Here’s an old old specbio question.
We on Earth are made of fat suspended in sugary seawater. That is, phospholipids, with one pole salty and water-loving and the other pole oily and water-hating, surround blobs of water to form cells. The water dissolves sugars, which are useful as fuel, building material, and data storage, and suspends proteins, which do work. Water is useful in this way, because it’s relatively non-reactive, but it’s polar, so it separates molecules from each other without ripping them apart.
How could things be different? What about sulfur dioxide as an alternative? Hydrogen sulfide? Both are polar but non-reactive. Acetic acid is polar, although rather reactive. Silicones are non-reactive. Are polar silicones possible? Acetic acid and silicon also have the useful properties of decreasing in density when they freeze (like ice does in water). Ammonia has a higher specific heat capacity than water (useful for regulating a planet’s temperature), and it’s also polar, although it is more reactive than water.
Ammonia is very tempting, since I’m working on low-temperature biomes right now. But which other solvents do you think are worth digging into? Are there any I missed?