I`m not a chemist, so someone might correct me, but my understanding is that it relates to at least two different factors:
First of all, polarity. More polar molecules will more likely stay in solution even if the pH is raised. This is the case for mescaline and bufotenine. Harmaline is slightly less polar than mescaline, and though it does precipitate out of a ph11+ basic solution, it seems some of it still stays in solution, possibly around 10-20%. You can check out a list of polarity of some substances
here (high xlogp = less polar , low xlogp = more polar).
Then there might also be other factors involved that affect crystallization, including what is in the solution together with the alkaloids. This might be the case with DMT. If for example you dissolve reasonably pure DMT fumarates in water and add a base, the DMT freebase will precipitate. On the other hand if you have a crude mimosa tea and add a base, you might never see any DMT precipitate. Possibly other plant chemicals keep the DMT dissolved, or prevent crystallization in general. In
this post, infundibulum suggested a possible mechanism through which sodium acetate might old DMT in solution, which would also explain why when basing a DMT acetate solution often the DMT doesn`t crystallize, but it does when basing a DMT fumarate solution.
As an interesting side fact somewhat related to this, often it happens that while a substance may not be soluble in a specific solvent, if that specific solvent has other substances dissolved, it may dissolve the previously insoluble substance. This is the case with DMT N-Oxide and naphtha. While naphtha does not dissolve DMT N-oxide, if the naphtha has a certain amount of plant oils dissolved in it, it could dissolve DMT N-Oxide (there is a published paper that describes this which is mentioned in Trout`s Notes). It is like binary solvents, when you mix solvents, the polarity of the solvent changes, so some things that may have been soluble before aren`t anymore, or vice versa.
Hope that helped
