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Forgive my ignorance if I am way off, but I was having a look at the crystallization of a number of different substances (e.g. proteins) through the hanging drop vapour diffusion method.

The examples given use a precipitating agent (e.g. $10~\%\ \ce{NaCl}$) at the bottom of the well and then you put the liquid protein you are looking at upside down on the top cover and the water moves from the protein into the precipitating agent, slowly crystallizing the protein.

So my question is, for simplicity would it be possible to use a divided container (e.g. petri dish) which has two compartments that share the same atmosphere to achieve the same thing, that is have a container that has a salt solution on one side, and the solution I wish to crystallize on the other?

Would this likely work?

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  • $\begingroup$ Yeah, that might work. $\endgroup$
    – Ivan Neretin
    Jun 2, 2016 at 7:31

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The process you are describing is essentially the sitting drop crystallisation.

Yes, it is used. Frequently, sitting drop is used in robotic setups, because robots have a much harder time creating hanging drops. With a sitting drop, it becomes simple; just pipet a drop into the sitting drop reservoir.

Gerhard mentioned that the hanging drop method is the preferred one for manual handling since it becomes easier to handle the crystals. Possibly because they sit at the bottom of the hanging drop rather than stick to the ground of a sitting drop’s reservoir.

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  • $\begingroup$ I think sitting drop is used much more than hanging drop, also when manually setting up crystallization screens. One of the additional reasons to use a hanging drop setup is that (usually) you use a bigger drop, so you can get bigger crystals. $\endgroup$
    – VonBeche
    Jun 2, 2016 at 9:29
  • $\begingroup$ @vonBeche: actually, it is the other way round: hanging do experiments are limited to around 5 ul (otherwise the drop won't stay on the cover slide any longer), whereas there is no upper limit to sitting drop. When sitting drop is used for screening, lower volumes can be used through robotics to minimize sample consumption - but this has nothing to do with the limits of the method. $\endgroup$
    – Gerhard
    Jun 2, 2016 at 11:29
  • $\begingroup$ The main reason to use hanging drop to my mind is that they are easier to work with for crystal manipulation and that crystals tend to stick less to the surface, but drop to the surface of the drop. $\endgroup$
    – Gerhard
    Jun 2, 2016 at 11:33
  • $\begingroup$ @Gerhard I hope you don’t mind that I shamelessly copied that into my answer ;) I only had a very short introductory lab course into protein crystallisation, so I’ll admit not being an expert … and it was rather long ago … $\endgroup$
    – Jan
    Jun 2, 2016 at 12:06
  • $\begingroup$ @Jan: no worries... $\endgroup$
    – Gerhard
    Jun 2, 2016 at 12:42

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