Hacker News new | past | comments | ask | show | jobs | submit login
On the existence of two states in liquid water [pdf] (bu.edu)
112 points by anigbrowl on Dec 28, 2016 | hide | past | web | favorite | 30 comments

John Baez has some interesting things to say about different structures that appear in water:


And these things have a very strong temperature dependence. I wonder if it has anything to do with the current discussion.

Interesting that the low end of this phase transition range coincides with the maximum safe temperature for mammals and birds. It could be that the delicate biological mechanisms we've developed over the years are highly sensitive to some of the bulk characteristics that change in this range.

The paper talks about this. It's not just mammals and birds, proteins in general become less stable over 60C:

"This raises the question of whether temperature-driven structural changes in water affect biological macromolecules in aqueous solutions and in particular in proteins... It was found that the temperature stability range of the protein is confined to the reversible interval 45–65°C. ... In all cases the critical temperature of the protein denaturation is very close to the crossover temperature T* observed in all the properties of liquid water reviewed in this work."

This is probably why sous vide temperature is around 60C.

Although highly applicable you have to remember evolution is a thing. Proteins where there are no selective pressure to operate at high temperature are likely optimal in the ranges in that state of water. Hyperthermophiles live at 80degC and above only, they're still made of proteins. Their protein structures are highly similar to other organisms found at lower temperatures, but with modifications such as additional disulphide bonds that increases stability at high temperature. Most of these thermophilic enzymes operate very inefficiently at cooler temperatures or not at all. We already have that sort of broad insight from just looking over evolution and ecological niche.

The more interesting thing this finding has to offer is just understanding at a finer detail how proteins interact with water at all, and if there are any properties specific to each state. There might even be cool things like proteins that switch function given the water phase transition. You might find this sort of thing in chaperones related to heat shock for example.

I wouldn't use 'probably' at all. The level of proof submitted is incredibly light - it only inspects two and a half proteins - and doesn't attempt to inspect the relationship between its proposed mechanism (change in hydration shell density) and protein denaturation.

They show two graphs of protein denaturation curves showing maximum rate change in 50-65 degree range, and a curve of a different protein's hydration shell density changing. At the very least, showing correspondence between hydration shell density and denature curves within a single protein would be significantly more convincing.

While protein folding and interaction is devilishy tricky to compute, the basic idea that injecting extra energy into a system thats held together only by weak hydrogen bonds will disrupt structure and function hardly requires invocation of additional forms of water.

This isn't to say that the claims may not be true. But I would not jump to "probably".

In fact, your quoted statement doesn't even say that proteins become less stable, what the quoted statement says is that a SINGLE protein (lysozyme) undergoes irreversible structural changes over 65 degrees.

We know of a variety of high temperature resistant proteins (Taq Polymerase for example). While is certainly true that most "ordinary" (ie non extremopile) proteins will probably suffer irreversible structural changes in about that temperature change, it's not super great proof.

> This is probably why sous vide temperature is around 60C.

But why are sauna temperatures above this, being in the range of 70C-90C?

Thats because you have enough thermal mass and evaporative cooling capacity to withstand those temperatures for a short period of time - ie, very little of your body will experience drastically elevated temperatures for long - if at all. Remember that air (even humid air) is not a super great heat conductor - so while the air might be very hot, it's going to be pretty bad transferring that into your body, which in turn has a lot of mass to distrube heat over, and good conductivity to move heat away from contact areas. And that whole sweat thing works pretty well too (especially in a dry sauna).

Being submerged into a 90 degree water bath will probably rapidly hideously wound you and/or kill you.

That small organisms cannot survive saunas, only large organisms with temperature regulation ("warm-blooded"), is probably a design feature.

This and because you don't stay in a Sauna for more than a few hours

I think it is cool that there is evidence for these two states in water. I don't think, however, that the biological relevance was made particularly clear. There is hardly any life on earth for which these temperatures (upwards of 45C) play a role, and consequently, any effect on proteins would be 'out of context' within which protein function was under selective pressure. Whether or not protein stability is affected by these transitions of water states could therefore be purely coincidental. Having said this, however, one could perhaps learn more about how water affects protein function in 'normal' temperature ranges by breaking function with the other water state (but I don't understand this well enough to think of a way how to do this).

> There is hardly any life on earth for which these temperatures (upwards of 45C) play a role, and consequently, any effect on proteins would be 'out of context'

It makes me wonder what the pressure dependence is for this phase change. http://www1.lsbu.ac.uk/water/water_phase_diagram.html

Pressures inside a particular piece of cellular machinery can be much higher than 0.1 MPa (1 bar).

