Many astrobiologists think that water is a key ingredient for life. And not just because life on Earth can't manage without it.
Water has a weird set of properties that other chemicals simply do not share. One famous example is that water expands when it freezes, ensuring that ice floats rather than sinks. That's important because if it didn't, lakes and oceans would freeze from the bottom upwards, making it hard for complex life to survive and evolve.
These and other properties are the result of water molecules' ability to form hydrogen bonds with each other and this gives these molecules some very special properties.
Today, George Reiter at the University of Houston and a few buddies put forward evidence that water is stranger than anybody thought. In fact, they go as far as to say that when confined on the nanometre scale, it forms into an entirely new type of quantum water.
The background to this is that the electrons in donor and acceptor molecules in hydrogen bonds are indistinguishable, meaning they can travel from one molecule to the next. When the molecules are confined in some way, they can spread some distance, when in a solid for example.
But water molecules can be confined in other ways too. And when that happens, the electronic structure of liquid water becomes a connected network.
That raises an important question: how does the behaviour of molecules in this electronic network differ from the behaviour of molecules in bulk water interacting in an ordinary way?
Reiter and co say they have measured the properties of confined in the tiny space inside carbon nanotubes at room temperature and found some important differences. They've done this by filling nanotubes with water and bombarding them with an intense beam of neutrons at the Rutherford Appleton Lab in the UK. The way the neutrons scatter reveals the momentum of the protons inside the nanotubes.
It turns out that the protons in this nano-confined water at room temperature behave in an entirely different way to those in bulk water. Protons are known to be sensitive to the electronic fields around them. So when these fields form into unusual electronic networks, it's no surprise the protons behave differently.
"The departures of the momentum distribution of the protons from that of bulk water are so large, that we believe that the nano-confifined water can be properly described as being in a qualitatively different quantum ground state from that of bulk water," they say.
They even suggest that there could be some kind of quantum coherence that spreads out through the electronic network. If that's the case, it should be possible to measure how this decoheres in future experiments.
That's a big deal. Reiter and co chose carbon nanotubes because they are an analogue of the conditions water faces when passing through living systems, through ion channels in cell membranes, for example. Biologists have long known that flow through these channels is orders of magnitude greater than conventional fluid dynamics predicts. Perhaps this new state of quantum water is the reason why.
Reiter and co also say that this quantum water can only exist when it is surrounded by neutral molecules such as the carbon in nanotubes and not in the presence of many commonly studied materials, such as proton exchange membranes like Nafion. This is made of molecules that conduct protons in an entirely different way and so prevents the formation of quantum water.
The implication, of course, is that the proton exchange membranes used in everything from chemical production to fuel cells could be dramatically improved by using a neutral carbon-based material.
In fact, this phenomenon may be a crucial factor in the very mechanism of life itself. Exciting stuff!
Ref: arxiv.org/abs/1101.4994: Evidence Of A New Quantum State Of Nano-Confifined Water