Hello! Please suggest what techniques can be used for crystallization via gel. I am interested in simple techniques that do not require special equipment. I have only sodium metasilicate and agar at my disposal ( from from gelling agents). Crystallization object are small organic molecules (drugs) and large organic molecules such as porphyrins and metalloporphyrins.
Thanks in advance
Dear Nikita, that's indeed a very interesting technical question. During the past decades we crystallized hundreds of new inorganic and organometallic compounds. However, we always used a variety of organic solvents or water for crystallization, but never gels. Despite this I can suggest to you the following potentially useful articles which might help you in your analysis:
A Simple Technique to Improve Microcrystals Using Gel Exclusion of Nucleation Inducing Elements
This paper has been published Open Access and can be freely downloaded (see attached pdf file).
Crystal growth in gelled solution: applications to coordination polymers
Article Crystal growth in gelled solution: Applications to coordinat...
This article has been posted by the authors as public full text on RG so that you can freely download a pdf.
Crystallization screening directly in electrophoresis gels
http://hera.ugr.es/doi/15089800.pdf (also attached)
Also please have a look at the followng instructive link:
Crystallization in Gels
http://www.cryst.chem.uu.nl/lutz/growing/gel.html
It is pointed out here that "Crystallization in gels is an excellent (and unfortunately seldom used) technique for obtaining single crystals of compounds with low solubility."
I hope you will find these references useful. Good luck with you crystallization experiments and best wishes, Frank Edelmann
We did a lot of crystallizations in gels, for example, metal-carboxylate coordination polymers. A most simple technique is as follows:
1.00 g of "liquid glass" solution is diluted with water to 15.00 g. Then the
solution of HClO4 was neutralized (by bromcresol purple) with the above diluted silicate. The resulting solution (initially it is liquid just like water) was placed in the U-shape vial and left for 1-2 days giving more or less mechanically stable gel. The reagent solutions (for example, aq. solutions of carboxylic acids and metal salts) were carefully layered over the gel, in two different sections of U-tube. Interdiffusion of the solutions through the gel layer often yields good crystals, within a period of 20-50 days. This period as well as the mechanical robustness of the gel may be easily controlled while varying the concentration of the initial HClO4.
The best is 0.05 M. With 0.1 M HClO4 the resulting gel will be so solid that diffusion will need many months to proceed, but with 0.01 M HClO4 the gel will be semi-liquid making difficulties for layering solutions of the components.
Kostiantyn V. Domasevitch, thanks for your response. There is a question. If I have only one substance, that is, I do not need to crystallize salt or MOF. Only one organic substance. Should be fill the solution with the substance only in one section of U-tube? All guides tell you how to get salt, but how do you get a one-component single crystal?
That is much simpler! In the case of "gel crystallization" you need gel mostly as a membrane, separator between two reacting solutions to make reaction very slow.
When the problem is to re-crystallize individual compound only, you need slightly other thing. Make deposition of the crystals to be very slow.
When your compound is soluble in hot solvent, but deposites on cooling - prepare hot solution and place it, in stoppered vial, in a Dewar bottle with hot water. Cooling to r.t. over about 2 d often yields good crystals.
Another way is vapor diffusion. Say, your compound is soluble in EtOH but insoluble in ether. Prepare saturated solution in EtOH, place the vial inside larger vial (flask or desiccator) containing ether (several times larger volume) and fit with stopper. Within next several days the vapors of ether will slowly diffuse into the solution of the compound in EtOH and this will precipitate the solute. For this very simple technique, two solvents have to be miscible. Water and ether will not work. For aqueous solutions the second component may be water-soluble THF. As well, diffusion of CH2Cl2 or CHCl3 vapors into solutions in alcohols is also applicable.
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