Re: Life in non-water solvents

Dear Tomas,

I will try to address your points in the order you present them:

1) In response to your question regarding the ability of the formation of micelles and bilayers in a nonpolar solvent, this is indeed possible. As a PubMed search for “reverse micelles” demonstrates, the study of these structures is an ongoing research topic. Furthermore, reverse micelles are biologically relevant, and have been used by research groups studying a variety of biological systems. For a brief review, see:

Nancy E. Levinger, Water in Confinement, Science, 298(5599):1722-1723, 29 November 2002.

I have not been able to find any evidence of ‘reverse’ lipid bilayers in the literature however. I suspect that such structures are unlikely to form for the following reasons: Lipids are freely soluble in apolar solvents, but are capable of forming the reverse micelles discussed above when water is present in the mixture. These structures are then formed as a means of sequestering water from the surrounding non-polar solvent.

2) Given the answer to your first question, I think that it is likely that a ammonia-water mixture could indeed form reversible micelles. Under the conditions you are interested in, the ration of ammonia:water will be about 1:2. Ammonia is a polar molecule, so it will be preferred to be solvated by water as opposed to a non-polar solvent. I suspect that the water molecules would then drive formation of the reversible micelles as discussed above.

3) The ammonia-water ice mixture you are asking about depends upon the molar fraction of each chemical species. Leliwa-Kopystynski presented a paper showing the phase diagram for ammonia-water ice which has some statistics for the density of ammonia-water systems at atmospheric pressure. A mixture of 1 NH3 with 2 H2O at atmospheric pressure has a melting point of 176 K, ~100 Kelvins below water’s normal melting point. The density of this mixture in liquid and solid forms are 0.9454 and 0.9628 g/cm3, respectively. So, a mixture of ammonia-water ice in solution will be denser than the corresponding liquid.

Leliwa-Kopystynski J, Maruyama M, Nakajima T. The Water-Ammonia Phase Diagram up to 300 MPa: Application to Icy Satellites, Icarus, 159, 518-528 (2002).