2011 Nerenberg Lecture: A Fourth Phase of Water (Gerald Pollack)
The 2011 Nerenberg Lecture was given by Gerald Pollack at the University of Western Ontario on March 30th, 2011. Prof. Pollack is part of the Systems and Quantitative Biology group at the University of Washington where his research areas include: Interfacial Water and Energy, Cell Biology and the Molecular Basis of Biological Motion. The following article is take from an interview with Prof. Pollack about this research by Mitchel Zimmer at the University of Western Ontario. by Mitchell Zimmer
As Professor Christopher Essex of the Applied Mathematics Department commented before the 2011 Nerenberg lecture on March 30, this speaker series tries to raise “slightly adventurous ideas” to a broad audience. Gerald Pollack from The University of Washington had done just that by introducing the concept of a fourth phase of water beyond ice, liquid or vapour.
The traditional view is that water molecules are a dipole where the oxygen at one end carries the negative charge and the hydrogen atoms are positive at the other. The molecules adhere to a charged surface in an ordered and aligned layer and so does the next layer, but it doesn’t do so indefinitely, so this order only goes for a few layers. “That idea is completely wrong,” says Pollack, “what really happens is that the ordering of water molecules extends out extremely far from the surface and that idea has a huge impact on everything we know about aqueous chemistry – including clouds.”
The experiment that started Pollack’s trek in exploring this phase of water began when he placed a sample of polyvinyl alcohol gel into a suspension of latex microspheres in water. He noticed that the microspheres began migrating into the water from the interface where the gel and water contact to a distance of 16 micrometers. Other materials used in place of the original gel showed similar results. After observing these phenomena one of Pollack’s grad students suggested that the clear regions should be called “exclusion zones”. They had thought they had come across something new, but as they looked into literature that found that the phenomena has been noted before in 1912 by Sir William Harvey. He suggested that there was some sort of interfacial zone in water that behaved differently from the rest.
At this point Pollack explained what surfaces nucleated these exclusion zones. Hydrophilic surfaces (meaning water loving) surfaces had the characteristic of allowing water to spread out. Hydrophobic surfaces (water hating) are easy to spot since these are surfaces where water beads up. Hydrophilic surfaces generate the exclusion zones and this includes a variety of materials from muscle fibres to plant roots to synthetic materials of just one molecule thick. The best material observed so far is a synthetic called Nafion which can produce an exclusion a half on a millimetre thick. The exclusion zone can exclude a wide variety of materials such as microspheres, red blood cells, colloidal gold, quantum dots and even proteins like albumin.
So how is the water in the exclusion zone (EZ) different from ordinary liquid, or bulk, water?
“The exclusion zone has a negative charge, the rest is bulk water filled with positive charge, presumably protons or hydronium ions. Basically, really what you have there is a charged battery of water… It seems stupid but if you go look up in the skies sometimes you can see another example of a charged battery. Basically, what you have up there is water 80% of lightning flashes are between water and water. The potential difference between these is… a few thousand kilovolts.” Since energy has to come from somewhere, Pollack investigated to find out what charges the battery. His answer was simply “The Sun.” More specifically he said that photons are important for the process and the light near infrared (around the three micrometer wavelength) makes the EZ grow. When all of this energy is entering a system, it must be doing some work. Pollack showed a video clip where a nafion tube was submerged in water and the water flowed through the tube spontaneously. “This is a difficult concept to grasp,” said Pollack, “but think of plants, they use the energy of photons to make work.”
Pollack noted that the EZ has a negative charge but dipoles don’t have a negative charge. When the exclusion zone is analysed spectroscopically it absorbs light at 270 nanometres which is typical of electrons set up in a ring structure (called π electrons). Ice shows similar sheets consisting of a chicken wire like ring structure but protons glue the oxygens between the layers making ice solid and giving it a neutral charge. If the protons are pulled away, and position between one layer and the next shifts so that the oxygens don’t sit directly on top of each other, the sheets can be more densely packed. The sheets can also be shifted in six different directions and the same result occurs. “This is important because if you think of a stack of these, they can shift just a matter of degrees and as the layers stack, they can form a helix.” “A helix is nice because many biological proteins are helical and nucleic acids are helical, so what you can imagine is one of the macromolecules lined up this way interfacing very nicely with water.”
If the fourth phase of water has a crystalline structure and crystals stick together, what kind of behaviour would we expect? Pollack used a common dessert as an example. “Gelatin dessert is about 95% water,” he said. “So the question arises, why doesn’t the water dribble out? There are some gels that are 99.95% water. The water doesn’t dribble out. Well, there are osmotic arguments but they are hard to apply when you have 99.95% water. If you look at a gel, it consists mostly of empty space. It’s filled with water. There are nucleating surfaces with a hydrophilic charge and they are going to nucleate, ordering the water into exclusion zone water.” Pollack went on to say, “ It is a liquid crystal that sticks to the surface and therefore it is not going to come out. … so when you feel the Jell-O as a dessert and it feels like a gel and you say ‘Why does it feel that way?’ You might think that it is not necessarily the matrix or the polymer or the protein, in some cases it is a vanishing small component, but it’s the water.”
There is another phenomenon that can be explained through water showing exclusion zone properties. A common parlour trick is to float a needle or a coin in a glass of water. “How is this possible?” Pollack asks. “Some of you know that water has an anomalous high surface tension. But it’s not that high, the idea is that it comes from a single molecular layer at the surface.” Pollack thinks that there is some other mechanism at work. “To think that one molecular layer can achieve all this is really the question. So we began to study the interface between water and air.” He noticed that a “crystalline structure grows at the interface between air and water. It is a stable zone and it looks like an exclusion zone, it also has a negative charge as well as a constant thickness.”
Exploring this fourth phase of water provides a different way to look at chemistry, biology and physics. “If you don’t understand the behaviour of water,” says Pollack, “you can’t understand how a cell works.” If each of the phenomena that make up exclusion zones in water: negative charge, self assembly, potential energy which is powered by the Sun, it sounds quite similar to the functions of a cell. It also hints at a possible origin of life on the planet.
The Nerenberg Lecture series are in memory of Morton (Paddy) Nerenberg, a much-loved Western professor for more than a quarter of a century who was also a founding member of the Applied Mathematics Department. A respected teacher and researcher, Nerenberg believed that scientific and mathematical ideas belonged to everyone. He was also concerned that these same ideas were becoming less accessible to the public at large. After his death in 1993, the lecture series was established to honor his appreciation for the democracy of ideas.