Science by Marilyn: Alternative Biochemistries - Solv

[Samantha York]

Alternative Biochemistries Part 2 - Solvents

Obviously here on Earth the solvent of choice is water. Water is the choice of media for the transport of molecules around a body. Water has several advantages that makes for a good solvent. The first is that it is one, if not the highest compound commonly found in the universe. It has a fairly wide liquidity range; it is polar so that it can dissolve salts along with proteins and various forms of nucleic acids. It has a high amount of specific heat and vaporization allowing good thermal regulation. The amphoteric properties of water allow it to act as a base or acid and thus participate in many chemical reactions. In addition, in its solid state as ice it is less dense then in its liquid from and this ice can act as insulation to deeper liquid water and is transparent allowing for sunlight to permeate allowing for photosynthesis.
So given all this it is difficult but not impossible for other substances to be good solvents for life to exist.
The most likely alternative candidate to water would be ammonia. Ammonia remains liquid at much lower temperatures, has polar properties, and is able to dissolve quite a few ions as well as most organic compounds. A simple substitution of the OH group in most alcohols, sugars and fatty acids with a NH2 would allow those compounds to dissolve as well. At standard atmospheric pressure its liquidity range is not as much but at high pressures it demonstrates a very wide range. Ammonia is also present in fairly large amounts in the universe.
Sulfuric acid is another possibility. It has a wide range of liquidity, capable of dissolving many compounds but while it can act as a base and acid the chemistry tends to favour acid. Sulfuric acid can exist in decent amounts in the universe as well.
Formide, hydrogen cyanide and hydrogen fluoride are possibilities but each has more problems that would probably exclude them from being solvents for complex life.
Non-polar solvents have been considered but the chemistry probably does not support life without some sort of radically different chemistry. Nonetheless some of these are methane, hydrogen and nitrogen.