How To Grow Crystal

Posted on April 16, 2008

There are a lot of reasons to grow crystals in research, but none of them are more important than the journal bump they cause. As it turns out, even collecting a crystal can be its own publication, albeit in a less than interesting journal. Therefore, it is with great efforts that we try to grow crystals.

For those of us in the natural products game, crystals all but remove the ambiguity with any relative stereochemistry. This way, we only have two possible molecules to make. SURE, you can say you’ve made heptacene and stabilized it by various things, but you’re assured a JACS or Angew paper if you can give ‘em a cif file. And since blogs are useless (imho) if they fail to inform, I’ll show you how ‘ol Kyle grows up his crystals.

I do my own data collection at our world famous crystal structure facility, mount my own crystals, solve my own diffractions and whatnot, so I’ve vested a lot of interest in this sort of stuff. That isn’t to say I’m an expert, of course. Now, all I do is organic crystals that aren’t air or moisture sensitive. So this isn’t an exhaustive review by any means. For a more in depth guide, I suggest you look at this.

First thing I usually try is to do a vial-in-vial vapor diffusion. This is a simple little ditty in which one places their compound inside of a small vial in a solvent it is reasonably soluble in and putting it in a larger vial filled with volatile solvent that it is not soluble in at all. Overtime the volatile solvent will evaporate up and into the less volatile solvent and slowly dissolve and diffuse in there. As the polarity SLOWLY changes, the thermodynamic wonders of crystallization occur. In the case to the left, I’ve put some of my new synthetic target, Tiklemaitaint A, into a vial filled with dichloromethane and I’ve allowed pentane to slowly diffuse into it. If you look closely you’ll see some pretty crystals.

Another method that’s very popular is to simply allow for slow diffusion. This method is more straight forward. You simply layer one solvent on top of another and the slow diffusion process causes crystals to form in the middle. So, that’s pretty easy. Then again, the easiest way is to just keep some of your crap in an NMR tube and forget about it and then one day look over and discover amazing crystals That’s possibly the best way to do it, since there’s no effort and it’s always a surprise.

You can also cap your NMR tube (or any vial, really) and drop it into a (really good) dewar with some hot solvent. Cap that baby tight and put it in the freezer. Hopefully, it will take a few days for the solvent to get down to zero, at which point you can extract your vial and MAYBE see some crystals. If you’re lucky enough to work where there is a -72 chill room (or -20 or -50) (a deep freezer works too, if you have the space) where you can just plop it in. (If it’s owned by the asshole biochemists, tell them it’s DI/DI sugar water. It’s alright to lie to biochemists. They’ll believe anything if you tell them entropy made you do it.) I’ve never tried to make crystals at the low temperature. I can’t imagine mounting them would be that fun.

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