Rates and Equilibria of Vial-In-Vial Vapor Diffusion for Common Laboratory Solvents

Vapor diffusion crystallization is the chief method of crystallization used throughout the world for preparing X-ray crystals. While the extensively studied hanging drop method remains the most popular, almost no research has been done, despite its frequent use, on the vial-in-vial method, which can be effective for both preparative and analytical amounts unlike the hanging drop method. Indeed, the literature contains no mention of either the kinetics or equilibrium for vial-in-vial vapor diffusion, and the rules for proper technique remain largely empirical. Included herein are the results of an extensive study of the rates and equilibria governing vial-in-vial vapor diffusion. A large table is included which lists various combinations of laboratory solvents which researchers can consult when selecting solvents for their system. We attempt to characterize the underlying forces which drive vapor diffusion, and we propose two tentative methods of modeling the kinetics data to provide a quantitative measure of the rates and/or equilibria. Finally, we examine common variations in configurations which may affect the researcher’s results.