Question

The hanging drop vapor diffusion technique is a popular method for the crystallization of macromolecules. Please demonstrate the principle here.

Answer 1

The hanging drop vapor diffusion technique, as mentioned, is a popular method for the crystallization of macromolecules. The principle is quite straightforward. A drop composed of a mixture of sample and reagent is placed in vapor equilibrium with a liquid reservoir of reagent. Typically, the drop contains a lower reagent concentration than the reservoir. To achieve equilibrium, water vapor leaves the drop and eventually ends up in the reservoir. As water leaves the drop, the concentration of the macromolecule (as well as the concentration of the reagent) increases, which eventually leads to a relative supersaturation of the solution, which can then induce the crystallization of the macromolecule, if the conditions are adequate.