Slashdot Mirror
Water Suddenly Becomes Mysterious
An anonymous reader writes "Logical to assume that scientists know the structure of water. But wrong. A study in April by Anders Nilsson from the Stanford Linear Accelerator Center concluded the molecular bonds are looser than thought. Now a new study by Richard Saykally's group at UC Berkeley appears to debunk the April results. So a new debate is born. Both scientists agree on one thing: They don't fully understand how water molecules interact."
among common substances, water is perhaps the weirdest. Here is why:
-the solid is less dense than the liquid (ice floats). This is key for life, as otherwise lakes would freeze from the bottom up and freeze solid. The ice that forms on top now acts as an insulator.
-there are 12 known varieties of ice, depending on pressure and temperature conditiions. Not all of them have a hexagonal crystal strucuture.
-for it's size, water boils at a very high temperature. This is due to the organization of the liquid into hexagonal rings of 6 molecules, preventing any from evaporating.
-it's one of the few common substances that we see in all 3 phases. (i.e. you don't see solid vodka around, nor gaseous iron, etc)
-it's the best known solvent in existance (i.e. it dissolves the most stuff).
The list goes on and on. Water is actually fairly miraculous.
-Ryan
AUWYHSTOT (Acronyms are Useless When You Have to Spell Them Out Too)
I think most people don't realize that even before these results we didn't have a good grasp of water. This controversy dumps a whole load of new fuel into the large fire. The following issues are more simulation and protein related, but maybe they give brief insight into how much we don't know:
:)
None of the (molecular dynamics, "MD") computer models of water are currently sufficient to reproduce all of the experimentally observered properties of water. This is a relatively big point of contention when simulating proteins as water needs to be accounted for. There are experimentalists that chide the theorists, even saying that they won't fully believe MD results until a decent model of water has been built.
We also don't quite know what the first hydration shell around a protein looks like. Imagine this is being the closest "coat" of water around a protein. This ordering of water could be a key component to understanding the properties/behavior of protein surfaces in binding to other molecules.
In addition, water mediated interactions between proteins is almost a completely open question. As far as I know, we don't really know how to approach the problem in an elegant manner and there have been no studies that reasonably address this at a detailed molecular level (partially due to the above two issues) even in a heuristic sense.
There is a huge literature on water. A good deal of work has been done on the above three issues and other big open issues with water that I won't go into depth on. Needless to say water has been and will continue to be a mystery for quite a while.
...and if there isn't some consideration taken for the work of Masaru Emoto then any study is liable to be missing a few hints. He's suggesting that consciousness has a measure effect upon water. In most of the science world, that's Weird Shit, as we can only relate such phenomena to quantum mechanics.
.
-shpoffo
Hear, hear! Molecular dynamics of large molecules like proteins is complete voodoo, but the emperor isn't listening, nobody wants to believe this. Given the difficulty modeling water any attempt to model a protein (likely surrounded by water) is like trying to fly a jet before you can crawl. I spent a couple of years working with computational chemists. It was astonishing how many tweakable parameters simulations had. There is only one set of laws of physics - there should be nothing to tweak. But computational 'chemists' would tweak and tweak all day. And after the x-ray crystallography results came in they'd say "see, the modeling worked, on the 23rd of last month the sim I ran at 3pm used these parameters and they came out just like these results." The whole area is a joke.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
Well, I did my Ph.D. on ultrafast infrared spectroscopy of water between 1997 and 2001 and things have changed since the mid-90s. The dynamics of the hydrogen-bond network in liquid water happens mainly on a timescale of a few picoseconds, which is actually in agreement with estimates based on NMR measurements several decades ago.
I'm not sure what you mean by "ball-and-stick models". The structure of the hydrogen-bond network changes continuously and rapidly, but it is quite reasonable to visualize the structure at a particular moment with balls and sticks. However, I am skeptical of theories that water molecules form persistant clusters such as 6-rings in liquid water, since one can measure in a number of different ways how fast individual molecules change their orientation. If the molecule were locked in a cluster, this reorientation ought to be much slower because of thermodynamic reasons---it is easier to turn a single molecule than six at the same time.
By the way, it is funny to see what happens when one publishes those kinds of measurements on the memory in the structure of the hydrogen bond network in water and water surrounding other molecules. Somehow, the homeopathy believers use this as a "scientific proof" that water has a memory for dissolved substances, conveniently forgetting that this memory lasts far less than one billionth of a second.
Avantslash: low-bandwidth mobile slashdot.