss of entropy (the loss of disorder involved in the process of condensing matter from gas to liquid).

One of the most striking examples of anisotropic liquids is that of magnetic liquids, characterized by magnetic particles that 'float' within a simple liquid, such as water or oil. In ordinary isotropic liquids, the condensed state of matter is formed by the clustering of particles, each clinging to a relatively large number of other particles (between 6 and 12). In contrast, magnetic liquids in dilute solutions form chains where each particle adheres to only two other particles at most, in a north-south-north-south structure. The bonding energy between these particles is highly dependent on their magnetic orientation. When two such magnets are aligned (i.e. their poles are positioned north to north or south to south) they repel each other; but when the nearby poles are of opposite orientation, the magnets mutually attract - which results in the north-south pole structure. This chaining structure in magnetic liquids prevents the usual type of condensation; because each of the particles is in contact with only two of its neighbors, it has less bonding energy. Therefore, until recently, the accepted scientific wisdom was that magnetic liquids could not undergo the usual gas-to-liquid condensation.

Safran and Tlusty's research sheds new light on this belief. Using a theoretical model, the scientists have shown that magnetic liquids can undergo condensation. Their conclusion seems from the fact that the magnetic chains 'prefer' to form Y-like junctions that bring together three chains (the energy 'cost' of this state is lower than the 'cost' of having both ends of a chain free). Thus magnetic chains in a dilute solution tend to form large and complex networks. In their study, recently published in Science, the researchers suggest that these network junctions strive for a balance between a state that 'costs' a minimum of energy and a state of maximum entropy. The network finds it 'worthwhile' to create more and more junctions, thus increasing its entropy while making the network denser and more complex. When the system of junctions making up the network is dilute, the material is in the gaseous phase; but when the network becomes more dense, the substance condenses to increase the junction entropy and makes the transition from a gas to a liquid.

This finding overturns the previously accepted view that the condensation of magnetic liquids is impossible without the involvement of additional, isotropic forces. In these systems, it is actually the increase in network entropy that stabilizes the condensed liquid state. No other forces are necessary. Further experimentation, resulting in confirmation of the scientists' 'network model,' might lead to the emergence of an entirely new field of technological applications. For instance, a better understanding of the physical properties of anisotropic liquids, and especially of their great sensitivity to changes in magnetic or electric fields, is important for developing advanced computers and other micro-machines.

Prof. Safran holds the Fern and Manfred Steinfeld Professorial Chair.