Just hoping for a bit of help understanding the chemistry involved here.

Freebase DMT is insoluble in water whilst freebase mescaline is moderately soluble. Why is this?

My understanding was that if the pH is below the pKa, an organic base should be protonated and so be soluble. (Wikipedia seems to say this, although I have yet to find out why.) DMT's pKa=8.68, mescaline pKa=9.56. Both are well above 7 so shouldn't both dissolve in water?

Is it just the fact that DMT's pKa is a bit lower so this is exceeded more easily by the small amount that dissolves and raises the pH? Being a logarithmic scale I suppose a small difference in pKa relates to a large difference in maximum concentration.

The three methoxy groups on mescaline have appreciable electrostatic interactions with polar water molecules. Thus making mescaline pretty soluble in water. While DMT is largely non-polar in nature. Edit - doesn't have much to do with the protonation of the amines(pKa's and such). Notice how it is free-base mescaline that is soluble in the water and not the acid 'salt'(which is very soluble in water).

Intermolecular forces, and electronegativity as some key-words if you're more curious about this.

Hopefully this is what you were looking for.