Chances are that tannins, like most molecules soluble in water, are polar, meaning there is a positive and negative charge on different sides of the individual molecules. I imagine that these charges are attracted to the magnet.
The numerous O-H structures on the tannin molecule make it
extremely polar, because the charge is unevenly distributed across the O-H bond. More negatively charged electrons gather around the electronegative O atom, giving it a more negative charge. Conversely, the H atom in the O-H bond is more positive, because H is not so electronegative. It doesnt like electrons as much as O, so its electron tends to hover nearer to the O atom, which has a higher affinity for electrons. This is the basic definition of polarity.
The same is true for the N-H bond on the DMT molecule, rendering it somewhat polar. However, polarity is relative. The N-H bond is less polar than the O-H bond, because N is less electronegative than O(likes electrons a bit less). Since there are far more polar residues on the tannin molecule than the DMT molecule, and the N-H bond is less polar than the O-H bond, DMT is not nearly as polar as the tannin molceule.
The CH3 residues on the DMT molecule are not polar, because the electrons are spread symmetrically across the CH3 residue.
So the tannins are highly attracted to the magnet, but not so much the DMT.
This of course, is entirely my own speculation and could be completely false!
I'm interested to hear from more adept chemists!
aliendreamtime attached the following image(s):
Tannin.gif
(5kb) downloaded 148 time(s). DMT.gif
(3kb) downloaded 149 time(s).