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Comment by kmonad | Hacker News Reader

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).

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> 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.

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