[3dem] Alasdair and vitreous water.

[Jacques Dubochet]

Dear Member of the 3DEM List,

We all enjoyed the good news about Alasdair McDowall. 

There is more. 

An article by Tulk at all in the 23d of May issue of Nature offers, for the first time in my view, a plausible hint about the real nature of the vitreous water that Alasdair was the first to produce and see in an electron cryo-microscope, nearly 4 decades ago. In case you haven't noticed this article, read the following

I will be thankful for any comment. 

Jacques Dubochet
University of Lausanne
Switzerland
What is vitrification that owes me a Nobel prize ? A mystery which seems, at last, to become more understandable.

Once, in the early 80s, while we were trying to do something really useful out of electron cryo-microscopy, Alasdair McDowall decided to freeze water in liquid ethane rather than in liquid nitrogen. And so, for the first time, we could see vitreous water. Our observation submitted to Nature was shortly rejected with the remarkable comment, “you can’t bend Nature”. The editor was wrong. He should have known it since the discovery that vitreous water can be obtained by flash cooling of liquid water was already published, or was in press, in the same journal (Mayer and Brüggeller,1980). Nevertheless, the severe comment had its good reasons. Fifty years of work had shown that cooling of pure water always results in ice crystals. Experiments and theory – in particular by Father Basile Luyet and his gifted colleagues such as D. H. Rasmussen and A. Mackenzie – led to this apparently unavoidable conclusion.

What is then “our” mysterious vitreous water which is so useful to electron cryo-microscopists?

The situation became more complicated when Mishima et al. (1984, 1985) found that a form of vitreous water can be obtained by squeezing normal ice (ice I) by high pressure at liquid nitrogen temperature (77 K) . The material remains stable when brought to normal pressure. They called it HDA for high density amorphous water. The next observation - truly remarkable - is that, upon warming at ambient pressure, HDA does not crystallise but is first transformed into another form of vitreous water, LDA, low density amorphous, which seems to be very similar to “our” vitreous water. Further work indicated that the transition from HDA to LDA can be reversed and that the transformation seems to be discontinuous like any bona fide first order transition. Apparently there are two well-distinct states of vitreous water.

This is difficult to swallow. As I understand it, it means that there are two kinds of orders in vitreous water and that each water molecule knows which one it belongs to. Things are simple when we consider liquid water and ice I, for example. Upon warming at normal pressure all the water molecules of an ice crystal know that they are approaching zero °C and that they can’t remain in this state if more heat is brought to the system. The specific vibrations of the ice lattice (phonons) is the messenger that keeps each molecule informed. But what happens between two states of vitreous water ? What tells each molecule that it belong to HLA or LDA? What is the corresponding long range order that must necessarily hide somewhere ? For me, this situation was painfully mysterious.

The present work by Tulk at all. (2019) (also read the explanation by J.S.Tse (2019)) is for me a big relief. What they did is simple, in principle; they just took time ! Along the line initiated by Mishima, they compressed ice I at 100 K but they did it in incremental steps, waiting an hour at each step. No HDA was formed under these conditions but, with increasing pressure, the material was transformed into different forms of crystalline ice. Confirming previous results, HDA was produced when the pressure was increased without pausing. They conclude that HDA is the kinetically arrested transformation between ice I and some forms of high density ice crystals; it is not a thermodynamically defined state.

I feel comfortable with the idea that “our” vitreous water can be understood along the same principle: it is not a thermodynamically define state capable of first order phase transition but a kinetically arrested volume of liquid water in its way towards some form of ice crystal.

At least one question remains. What is the “feeling” of a biological structure embedded in vitreous ice? Does it “suffer” during vitrification ? How far can we trust what we observe by electron cryo-microscopy ?

I am confident that members of the 3DEM community will address these questions in the light of the above Tulk at all results and I look forward to learning about their answers.

Thank you in advance. 
 
Mayer, E., & Brüggeller, P. (1980). Complete vitrification in pure liquid water and dilute aqueous solutions. Nature, 288(5791 (11.12.1980)), 569-571.

Mishima, O., Calvert, L. D., & Whalley, E. (1984). "Melting ice" I at 77 K and 10 kbar : a new method of making amorphous solids. Nature, 310, 393-395.

Mishima, O., Calvert, L. D., & Whalley, E. (1985). An apparently first-order transition between tow amorphous phases of ice induced by pressure. Nature, 314, 76-78.

Tse, J. S. (2019). A twist in the tale of the structure of ice. Nature, 569(7757), 495-496.

Tulk, C. A., Molaison, J. J., Makhluf, A. R., Manning, C. E., & Klug, D. D. (2019). Absence of amorphous forms when ice is compressed at low temperature. Nature, 569(7757), 542-545.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20190614/3d0ef2bf/attachment-0001.html>