There's nothing on the article about thermal expansion and heat coefficient. So I'm assuming in both states they are the same.

If so, there is really no reason to expect this state change to be much affected by pressure.

There also seems to be no latent heat absorbing¹, and from the widely varying changing temperature, I imagine both states coexist on those ~20°C. Water is really weird.

1 - Otherwise people would have discovered this long ago.

I just realized you're forgetting a huge class of life -- soil organisms. Compost heaps contain the most diversity of life when "cooked" between 55C and 65C.

There's this:

> In addition, Raman scattering measurements, obtained using multivariate curve resolution (Raman-MCR) have been used to explore the hydrophobic hydration of linear alcohols from methanol to heptanol [25]. The authors conclude that below 60°C the hydration shells have a hydrophobic-enhanced water structure with a greater tetrahedral order and fewer weak hydrogen bonds than the surrounding bulk water. This configuration disappears above 60°C and is replaced by a structure with weaker bonds. These findings support the existence of two different hydration shells in liquid water with a crossover temperature of ≈60°C.

So it seems that proteins have evolved to stabilize the "ice-like" structure in hydration shells, and in turn depend on those hydration shells to stabilize their 3D structure. Above 50-60°C, that doesn't work. But there are some Archaea that do quite well at 100°C. Their proteins presumably do a better job of stabilizing the "ice-like" structure in hydration shells.

Interestingly, geothermal vents--such as those found on Earth and possibly Europa--come out at about 60-460C. They are thought to be good origin of life candidates. Behavior of proteins in this state sounds pretty interesting in that light.

ELI5 please?

the conclusion probably says it all?

"In conclusion, a review of the physical properties of water in the 0–100°C temperature range reveals a bilinear behaviour that defines a crossover temperature at 50 ± 10°C. This observation supports the hypothesis that there are two states of liquid water. We find that these two states play an important role in the thermal and optical properties of nanomedical systems. Finally, our preliminary findings suggest that the structure of liquid water strongly influences the thermal stability of proteins. More in-depth research on the thermal stability of proteins dispersed in liquid water is needed."

Yes, but just what are those states? I see no explicit hypotheses. The clearest hint that I see is that the calculated dipole moment is 2.3 Ds at 0–60°C, "which is close to the value for ice", and 1.8 Ds at 60–100°C, "which is comparable to that reported for the vapour phase". Lower dipole moment means weaker hydrogen bonding, and less tetrahedral structure.

> Yes, but just what are those states?

That's covered in the introduction.

> Despite these efforts, the structure of liquid water is still not fully understood.

> This suggests that there are of two states in bulk liquid water that differ in the amount of their dipole moment. Unfortunately, a correlation between the dipole moment and the microscopic structure of these two states has not yet been determined.

Yes, I should have quoted those bits.

The (purported) states are very similar. They have slightly thermal conductivities, electrical conductances etc. but still have all the usual properties of water (as they must, since we observe 60 degree and higher water all the time, and it still behaves like water).

> Lower dipole moment means weaker hydrogen bonding

Wouldn't weaker hydrogen bounding imply on much lower surface tension?

There is some smaller tension, but the trend is really tiny.

Well, all of the reported differences are small changes in temperature dependence. Water is a strange thing. But for the strong hydrogen bonding, it would be a gas at ambient temperatures. Consider methane and ammonia, for example.

So I don't think that they've found a new phase of water. Rather, as the title states, they argue that liquid water is a mixture of two states, one ice-like with strong hydrogen bonding and tetrahedral structure, and the other more disordered, gas-like, with weaker hydrogen bonding. It's just that there's something like a figure/ground transition at 50-60°C. Going from islands of "gas-like" structure in a sea of "ice-like" structure, to islands of "ice-like" structure in a sea of "gas-like" structure.

oh ok, I don't think they know yet - still some research to be done, the states have just been identified

I wonder if this is related to https://en.wikipedia.org/wiki/Mpemba_effect

Unlikely, see "When does hot water freeze faster then cold water? A search for the Mpemba effect" by James D. Brownridge: https://arxiv.org/abs/1003.3185

Is this why hot water from a tap sounds notably different from cold?

It has to do with the size of the produced air bubbles and the mechanics of/lengths of the columns of falling water. But that said, this could play a bit of a role in those reasons.

I don't think most taps reach 60° C. That would be 140° F in freedom units…

Most likely that's due to different amounts of dissolved air in the water.

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact