[macman104]

I am doing a reaction, where I take iron nanocrystals (Fe3O4) and dissolve them in toluene which are then reacted with DMSA (2,3-dimercaptosuccinic acid) in DMSO.  This effects a ligand exchange capping the nanocrystals with the water soluble DMSA molecules.

I run into a problem.  If I try and add water to move the crystals from the organic to the aqueous environment, the DMSO and water are miscible and I'm left with a solution that I have no clue how to separate.  This is where I'm currently at, and now I can't figure out how to separate the two liquids.  I have hoped I could find a solvent that has a preference for one over the other, thus restoring my two separate phases.

Currently salting-out, if possible is not necessarily an option, because I am interested in the aqueous portion, so I want to avoid contamination with salts.

Thanks for any thoughts.

[Yggdrasil]

Try treating the solution with organic base to deprotonate the DMSA.  This may help the nanocrystals to partition into the aqueous phase, and if the base is non-polar enough, little should contaminate the aqueous phase.

A very similar strategy is was used in the following paper to make quantum dots water soluble (http://dx.doi.org/10.1021%2Fja991662v).

[macman104]

Try treating the solution with organic base to deprotonate the DMSA.  This may help the nanocrystals to partition into the aqueous phase, and if the base is non-polar enough, little should contaminate the aqueous phase.

A very similar strategy is was used in the following paper to make quantum dots water soluble (http://dx.doi.org/10.1021%2Fja991662v).

Thanks for the suggestion, I'll access that article when I go to campus tomorrow.  The issue seems to be that after following the protocol in the paper, the particles are supposed to be redispersed in water, however, attempting to do that fails (as in the particles do not disperse in the water).  Upon suggestion from my professor I've sent an email to the article author asking for some clarification, but I'm trying to troubleshoot on my own in the meantime.

Do you have any suggestion for a base to use?  I imagine I don't need something very strong.  However, I'm not sure of something that isn't very water soluble.

[Yggdrasil]

The authors of the paper I posted use 4-(dimethylamino)pyridine, but their organic phase was DMF, not DMSO.  Getting your particles to redisperse could be an issue with the ionic strength of the aqueous solution, since this is an important factor in producing colloidal solutions. That's really the extent of my knowledge of preparing colloidal solutions, though, so I can't be much more help other than to suggest looking for information on DLVO theory for how ionic strength would affect colloids.